Defective TiO2-supported Cu nanoparticles as efficient and stable electrocatalysts for oxygen reduction in alkaline media

Abstract

Nanocomposites based on TiO₂-supported copper nanoparticles were prepared by a hydrothermal method where copper nanoparticles with or without the passivation of 1-decyne were chemically grown onto TiO₂ nanocolloid surfaces (and hence denoted as CuHC10/TiO₂ and Cu/TiO₂, respectively). Transmission electron microscopy measurements showed that the size of the hybrid nanoparticles was 5–15 nm in diameter with clearly defined lattice fringes for anatase TiO₂(101) and Cu(111). The formation of anatase TiO₂ nanoparticles was also observed by X-ray diffraction measurements. FTIR measurements confirmed successful attachment of alkyne ligands onto the surface of the copper nanoparticles via Cu−C interfacial bonds in CuHC10/TiO₂. XPS measurements suggested the formation of CuO in both samples with a higher concentration in Cu/TiO₂, and interestingly Ti³⁺ species were found in CuHC10/TiO₂ but were absent in Cu/TiO₂ or TiO₂ nanoparticles. Electrochemical studies demonstrated that both Cu/TiO₂ and CuHC10/TiO₂ exhibited a markedly improved electrocatalytic performance in the oxygen reduction reaction, as compared to TiO₂ nanocolloids alone, in the context of the onset potential, the number of electrons transferred and the kinetic current density. Importantly, among the series, CuHC10/TiO₂ exhibited the best ORR activity with a high current density, an almost four-electron reduction pathway and long-term stability after 4000 cycles at high potentials, which may be ascribed to the defective TiO₂ structures in combination with surface ligand engineering.