Aruna Mohanty, Young Eun Song, Jung Rae Kim et al.

Membranes • 2021

A class of phenolphthalein anilide (PA)-based poly(ether sulfone) multiblock copolymers containing pendant quaternary ammonium (QA) and imidazolium (IM) groups were synthesized and evaluated as anion exchange membrane (AEM) materials. The AEMs were flexible and mechanically strong with good thermal stability. The ionomeric multiblock copolymer AEMs exhibited well-defined hydrophobic/hydrophilic phase-separated morphology in small-angle X-ray scattering and atomic force microscopy. The distinct nanophase separated membrane morphology in the AEMs resulted in higher conductivity (IECw = 1.3–1.5 mequiv./g, σ(OH−) = 30–38 mS/cm at 20 °C), lower water uptake and swelling. Finally, the membranes were compared in terms of microbial fuel cell performances with the commercial cation and anion exchange membranes. The membranes showed a maximum power density of ~310 mW/m2 (at 0.82 A/m2); 1.7 and 2.8 times higher than the Nafion 117 and FAB-PK-130 membranes, respectively. These results demonstrated that the synthesized AEMs were superior to Nafion 117 and FAB-PK-130 membranes.

Guangyi Zhang, Zhongchen Wang, Mengshuo Liu et al.

Journal of The Electrochemical Society • 2023

Green and sustainable techniques are in great demand for the remediation of heavy metal-contaminated soil. Cadmium ion (Cd 2+ ) in soil could be extracted under the internal electric field and participating on the surface of the electrode. Here, we proposed a sediment microbial fuel cell (SMFC) for the electrokinetic remediation of cadmium (Cd) contamination soil. Within the 7 weeks of SMFC operation, the removal efficiency for total Cd could be up to 70.04 ± 0.45%, which was significantly higher than that obtained by open circuit SMFC. The maximum output power density was 71.00 ± 0.82 mW m −2 with a current density of 0.60 ± 0.03 A m −2 . Results obtained by electrochemical impedance showed that the inter resistance of SMFC was 944 ± 14 Ω. High-throughput sequencing revealed that the Alpha-, Beta- and Gammaproteobacteria increased to 67.85%–80.99% in the SMFC. The relative abundance of Cd 2+ /Zn 2+ -exporting ATPase, participating in Cd 2+ reduction, in SMFC varied from 25.83% to 30.68%, which were significantly higher than that of control (11.21% to 19.94%). Our findings have presented an effective energy-saving method for the remediation of heavy metal-contaminated soils.

Yuhong Zhou, Simeng Zhao, Lu Yin et al.

Electroanalysis • 2018

Abstract A novel membrane‐less microbial fuel cell (ML‐MFC) which used the baffles instead of the ion exchange membrane (IEM) was developed for ammonium‐containing wastewater treatment and electricity generation. By means of installing an ideal nitrifying unit between the anodic and cathodic chamber, the novel ML‐MFC accomplished organics degradation and nitrogen removal without additional loop. The removal efficiencies of COD, NH 4 + −N and TN achieved 97.07±0.47 %, 91.76±3.32 % and 87.66±1.59 %, respectively. Meanwhile, the effluent pH was near neutral and turbidity was quite low. In addition, the maximum power density of 1.007±0.032 W/m 3 was obtained. Combined with the analysis of microbial community, electroactive bacteria (EAB) Desulfovibrio , Comamonas and Thiobacillus were enriched in biofilm. Considering the superior effluent quality and the promising energy potential, the novel ML‐MFC has good application prospects in efficient and sustainable wastewater treatment.

Yatin Patil, Sunil Kulkarni, Kenneth A. Mauritz

Journal of Applied Polymer Science • 2011

Abstract Nafion® membranes were modified via in situ , catalyzed sol–gel reactions of titanium isopropoxide to form titania particles in the polar acid domains. FTIR spectroscopy showed successful intraparticle chemical bond formation with incomplete condensation of TiOH groups. Although such modification can lower membrane fuel cell performance, this study was aimed at reducing membrane degradation without significantly altering performance in the sense of material optimization. These incorporated particles did not change membrane equivalent weight and the water uptake was similar to that of the unmodified Nafion® membrane. Membrane dimensional stability, mechanical properties, and ability to withstand contractile stresses associated with humidity change at 80°C and 100% RH were improved. An open circuit voltage (OCV) accelerated degradation test showed the titania modification held voltage better than the unmodified membrane. Performance deterioration of Nafion® after the OCV test was much higher than that of the modified membrane and the fluoride emission of the latter was lower. The degraded Nafion® membrane failed when subjected to creep, whereas the modified membrane remained intact with significantly low deformation. This inorganic modification offers a simple way to enhance membrane durability by reducing both physical and chemical degradation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Sandy L. Calderon, Pilar García Avelino, Angélica María Baena-Moncada et al.

Sustainable Environment Research • 2020

Abstract This study is focused on electrical energy generation in a double-compartment microbial fuel cell. Carbon felt impregnated with multi-walled carbon nanotubes was used as an anode, which contained gold nanoparticles and Shewanella spp. grown under aerobic conditions was used as a biocatalyst. The electrodes, used before and after biofilm growth, were characterized by scanning electron microscopy and cyclic voltammetry. The results revealed the formation of Shewanella spp. colonies on the electrode surface and electrochemical activity under aerobic and anaerobic conditions. During biofilm growth in Luria Bertani medium, a stabilized average power density of 281 mW m − 2 was recorded. Subsequently, the cell reached a maximum current density of 0.11 mA cm − 2 after 72 h of operation and a coulombic efficiency of 65% under anaerobic conditions.

Omar José Duarte-Urbina, F. Fernández-Luqueño, G. Vargas-Gutiérrez et al.

ECS Meeting Abstracts • 2018

Microbial fuel cells (MFCs) represent a sustainable alternative to generate energy from wastewater treatment, reducing the consumption and pollution of fossil fuels, which are used in traditional technologies. An effective way to improve the performance of MFCs is the use metal-free carbon-based anode catalysts, which have shown high catalytic activity with significantly lower cost than noble metals. In this study, the synthesis and characterization of methanol-functionalized carbon catalysts is reported. Onion waste has been thermochemically treated via carbonization, chemical activation with ZnCl 2 and pyrolysis at 400, 600 and 800 ºC (named CCA4, CCA6 and CCA8, respectively). Graphite flakes have been ball milled in the presence of thiourea and ZnCl 2 , followed by pyrolysis at a 500 ºC in order to obtain the graphene catalyst (named GNS). Subsequently, the carbons have been submitted to surface functionalization with methanol using the intermittent microwave heating technique to produce the CCA4f, CCA6f, CCA8f and GNSf catalysts. Anodes have been fabricated by depositing catalytic layers (separately) of CCA4f, CCA6f, CCA8f and GNSf on gas diffusion electrodes. The catalytic activity of the anodes has been evaluated by cyclic voltammetry (VC) in a three electrodes half-cell, using Pharmaceutical Wastewater (PWW) as electrolyte, and compared to that of a gas diffusion electrode without catalyst. The results show that the mechanochemical treatment of graphite in the presence of thiourea modifies its crystalline structure producing the heteroatoms-doped GNS. Meanwhile, CCA4, CCA6 and CCA8 have an amorphous structure self-doped with the N and S heteroatoms. The catalysts are thermally stable at 700 ºC and exhibit a highly heterogeneous morphology. Nitrogen adsorption-desorption and BET analyses indicate that the activation with ZnCl 2 promotes the formation of mesoporous structures with average pore size ranging from 11.38 (GNSf) to around 2 nm (CCA4f, CCA6f and CCA8f). Moreover, the specific surface areas of CCA4f, CCA6f and CCA8f (1468, 1611 and 1269 m 2 g -1 , respectively) are approximately 20 times higher than that of GNSf (69.7 m 2 g -1 ). The electrochemical characterization demonstrates that the increase in activation temperature improves the catalytic activity of the CCAf series of catalysts for the oxidation of organic matter in the PWW electrolyte. The current density (j) decreases in the order CCA8f>CCA6f>CCA4f. On the other hand, the catalytic activity of GNSf is less than those of CCA8f and CCA6f, but similar to CCA4f. The results show that the metal-free CCAf carbons have the potential to be used as anode catalysts in MFCs.

Qing Wu, Jieqiong Liu, Qiannan Li et al.

International Journal of Environmental Research and Public Health • 2022

Efficient and sustainable technologies for cleaning of contaminated water and sediments are in urgent demand. In this study, a new type of sediment microbial fuel cell coupled floating bed (FB-SMFC) was developed to repair eutrophic water and sediment in a cleaner way. The effect of electrode spacing on the power generation capacity and the synchronous remediation of pollutants from eutrophic water and sediment were studied. When the electrode distance was 60 cm, the maximum power generation and pollutant removal effects were obtained. At the end of the experiment, the maximum output voltage was 0.4 V, and the chemical oxygen demand (CODCr, potassium dichromate method), total nitrogen (TN), and total phosphorus (TP) contents in the overlying water were 8 mg/L, 0.7 mg/L, and 0.39 mg/L. The corresponding removal rates were 88.2%, 78.8%, and 59.0%, respectively. The removal rates of organic matter and TN in the sediment were 12.8% and 86.4%, respectively, and the fixation rate of TP was 29.2%. Proteobacteria was the dominant phylum of bacteria in the sediment and anode. Many anaerobic bacteria were found in the overlying water, which facilitated denitrification. Overall, the results of this research revealed a highly efficient and reliable strategy for eutrophic water and sediment remediation, aquatic ecosystems restoration, and human health protection.

Topal Leyla, Carolina Nunes Kirchner, Wiebke Germer et al.

International Journal of Renewable Energy Development • 2014

The effects of different temperatures (55, 65, 75 and 85 °C) and cathode gas compositions (O2, synthetic air, air and 90% synthetic air+10% CO2) on alkaline anion exchange membrane fuel cell (AAEMFC) were evaluated. Membrane electrode assemblies (MEA) were fabricated using commercial anion exchange membrane (AEM) in OH- form and Pt catalyst. Polarization curves and voltage responses during constant current were performed in order to describe the influences of temperature and gas composition on the AAEMFC performance. The experimental results showed that the fuel cell performance increases with elevating temperatures for all applied gas compositions. Highest power density of 34.7 mW cm-2 was achieved for pure O2 as cathode feed. A decrease to 20.3 mW cm-2 was observed when cathode gas composition was changed to synthetic air due to reduction of the O2 partial pressure. The presence of CO2 in atmospheric air applied to the cathode stream caused a further drop of the maximum power density to 15.2 mW cm-2 driven by neutralization of OH- ions with CO2.

