Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H 2

Significance The use of catalysis assisted by light is a promising route to convert solar energy into chemical fuels such as H 2 . Photon absorption promotes electrons in semiconductor catalysts from the valence to the conduction band of those solids, and the excited electrons may be used to reduce protons in water to produce hydrogen gas. Unfortunately, those electrons tend to rapidly return to their ground state instead. The addition of metals has been shown to enhance photocatalytic activity, and that has been explained by their ability to trap the excited electrons and quench the electron–hole recombination process that neutralizes the photoexcitation. Here we challenge the validity of this model and provide an alternative explanation for the enhancement. A new thinking about this mechanism may result in new searches for appropriate cocatalysts.