Linking Bacterial Metabolism to Graphite Cathodes: Electrochemical Insights into the H₂-Producing Capability of Desulfovibrio sp.

Abstract

Microbial biocathodes allow converting and storing electricity produced from renewable sources in chemical fuels (e.g., H₂) and are, therefore, attracting considerable attention as alternative catalysts to more expensive and less available noble metals (notably Pt). Microbial biocathodes for H₂ production rely on the ability of hydrogenase-possessing microorganisms to catalyze proton reduction, with a solid electrode serving as direct electron donor. This study provides new chemical and electrochemical data on the bioelectrocatalytic activity of Desulfovibrio species. A combination of chronoamperometry, cyclic voltammetry, and impedance spectroscopy tests were used to assess the performance of the H₂-producing microbial biocathode and to shed light on the involved electron transfer mechanisms. Cells attached onto a graphite electrode were found to catalyze H₂ production for cathode potentials more reducing than −900 mV vs. standard hydrogen electrode. The highest obtained H₂ production was 8 mmol L⁻¹ per day, with a Coulombic efficiency close to 100 %. The electrochemical performance of the biocathode changed over time probably due to the occurrence of enzyme activation processes induced by extended electrode polarization. Remarkably, H₂ (at least up to 20 % v/v) was not found to significantly inhibit its own production.