Development and characterization of a halophilic H₂-producing microbial biocathode enriched from sulfidogenic salt...

Halophilic and halotolerant microbial communities offer a promising strategy to enhance bioelectrochemical hydrogen production while suppressing competing methanogenic activity in saline environments. In this study, a halophilic hydrogenotrophic sulfate-reducing enrichment culture was developed from sulfidogenic sediments of Chott El-Jerid, a hypersaline lake in Tunisia, and applied as inoculum of a biocathode. Short-term (6 h) bioelectrochemical tests at cathode potentials between -0.6 and -1.2 V vs. SHE demonstrated a strong bioelectrocatalytic effect, with H₂ production rates up to ∼75 μmol L^-1h^-1 at -1.0 V, nearly an order of magnitude higher than abiotic controls. Long-term operation (212 h) at -1.0 V confirmed the stability of hydrogen evolution (∼80 μmol L^-1h^-1) and negligible methane formation, with ∼50% of the consumed electrical charge recovered as H₂. Cyclic voltammetry revealed that intact microbial cells, rather than soluble redox mediators, were likely responsible for the observed catalysis. Microbial community analysis showed the enrichment of Desulforadius spp. (>75% relative abundance) in the microbial culture, highlighting the role of hydrogenotrophic sulfate-reducing bacteria in driving efficient H₂ evolution under high-salinity conditions. These findings demonstrate, for the first time, that halophilic biocathodes can provide selective, robust, and long-term bioelectrocatalysis, offering new opportunities for sustainable hydrogen production.