Improved H-adsorption ability of Cu in CuNi alloy nanodots toward the efficient photocatalytic H2-evolution activity of TiO2

Abstract

Compared with the noble metal Pt, the non-noble metal Cu as a cocatalyst exhibits a low hydrogen-evolution activity owing to its weak Cu–H bond (11 kcal mol⁻¹), which inhibits hydrogen adsorption on Cu atoms for the hydrogen-evolution reaction of photocatalysts. Considering that the introduction of Ni with a strong Ni–H bond into Cu is beneficial for strengthening the H-adsorption ability of Cu, in this paper, the low-cost transition-metal Ni was directly introduced into Cu to form CuNi alloy nanodots as photocatalytic cocatalysts to enhance the hydrogen-evolution rate of TiO₂. The CuNi alloy nanodots (2–3 nm) were photodeposited on the surface of a reduced graphene oxide (rGO)-modified TiO₂ photocatalyst to generate CuNi-rGO/TiO₂ by the pre-adsorption of Cu²⁺ and Ni²⁺ ions on graphene oxide (GO). Photocatalytic hydrogen-production data manifested that the CuNi-rGO/TiO₂ photocatalyst achieved the highest hydrogen-production rate (10 411 μmol h⁻¹ g⁻¹), which was 53.7, 38.7, 1.8, and 2.2 times higher than that of pure TiO₂, rGO/TiO₂, Cu-rGO/TiO₂, and Ni-rGO/TiO₂, respectively. Density-functional-theory (DFT) calculations and mechanistic investigation showed that the introduction of Ni into Cu to form CuNi alloy nanodots improved the H-adsorption ability of Cu and optimized the H-adsorption free energy close to zero (0.046 eV) for boosting the hydrogen production rate of TiO₂. This research presents a promising design of bimetallic alloy structures as H₂-production cocatalysts for efficient photocatalysts.