Fig. 1: Reactor performance in the tests at a pH set-point of 8.5.

a Contents of CH4, H2, and CO2 in the headspace along with the electrolyte pH. b Average CH4, H2, and CO2 concentrations in the feed and upgraded gas. c Average NH3 and H2S concentrations in the feed and upgraded gas. d The Fe-to-electron ratio (RFe/e) and the CO2-to-Fe ratio (\({{{\mbox{R}}}}_{{{{\mbox{CO}}}}_{2}/{{\mbox{Fe}}}}\)). The vertical dotted line in (a) represents the start of continuous gas feeding (i.e. the commencement of experimental phase). All values are means ± standard in deviations of triplicate tests.