Unraveling the Mechanism of Photocatalytic Water Splitting in α‑Ga₂O₃ Loaded with a Nickel Oxide Cocatalyst: A First-Principles Investigation

In the heterogeneous photocatalytic overall water-splitting reaction, introducing suitable cocatalysts has an important effect on improving the photocatalytic performance. However, the working mechanism of cocatalysts is still not fully understood. In this work, we have performed density functional theory calculations on α-Ga2O3 loaded with the nickel oxide cocatalyst, which is a highly active photocatalyst of decomposing water in the UV region. We have investigated the adsorption behavior of NinOn (n = 1, 2, 4, 6) clusters on (001) and (012) surfaces of α-Ga2O3. It is found that all NinOn clusters adsorb strongly on both (001) and (012) surfaces, with adsorption energies ranging from −3.9 to −6.6 eV. The more stable adsorption configurations have a larger number of new interfacial bonds formed between the surface and the cluster. The calculated density of states demonstrates that the adsorption of NinOn clusters on the (012) surface is more favorable to the separation and transfer of photogenerated electrons and holes. Our results reveal that on the α-Ga2O3 surfaces covered with the nickel oxide cocatalyst, the active site of hydrogen evolution reaction is the oxygen atom on the surface, and the interfacial dissociation of water is most stable because of the formation of more bonds. The favorable site of oxygen evolution reaction is on the highly unsaturated Ni atoms in NinOn clusters. The two-half reactions of decomposing water occur at the different sites in the photocatalytic system, which benefits the separation of electrons and holes. Our calculations have reasonably explained the experimental observation on the significant enhancement of activity for photocatalytic water-splitting reaction after loading the nickel oxide cocatalyst in α-Ga2O3