Licheng Zhang, Xiao Chen, Chi Zhang et al.

Journal of Chemical Technology & Biotechnology • 2025

Abstract Background The continuous flow double‐sludge anaerobic/aerobic/anoxic process is a good choice for removing nitrogen (N) and phosphorus (P) simultaneously, although these are difficult to remove efficiently. Microbial fuel cells (MFCs) can extract energy from wastewater and use electrons to remove pollutants. This study proposes a novel integration of MFCs with the continuous flow double‐sludge AOA process, investigating the system's performance across different carbon (C)/N ratios (2, 3.5, 5 and 6.5) in terms of pollutant removal, electricity generation and microbial community structure. Result When the influent C/N ratio was 3.5, the average removal rates of chemical oxygen demand, ammonium (NH 4 + )‐N, and phosphate (PO 4 3− )‐P were 92.01%, 79.68% and 92.91%, respectively, and the average simultaneous nitrification and denitrification (SND) and SND P removal (SNDPR) rates of nitrogen oxide (NO x − )‐N were 53.30% and 42.09%, respectively. The diversity and abundance of microbial community were at a good level, and the relative abundance of Dechloromonas , Pseudomonas and Candidatus_Competibacter reached 4.16%, 2.16% and 4.61%, respectively, at C/N = 3.5. Conclusions Significant differences in pollutant removal were observed under different C/N conditions, with electron acceptors emerging as the biggest factor affecting power generation. According to the microbiological results, the combination of lower C/N ratios and higher PO 4 3− ‐P contributed to the enrichment of key functional microorganisms. © 2025 Society of Chemical Industry (SCI).

S. Wernick

Transactions of The Electrochemical Society • 1931

The electrodeposition of Cd from CdSO 4 solutions was studied, with the object of determining the effect of variation of pH of the solution, current density and temperature of the electrolyte on the crystal structure and grain size of the deposit; and on the anode and cathode efficiencies and the electrode efficiency ratio. The pH of a simple solution of CdSO 4 rises rapidly with progressive deposition, and requires to be buffered in order to maintain a uniform pH. At the same time, the crystal structure of the deposit becomes progressively less granular, but subsequently (at a pH above 6), more crystalline, dark and less adherent. An optimum range of pH is approximately 5 to 5.7. The effect of aluminum sulfate, sodium acetate, boric acid and sodium chloride as buffering agents was examined. The best buffer within the desired range of pH was a mixture of boric acid and sodium chloride. CdSO 4 solution with this buffer was adopted as a standard electrolyte. Increasing c.d. has only a small effect on anode and cathode efficiency, the variation being 1.6 per cent and 1.4 per cent respectively, and the electrical efficiency ratio is also little affected. There is however a marked effect on the grain size of the deposit, which consists of large crystal aggregates at low c.d. and is relatively fine grained and also more adherent at higher c.d. “Treeing” occurs when the c.d. exceeds 4.5 amp./s. dm. Increasing temperature has a relatively more marked effect on the electrode efficiencies than c.d. The anode efficiency rises notably at the higher temperatures examined, and the cathode efficiency decreases somewhat, resulting in a progressive increase in the electrical efficiency ratio. The effect on the deposit is at first in the direction of refinement of the grain size, but at higher temperatures, a coarser, crystalline structure develops. It is concluded that temperatures in excess of 40° to 50° C. are undesirable in depositing Cd from CdSO 4 solutions. The “structureless” type of deposit obtainable from cadmium cyanide solutions is unobtainable from CdSO 4 solutions in the absence of an “addition agent.”

Sofia Boulmrharj, Mohammed Khaidar, Mohamed Bakhouya et al.

Sustainability • 2020

The search for new fuels to supersede fossil fuels has been intensified these recent decades. Among these fuels, hydrogen has attracted much interest due to its advantages, mainly cleanliness and availability. It can be produced from various raw materials (e.g., water, biomass) using many resources, mainly water electrolysis and natural gas reforming. However, water electrolysis combined with renewable energy sources is the cleanest way to produce hydrogen while reducing greenhouse gases. Besides, hydrogen can be used by fuel cells for producing both electrical and thermal energy. The aim of this work was towards efficient integration of this system into energy efficient buildings. The system is comprised of a photovoltaic system, hydrogen electrolyzer, and proton exchange membrane fuel cell operating as a cogeneration system to provide the building with both electricity and thermal energy. The system’s modeling, simulations, and experimentations were first conducted over a short-run period to assess the system’s performance. Reported results show the models’ accuracy in analyzing the system’s performance. We then used the developed models for long-run testing of the hybrid system. Accordingly, the system’s electrical efficiency was almost 32%. Its overall efficiency reached 64.5% when taking into account both produced electricity and thermal energy.

Daouda Fofana, Sadesh Kumar Natarajan, Pierre Bénard et al.

ISRN Electrochemistry • 2013

Platinum cluster formations have been investigated as a way to reduce the amount of Pt at the cathode of polymer electrolyte membrane fuel cells. One, two, and three layers of Pt (0.05 mg/cm 2 ) sputtered directly on microporous layers of gas diffusion layers with and without interfacial carbon-Nafion layers and carbon-polytetrafluoroethylene (CPTFE) layers have been used as a cathode. Comparison with experimental results had showed that the best performance was obtained with three layers of Pt sputtered on carbon-Nafion containing 34.8 wt.% of Nafion and sputtered carbon-polytetrafluoroethylene containing 16.9 wt.% of polytetrafluoroethylene. High limiting current densities (>1.1 A/cm 2 ) have been reached with cathode Pt loading as low as 0.05 mg/cm 2 . SEM imagery and cyclic voltammetry characterization have been performed to consolidate this study. High Pt utilization can be showed by this method. The factor influencing Pt utilisation in the oxygen reduction reaction is intrinsically related to Pt clusters formation and helps in enhancing the PEMFC performance with low Pt loading.

Chin‐Tsan Wang, Aristotle T. Ubando, Vimal Katiyar et al.

International Journal of Energy Research • 2020

Summary Microbial fuel cells (MFCs) are considered as power generation devices for sustainable energy. However, the power generated is insignificant compared to other energy production devices. In this study, a mini autonomous biosensor (MAB) based on MFCs has been designed for detecting hazardous hexavalent chromium in wastewater. Hexavalent chromium has been classified as a human carcinogen causing serious birth defects due to its mutagenic and teratogenic properties. The power generated by the MAB has been investigated to study the feasibility of providing power to itself. In addition, electrochemical analyses of conductive silver paste and carbon cloth as the anode were conducted in the MAB for detecting hexavalent chromium in the anode chamber. Results show that a maximum voltage of 518.17 mV and a power density of 1.075 mW/cm 2 could be achieved using carbon cloth with an external resistance of 1000 Ω, while a higher limiting current density of 0.015 mA/cm 2 could be achieved with conductive silver glue as the anode electrode. Besides, the voltage output of the MAB decreased rapidly with the addition of hexavalent chromium into the wastewater. Also, the recovery time for the MAB was much shorter than found in previous studies. The MAB demonstrated potential for simultaneous production of electricity and detection of hexavalent chromium, which would open up avenues for autosensing applications in the environment as well as smart powering devices. Results indicate that the MAB with conductive silver glue as anode electrode is feasible for detecting hexavalent chromium in wastewater.

Syarifah Noor Syakiylla Sayed Daud, Muhammad Noorul Anam Mohd Norddin, Juhana Jaafar et al.

High Performance Polymers • 2019

Sulfonated poly(ether ether ketone) (sPEEK) membrane is a promising proton-conducting membrane for fuel cell. However, the performance and lifetime of sPEEK membrane depend on the degree of sulfonation (DS). High DS of sPEEK increases the performance, but the mechanical properties could deteriorate progressively which affect its lifetime. Thus, this study investigated the effect of adding polyvinylidene fluoride (PVDF) into high DS (80%) of sPEEK through solution blending method toward its physicochemical properties and morphology structures. The PVDF concentration was varied to 5, 10, 15, and 20 wt% relative to the sPEEK content. The existence of hydrophobic PVDF in 80% sPEEK improved the mechanical properties where the water uptake and swelling degree of membrane decreased, whereas the tensile strength increased. The sPEEK/PVDF 15 exhibited the highest proton conductivity (46.23 mS cm −1 ) at 80°C. Incorporating PVDF into high DS of sPEEK enhanced the mechanical properties which can be used as a proton-conducting membrane for fuel cell that may improve the performance and prolong the lifetime of the cell.

Kayoung Park, Magnus So, Masaki Goto et al.

