Benchmarked Photoelectrochemical Water Splitting by Nickel-Doped n-Type Cuprous Oxide

Herein, Ni is for the first time put forward as a promising dopant to promote the photoelectrochemical property of cuprous oxide (Cu2O) with particularly n-type conduction. An electrochemical route is utilized to deposit Ni:Cu2O on the indium tin oxide (ITO) coated glass as a dense thin film with tree-like morphology, as revealed through scanning electron microscopy. Particularly, the incorporation of Ni that is verified via X-ray diffractometry leads to a compressive stress compensating well the tensile strain within Cu2O, which originates otherwise from large lattice mismatch between Cu2O and ITO. This in turn improves the crystallinity of the Ni:Cu2O thin film. More importantly, X-ray photoelectron spectroscopy indicates that the substitution of Ni(II) for Cu(I) boosts the carrier concentration to 8.4 × 1018 cm–3, as further evidenced by the Mott–Schottky analysis. Those enhancements along with an advantageous band structure including a flat-band potential of −1.1 V and a bandgap of ∼2.1 eV that is alternatively derived from UV–vis spectroscopy allow Ni:Cu2O to deliver an outstanding photocurrent of 2.5 mA cm–2 (at 0.3 V vs Ag/AgCl) for solar water splitting. Such performance well-surpasses those of other reported n-type Cu2O photoanodes more than 2-fold, attesting the great promise of Ni:Cu2O in this work for solar-related applications.