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

• Halophilic biocathode enables selective H 2 production under hypersaline conditions. • H 2 evolution rates up to one order of magnitude higher than abiotic controls. • Stable long-term H 2 production with negligible methane formation. • Desulforadius -dominated culture drives cell-associated bioelectrocatalysis. • Halophilic conditions suppress methanogenic competition for cathodic H 2 . 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 H 2 production rates up to ∼75 μmol L −1 h −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 −1 h −1 ) and negligible methane formation, with ∼50% of the consumed electrical charge recovered as H 2 . 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 H 2 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