Integrating photosystem II into a porous TiO2 nanotube network toward highly efficient photo-bioelectrochemical cells

The fabrication of artificial photosynthetic systems to convert solar energy into electrical power is of great importance to meet human needs for energy; photosystem II (PSII), the core enzyme for water splitting in natural solar energy conversion processes can be introduced for this purpose. However, there remain significant challenges in the facile preparation of such semi-artificial photoanode systems with enhanced photocurrent responses. Herein we report a hybrid photoanode system consisting of PSII from spinach integrated into an indium-tin oxide electrode modified with nanotubular titania that is synthesized by using cellulose paper as a scaffold. This electrode provides a well-defined hierarchical nanostructure for protein loading, and the fine titania nanocrystals facilitate electron transfer from PSII to the electrode. The resulting semiconductor-protein hybrid photo-bioelectrochemical system enhances direct electron transfer (1.3 mu A cm(-2)) and mediated electron transfer (10.6 mu A cm(-2)) photocurrents.