ECS Meeting Abstracts • 2020

In order to improve the cell performance of polymer electrolyte fuel cells (PEFCs), it is essential to design the cathode catalyst layers (CLs) with the optimal morphology considering the mass transport such as electron, proton, and oxygen as well as an electrochemical reaction. As designing the cathode CLs, it is required to consider the fabrication method, compositions of catalyst ink, ionomer loading, resulting in effect of the cell performance. Particularly, ionomer as the pathway for proton conduction strongly influences proton transfer resistance and oxygen diffusion resistance. Too much ionomer included to CLs obstructs oxygen diffusion, and decreases the porosity and average void size in the CLs. Also, the thickness of the ionomer on Pt particles is increased, leading to an increase in the overvoltage. These results in performance loss. Thus, it is needed to reduce ionomer loading in the CLs. However, low ionomer loading reduces the ability of proton conductions, resulting in lower performance by an increase in proton transfer resistance. In our previous study, we introduced silica-coated Pt catalysts in order to control ionomer loading [1]. Silica-coated Pt catalysts, developed by Takenaka et al. have maintained a high activity for the oxygen reduction reaction during the durability tests because silica coating has merits of suppression of Pt particle agglomeration and diffusion of Pt cations in the catalyst, and easy control of surface characteristics like hydrophobicity or hydrophilicity [2]. In our previous study, we experimentally examined the effects of silica coating in the CLs on the catalyst ink, morphology of CLs, cell performance. As these results, catalyst ink for silica-coated Pt catalyst maintained good dispersion and high stability compared to that of non-coated Pt catalysts. In addition, the performance at 0.6 V for the silica-coated Pt catalysts with low ionomer loading showed higher than that of non-coated Pt catalysts at all the relatively humidity (RH). In particular, at low humidity conditions (20% RH), the silica-coated Pt catalysts showed significantly enhanced performance compared with non-coated Pt catalysts. These results suggest that the hydrophilic groups included in silica layers contribute to the improvement of proton conductivity. In this present study, we examined the numerical analysis of silica-coated Pt catalysts in order to understand the effect of silica coating on the performance in detail, such as current density distribution, overvoltage. In our research group, in order to understand the effect of nano and mesoscale structure of Pt/Carbon catalyst layer on cell performance and internal phenomena, various simulation models which included the effect of the structure of carbon aggregate, ionomer coverage, and formation of agglomerate, have already been developed with some experimental knowledge such as FIB-SEM observation, the actual pore size distribution of CLs, relative oxygen diffusion coefficient, agglomerate size distribution measurement in CL ink [3-5]. These simulation models were applied to the numerical analysis of the silica-coated Pt catalysts in the CLs. In our presentation, we will discuss the effect of silica coating on Pt catalysts in CLs on the cell performance analyzed numerically. Acknowledgment This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. References [1] K. Park et al., Int. J. Hydrogen Energy, 45, 1867–1877 (2019). [2] S. Takenaka, M. Goto, Y. Masuda, S. Emura, and M. Kishida, Int. J. Hydrogen Energy, 43, 7473–7482 (2018). [3] G. Inoue et al., J. Power Sources, 439, 227060 (2019). [4] M. So et al., Int. J. Hydrogen Energy, 44, 28984–28995 (2019). [5] T. Terao et al., J. Power Sources, 347, 108–113 (2017).

Angelo Esposito, Pierpaolo Polverino, Cesare Pianese et al.

ASME 2010 8th International Fuel Cell Science, Engineering and Technology Conference: Volume 1 • 2009

Proton Exchange Membrane Fuel Cell performance significantly depends on electrode water content. Indeed, an excess of liquid water in the pores of the gas diffusion layer (GDL) and in the gas flow channel (GFC) can drastically bring down the output power. Depending on the operating conditions, liquid water emerging from the GDL micro-channels can form droplets, films or slugs in the GFC. In the regime of droplets formation, the interaction with the gas crossing-flow leads to an oscillating mechanisms that is fundamental to studying the detachment from the GDL surface, as the authors have shown in a previous publication. In this work, a numerical model of a droplet growing on the GDL surface is developed to describe the interaction between droplet cross-flowing gas stream. The droplet shape and its deformation are reconstructed assuming a known geometry. Therefore, a lumped force balance is enforced to determine the center of mass motion law. Oscillation frequencies during growth and at detachment are found as a function of droplet size. The model is also exploited to find the relationship between droplet critical detachment size and gas velocity. The numerical results are compared with the droplet frequency-size and detachment size-gas velocity experimental results previously presented by the authors. The matching between the numerical and experimental data is very good and is a mean of validation for the model. The low computational burden and the conciseness of the results make the model suitable for applications such as control and optimization strategies development to enhance PEMFC performance. Additionally, the model can be exploited to implement monitoring and diagnostic algorithm.

Christopher Leon Schreiber, Anna Kapulwa, Junji Inukai

ECS Meeting Abstracts • 2024

Introduction: Despite the high potential and expected major impact of PEFCs on the economy of the future, there are still challenges to overcome, before commercialized. PEFCs operated at temperatures higher than 100°C are expected to be used especially in the heavy-duty vehicle department due to their use of smaller and lighter radiators and lower susceptibility to catalyst poisoning. To achieve this goal however, PEFCs operated above 100°C need higher performance, stability, and durability, while reducing the cost at the same time. The performance, durability and stability of a fuel cell are related to the distribution of physical and chemical parameters, e.g. oxygen partial pressure ( p (O 2 )). During the operation of the fuel cell, the distribution of those parameters is inhomogeneous. [1] Therefore, we used an in-house developed 2-dimensional non-destructive real-time/space visualization system to achieve an understanding of the inside the fuel cell during operation at higher temperatures. Experimental: The PEFCs used for this experiment have an active area of 4 cm 2 with 10 straight gas flow channels. To visualize the oxygen partial pressure, an oxygen sensitive dye (PtTFPP) was used. PtTFPP has absorption peaks at 407, 530 and 540 nm and an emission peak at 650 nm. The emission peak is quenched by oxygen partial pressure, and the emission intensity decreases monotonically with increasing oxygen partial pressure (Fig.1). The oxygen sensitive dye was applied on the surface of the cathode side GDL. For the excitation, a laser with a wavelength of 532 nm was used and the emitted light was captured by a CCD camera. [2] The laser light was first diffused and then guided by mirrors into the cell. In order for the laser light to enter the fuel cell the cathode side endplate, which was usually made of metal, was exchanged with a transparent quartz glass endplate. Visualizations were carried out at 90, 100, and 110 o C at a constant water vapor pressure of 37.97 kPa, which equaled 53.6, 36.8, and 25.9% RH, respectively. Prior to the visualization, calibrations at 15, 18, 21, and 24% O 2 concentration, and performance tests in form of IV and CV were carried out for each temperature. The gas flow rate during the experiments was set to 100 mL min -1 Air/H 2 (parallel flow) at cathode and anode, respectively. For the oxygen concentration of 24% diluted (with N 2 ) oxygen with a total flowrate of 100 mL min -1 was used. Results and Discussion: The IV performance tests showed decreasing cell performance with increasing temperatures, which was expected because of the increasing resistance due to drying out of the membrane. Furthermore, a decrease of the ECSA was observed with increasing temperatures. The 2D-Visualization showed that oxygen partial pressure on the surface of the GDL beneath the gas flow channels was much higher than theoretically calculated. Furthermore, at lower current densities the oxygen partial pressure was higher in the outlet than at the inlet of the cell, which was unexpected (Fig. 2). It was previously shown (Kakizawa et al.) that liquid water accumulates near the outlet of the cell. The accumulated liquid water as well as the water vapor at elevated temperatures is expected to hinder the diffusion of O 2´ to the catalyst layer which could explain the increased oxygen partial pressure near the outlet and the decreased oxygen partial pressure near the inlet. However, power is generated, and oxygen was consumed elsewhere in the cell, namely inside the GDL close to the catalyst layer. This model will be researched using a 3-dimensional visualization system in the future. [1] Y. Kakizawa, C. L. Schreiber, S. Takamuku, M. Uchida, A. Iiyama, J. Inukai, Visualization of the oxygen partial pressure in a proton exchange membrane fuel cell during cell operation with low oxygen concentrations, J. Power Sources, 483, 229193 (2021). [2] Y. Kakizawa, T. Kobayashi, M. Uchida, T. Ohno, T. Suga, M. Teranishi, M. Yoneda, T. Saiki, H. Nishide, M. Watanabe, A. Iiyama, J. Inukai, Oscillation mechanism in polymer electrolyte membrane fuel cell studied by operando monitoring of oxygen partial pressure using optical probes, J. Surf. Finish. Soc. Jpn, 72, 230 (2021). Figure 1

Takao Watanabe, Yoshiyuki Izaki, Yoshihiro Mugikura et al.

Electrical Engineering in Japan • 1993

Abstract The molten carbonate fuel cell (MCFC) power plant is expected to be one of the most promising future power generation systems for the electric utilities because of its high efficiency, environmental suitability and capability of using coal as fuel. To obtain such attractive performance, it is necessary for the plant to adopt the gas‐recycling operation system. The authors tested a 6‐kW class MCFC stack with three types of gas recyclings, i.e., cathode, anode and carbon dioxide ones, including pressurized conditions. This paper describes the test results and the effects of the gas‐recycling operations. Cathode gas recycling is proved to be able to control the stack temperature and give the flexibility for setting oxygen utilization. Anode gas recycling is proved to be able to suppress the methane formation and decrease the deviation of the stacked cell voltages. Including the starting‐up process, it is proved that the electricity can be generated from the stack without supplying carbon dioxide from outside the system by carbon dioxide gas recycling. In such a process using a burner for carbon dioxide gas recycling, burner temperature must be controlled to a certain value. It is important to adjust the fuel supplying rate, load current and cathode gas‐recycling ratio to each other. At the load change process, constant gas utilization operation is not effective in changing the burner temperature.

Rustiana Yuliasni, Nur Zen, Nanik Indah Setianingsih

Jurnal Riset Teknologi Pencegahan Pencemaran Industri • 2020

This study aimed to identify the effect of substrate concentration on the performance of A Three chambers Microbial Salinity Cell (a three chambers MSC). In this study, 3 three chambers MSC was made of plexy glass with total volume of 200 ml. Alumunium wrapped with with platinum on vulcan carbon cloth were used as electrodes,with each working area 63 cm2. The results showed that a Three chambers Microbial Salinity Cell was able to generate electricity and at the same time removed salinity. The degree of electricity deneration and salinity removal were influenced by initial substrate concentration in the anode chamber. The higher substrate concentration, the better performance of MSC. The best performance of MSC achieved when COD was 2034 mg/L, resulted in maximum voltage of 0. 44 V, and maximum current density of 0.29 mA/m2. With % CE was 5.4%. The maximum conductivity increase in salinity chamber was from 11.2 µS/cm to 1027 µS/cm (salinity 0.57% ppt).

Guo-Yao Leow, Sze-Mun Lam, Jin-Chung Sin et al.

E3S Web of Conferences • 2024

In this study, an innovative and efficient carbide lime-assisted plant-microbial fuel cell (Ca-P-MFC) system was developed for treating dyestuff effluent and generating electricity. This system featured a carbon brush anode and a cupric oxide/carbon (CuO/C) cathode. The Ca-P-MFC system revealed outstanding performance compared to both the P-MFC and CW systems. At a carbide lime loading of 200 mg L −1 , the Ca-P-MFC system achieved an impressive methylene blue decomposition efficiency of 86.6% and a maximum power density ( P ) of 60.2 mW m −2 . The improved performance can be attributed to the incorporation of carbide lime, which promoted microbial reactions extending from the electrode surfaces throughout the operational area of the system. Furthermore, carbide lime served as an effective electron carrier, facilitating electron transfer across the system. The optimal loading of carbide lime was systematically evaluated in the developed Ca-P-MFC system, providing comprehensive insights into the mechanism of P-MFC.

