Interface-Engineered Methanogenic Nanobiohybrids Redirect Hydrogen Flux for Efficient CO2 Fixation.

Nanobiohybrids that integrate synthetic materials with living microbes offer a powerful strategy for CO2 fixation, chemical production, and environmental remediation, yet their efficacy is often limited by inefficient interfacial electron delivery. Zerovalent iron (nZVI) is a potent abiotic reductant, but its rapid, nonspecific hydrogen release and inherent cytotoxicity hinder productive coupling with microbial metabolism. Here, we overcome this limitation through interfacial engineering, creating a silicate-modified nZVI (Si-nZVI) hybrid with the methanogen Methanosarcina barkeri. This tailored interface enables near-theoretical yields of methane (4256 μmol g-1 Fe) generated from CO2, with 99.5% selectivity over surface hydrogen evolution. Combined spectroscopic, biochemical, and computational analyses reveal that surface Si-O bonds stabilize reactive hydrogen atoms (•H*), steering electron and proton flux toward a coupled transfer pathway that bypasses wasteful H2 generation and directly feeds methanogenesis. Transcriptomic profiling confirms enhanced hydrogenase activity and improved cellular fitness. The silicate interface also mitigates iron corrosion and improves microbial fitness under anaerobic conditions. This work establishes hydrogen-speciation control as a design principle for iron-based biohybrid systems and provides an environmentally relevant strategy for CO2 biomethanation, biogas upgrading, and other hydrogenotrophic bioprocesses.