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

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 H-2 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 (H-2 + O-2 -> H2O), leading to a decrease in the overall photocatalytic H-2 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 H-2 production rate of 0.381 mu mol h(-1) cm(-1) at a density of 0.41 x 10(5) Pd atoms mu m(-2). Overall, the results provide a path to a highly efficient photocatalytic performance for water splitting by the suppression of the H-2/O-2 recombination, which can be effectively achieved using Pd in the form of SAs as photocatalytic co-catalysts.

Automated summary

This study demonstrates the decoration of anodic TiO2 nanotubes with single atoms of noble metals Pt, Pd, Rh, and Au using a simple dark deposition approach. Among these noble-metal single atoms, Pd exhibits the highest hydrogen production rate and can effectively inhibit the recombination of hydrogen and oxygen, leading to enhanced photocatalytic performance for water splitting.