[object Object], [object Object], [object Object] et al.

Interdisciplinary materials • 2025

Mixed electronic-ionic conductors are crucial for various technologies, including harvesting power from humidity in a durable, self-sustainable, manner unrestricted by location or environment 1,2 . Biological proteins have been proposed as mixed conductors for 50 years 3,4 . Recently, Geobacter sulfurreducens pili filaments have been claimed to act as nanowires to generate power 5,6 . Here, we show that the power is generated by G. sulfurreducens -produced cytochrome OmcZ nanowires that show 20,000-fold higher electron conductivity than pili 7 . Remarkably, nanowires show ultrahigh electron and proton mobility (>0.25 cm2/Vs), owing to directional charge migration through seamlessly-stacked hemes and a charged, hydrogen-bonding surface, respectively. AC impedance spectroscopy and DC conductivity measurements using four-probe van der Pauw and back-gated field-effect-transistor devices reveal that humidity increases carrier mobility by 30,000-fold. Cooling halves the activation energy, thereby accelerating charge transport. Electrochemical measurements identify the voltage and mobilities required to switch pure electronic conduction to mixed conduction for power generation. The high aspect ratio (1:1000) and hydrophilic nanowire surface captures moisture efficiently to reduce oxygen reversibly, generating large potentials (>0.5 V) necessary to sustain high power. Our studies establish a new class of biologically-synthesized, low-cost and high-performance mixed-conductors and identify key design principles for improving power output using highly-tunable electronic and protein structures.

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Waste Management • 2023

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PLoS ONE • 2014

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Photochemical & Photobiological Sciences • 2022

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Energies • 2022

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Biotechnology for Biofuels • 2016

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Applied Water Science • 2022

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Annales de Chimie Science des Matériaux • 2023

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Journal of Power Sources • 2024

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Indonesian Journal of Electrical Engineering and Computer Science • 2025

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Indonesian Journal of Electrical Engineering and Computer Science • 2025

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Processes • 2026

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International Journal of Environmental Science and Technology • 2024

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International Journal of Environmental Science and Technology • 2023

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Preprints.org • 2026

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Processes • 2022

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Biotechnology for Biofuels and Bioproducts • 2025

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Journal of Functional Biomaterials • 2025

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Materials Letters • 2018

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Environmental Science and Pollution Research • 2021

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Journal of Solid State Electrochemistry • 2022

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Applied Microbiology and Biotechnology • 2025

Microbial fuel cells (MFCs) offer a promising alternative for sustainable wastewater treatment and energy recovery. However, the mechanisms underpinning electrogenic biofilm formation remain poorly understood. This study investigates the spatial and temporal dynamics of microbial community assembly using a novel multi-electrode MFC design under two substrate conditions: acetate and starch. Pre-inoculation of three designated electrodes led to successful current generation within 110 h in both MFCs, while a dispersed inoculation strategy failed to establish electrogenic biofilms despite equivalent inoculum volume. Electrode positioning significantly influenced start-up, with vertical alignment above inoculated electrodes facilitating faster colonisation and current generation than lateral spacing. Notably, starch-fed MFCs exhibited more rapid and widespread biofilm proliferation, suggesting that complex microbial consortia may disperse more efficiently than single-function electrogens. Community sequencing revealed spatial heterogeneity and a shift from diverse to more optimised anodic communities over time. Geobacter initially dominated, but community succession was shaped by substrate complexity, competition, and spatial structure. Interestingly, non-inoculated electrodes often outperformed inoculated ones, indicating that deterministic selection pressures favoured more efficient biofilms. However, long-term current production declined, particularly under batch conditions, suggesting that population drift and limited microbial renewal limited sustained performance. This study is the first to characterise electrogenic biofilm assembly in a multi-electrode MFC, highlighting the interplay between stochastic dispersal and deterministic selection. These findings underscore the importance of inoculation strategy, substrate selection, and continuous microbial replenishment for optimising MFC performance and real-world applicability. KEY POINTS: • Substrate complexity shaped colonisation and distinct microbial communities. • Vertical electrode positioning enhanced colonisation and start-up efficiency. • Temporal succession led to specialised but less diverse electrogenic biofilms.

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