Capacitive biocathodes driving electrotrophy towards enhanced CO2 reduction for microbial electrosynthesis of fatty acids

Synoptic view of biocathodes used in MES and elucidating the importance of capacitance linked with electrotrophy for enhanced CO2 reduction towards microbial electrosynthesis of renewable chemicals. [Display omitted] •Hybrid electrode material exhibited higher electrotrophy and CO2 reduction.•Acetic acid production was relatively higher in hybrid biocathode.•Electrotrophy and capacitance critically regulated microbial electrosynthesis.•Long term operated biocathodes displayed lowered resistance in impedance spectra.•Ethanol formation was observed specifically in carbon based biocathodes. Electron transfer towards biocathode is a rate limiting step for CO2 reduction during microbial electrosynthesis (MES). Current study is designed to offer an understanding on electrotrophy using four different electrode materials viz., carbon cloth (CC), stainless-steel mesh (SS), combination of both (CC-SS) and a hybrid material (CC-SS-AC with activated carbon (AC)) as capacitive biocathodes for MES. Non turn-over and turn-over electrochemical investigations revealed electrode properties in terms of electron transfer, capacitance and redox catalytic currents relatively higher with CC-SS-AC and CC-SS. Acetic acid production was higher in CC-SS-AC (4.31 g/l) than CC-SS (4.21 g/l), CC (3.5 g/l) and SS (2.83 g/l) along with noticeable ethanol production with all the biocathodes except SS. Interestingly, long-term operation of all biocathodes witnessed reduction in resistance visualized through Nyquist impedance spectra relatively efficient with CC-SS-AC. Biocompatible property of CC-SS-AC with increased surface area was presumed to be a critical factor for enhancing electrotrophy linked with capacitive nature of biocathode towards enhanced bioelectrochemical CO2 reduction.