One-step synthesis of novel Cu₂ZnNiO₃ complex oxide nanowires with tuned band gap for photoelectrochemical water splitting

Although alloying and nanostructuring offer a great opportunity for enhancing photoelectrochemical behavior and band gap tuning, these methods have not been investigated extensively. This article reports the synthesis of Cu₂ZnNiO₃ complex oxide nanowires (∼200 nm) grown on German silver alloy via a one-step optimized hydro­thermal route and their utilization to split water photoelectrochemically. Surface characterizations were used to elucidate the formation mechanism of the Cu₂ZnNiO₃ complex oxide nanowires. The nanowires exhibited an exceptional visible light absorption extending from 400 to 1400 nm wavelengths with a tuned band gap of ∼2.88 eV calculated from the corresponding Tauc plot. In tests to split water photoelectrochemically, the nanowires generated a significant photocurrent of up to −2.5 mA cm⁻² at −0.8 V versus Ag/AgCl and exhibited an exceptional photostability which exceeded 2 h under light-off conditions with no photocurrent decay. Band edge positions related to water redox potentials were estimated via Mott–Schottky and diffuse reflectance spectroscopy analysis with the density of charge carriers reaching as high as 5.15 × 10¹⁸ cm⁻³. Moreover, the nanowires generated ∼1100 µmol of H₂ in 5 h. These photoelectrochemical results are much higher than the reported values for similar structures of copper oxide, zinc oxide and nickel oxide separately under the same conditions, which can be attributed to the advantages of Cu, Zn and Ni oxides (such as visible light absorption, photostability, and efficient charge carrier generation and transport) being combined in one single material. These promising results make German silver a robust material toward photoelectrochemical water splitting.