Harnessing solar energy for the production of clean hydrogen fuels by a photoelectrochemical (PEC) cell represents a very attractive but challenging alternative. This review focuses on recent developments of some promising photoelectrode materials, such as BiVO₄, a-Fe₂O₃, TaON, and Ta₃N₅ for solar hydrogen production. Some strategies have been developed to improve PEC performances of the photoelectrode materials, including: (i) doping for enhancing visible light absorption in the wide bandgap semiconductor or promoting charge transport in the narrow bandgap semiconductor, respectively; (ii) surface treatment for removing segregation phase or surface states; (iii) electrocatalysts for decreasing the overpotentials; (iv) morphology control for enhancing the light absorption and shortening transfer distance of minority carriers; (v) other methods, such as sensitization, passivating layer, and band structure engineering using heterojunction structures, and so on. Photochemical durability of the photoelectrodes is also discussed, since any potential PEC technology must balance efficiency against cost and photochemical durability. Photochemical durability may be amended by optimizing the photoelectrode, electrocatalyst, and electrolyte at the same time. In addition, solar seawater splitting is briefly introduced because it has received attention recently. Finally, trends in research in PEC cells for solar hydrogen production are detailed.

Hydrogen is a very promising candidate as a future energy carrier. It is attractive to produce hydrogen from solar energy and seawater, the most abundant renewable energy source and the most abundant natural resource on the earth. To date, there is no report on a stable photoelectrode with a high incident photon conversion efficiency (IPCE) in seawater splitting under irradiation by visible light. Herein, we report an efficient and stable system for seawater splitting based on a multi-metal oxide BiVO₄ after modification. The results indicated that modified BiVO₄ had a photocurrent density of 2.16 mA cm⁻² at 1.0 V_RHE in natural seawater under AM 1.5G sunlight (1000 W m⁻²) and exhibited the highest IPCE at 1.0 V_RHE in the visible light region of 440–480 nm among all known oxide photoanodes.

Monoclinic clinobisvanite bismuth vanadate is an important material with wide applications. However, its electronic structure and optical properties are still not thoroughly understood. Density functional theory calculations were adopted in the present work, to comprehend the band structure, density of states, and projected wave function of BiVO₄. In particular, we put more emphasis upon the intrinsic relationship between its structure and properties. Based on the calculated results, its molecular-orbital bonding structure was proposed. And a significant phenomenon of optical anisotropy was observed in the visible-light region. Furthermore, it was found that its slightly distorted crystal structure enhances the lone-pair impact of Bi 6s states, leading to the special optical properties and excellent photocatalytic activities.