Facile synthesis of Ni-doped WO3 nanoplate arrays for effective photoelectrochemical water splitting

A two-step hydrothermal process for preparing Ni-doped WO3 nanoplate arrays (NPAs) is developed, and the obtained samples were used as a photoanode to produce a highly active and stable electrocatalyst for photoelectrochemical (PEC) water splitting under visible light. The NPAs are formed as a single-phase solid solution with high purity. X-ray photoelectron spectroscopy measurement verifies the binding energy of W element is negatively shifted due to the substitution of W6+ by Ni2+ in the monoclinic lattice and thereby the formation of Ni-O-W bonds. Notably, the two-step 3 at% Ni-doped WO3 NPAs exhibits the highest PEC performance, compared with pure and one-step Ni-doped WO3 NPAs. At 1.0 V (vs Ag/AgCl), the current density of two-step 3 at% Ni-doped WO3 is 0.80 mA/cm(2), which is about 1.74- and 2.35-fold of that of WO3 (0.46 mA/cm(2)) and one-step 3 at% Ni-doped WO3 (0.34 mA/cm(2)), respectively. The PEC performance of WO3 NPAs can be modified by Ni doping in a two-step hydrothermal process; both the changes of band gap and electrochemically active surface area (ECSA) are playing important roles on improving the activity of the WO3 NPAs photoanode.