Impact of Current Collectors with Different Electrocatalytic Activities on Hydrogen Production in Microbial Electrolysis Cells with Flowable Cathodes

Nickel-loaded activated carbon (Ni/AC) flow cathodes have shown great potential for scaling up microbial electrolysis cells (MECs) due to their low cost and flexibility on the scale. The role of a current collector in the flow electrode is crucial, but the impact of current collector materials (in terms of the specific surface area and electrocatalytic activities toward hydrogen evolution reaction, HER) on flow cathode performance has not been explored. A nickel foam (NF) displayed the lowest overpotentials (-0.82 V vs Ag/AgCl) for HER when coupled with the minimum powder loading (0.125 wt % or Ni/AC(0.125)) compared to stainless steel (SS) and titanium (Ti) current collectors at -10 A/m(2). Consequently, the Ni/AC flow cathode with NF (NF-Ni/AC(0.125)) demonstrated higher hydrogen production rates (2.3 +/- 0.25 L-H-2/L-d) than the SS-Ni/AC(0.125) and Ti-Ni/AC(0.125). The superior HER activities and hydrogen production rates with NF are due to the relatively higher electrocatalytic activities of NF itself and the larger specific surface area (128 m(2)/m(2)-projected area) that likely enhances interactions between current collectors and suspended particles. NF-Ni/AC(0.125) showed less utilization coverage for Ni/AC suspended particles than SS-Ni/AC(0.125) and Ti-Ni/AC(0.125), indicating that the active portion of the flow cathodes varies depending on the physicochemical properties of the current collectors.