Carbon Nanotube-Graphitic Carbon Nitride Hybrid Films for Flavoenzyme-Catalyzed Photoelectrochemical Cells

In green plants, solar-powered electrons are transferred through sophistically arranged photosystems and are subsequently channelled into the Calvin cycle to generate chemical energy. Inspired by the natural photosynthetic scheme, a photoelectrochemical cell (PEC) is constructed configured with protonated graphitic carbon nitride (p-g-C₃N₄) and carbon nanotube hybrid (CNT/p-g-C₃N₄) film cathode, and FeOOH-deposited bismuth vanadate (FeOOH/BiVO₄) photoanode for the production of industrially useful chiral alkanes using an old yellow enzyme homologue from Thermus scotoductus (TsOYE). In the biocatalytic PEC platform, photoexcited electrons provided by the FeOOH/BiVO₄ photoanode are transferred to the robust and self-standing CNT/p-g-C₃N₄ hybrid film that electrocatalytically reduces flavin mononucleotide (FMN) mediator. The p-g-C₃N₄ promotes a two-electron reduction of FMN coupled with an accelerated electron transfer by the conductive CNT network. The reduced FMN subsequently delivers the electrons to TsOYE for the highly enantioselective conversion of ketoisophorone to (R)-levodione. Under light illumination (>420 nm) and external bias, (R)-levodione is synthesized with the enantiomeric excess value of above 83%, not influenced by the scale of applied bias, simultaneously exhibiting stable and high current efficiency. The results suggest that the biocatalytic PEC made up of economical materials can selectively synthesize high-value organic chemicals using water as an electron donor.