Nanostructured Semiconductor Photoelectrodes Complexed with Natural Photosystems I and II for Bias-Free Tandem Biophotovoltaics

Abstract

Natural photosynthesis can offer attractive models for light-harvesting antennae, electron- and proton-transfer units, and catalytic clusters for photovoltaics and solar fuel production. However, photoelectrodes with natural photosystems exhibit relatively low performances due to poor interfacial electron transfer. Here, we present efficient bias-free biophotovoltaics (BPVs) based on dual heterostructure photoelectrodes comprising natural photosystems and semiconductor nanostructures. The photocathode and photoanode were prepared using photosystem I (PSI)-protonated carbon nitride (p-C3N4) nanosheet complexes and a photosystem II (PSII)–TiO2 nanoparticle film, respectively. The linker-free complexation of PSI and PSII with nanostructured semiconductors efficiently suppressed the recombination of photogenerated charges for efficient light harvesting and photoconversion. In particular, the oriented coupling of the negatively charged luminal side of PSI to protonated carbon nitride synergistically increased the photoelectron generation and charge transfer, resulting in the generation of a photocurrent density 28 times higher than that of randomly oriented PSI. Under one-sun simulated illumination, the BPV cell with the PSI-p-C3N4 and PSII–TiO2 tandem structure exhibited a photocurrent of 7.7 μA cm–2 without any external bias and a cell power up to 0.9 μW cm–2. This work provides a simple self-assembly method to construct efficient nanobio complex photoelectrodes based on natural photosystems coupled with semiconductor nanostructures in a favorable orientation for efficient and stable interfacial electron transfer.