Inhibition of H₂ and O₂ Recombination: The Key to a Most Efficient Single‐Atom Co‐Catalyst for Photocatalytic H₂ Evolution from Plain Water

Abstract In the present work, it is shown that anodic TiO₂ nanotubes (NTs) can be decorated with Pt, Pd, Rh, and Au single atoms (SAs) by a simple “dark deposition” approach. Such TiO₂ NTs with surface trapped noble metal SAs provide a high activity for photocatalytic H₂ generation from pure water, i.e., in absence of a sacrificial agent. However, noble metals also act as active centers in the undesired hydrogen back‐oxidation (H₂ + O₂ → H₂O), leading to a decrease in the overall photocatalytic H₂ production efficiency. Here it is reported that the use of noble metal co‐catalysts, in the form of single atoms, can inhibit this recombination. From the different noble‐metal SAs investigated, Pd SAs yield the highest H₂ production rate of 0.381 µmol h⁻¹ cm⁻¹ at a density of 0.41 × 10⁵ Pd atoms µm⁻². Overall, the results provide a path to a highly efficient photocatalytic performance for water splitting by the suppression of the H₂/O₂ recombination, which can be effectively achieved using Pd in the form of SAs as photocatalytic co‐catalysts.