Inorganic/whole-cell biohybrid photocatalyst for highly efficient hydrogen production from water

To obtain a clean hydrogen production system, we have developed an inorganic-bio hybrid photocatalyst system based on the combination of anatase TiO₂, methylviologen (MV) as an electron mediator, and a whole-cell biocatalyst consisting of [FeFe]-hydrogenase and maturase gene-harboring recombinant Escherichia coli; however, the apparent quantum yield at 300 nm (AQY₃₀₀) for hydrogen production was low (0.3%). The system consists of a two-step reaction: (1) photocatalytic MV reduction by TiO₂, and (2) hydrogen production with reduced MV using a biocatalyst. The enhancement of step 1 under biocatalyst-friendly conditions was investigated in an attempt to further improve the reaction efficiency. Among the condition tested, the use of 100 mM Tris-HCl (pH 7), 150 mM NaCl, and 5% (v/v) glycerol with P-25 TiO₂ especially enhanced the step 1 reaction by a 300-fold increase in the MV reduction rate compared with previously tested reaction condition (100 mM Tris-HCl (pH 7), 150 mM NaCl, 5% (v/v) glycerol, and 100 mM ascorbate with anatase TiO₂). Under the enhanced step 1 reaction, AQY₃₀₀ and AQY₃₅₀ for photocatalytic MV reduction reached 60.8% and 52.2%, respectively. The enhanced step 1 reaction thus significantly improved the overall photocatalytic hydrogen productivity of the hybrid system and AQY₃₀₀ and AQY₃₅₀ reached 26.4% and 31.2%, respectively. The inorganic-whole-cell biohybrid system can therefore provide noble metal-free, efficient, and clean hydrogen production.