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
methaneusingatwo-chamberelectrochemical 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
anoverallenergyefficiencyof80%(electricalenergyandsubstrate
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
|
|
