Direct Biological Conversion of Electrical Current into Methane by Electromethanogenesis

TLDR

New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. The study demonstrates that methane can be directly produced via electromethanogenesis using a methanogen‑containing biocathode in electrochemical systems or microbial electrolysis cells. They employed a two‑chamber electrochemical reactor with an abiotic anode and a methanogen biocathode, applying a potential below −0.7 V (vs Ag/AgCl) to reduce CO₂ to methane without precious metal catalysts. The system achieved 96 % current capture efficiency at −1.0 V, with the biocathode markedly increasing current density and suppressing hydrogen evolution, confirming direct methane production from current; dominated by *Methanobacterium palustre*, it yielded 80 % overall energy efficiency in a single‑chamber MEC, demonstrating that electromethanogenesis can convert renewable electricity into methane while capturing CO₂.

Abstract

New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. Here we demonstrate that methane can directly be produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis. At a set potential of less than −0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At −1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane production directly from current and not from hydrogen gas. The biocathode was dominated by a single Archaeon, Methanobacterium palustre. When a current was generated by an exoelectrogenic biofilm on the anode growing on acetate in a single-chamber MEC, methane was produced at an overall energy efficiency of 80% (electrical energy and substrate heat of combustion). These results show that electromethanogenesis can be used to convert electrical current produced from renewable energy sources (such as wind, solar, or biomass) into a biofuel (methane) as well as serving as a method for the capture of carbon dioxide.