title: Direct biological conversion of electrical current into methane by electromethanogenesis.
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.
authors: Engineering Environmental Institute and Department of Civil and Environmental Engineering, 212 Sackett Building, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors: Shaoan
authors: S
authors: Cheng
authors: Defeng
authors: D
authors: Xing
authors: Douglas F
authors: DF
authors: Call
authors: Bruce E
authors: BE
authors: Logan
mesh_terms: D001674:Bioelectric Energy Sources / Q000382:microbiology; D018441:Biofilms; D002245:Carbon Dioxide / Q000378:metabolism; D004560:Electricity; D055664:Electrochemical Techniques; D004566:Electrodes; D004583:Electrons; D008697:Methane / Q000378:metabolism*; D017014:Methanobacterium / Q000166:cytology / Q000502:physiology / Q000648:ultrastructure
chemical_list: D002245:Carbon Dioxide; D008697:Methane