An overview of cathode materials for microbial electrosynthesis of chemicals from carbon dioxide

The applicability of microbial electrosynthesis (MES) for chemical synthesis from carbon dioxide (CO2) requires improved production and energetic efficiencies. Microbial catalysts, electrode materials, and reactor design are the key components which influence the functioning of such processes. In particular, cathode materials critically impact the electricity-driven CO2 reduction process by microorganisms. Interest in cathode surface modifications for improving MES processes is thus consistently increasing. In this paper, the recent developments and spatial modification of cathode materials for microbial CO2 reduction are systematically reviewed. The characteristics of commercially available materials, their modifications, and developments in new materials that have been used as cathodes for MES are summarized. Key cathode-microorganism interactions that led to improved CO2 conversion are then discussed. The cathode surface modification approaches have focused mainly on improving the surface area and surface chemistry of the materials. Although the modified cathode surfaces improved biofilm growth in direct electron uptake based bioconversions, they have achieved lower acetate production rates than that of hydrogen-based MES processes thus far. Research efforts on different materials suggest that the three-dimensional cathodes that can retain more biomass, in particular in hydrogen-based bioconversions, are promising for further improvements in production efficiencies. Further efforts toward reducing the energy inputs for achieving energetically efficient MES processes by using electrocatalytically efficient cathodes are needed.