Photo-Electro-Biochemical H₂ Production Using the Carbon Material-Based Cathode Combined with Genetically Engineered...

Abio/bio hybrids, which incorporate biocatalysts that promote efficient and selective material conversions under mild conditions into existing catalytic reactions, have attracted considerable attention for developing new catalytic systems. This study constructed a H₂ -forming biocathode based on a carbon material combined with whole-cell biocatalysis of genetically-engineered-hydrogenase-overproducing Escherichia coli for the photoelectrochemical water splitting for clean H₂ production. Low-cost and abundant carbon materials are generally not suitable for H₂ -forming cathode due to their high overpotential for proton reduction; however, the combination of the reduction of an organic electron mediator on the carbon electrode and the H₂ formation with the reduced mediator by the redox enzyme hydrogenase provides a H₂ -forming cathodic reaction comparable to that of the noble metal electrode. The present study demonstrates that the recombinant E. coli whole cell can be employed as a part of the H₂ -forming biocathode system, and the biocathode system wired with TiO₂ photoanode can be a photoelectrochemical water-splitting system without external voltage assistance under natural pH. The findings of this study expand the feasibility of applications of whole-cell biocatalysis and contribute to obtaining solar-to-chemical conversions by abio/bio hybrid systems, especially for low-cost, noble-metal-free, and clean H₂ production.