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

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), 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 TiO. The CuNi alloy nanodots (2-3 nm) were photodeposited on the surface of a reduced graphene oxide (rGO)-modified TiO photocatalyst to generate CuNi-rGO/TiO by the pre-adsorption of Cu and Ni ions on graphene oxide (GO). Photocatalytic hydrogen-production data manifested that the CuNi-rGO/TiO photocatalyst achieved the highest hydrogen-production rate (10 411 μmol h g), which was 53.7, 38.7, 1.8, and 2.2 times higher than that of pure TiO, rGO/TiO, Cu-rGO/TiO, and Ni-rGO/TiO, 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 TiO. This research presents a promising design of bimetallic alloy structures as H-production cocatalysts for efficient photocatalysts.