Tatsuya Hatanaka, Kenji Kudo, Takamasa Nonaka et al.

ECS Meeting Abstracts • 2017

Polymer electrolyte fuel cells (PEFCs) are already put into the market as the power source for hydrogen fuel cell vehicles (FCVs), but further technical advancement is necessary to achieve both higher cell performance and lower cost required for wider distribution. Regarding the latter requirement, a precious metal-free cathode is an attractive alternative and various candidates have been examined such as nonprecious metal-containing or metal-free carbon-based catalysts, metal oxides, oxynitrides, and metal chalcogenides [1]. In spite of extensive researches, however, the cell performances and stabilities using those materials are still significant lower than conventional Pt-based cells. Another approach for a precious metal-free cathode is to flow a catholyte containing oxidized-state redox mediator through porous carbon electrode. The system is similar to a redox flow battery, and the reduced-state mediator is oxidized with air in another compartment (we call this system as "redox flow fuel cell"; RFFC). ACAL Energy Inc. has reported comparable cell performance to Pt-based one by this concept and also excellent durability in a potential cycle test [2]. In this paper, a molybdovanado phosphoric heteropoly acid, a kind of polyoxometalate (POM) is mentioned as a mediator; however, the characteristics of the catholyte were not described in detail. For better system efficiency, high cell performance must be achieved at high catholyte utilization, which is required to minimize the external pump energy consumption. High catholyte utilization, however, means low mediator oxidation states (i.e. state of charge; SOC) at the outlet. Therefore, the high cell performance even with low SOC catholyte is necessary. In this study, we examined the cell performances of RFFCs as functions of SOC using a molybdovanado phosphoric heteropoly acid as the mediator, and conducted ex-situ catholyte analysis using XAS, 31 P-NMR, 51 V-NMR and pH measurements to clarify the reactions in the catholyte of RFFCs. Membrane electrode assemblies (MEAs) were constructed using NR212 perfluorinated membrane (DuPont), a precious metal-free carbon cloth for the cathode and a Pt/C catalyst layer coated MPL/GDL for the anode. The electrode area was 1cm 2 and the interdigitated carbon flow field was used for the cathode. The catholyte, 140 cc of 0.3 M aqueous solution of H 6 PMo 9 V 3 O 40 (V3-POM) powder purchased from Nippon Inorganic Colour & Chemical Co., was circulated to the cathode with a tube pump at the flow rate of 14 cc/min. Fully humidified hydrogen gas was supplied to the anode at the flow rate of 100 cc/min. The cell performance was measured at the temperature maintained at 40˚C. The SOC of the catholyte was controlled by the time of period of constant current (0.3 A/cm 2 ) discharge. Small amount of catholyte (~1 cc) was sampled at each SOC and used for analysis, XAS, 31 P-NMR, 51 V-NMR and pH measurements. The obtained cell performance was shown in below. OCV exceeded 1.0V at SOC=100%, and iR-corrected cell voltage at 0.3A/cm 2 was about 0.86V. This performance is excellent as a precious metal-free cathode cell and comparable to a typical conventional Pt-based cathode cell. This result indicates that the RFFC has a good potential for a high energy conversion FC system. The ohmic resistance was found to be about 500mΩcm 2 by high frequency impedance measurements, five times as large as a typical conventional PEFC with a similar structure. The post analysis of MEA by cross-sectional EPMA revealed that membrane contained vanadium, but no molybdenum nor phosphor, suggesting decomposition of V3-POM. The dependence of OCV on SOC was found to be significantly larger than expected from the Nernst equation ( E = E 0 + RT / nF ln(x ox /(1-x ox ); where x ox is the concentration of the oxidized mediator). This discrepancy indicates that the redox reaction of the catholyte is not simple and that V3-POM is not suitable for a high utilization operation because the OCV at low SOC is too low to obtain a high cell voltage. The redox species was confirmed as vanadium by ex-situ XAS measurements conducted at BL33XU in SPring-8, Japan. The detail of reaction mechanism of V3-POM revealed by NMR and pH measurements will be discussed in the presentation. Reference: [1] M. Shao, Q. Chang, J. Dodelet, and R. Chenitz; Chem. Rev., (2016), 116, 3594–3657. [2] A. Creeth; Fuel Cells Bulletin (2011) 12–15.

Sari Tasa, Teppo Aapro

Journal of Fuel Cell Science and Technology • 2006

Mobile device manufacturers would like to provide totally wireless solutions—including charging. Future multimedia devices need to have longer operation times as simultaneously they require more power. Device miniaturization leaves less volumetric space available also for the energy source. The energy density of the Li-ion batteries is high, and continuously developed, but not at the same speed as the demand from devices. Fuel cells can be one possible solution to power mobile devices without connection to the mains grid, but they will not fit to all use cases. The fuel cell system includes a core unit, fuel system, controls, and battery to level out peaks. The total energy efficiency is the sum of the performance of the whole system. The environmental performance of the fuel cell system cannot be determined yet. Regulatory and standardization work is on-going and driving the fuel cell technology development. The main target is in safety, which is very important aspect for energy technologies. The outcomes will also have an effect on efficiency, cost, design, and environmental performance. Proper water, thermal, airflow, and fuel management of the fuel cell system combined with mechanical durability and reliability are the crucial enablers for stable operation required from the integrated power source of a mobile device. Reliability must be on the same level as the reliability of the device the energy source is powering; this means years of continuous operation time. Typically, the end-users are not interested of the enabling technologies nor understand the usage limits. They are looking for easy to use devices to enhance their daily life. Fuel cell technology looks promising but there are many practical issues to be solved.

Subhendu Bhandari, Soumya Pandit, Chetan Pandit et al.

Research Square • 2024

Abstract In the present study, Polyaniline (PANI)/ Carbon Felt (CF) composite electrodes were developed to be used as an anode in a Microbial Fuel Cell (MFC) for the enrichment of specific electroactive organisms on the anode. Comparative analysis of two approaches of Phenol degradation namely adsorption & biodegradation and for simultaneous generation of bio-electricity. Sulfuric acid-doped PANI was electrochemically synthesized in aqueous medium and deposited in-situ on the carbon felt anode followed by its characterization using SEM, XRD, and CV. To use these in MFC, different concentrations of PANI ranging from 0.25 mg/cm 2 to 1.25 mg/cm 2 , was deposited onto CF via potentiostatic electrodeposition technique and compared. The morphological analysis using FESEM of the anode revealed homogenous deposition of nanostructured PANI onto the surface of CF. Further characterization of PANI/CF composite shows that PANI has improved the surface area of the anode, thereby, increasing the conductivity of the anode and promoting biofilm attachment to the anode. The PANI/ CF composite anode with loading rate of 1.0 mg/cm 2 showed the best results with maximum power density of 584.2 mW m -2 and lowest charge transfer resistance of 49.6 Ω. The reduction of COD and total phenol of wastewater were 73% and 88% respectively. The obtained results from this study show that the power production and efficiency of the MFCs can be improved greatly by using Sulphate containing PANI/ CF composite as an anode material. The CLSM results indicated that PANI facilitates in promoting EAB biofilm which in turn helps in achieving enhanced power output.

Kyoung‐Yeol Kim, Euntae Yang, Mi‐Young Lee et al.

Journal of Chemical Technology & Biotechnology • 2013

Abstract BACKGROUND An ultrafiltration microbial fuel cell ( UF‐MFC ) is a novel technology that can simultaneously produce high‐quality effluent and electricity during wastewater treatment. To increase the power density and mitigate the inevitable biofouling phenomena in UF‐MFCs , the anode direct contact ( ADC ) method was tested. ADC application in UF‐MFCs improves the power densities by reducing the distance between the anode electrode and UF membrane (lowering the internal resistance), and mitigates biofouling on the UF membrane surface due to the direct contact of the porous anode electrode with the membrane surface. RESULTS The maximum power density increased from 76.6 ± 2.5 mW m −2 to 129.4 ± 13.9 mW m −2 after applying the ADC , with the internal resistance decreasing from 0.49 Ω m 2 to 0.23 Ω m 2 . The concentrations of extracellular polymeric substances ( EPS ) and total cell number were also analyzed as indicators for measuring biofouling on the UF membrane surface. EPS proteins and total cell numbers were reduced (62.8% and 64.9% each) with ADC application after 70 h operation, though no differences were observed in the specific permeate flux. CONCLUSION ADC application is simple and its use can enhance the power densities and mitigate the biofouling phenomena of UF‐MFCs . © 2013 Society of Chemical Industry

Rojas-Flores Segundo, Cabanillas-Chirinos Luis, Nélida Milly Otiniano et al.

Sustainability • 2025

The intensification of agricultural production due to high global demand has led to uncontrolled waste production from this industry, creating an environmental imbalance due to inadequate waste management. In developing regions, the lack of access to electricity has become a critical problem, affecting people’s health, education, and economy. To address this issue, alternative and sustainable ways of generating electricity have been explored. This research focuses on the potential of using asparagus waste in single-chamber microbial fuel cells (MFCs) at different pH levels (4, 4.7—target, 7, and 9) to achieve optimal performance. It has been demonstrated that using this substrate, the MFC at pH 7 obtained the best results on the seventh day, generating an electric current of 4.859 mA and a maximum voltage of 0.965 V. The substrate showed an oxidation-reduction potential of 312.821 mV, a chemical oxygen demand reduction of 76.47%, and an electrical conductivity of 254.854 mS/cm. Additionally, it managed to generate a power density of 2.149 mW/cm2 at a current density of 5.979 mA/cm2. MFCs at different pH levels (4, 4.7—target, 7, and 9) demonstrated their potential to generate electrical energy by powering an LED light when connected in series. This research holds promise in promoting sustainable energy solutions for the future.

B. Passmore, J. Hornberger, B. McPherson et al.

Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) • 2011

A high temperature, high performance power module was developed for extreme environment systems and applications to exploit the advantages of wide bandgap semiconductors. These power modules are rated > 1200V, > 100A, > 250 °C, and are designed to house any SiC or GaN device. Characterization data of this power module housing trench MOSFETs is presented which demonstrates an on-state current of 1500 A for a full-bridge switch position. In addition, switching waveforms are presented that exhibit fast transition times.

