Photocatalytic hydrogen production on nickel-loaded LaxNa1−xTaO3 prepared by hydrogen peroxide-water based process

Abstract

A green production process for producing nickel-loaded LaxNa1−xTaO3, using a hydrogen peroxide-water based solvent system (HW-derived), is reported. The H2 evolution of the HW-derived sample is about 1.8 times higher than samples made using ethanol as a solvent. The activity of the sample can be further increased 9.3 times by depositing nanosized nickel as a co-catalyst on the surface of the La0.02Na0.98TaO3. Possible mechanisms of H2 evolution from pure water and from aqueous methanol solutions using nickel in three states (i.e.Ni metal, NiO oxide, and Ni/NiO core/shell)-La0.02Na00.98TaO3, are discussed systematically for the first time. It is clearly shown that the activity of hydrogen generation from pure water is in sequence: Ni/NiO > NiO > Ni, whereas the activity sequence with respect to aqueous methanol is: Ni > Ni/NiO > NiO. Metallic Ni presents the most active sites and favors the formation of hydrogen from aqueous methanol. The Ni in Ni/NiO core/shell induce the migration of photogenerated electrons from the bulk to catalyst surface, while NiO act as H2 evolution site and prevent water formation from H2 and O2. The recombination is interrupted by the effective capture of the holes by methanol acting as a sacrificial reagent, thereby leading to higher hydrogen evolution. In contrast, the competition between the recombination and the charge-transfer reaction occurs in pure water leading to a possible back reaction between H2 and O2 on the photocatalyst's surface. The photocatalyst synthesis avoids the use of organic solvents and thereby contributes to the environmentally friendly production of hydrogen.