Production of hydrogen fuel from sunlight and water offers one of the most promising pathways for carbon neutrality. Some solar hydrogen production approaches, e.g., photoelectrochemical water splitting, often requires corrosive electrolyte, limiting their performance stability and environmental sustainability. Alternatively, clean hydrogen can be produced directly from tap water, or seawater by wireless photocatalytic water splitting. The solar-to-hydrogen (STH) efficiency, however, is still lower than 3%. Herein, we have developed a unique strategy to overcome the efficiency bottleneck. A high STH efficiency of 9.2% was achieved by utilizing pure water, concentrated solar light, and visible-light-responsive InGaN photocatalyst. The success of this strategy was explained by the synergistic effects of promoting forward hydrogen-oxygen evolution and inhibiting the reverse hydrogen-oxygen recombination by operating at an optimal reaction temperature (~70 °C). Such an optimal temperature can be readily achieved by harvesting the previously wasted infrared light of the solar spectrum without other energy consumption. This temperature-dependent strategy also leads to the STH efficiencies of ~7% from the widely available tap water and seawater. A large-scale photocatalytic water splitting system with a natural solar light capacity of 257 W on a 4 cm × 4 cm photocatalyst wafer achieves a STH of 6.2% at ~70 oC. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar and water, overcoming some of the major barriers for green hydrogen economy.