Dina Koltysheva, Kateryna Shchurska, Yevhenii Kuzminskyi

Innovative Biosystems and Bioengineering • 2024

Background. The possibility of converting organic compounds into electrical energy in microbial fuel cells (MFCs) makes MFCs a promising eco-friendly technology. However, the use of platinum or hexacyanoferrates may increase costs or lead to secondary environmental pollution. The use of microalgae in the cathode chamber is a promising solution to these problems. Objective. We aimed to establish the dependence of electrical energy generation and the efficiency of the appli­cation of a specific type of algae on the type and mode of lighting. Methods. In the study, two-chamber H-type MFC with salt bridge was used. Fermented residue after methanogenesis was used as inoculum in the anode chamber, and microalgae cultures Chlorella vulgaris, Desmodesmus armatus, and Parachlorella kessleri were used as inoculum in the cathode chamber. Results. MFCs with microalgae demonstrate the ability to generate current under different light sources. The maximum voltage for the MFC with an anode biofilm and with microalgae in the cathode chamber is 13–15% lower compared to the MFC with an abiotic cathode (840 ± 42 mV). The maximum current is 2–6% lower than the control (480 ± 24 mA) for the MFC with Chlorella vulgaris and the MFC with Parachlorella kessleri, and 8% higher for the MFC with Desmodesmus armatus compared to the MFC with an abiotic cathode. The MFCs with microalgae are capable of generating electrical energy for an extended period. Conclusions. With a pre-grown anodic biofilm, both the current and voltage maintain relative stability when the light source is changed. The potential use of solar lighting broadens the applicability of the MFCs with microalgae, as it eliminates the need for additional costs associated with artificial light sources.

Irene Merino-Jimenez, Carlo Santoro, Santiago Rojas-Carbonell et al.

Catalysts • 2016

A comparison between different carbon-based gas-diffusion air-breathing cathodes for microbial fuel cells (MFCs) is presented in this work. A micro-porous layer (MPL) based on carbon black (CB) and an activated carbon (AC) layer were used as catalysts and applied on different supporting materials, including carbon cloth (CC), carbon felt (CF), and stainless steel (SS) forming cathode electrodes for MFCs treating urine. Rotating ring disk electrode (RRDE) analyses were done on CB and AC to: (i) understand the kinetics of the carbonaceous catalysts; (ii) evaluate the hydrogen peroxide production; and (iii) estimate the electron transfer. CB and AC were then used to fabricate electrodes. Half-cell electrochemical analysis, as well as MFCs continuous power performance, have been monitored. Generally, the current generated was higher from the MFCs with AC electrodes compared to the MPL electrodes, showing an increase between 34% and 61% in power with the AC layer comparing to the MPL. When the MPL was used, the supporting material showed a slight effect in the power performance, being that the CF is more powerful than the CC and the SS. These differences also agree with the electrochemical analysis performed. However, the different supporting materials showed a bigger effect in the power density when the AC layer was used, being the SS the most efficient, with a power generation of 65.6 mW·m−2, followed by the CC (54 mW·m−2) and the CF (44 mW·m−2).

Mostafa Ghasemi, Mehdi Sedighi, Yie Hua Tan

Sustainability • 2021

In this paper, we reported the fabrication, characterization, and application of carbon nanotube (CNT)-platinum nanocomposite as a novel generation of cathode catalyst in microbial fuel cells (MFCs) for sustainable energy production and wastewater treatment. The efficiency of the carbon nanocomposites was compared by platinum (Pt), which is the most effective and common cathode catalyst. This nanocomposite is utilized to benefit from the catalytic properties of CNTs and reduce the amount of required Pt, as it is an expensive catalyst. The CNT/Pt nanocomposites were synthesized via a chemical reduction technique and the electrodes were characterized by field emission scanning electron microscopy, electronic dispersive X-Ray analysis, and transmission electron microscopy. The nanocomposites were applied as cathode catalysts in the MFC to obtain polarization curve and coulombic efficiency (CE) results. The catalytic properties of electrodes were tested by linear sweep voltammetry. The CNT/Pt at the concentration of 0.3 mg/cm2 had the highest performance in terms of CE (47.16%), internal resistance (551 Ω), COD removal (88.9%), and power generation (143 mW/m2). In contrast, for the electrode with 0.5 mg/L of Pt catalyst, CE, internal resistance, COD removal, and power generation were 19%, 810 Ω, 96%, and 84.1 mW/m2, respectively. So, it has been found that carbon nanocomposite cathode electrodes had better performance for sustainable clean energy production and COD removal by MFC.

Paweł P. Włodarczyk, Barbara Włodarczyk

Catalysts • 2019

Microbial fuel cells (MFCs) are devices than can contribute to the development of new technologies using renewable energy sources or waste products for energy production. Moreover, MFCs can realize wastewater pre-treatment, e.g., reduction of the chemical oxygen demand (COD). This research covered preparation and analysis of a catalyst and measurements of changes in the concentration of COD in the MFC with a Ni–Co cathode. Analysis of the catalyst included measurements of the electroless potential of Ni–Co electrodes oxidized for 1–10 h, and the influence of anodic charge on the catalytic activity of the Ni–Co alloy (for four alloys: 15, 25, 50, and 75% concentration of Co). For the Ni–Co alloy containing 15% of Co oxidized for 8 h, after the third anodic charge the best catalytic parameters was obtained. During the MFC operation, it was noted that the COD reduction time (to 90% efficiency) was similar to the reduction time during wastewater aeration. However, the characteristic of the aeration curve was preferred to the curve obtained during the MFC operation. The electricity measurements during the MFC operation showed that power equal to 7.19 mW was obtained (at a current density of 0.47 mA·cm−2).

S. Latorrata, M. Sansotera, M. Gola et al.

Fuel Cells • 2020

Abstract In this work, perfluoropolyether (PFPE) functionalization was used as hydrophizing treatment for gas diffusion layers (GDLs) in polymer electrolyte membrane fuel cells (PEMFCs), instead of standard PTFE coatings, aiming to enhance the hydrophobicity of the gas diffusion media and to reduce the mass transfer limitations in the final device. Carbon cloth diffusion layers and carbon black were functionalized by decomposition of a PFPE peroxide. PFPE‐functionalized carbon black was employed in the preparation of an ink suitable for obtaining microporous layers (MPLs) by deposition onto macroporous backing layers. Dual‐layer gas diffusion media showing superhydrophobic behavior due to different hydrophobizing treatments were compared with conventional PTFE‐based materials, by testing in a single PEMFC working at two different temperatures and at low and high relative humidity conditions. Such tests demonstrated improved performances over conventional GDLs for pure PFPE‐based samples in terms of both overall electrical performance and reduced diffusive limitations in high current density conditions. The maximum output power achieved with the novel PFPE‐based compounds was 460 mW cm −2 at 80 °C and relative humidity (RH) 100% while the best improvement (10%) with respect to conventional GDLs was realized at 80 °C and RH 60%.

