Effects of bicarbonate and cathode potential on hydrogen production in a biocathode electrolysis cell

A biocathode with microbial catalyst in place of a noble metal was successfully developed for hydrogen evolution in a microbial electrolysis cell (MEC). The strategy for fast biocathode cultivation was demonstrated. An exoelectrogenic reaction was initially extended with an H₂-full atmosphere to enrich H₂-utilizing bacteria in a MEC bioanode. This bioanode was then inversely polarized with an applied voltage in a half-cell to enrich the hydrogen-evolving biocathode. The electrocatalytic hydrogen evolution reaction (HER) kinetics of the biocathode MEC could be enhanced by increasing the bicarbonate buffer concentration from 0.05 mol·L^-1 to 0.5 mol·L^-1 and/or by decreasing the cathode potential from -0.9 V to -1.3 V vs. a saturated calomel electrode (SCE). Within the tested potential region in this study, the HER rate of the biocathode MEC was primarily influenced by the microbial catalytic capability. In addition, increasing bicarbonate concentration enhances the electric migration rate of proton carriers. As a consequence, more mass H⁺ can be released to accelerate the biocathode-catalyzed HER rate. A hydrogen production rate of 8.44 m³·m^-3·d^-1 with a current density of 951.6 A·m^-3 was obtained using the biocathode MEC under a cathode potential of -1.3 V vs. SCE and 0.4 mol·L^-1 bicarbonate. This study provided information on the optimization of hydrogen production in biocathode MEC and expanded the practical applications thereof.