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.