Theoretical insight into the roles of cocatalysts in the Ni-NiO/β-Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e photocatalyst for overall water splitting

Abstract

\u3cp\u3eThe formation and stability of Ni\u3csub\u3en\u3c/sub\u3e and (NiO)\u3csub\u3en\u3c/sub\u3e (n = 1-4) clusters on the β-Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e surface have been studied by means of first-principles density functional theory calculations. It is found that the optimum interaction of the Ni\u3csub\u3en\u3c/sub\u3e and (NiO)\u3csub\u3en\u3c/sub\u3e clusters with the surface requires different surface sites. This optimizes the formation of interfacial bonds between the atoms from clusters and the coordinatively unsaturated atoms from the surface. The stability of the adsorbed Ni clusters increases with the number of Ni atoms. In a Ni\u3csub\u3en\u3c/sub\u3e/Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e system, as the Ga unoccupied states overlap with the unoccupied Ni state, the excited electrons transferred from Ga to Ni participate in the proton reduction reaction. Our calculations show that (NiO)\u3csub\u3en\u3c/sub\u3e clusters strongly adsorb on the Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e surface due to the negative adsorption energies within -1.9 eV to -3.7 eV. For (NiO)\u3csub\u3en\u3c/sub\u3e/Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e, occupied states from the (NiO)\u3csub\u3en\u3c/sub\u3e cluster may accept the holes from O atoms in the Ga\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e surface to take part in the photocatalytic water oxidation reaction.\u3c/p\u3