Ni3S2-Decorated TiO2 nanotube arrays as effective photoanodes for photoelectrochemical water splitting

Cocatalyst nickel sulfide (Ni3S2) was successfully loaded onto TiO2 nanotube array (TiO2 NTA) photoanodes for the first time by a simple two step hydrothermal process. The prepared Ni3S2/TiO2 NTA photoanode shows better photoelectrochemical (PEC) water splitting activity compared to pure TiO2 NTAs. The surface photovoltage (SPV) spectroscopy and transient photocurrent measurements provide direct evidence for the efficient charge separation of the Ni3S2/TiO2 NTA photoanode. Furthermore, the work function measurement proved the formation of the interfacial electric field at the interface of Ni3S2 and TiO2, which is the main driving force of charge separation. Photoelectrochemical impedance spectroscopy (PEIS) measurements and oxygen evolution reaction (OER) polarization curves confirmed that the Ni3S2/TiO2 NTA photoanode effectively reduces the interfacial charge transfer resistance and suppresses the overpotential of water oxidation, which make the photogenerated holes take part in the water oxidation reaction easily. These results demonstrate that Ni3S2 could be an excellent cocatalyst when applied in PEC water oxidation.