Chemically modified nanostructures for photoelectrochemical water splitting

• Photoelectrochemical water splitting for hydrogen generation.
• Nanostructured electrodes increase surface area and reduce carrier diffusion length.
• Element doping improves optical and electronic properties of photoelectrodes.
• Surface modifications increase light absorption and charge separation.
• Electrochemical catalysts suppress overpotential for water oxidation and reduction.

Hydrogen gas is chemical fuel with high energy density, and represents a clean, renewable and carbon-free burning fuel, which has the potential to solve the more and more urgent energy crisis in today's society. Inspired by natural photosynthesis, artificial photosynthesis to generate hydrogen energy has attracted a lot of attentions in the field of chemistry, physics and material. Photoelectrochemical water splitting based on semiconductors represents a green and low cost method to generate hydrogen fuel. However, solar to hydrogen conversion efficiency is quite low, due to some intrinsic limitations such as bandgap, diffusion distance, carrier lifetime and photostability of semiconductors. Although nanostructured photoelectrodes improve the photoelectrochemical water splitting performance to some extent, by increasing electrolyte accessible area and shortening minority carrier diffusion distance, nanostructure engineering cannot change their intrinsic electronic properties. More importantly, recent development in chemically modification of nanostructured electrodes, including surface modification with catalyst and plasmonic metallic structures, element doping and incorporation of functional heterojunctions, have led to significant enhancements in the efficiencies of charge separation, transport, collection and solar energy harvesting. In this review, we provide an overview of the recent process in photoelectrochemical water splitting by using chemically modified nanostructured photoelectrodes. Finally, we also discuss the current challenges and future opportunities in the area of photoelectrochemical water splitting.