A Ni2P nanocrystal cocatalyst enhanced TiO2 photoanode towards highly efficient photoelectrochemical water splitting

Developing low-cost oxygen evolution reaction (OER) cocatalysts with high conductivity and excellent catalytic activity is highly desirable for mitigating interfacial charge recombination and accelerating the OER reaction kinetics of the semiconductor photoanode for photoelectrochemical (PEC) water splitting. Herein, a hybrid photoanode integrating a high-quality light absorber, a bilayer TiO2 nanorod-inverse opal (NR-IO) semiconductor and an efficient OER cocatalyst consisting of colloidal Ni2P nanocrystals is constructed via a spin-coating process. The resulting TiO2/Ni2P NR-IO photoanode yields an impressive photocurrent density of 1.93 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE) under simulated solar illumination (AM 1.5G, 100 mW cm−2), corresponding to a more than 2-fold increase compared to the pristine TiO2 NR-IO. The photoelectrochemical electrochemical impedance spectroscopy (PEIS) and photoluminescence (PL) results reveal that the Ni2P cocatalyst not only accelerates the interfacial charge transfer from TiO2 NR-IO to Ni2P but also efficiently transmits the holes to participate in aqueous OER. Moreover, the Ni2P cocatalyst effectively prevents the substantial dark current observed with fully covered transition-metal-phosphide shell modification. This work is expected to spur more insights into integrating semiconductors with proper OER cocatalysts for highly efficient and stable solar water spitting.