, Azhar Uddin

• 2019

With the issue of the rise of anthropogenic CO2, global warming and rise of the primary energy demand, strong measures for the energy transition and the diversification with renewables and existing fossil-based infrastructure are required. Also, carbon capture and utilization of CO2 would also be needed. In that sense, thermochemical redox cycles gain particular interest to produce synthetic fuels, which can be used for energy generation and production of chemicals. In a two-step redox cycles, metal oxides acts as oxygen carriers and undergo looping between two reactors. In the reduction reactor, metal oxide is reduced with release of oxygen (solar-thermal) or produces syngas (for fuel reduction) whereas, in oxidation, CO2/H2O splits for form syngas when in contact with the metal oxide. Ceria being readily available at large scale and due to its nature of undergoing reduction non-stoichiometrically at low temperature makes it a good candidate. In the present thesis, a detailed investigation of thermochemical dissociation of CO2 and H2O considering solar thermal and fuel reduction with a focus on non-structured reactors is carried out. For the solar-driven cycle, an assessment of counter-current flow moving bed reactors for reduction and oxidation is performed and a chemical looping (CL) unit is added to a 100 MW power plant. With an operating temperature of 1600oC and 10-7 bar pressure, a maximum power output of 12.9 MW with solar to electricity efficiency of 25.4% is calculated. This additional power would bring down the efficiency loss due to carbon capture from 11.3 to 6%. Even though a considerable efficiency is obtained on very optimistic operating conditions, it still requires a huge solar field. Economics revealed that with a carbon tax of $40/tone of CO2 the levelized cost of electricity (LCOE) achieved is 17.8 times higher than the existing market price (without carbon capture). If a higher carbon tax of 80$/MWh is considered that it would still be 6.28 times higher for a plant with a carbon tax. As an alternative, methane-driven CL unit is integrated into a power plant to access the overall system efficiency and amount of efficiency regain after carbon capture. Since there exists no solid-state kinetic model in the literature for methane driven CO2/H2O splitting cycle, an experimental investigation was performed which revealed that an Avrami-Erofe’ev (AE3) model fit best to both oxidation and reduction, with activation energies of 283 kJ/mol and 59.7 kJ/mol, respectively. A comparative assessment was performed to investigate the influence of kinetics. A CL unit based on thermodynamics and kinetics (with moving bed reactors) were tested in a power plant. A drop of 20% in the efficiency of the CL unit was observed when the kinetic-based CL unit is considered. However, due to thermal balance within the system, a similar thermal efficiency of the overall plant was achieved as 50.9%. However, when the thermodynamic-based CL unit layout is considered there exists an excess heat which predicts the possibility of improving the efficiency. An economic assessment revealed a specific overnight capital cost of 2455$/kW, a levelized cost of CO2 savings of 96.25 $/tonneCO2, and a LCOE of 128.01 $/MWh. However, with a carbon tax of 6 $/tonneCO2, the LCOE would drop below 50 $/MWh. The methane-driven CL unit is later integrated as an add-on unit to a polygeneration plant that produces electricity and dimethyl ether. The results showed that the plant can produce 103 MWe and 2.15 kg/s of DME with energy and exergy efficiency of 50% and 44%, respectively. The capital investment required for the plantis about $534 million. With the carbon tax of $40/tonne of CO2, a current DME price of $18/GJ and an electricity price of $50/MWh would be achieved. Overall, the integration of the CL unit as an add-on unit to the power plant is more suitable than polygeneration with respect to the existing market price. El aumento del CO2 antropogénico y el calentamiento global y el aumento de la demanda de energía primaria hace que se requieran medidas para la transición energética y la diversificación con energías renovables e infraestructuras existentes basadas en combustibles fósiles. Además de implementar medidas para la captura y el secuestro de carbono, también se necesita desarrollar métodos para la utilización de CO2. En ese sentido, los ciclos redox termoquímicos son particularmente interesantes para producir combustible sintético que, a su vez, pueden utilizarse para la producción de otras substancias químicas. La rotura de CO2 / H2O (CL) mediante una vía termoquímica de dos pasos está compuesta por dos reacciones redox con un óxido metálico. El primer paso es la reducción de los óxidos metálicos al perder oxígeno y crear vacantes en la red a una temperatura más alta y convertirse en óxido de metal de valencia más baja. Durante la etapa de oxidación, los gases reactivos CO2 / H2O reaccionan con el óxido metálico reducido formando CO y H2. Se ha investigado el uso de diferentes óxidos metálicos en función de su capacidad de transporte de oxígeno y sus propiedades para realizar ciclos redox continuos a distintos valores de temperatura y presión. Después de un examen cuidadoso, se ha seleccionado a la ceria para la división de CO2 / H2O a gran escala. En el presente trabajo, se investigan las divisiones termoquímicas de CO2 / H2O impulsadas por energía solar y la reducción de metano para la producción de gas de síntesis, con especial atención a su aplicación en reactores no estructurados. Se evalúa el uso de reactores de lecho móvil basado en flujo contracorriente y reactores de lecho fluidizado que funcionan en diferentes regímenes de fluidización. Es un reactor de lecho móvil tanto para la etapa de reducción como para la etapa de oxidación se obtienen altas selectividades de CO y H2 con volúmenes óptimos del reactor, mientras que en un reactor de lecho fluidizado el volumen requerido es mucho más alto, lo que lo hace inviable. Los modelos de reactor se han desarrollado en Aspen plus y se validan a partir de la literatura. Un análisis de sensibilidad ha revelado que la unidad CL depende en gran medida de la temperatura y la presión. El análisis se ha ampliado integrando la unidad desarrollada de CL como una unidad adicional a una central eléctrica de 100 MW con captura de carbono. La eficiencia de la planta se ha investigado considerando sólo la división de CO2, sólo la del H2O y la mezcla de CO2 y H2O como alimentación al reactor de oxidación de la unidad CL. El resultado es de una potencia máxima de 12.9 MW con una eficiencia de energía solar a eléctrica de 25.4%. Esta potencia adicional reduciría la pérdida de eficiencia debido a la captura de carbono de 11.3 a 6%. Para lograr esto, el reactor de reducción de la unidad CL debe funcionar a 1600 ° C y 10-7 bar de presión. Estas condiciones necesitarían un enorme campo solar y la operación, en ausencia de almacenamiento térmico, se limitaría a unas pocas horas durante el día. El análisis técnico-económico ha revelado que el coste nivelado de la electricidad es de 1321 $/MWh sin incluir incentivos ni impuestos sobre el carbono. Posteriormente, se ha considerado la reducción del metano como una alternativa a la reducción térmica. Al principio, se realizaron análisis termodinámicos de la unidad de CL impulsada por metano. A partir del análisis, se ha demostrado que la temperatura mínima requerida es de 900°C con 50% de exceso de metano para la reducción, lo que supone una eficiencia de la unidad CL de 62% con un rendimiento óptimo de CO y H2. La división de CO2/H2O en el reactor de oxidación a una mayor temperatura de salida beneficiaría considerablemente la eficiencia energética del ciclo redox CL completo. La variación de la relación H2/CO en la salida con respecto a los parámetros de entrada variables que incluyen la composición del gas al reactor de oxidación se ha estudiado con el fin de especificar las condiciones operativas idóneas. Posteriormente, la unidad CL impulsada por metano se ha integrado como una unidad adicional a una central eléctrica de 500 MW alimentada por oxígeno. Se ha investigado el rendimiento de un sistema con un ciclo combinado de gas natural convencional con o sin captura de carbono. Se ha obtenido una eficiencia de sistema y eficiencia energética de 50.7 y 47.4%, respectivamente. La eficiencia del sistema podría mejorarse a 61.5%, sujeto a la optimización del sistema. La evaluación tecno-económica ha revelado un coste de capital durante la noche de 2455 $/kW con un coste de ahorro de CO2 de 96.25 $/tonelada CO2 y un LCOE de 128.01 $/MWh. Sin embargo, con créditos de carbono de 6 $/tonelada CO2, el LCOE caería por debajo de 50 $/MWh. Con l'aumento delle emissioni di CO2 antropogenica che contribuiscono al riscaldamento globale e l'incremento della domanda mondiale di energia primaria, sono richieste significative misure per favorire la diversificazione delle fonti e la transizione energetica tramite fonti rinnovabili a partire dalle infrastrutture esistenti basate su combustibili fossili. Prima ancora degli interventi per la cattura e il sequestro dell’anidride carbonica, anche l’utilizzo della CO2 rappresenta una misura necessaria al raggiungimento degli obiettivi di decarbonizzazione. In questo senso, i cicli redox termochimici hanno acquisito particolare interesse per la produzione di combustibile sintetico da utilizzare come intermedio nella produzione di altri prodotti chimici. La separazione chimica di CO2/H2O attraverso un ciclo termochimico – chemical looping splitting (CL) – in due fasi è composta da due reazioni redox con un ossido di metallo. La prima fase del ciclo avviene alla temperatura più elevata e consiste nella riduzione dell’ossido di metallo, che cede ossigeno creando vacanze nel reticolo e diventando ossido di metallo a bassa valenza. Durante la fase di ossidazione, i gas reagenti CO2/H2O reagiscono con l'ossido di metallo ridotto che forma CO e H2. Una mappatura dettagliata dei diversi ossidi di metallo è stata effettuata in base alla loro capacità di trasporto dell’ossigeno e alle proprietà nei cicli di ossido-riduzione a funzionamento continuo in condizioni di variazione di temperatura e pressione. Dopo un attento esame, l’ossido di Cerio - ceria - è stato selezionato per l'applicazione che può essere disponibile per la scissione CO2 / H2O su larga scala. In questo lavoro, sia la separazione termochimica di CO2/H2O alimentata tramite energia solare, sia i cicli con riduzione tramite metano, entrambi finalizzati all produzione di syngas sono stati studiati con particolare attenzione ai reattori non strutturati. Per il ciclo termochimico basato su energia solare, è stata effettuata la valutazione dei reattori a letto mobile a flusso in controcorrente e a letto fluido che operano in diversi regimi di fluidizzazione. Il reattore a letto mobile è stato individuato come il più performante sia per la riduzione che l’ossidazione, con elevate selettività verso CO e H2 e volumi ottimali del reattore, mentre una resa analoga con reattori a letto fluidizzato potrebbe essere ottenuta solo con volumi di reattore molto alti, rendendo questa scelta irrealizzabile nella pratica. I modelli di reattore sono stati sviluppati in Aspen plus e sono stati validati dalla letteratura. Un'analisi di sensitività ha rivelato che la performance dell'unità CL è in larga misura dipendente dalla temperatura e dalla pressione di riduzione. L'analisi è stata estesa integrando l'unità CL sviluppata come unità aggiuntiva di una centrale elettrica a ossicombustione da 100 MW con cattura di carbonio. L'efficienza dell'impianto è stata studiata considerando di alimentare il reattore di ossidazione dell'unità CL sia con CO2, sia con H2O, sia con una miscela di CO2 e H2O. I risultati indicano una potenza massima di 12,9 MW con un rendimento da solare a elettricità del 25,4% generabile grazie all’unità di CL. Questa potenza aggiuntiva ridurrebbe la perdita di efficienza dovuta alla cattura di carbonio dall'11,3 al 6%. Per ottenere ciò, il reattore di riduzione dell'unità CL deve operare a 1600 ° C con una pressione di 10-7 bar. Queste condizioni avrebbero bisogno di un enorme campo solare e l'operazione sarebbe limitata a poche ore durante il giorno senza l’integrazione di un accumulo termico. L'analisi tecno-economica ha rivelato che il costo livellato (levelizad cost) dell'elettricità era di 1321 $ / MWh, senza includere incentivi o tassazione sul carbonio. Successivamente, è stata considerata la riduzione della ceria con metano come alternativa alla riduzione termica. Inizialmente, sono state condotte analisi termodinamiche dell'unità CL con riduzione a metano. Dall'analisi è emerso che la temperatura minima richiesta era 900 °C per la riduzione con un eccesso di metano del 50%, che ha prodotto un'efficienza dell'unità CL del 62% con una resa ottimale di CO e H2. In questo caso, la scissione di CO2/H2O nel reattore di ossidazione consisteva nell'ossidazione completa esotermica della ceria, per cui una temperatura di uscita più elevata avrebbe notevolmente migliorato l'efficienza energetica del ciclo CL redox completo. La variazione del rapporto H2 / CO all'uscita rispetto ai vari parametri di input, compresa la composizione del gas inviato al reattore di ossidazione, è stata studiata per specificare le condizioni operative necessarie. Successivamente, l'unità CL a metano è stata integrata come unità aggiuntiva in una centrale elettrica a ossicombustione da 500 MW. Sono state studiate le prestazioni del sistema in una valutazione comparativa con un ciclo combinato convenzionale a gas naturale, un ciclo a ossicombustione con cattura di carbonio e l'impianto proposto. Sono stati ottenuti per l’impianto rispettivamente un rendimento del sistema e un'efficienza energetica del 50,7% e del 47,4%. L'efficienza del sistema potrebbe essere migliorata fino al 61,5% tramite l'ottimizzazione del recupero termico del sistema, valutata attraverso la pinch analysis del sistema. Una dettagliata valutazione tecno-economica ha rivelato un costo specifico del capitale di 2455 $ / kW (overnight cost), un costo livellato delle emissioni di CO2 evitate 96,25 $ / tonnellata di CO2, e un costo dell’elettricità (LCOE) di 128,01 $ / MWh. Tuttavia, considerando un incentivo di 6 $ / tonnellata di CO2 evitata, il LCOE scenderebbe sotto i 50 $ / MWh. L'unità CL a metano viene successivamente integrata come unità aggiuntiva in un impianto di poligenerazione che produce elettricità e dimetil-etere. I risultati hanno mostrato che l'impianto può produrre 103 MWe e 2,15 kg/s di DME con un’efficienza energetica ed exergetica del 50% e del 44% rispettivamente. L'investimento di capitale richiesto per l'impianto ammonta a 534 M$. Con un valoré per la carbon tax di $ 40 / tonnellata di CO2, il DME e l’elettricità raggiungerebbero la parità con gli attuali prezzi di mercato, pari a $18/GJ per il DME e $50/MWh per l’elettricità. I costi risultanti sono dovuti all'unità di separazione dell'aria richiesta per la centrale elettrica a ossicombustione e può essere ridotta sostituendo l'unità di separazione dell'aria con una tecnologia a membrana per la separazione dell'ossigeno. Poiché in letteratura non esiste un modello completo per cinetica dello stato solido che descriva la riduzione con metano della ceria, esso è stato ricavato per via sperimentale. Sono stati condotti esperimenti in un reattore tubolare orizzontale a letto fisso in un intervallo di temperatura di 900-1100 °C. E’ stata studiata la cinetica della scissione della CO2, essendo una reazione più complessa rispetto alla scissione dell'acqua, la cui cinetica è stata invece ottenuta dalla letteratura. In base all’analisi sperimentale condotta, il modello cinetico Avrami-Erofe'ev (AE3) è risultato essere il migliore per entrambe le reazioni, con le rispettive energie di attivazione ottenute rispettivamente come 283 kJ/mol e 59,68 kJ/mol. L'ordine della reazione è stato ricavato come relazione tra temperatura e concertazione dei reagenti. L'analisi è stata effettuata seguendo un approccio termodinamico, ma la reazione eterogenea dell'ossido di metallo e dei gas reagenti limita il raggiungimento dell'equilibrio durante la reazione e dipende sempre dal tipo di reattore scelto per x l'applicazione. Pertanto, un modello di reattore a letto mobile è stato sviluppato considerando la riduzione del metano ottenuta sperimentalmente e la cinetica di splitting della CO2 è stata incorporata per valutare i due impianti proposti: la centrale elettrica e l'impianto di poligenerazione. È stata osservata una riduzione del 20% nell'efficienza dell'unità CL. Tuttavia, grazie all’integrazione termica interna al sistema, l’efficienza termica dell'impianto complessivo è molto simile a quella raggiunta nell’analisi termodinamica, con un valore del 50,9%. Tuttavia, a differenza del layout termodinamico, non è disponibile calore in eccesso per migliorare ulteriormente l'efficienza del sistema. Oltre al riciclo e all'utilizzo della CO2, come criteri di valutazione della sostenibilità per il layout proposto sono stati analizzati anche l’occupazione del suolo terreno e il fabbisogno idrico. Sia il fabbisogno di terra che di acqua aumentano di 2,5 volte rispetto ad una centrale convenzionale a ciclo combinato a gas naturale. Inoltre, anche l’impianto di poligenerazione con produzione di energia elettrica e dimetil etere (DME) è stato studiato considerando un modello dell’unità CL basato sulla cinetica e ha rilevato che la produzione di DME scenderebbe da 2,15 kg/s a 1,48 kg/s e la potenza elettrica prodotta da 103 a 72 MW. Pertanto, la cinetica ha una forte influenza sulla prestazione complessiva del sistema, e considerarla nell’analisi porta a ridurre la produzione di energia e DME di circa il 30% con un aumento di costo del 30%. Complessivamente, l'integrazione dell'unità CL come unità aggiuntiva ad una centrale elettrica a ossicombustione risulta più adatta rispetto alla poligenerazione, considerando il prezzo di mercato attuale per le commodities prodotte.

