Enhanced hydrogen production in zero-gap bipolar membrane microbial electrolysis with binderless cathodes in real wastewater

Abstract

Producing pure hydrogen through microbial electro-fermentation is crucial for realizing a carbon–neutral society. To advance the commercialization of bipolar membrane microbial electrolysis cells (BPM-MECs), assessing their hydrogen production performance under actual wastewater conditions is essential. This study investigates a novel zero-gap BPM-MEC for biohydrogen production using various wastewater sources, including artificial wastewater, brewery wastewater (BW), food wastewater, and livestock wastewater (LW). Importantly, the use of real wastewater, particularly LW, demonstrated superior performance, with high current density and enhanced hydrogen production, driven by the efficient breakdown of volatile fatty acids. BW, rich in alcohols, also exhibited strong initial performance. Among the binderless cathodes tested, the NiCo/CC cathode significantly outperformed NiMo/CC and NiFe/CC, achieving a remarkable current density of 7.6 ± 0.5 A/m² and a hydrogen production rate of 21 ± 1 m³ H₂/m³·d. Notably, the binderless NiCo/CC cathode maintained a catalytic efficiency of 90 ± 5 % even in real wastewater conditions, while exhibiting exceptional energy efficiency (>132 ± 9.5 %) during the hydrogen evolution reaction under acidified NaCl conditions. The enhanced performance is attributed to its porous, uniform film-like layer of Ni with abundant grain boundaries and Co concentrated around them, providing additional active sites for hydrogen production.