On the Synergism between Cu and Ni for Photocatalytic Hydrogen Production and their Potential as Substitutes of Noble Metals

Abstract

A series of Cu(OH)2–Ni(OH)2/P25 photocatalysts was prepared by co-deposition–precipitation (total metal loading ≈1 wt %) and their performance was evaluated for H2 production. Among this series, the 0.8 Cu(OH)2–0.2 Ni(OH)2/P25 photocatalyst demonstrated very high H2 production rates in 20 vol % ethanol/water and 5 vol % glycerol/water mixtures (10 and 22 mmol h−1 g−1, respectively). Detailed analyses based on reaction kinetics, photoluminescence, X-ray photoelectron spectroscopy (XPS), and charge carrier scavenging suggest that both working catalysts are composed of Cu and Ni metals in their active phases. Cu0 is produced directly by the transfer of electrons from the conduction band of TiO2 to surface Cu(OH)2 nanoclusters, whereas Ni0 is formed indirectly through a process of gradual dissolution of Ni(OH)2 to yield aqueous Ni2+ owing to the acidic environment of the medium, followed by Ni2+ reduction by electrons from the TiO2 conduction band. The high rates of H2 production that match those obtained with noble metals can be explained owing to a considerably less negative ΔGo of Cu oxide formation when compared with that of Ni oxide formation and higher work function of Ni than that of Cu.