The use of stainless steel and nickel alloys as low-cost cathodes in microbial electrolysis cells

Microbial electrolysis cells (MECs) are used to produce hydrogen gas from the current generated by bacteria, but low-cost alternatives are needed to typical cathode materials (carbon cloth, platinum and Nafion™). Stainless steel A286 was superior to platinum sheet metal in terms of cathodic hydrogen recovery (61% vs. 47%), overall energy recovery (46% vs. 35%), and maximum volumetric hydrogen production rate (1.5 m³ m^-3 day^-1 vs. 0.68 m³ m^-3 day^-1) at an applied voltage of 0.9 V. Nickel 625 was better than other nickel alloys, but it did not perform as well as SS A625. The relative ranking of these materials in MEC tests was in agreement with cyclic voltammetry studies. Performance of the stainless steel and nickel cathodes was further increased, even at a lower applied voltage (0.6 V), by electrodepositing a nickel oxide layer onto the sheet metal (cathodic hydrogen recovery, 52%, overall energy recovery, 48%; maximum volumetric hydrogen production rate, 0.76 m³ m^-3 day^-1). However, performance of the nickel oxide cathodes decreased over time due to a reduction in mechanical stability of the oxides (based on SEM-EDS analysis). These results demonstrate that non-precious metal cathodes can be used in MECs to achieve hydrogen gas production rates better than those obtained with platinum.