Solar-to-Hydrogen Energy Conversion Based on Water Splitting

Artificial photosynthesis provides a blueprint to harvest solar energy to sustain the future energy demands. Solar-driven water splitting, converting solar energy into hydrogen energy, is the prototype of photosynthesis. Various systems have been designed and evaluated to understand the reaction pathways and/or to meet the requirements of potential applications. In solar-to-hydrogen conversion, electrocatalytic hydrogen and oxygen evolution reactions are key research areas that are meaningful both theoretically and practically. To utilize hydrogen energy, fuel cell technology has been extensively investigated because of its high efficiency in releasing chemical energy. In this review, general concepts of the photosynthesis in green plants are discussed, different strategies for the light-driven water splitting proposed in laboratories are introduced, the progress of electrocatalytic hydrogen and oxygen evolution reactions are reviewed, and finally, the reactions in hydrogen fuel cells are briefly discussed. Overall, the mass and energy circulation in the solar-hydrogen-electricity circle are delineated. The authors conclude that attention from scientists and engineers of relevant research areas is still highly needed to eliminate the wide disparity between the aspirations and realities of artificial photosynthesis.