Flowable Nickel-Loaded Activated Carbon Cathodes for Hydrogen Production in Microbial Electrolysis Cells

Microbial electrolysis cells (MECs) can electrochemicallyproducegreen hydrogen from waste streams. However, cathode materials havebeen a bottleneck for the practical application of MECs due to difficultiesin scale-up and high costs. To overcome current drawbacks, we haveexamined a novel flowable cathode in MECs, where nickel-loaded activatedcarbon (Ni/AC) powders were suspended in a buffering solution as acathode without electrode fabrication processes. The Ni/AC flow cathodewith higher Ni content and minimum Ni/AC loading (4 Ni-atom% and 0.125wt-AC.%, Ni-4/AC(0.125)) demonstrated the highestcatalytic activities (-0.86 V vs Ag/AgCl at -10 A/m(2)) among Ni/AC flow cathodes tested. This result indicatesthat pseudocapacitive behavior toward Faradaic reactions can be promotedby increasing Ni loadings on Ni/AC particles. The MEC with a Ni-4/AC(0.125) flow cathode produced comparable hydrogenproduction rates (1.62 & PLUSMN; 0.15 L-H-2/L-reactor-day) to the Pt control (1.64 & PLUSMN; 0.09 L-H-2/L-day)and 40% higher than the blank (only current collector without Ni/AC,1.29 & PLUSMN; 0.02 L-H-2/L-day) at a 4 h cycle. The impactsof carbon black blending remain unclear; there was a 10% increasein hydrogen production rates with the lowest carbon black content(0.06 wt %) in the Ni/AC flow cathode, but hydrogen production rateswere not further improved as carbon black content increased.