Revisiting the Underlying Chemistry Enhancing the Activity of Photoelectro- and Photo-Catalysts Concerning H2 Production

Nowadays, Hydrogen is one of the most abundant energy sources, and a promissory alternative fuel to replace fossil fuels due to its high calorific value, high energy density, easy generation, and low environmental impact. Although its production by chemical and electrochemical processes has become consolidated, its production using photo-catalytic and photo-electrocatalytic processes (i.e. light irradiation), still requires considerable research to exploit the sunlight, in order to promote the generation of a more sustainable fuel. In this regard, the chemical composition of the semiconductor materials acting as a catalyst during the proton reduction is critical to increase performance and yield. To this concern, the interaction of the photocathode interface with the reaction medium gives rise to a series of properties and factors that control the activity of a material, but they are typically overlooked during the catalyst synthesis and testing. Particularly, very little attention has been paid to reveal the intrinsic nature of the semiconductive materials, to find the characteristics of the crystalline structure, responsible for the properties and phenomena (molecular descriptors) influencing the photocatalysis. In order to clarify these issues, we comprehensively review defects, textural properties (specific area, pore distribution, particle pore size), among other factors influencing the photo- and photoelectro-catalytic activity of different semiconductor materials involved for H2 production.