Solar-driven photocatalytic and photoelectrocatalytic hydrogen evolution reaction: Advances, challenges, and future directions

Solar hydrogen production is a potentially viable solution to the climate change caused by the burning of fossil fuels, in along with the utilization of solar energy. Photocatalysis, photoelectrochemistry, photovoltaic-electrochemistry, solar thermochemistry, photothermal catalysis, and photobiology are the most extensively researched methods for the production of solar hydrogen. Among all the developed strategies, photocatalytic (PC) and photoelectrocatalytic (PEC) systems are highly recognized because they can utilize solar energy to produce chemical fuels. This review critically analyzes recent progress in semiconductor materials specifically heterostructured systems in optimizing hydrogen evolution reactions (HER). We classify and discuss the function of conventional heterojunctions, Z-scheme and S-scheme structures, plasmonic nanocomposites, and graphitic carbon nitride (g-C₃N₄) functionalization in enhancing visible-light absorption, charge separation, and redox potential matching. It also pinpoints the current challenges, including low solar-to-hydrogen efficiency and material scalability, and outline future directions for advancing efficient, stable, and scalable hydrogen production systems. This review seeks to give researchers a comprehensive and up-to-date overview of designing next-generation photocatalysts and hybrid systems for solar hydrogen production.