Solar Hydrogen

Hydrogen, produced through a zero‐pollution, sustainable, low‐cost, and high‐efficiency process, is regarded as the “ultimate energy” of the 21st century. Solar water‐splitting techniques have immense potential to make the idea a reality. Two promising approaches, photovoltaic‐electrolysis (PV‐EC) and photoelectrochemistry (PEC), have demonstrated solar‐to‐hydrogen conversion efficiency over 10%, which is the minimum required for competitively priced, large‐scale systems. Extensive studies of PV‐EC and PEC devices reported within the past five decades show increasing design complexity. To accurately describe the gap between laboratory research and practical application, the basic principles and concepts of PV‐EC and PEC are elaborated and clarified. The history of these developments is systematically summarized, and a comprehensive techno‐economic analysis of PV‐EC and PEC solar hydrogen production of 10 000 kg H2 day−1 is performed. The analysis shows that no solar hydrogen system is currently competitive with production methods based on fossil fuels, but the development of high‐efficiency water‐splitting electrolyzers with cost‐competitive components (especially for cation/anion exchange membranes) can accelerate progress. Photovoltaic‐electrolysis (PV‐EC) and photoelectrochemistry (PEC) have immense potential to establish an economically competitive large‐scale green hydrogen production system pursued by the entire energy sector. This review systematically elaborates the fundamental principles and the development history of PEC and PV‐EC, and evaluates the techno‐economic analysis of the scale‐up applications, pointing out the current situation and future development direction for both technologies.