, Cristina Rotoni

• 2025

Agricultural efficiency, including in floriculture, requires sustainable methods to increase productivity while reducing the environmental impact of chemical fertilizers and pesticides. Overuse of fertilizers leads to soil degradation, water pollution, and biodiversity loss. One promising alternative is the use of plant-beneficial microorganisms as biofertilizers. However, optimizing the use of these microbial inoculants—either as single strains or complex microbial communities—remains challenging, especially in balancing nutrient inputs and maximizing plant-microbe interactions in commercial flower production. In this thesis, chrysanthemum (Chrysanthemum indicum L.) was used as a model plant for vegetative propagation to investigate the interactions between plant genetics, microbial inoculation, and nutrient availability during early root development. The study aims to understand how genotype-microbiome-environment interactions shape plant growth and nutrient use efficiency in chrysanthemum cultivation. In Chapter 2, the genetic variability among chrysanthemum cultivars and its influence on rhizosphere bacterial and fungal communities were investigated. Results showed that different cultivars select distinct rhizosphere microbiomes while maintaining a shared core of microbial species. Genetic differences among cultivars influenced the composition of these microbial communities. In Chapter 3, microbial inoculations with bacterial isolates and arbuscular mycorrhizal fungi (AMF), along with AMF-accompanying microbiomes (AMFc), were tested on chrysanthemum growth and rhizosphere microbiome composition. AMFc had a stronger effect on microbiome assembly and plant growth compared to single bacterial strains, highlighting the potential of complex microbial inoculations. In Chapter 4, AMF propagation was examined over 11 cycles of millet cultivation using trap propagation methods. The study evaluated traits such as indole-3-acetic acid (IAA) production and phosphate solubilization. AMFc consistently increased IAA production, particularly under low microbial activity, underscoring the importance of AMF in maintaining beneficial soil microbiomes and improving nutrient cycling. In Chapter 5, co-inoculation with AMFc and two bacterial strains (SMF006 and SMF018) was tested for its effects on chrysanthemum growth and root architecture. Co-inoculation with AMFc and SMF006 enhanced root dry biomass and enriched beneficial microbial taxa, including Sphingomonas, Taibaiella, Trichoderma, and Penicillium. In Chapter 6, the effects of nutrient availability on the interaction between AMFc and bacterial isolate SMF006 were explored. Genomic analysis of SMF006 revealed plant growth-promoting traits like nitrogen fixation, siderophore production, and IAA production. Increased nutrient input reduced microbial recruitment in the endophytic and epiphytic communities, indicating that nutrient limitation enhances microbial recruitment and plant growth promotion. Overall, this thesis highlights the potential of combining AMFc with beneficial bacterial strains to enhance plant growth, and reduce the need for chemical inputs. By optimizing microbial inoculation strategies and understanding plant-microbe interactions, this research provides a framework for more sustainable and efficient flower production systems.

Babita Tripathi, Soumya Pandit, Aparna Sharma et al.

Catalysts • 2022

The present study explores the use of carbon dots coated with Iron (II, III) oxide (Fe3O4) for its application as an anode in microbial fuel cells (MFC). Fe3O4@PSA-C was synthesized using a hydrothermal-assisted probe sonication method. Nanoparticles were characterized with XRD, SEM, FTIR, and RAMAN Spectroscopy. Different concentrations of Fe3O4- carbon dots (0.25, 0.5, 0.75, and 1 mg/cm2) were coated onto the graphite sheets (Fe3O4@PSA-C), and their performance in MFC was evaluated. Cyclic voltammetry (CV) of Fe3O4@PSA-C (1 mg/cm2) modified anode indicated oxidation peaks at −0.26 mV and +0.16 mV, respectively, with peak currents of 7.7 mA and 8.1 mA. The fluxes of these anodes were much higher than those of other low-concentration Fe3O4@PSA-C modified anodes and the bare graphite sheet anode. The maximum power density (Pmax) was observed in MFC with a 1 mg/cm2 concentration of Fe3O4@PSA-C was 440.01 mW/m2, 1.54 times higher than MFCs using bare graphite sheet anode (285.01 mW/m2). The elevated interaction area of carbon dots permits pervasive Fe3O4 crystallization providing enhanced cell attachment capability of the anode, boosting the biocompatibility of Fe3O4@PSA-C. This significantly improved the performance of the MFC, making Fe3O4@PSA-C modified graphite sheets a good choice as an anode for its application in MFC.

Junyeong An, Hyung‐Sool Lee

ChemSusChem • 2014

Abstract Voltage reversal in stacked microbial fuel cells (MFCs) is a significant challenge that must be addressed, and the information on its definite cause and occurrence process is still obscure. In this work, we first demonstrated that different anodic reaction rates caused voltage reversal in a stacked MFC. Sluggish reaction rates on the anode in unit 1 of the stacked MFC resulted in a significantly increased anode overpotential of up to 0.132 V, as compared to negligible anode overpotential (0.0247 V) in unit 2. This work clearly verified the process of voltage reversal in the stacked MFC. As the current was gradually increased in the stacked MFC, the voltage in the stacked unit 1 decreased to 0 V prior to that of the stacked unit 2. Then, when the voltage in unit 1 became 0 V, it was converted from a galvanic cell to an electrochemical cell powered by unit 2. We found that the stacked unit 2 provided electrical energy for the stacked unit 1 as a power supply. Finally, the anode potential of the stacked unit 1 significantly increased over cathode potential as current increased further, which caused voltage reversal in unit 1. Voltage reversal occurs in stacked MFCs as a result of non‐spontaneous anode overpotential in a unit MFC that has sluggish anode kinetics compared to the other unit MFCs.

Raisa C.P. Oliveira, Maria J. Jeremias, Maria Margarida Mateus et al.

Fuel Cells • 2022

Abstract This work reports preliminary studies to develop new direct liquid fuel cells that employ two by‐products from kraft and sulfite pulp mills as the fuel, namely kraft black liquor (BL) and spent sulfite liquor (SSL). The composition and properties of BL and SSL are characterized, being determined a conductivity 40 times higher for BL than for SSL. The performance of the BL fuel cell (BLFC) and the SSL fuel cell (SSLFC) is assessed employing 5 M hydrogen peroxide solution as the oxidant at different pH values. For the BLFC, an anion‐exchange membrane (AEM) is used, and for the SSLFC, both AEM and cation‐exchange membrane (CEM) are tested. Different parameters that characterize the fuel cell performance (e.g., peak power density) are determined and compared with similar wastewater‐based fuel cells described in the literature. To the best of the authors’ knowledge, it is the first time two pulp mill by‐products (BL and SSL) are reported as fuels for application in fuel cells.

Andrew Odorona Odeh, Peter Ogbemudia Osifo, Hein J. P. W. Neomagus

ECS Transactions • 2013

Development and characterization of polymer electrolyte membrane (PEM) using low cost Chitosan were carried out by blending with sulphonated zirconium oxide, and assessed for its potential to serve as possible polymer electrolyte membrane fuel cell (PEMFC) application. Synthesized membranes were thus characterized by scan electron microscope (SEM) to define the morphology of the membrane. Fourier Transform Infra-red (FT-IR) to confirm the presence of functional groups. Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were used to verify the thermal stability of the membrane. Membrane water uptake was used to investigate the porosity and swelling ability of the membrane, while impedance spectroscopy was used to measure the proton conductivity of the membrane. The permeability of the membrane was determined using a diffusion cell that was developed at Vaal University of Technology. The results obtained revealed that the blending of the chitosan with sulphonated zirconium oxide improved the water uptake, thermal stability, proton conductivity and permeability of the composite membrane than Nafion 117, which is the commercially available membrane. The water uptake was in the range of 70-74% while that of Nafion 117 is in the bracket of 25-33%. The TGA and DSC analysis showed that the composite membrane developed is a glassy polymer with a glass transition temperature (T g ) of 184 o C. The proton conductivities were in the range of 10 -3 -10 -2 S/cm and tend to increase with increase in the composition of the sulphonated zirconium oxide use in synthesizing the composite membrane. The permeability obtained was in the range of 4 x 10 -6 – 7 x 10 -6 mol/m 2 .s.Pa. From the results of the proton conductivity and the permeability, the selectivity factor of the membrane, which is a measure of performance of the membrane were determined. This is in the range of 14 – 34.

Raymond Daniel Rodriguez Martinez, Maria Eugenia Alvarez Bermudez

Clean Energy • 2023

Abstract Growing energy demand is a current problem with greater incidence in the future. The research objective is to establish seed bases to give a leading role to plants used in anthropogenic production activities and consumption, and even plants belonging to wildlife in terms of energy production. The use of living plants to obtain electrical energy through a microbial-vegetable fuel cell is proposed as a mechanism to supply the energy demand with easy access worldwide, especially in areas far from urban centres. In this work, the voltage produced by microbial-vegetable fuel cells was measured using graphite electrodes and plants belonging to the species of aloe (Aloe vera), corn (Zea mays), black beans (Phaseolus vulgaris), tomato (Solanum lycopersicum) and moss (Dicranidae). They were selected for their presence in everyday life and their great commercial and agricultural value, reaching a maximum voltage of 884 mV from moss. There is evidence that all plants can be a source of energy to a greater or lesser extent and that their performance is given by the plant root interactions at the electrodes. However, an extensive root system can favour the accumulation of substrate after the hydrolysis of dead roots, provided that their presence does not interfere with microbial activity on the anodic surface. For this, using plants with low resistance to thermal stress can lead to a substrate richer in substances that can be decomposed. Therefore, it is recommended to use plants according to their life cycle and the morphology of their roots, and plants that can grow in waterlogged conditions or without direct contact with the Sun.

, Albert García Tormo

• 2011

Aquesta tesi tracta sobre amplificació de potència d'alt rendiment de senyals variables en el temps; concretament, tracta sobre conversió de potència eficient (amb mínimes pèrdues) de tensions DC continues en senyals de tensió no constants. Aquest tipus de conversió de potència està present en la majoria de dispositius electrònics d'ús quotidià, com ara telèfons mòbils i reproductors de música portàtils, així com també en dispositius d'alta potència com amplificadors d'àudio i estacions base de telefonia mòbil. Generalment l'energia està disponible en forma de tensió DC contínua (d'una bateria o d'una font d'alimentació). D'acord amb la informació a transmetre, aquesta energia s'ha de processar o transformar en un senyal variable en el temps de manera que, per exemple, es pugui convertir en àudio per un altaveu . La tendència de mercat és a reduir la mida i el pes dels dispositius electrònics i a oferir noves funcionalitats, incloent una llarga autonomia en dispositius alimentats per bateries. Millorar l'eficiència dels amplificadors de potència no només n'estendria l'autonomia, sinó que també permetria utilitzar dissipadors més petits i lleugers. Altres aplicacions com les d'alta potència o integrades també es beneficiarien de millores en l'eficiència dels amplificadors de potència. Els dispositius electrònics de processament de potència més eficients són els amplificadors commutats. Aquests utilitzen components reactius (bàsicament bobines i condensadors) per dur a terme un processament de potència idealment sense pèrdues, així com dispositius actius (transistors) controlats com interruptors (o bé tancats o bé oberts), per tal de controlar aquest procés. Tot i que es poden assolir eficiències molt altes amb amplificadors commutats, la precisió de seguiment pot no ser gaire bona. Es pot millorar la precisió de seguiment senzillament incrementant la freqüència de commutació (la freqüència a la qual es fan commutar els interruptors), tot i que, com que es requereix una certa quantitat d'energia per fer commutar cada interruptor (pèrdues de commutació), aquesta tècnica també deteriora l'eficiència de l'amplificador. Existeix doncs un comprimís entre la freqüència de commutació i la precisió de seguiment en els amplificadors commutats (compromís eficiència-distorsió). Els amplificadors commutats habitualment es dissenyen per treballar a una freqüència de commutació alta comparada amb l'amplada de banda que han de seguir. Mentre que amb aquesta estratègia de disseny (i tecnologia actual) es poden dissenyar amplificadors per seguir senyals de l'ordre de kHz, si s'aplica per seguir senyals de l'ordre de MHz, els amplificadors haurien de treballar a freqüències de commutació massa altes, inviables des del punt de vista de les pèrdues de commutació. Amb l'objectiu d'abordar el compromís entre distorsió i eficiència dels amplificadors commutats, aquesta tesi explora diferents tècniques per estendre l'amplada de banda relativa dels amplificadors commutats, és a dir, tècniques per reduir la relació entre la freqüència de commutació de l'amplificador i la seva amplada de banda de seguiment. Basant-se en una interpretació alternativa dels amplificadors commutats, com a procés de codificació i reconstrucció, les diferents tècniques d'extensió de banda que aquí s'exploren contemplen utilitzar modulacions alternatives, amplificació de potència multi-nivell, filtrat d'ordre elevat i polítiques de commutació millorades en els convertidors commutats. La caracterització de les prestacions en termes de freqüència de commutació, error de seguiment i robustesa davant no idealitats (incloent compatibilitat electromagnètica i acoblament entre canals) apunta la idoneïtat de l'amplificació de potència multi-nivell basada en moduladors asíncrons per dissenys que treballin a freqüències de commutació relativament baixes, és a dir, a freqüències de commutació comparables a l'amplada de banda del senyal a seguir i amplificar. This thesis is about power amplification of time-varying signals; more precisely, it is about efficient power conversion, i.e. with minimum losses, of DC constant voltages into non-constant voltage signals. This kind of power conversion is quite common in power-management circuits and electronics in general. It is present in most everyday use electronic devices, including mobile phones, portable audio players and routers, as well as in high-power devices such as audio amplifiers and wireless base stations. In most electronic devices, whether portable or not, the energy is available as DC constant voltage (typically from a battery or a power supply). According to the information to transmit, this energy must be processed or transformed into a time-varying analogue signal so that, for instance, it can be directly converted into audio by a speaker or radiated by an antenna. The market trend is to reduce the size and weight of electronic devices whilst offering new or enhanced functionalities, including long autonomy in battery-powered devices (mainly portable). Improving the efficiency of power amplifiers not only extends the autonomy, but also allows using smaller and lighter heatsinks. Other applications such as high-power or embedded would also benefit from efficiency improvements of switching amplifiers. The most efficient power-processing electronic devices are switching amplifiers. Switching amplifiers use reactive components (mainly inductors and capacitors) to perform an ideally lossless power processing, and active devices (transistors) driven as switches, either ON or OFF, to control this process. Whilst very high efficiencies can be achieved with switching amplifiers, their tracking fidelity may not be very high. The tracking fidelity can be improved by simply increasing the switching frequency (i.e. the frequency at which the active devices are driven), although, provided that a certain amount of energy is required to switch the state of each active device (switching losses), this technique also degrades the efficiency of the amplifiers. Therefore, there exists a trade-off between switching frequency and tracking fidelity in switching amplifiers (efficiency-distortion trade-off). Switching amplifiers are typically designed using a high switching frequency compared to the amplifier's tracking bandwidth. Whilst this design strategy leads to feasible designs for kHz-bandwidth applications (using state-of-the-art technology), when applied to MHz-bandwidth applications, it leads to designs operating at very high switching frequencies, unfeasible with regard to switching losses. With the scope of addressing the efficiency-distortion trade-off of switching amplifiers, this thesis explores different techniques to extend the relative bandwidth of switching amplifiers, i.e. techniques to reduce the ratio of the amplifier's switching frequency to the amplifier's tracking bandwidth. Based on an alternative interpretation of switching amplifiers, as an encoding-reconstruction process, the different bandwidth extension techniques consider using alternative modulations, multi-level power amplification, high-order filtering and enhanced switching policies in the switching converter. The performance characterisations in terms of switching frequency, tracking error and robustness against non-idealities (including electromagnetic compatibility and crosstalk) points out the suitability of multi-level power amplification based on asynchronous modulators for designs operating at relatively low switching frequencies, i.e. at switching frequencies in the same range than the bandwidth of the signal to track and power amplify.

Taichi Ogawa, Shogo Nakamura, Ryo Miyamoto et al.

ECS Transactions • 2023

The durability of cathode catalysts in polymer electrolyte fuel cells remains a significant technical issue. Start-stop cycles cause carbon support corrosion and Pt catalyst particle detachment from the support leading to a significant cell degradation. SnO 2 -supported electrocatalysts using carbon materials as the conducting framework have the potential to achieve both high activity and high durability. However, cell performance in the high current density range needs to be improved to apply them to heavy-duty vehicles. This study selected mesoporous carbon (MC) as the conductive framework because the use of mesopores could also improve load-cycle durability. In this study, the microstructure of the electrocatalyst layers using Pt/Sn 0.98 Nb 0.02 O 2 /MC is controlled to improve the power generation of the cells. In addition, Pt/Sn 0.98 Nb 0.02 O 2 /MC electrocatalyst demonstrates durability improvement against the start-stop cycles.