Coupling of CuWO ₄ Photoanode with NiWO ₄ Eletrocatalyst with Adequate Energy-Level Alignment for Enhanced Water Oxidation Performance

The restricted hole transfer from CuWO4 to electrocatalyst has resulted in a comparable or worse performance with respect to the bare CuWO4. This work attempts to address this challenge by making an in situ fabrication of a type-II CuWO4/NiWO4 heterojunction with a suitable energy-level alignment allowing for effective hole transfer from CuWO4 to NiWO4 electrocatalyst. We applied thermal annealing to the WO3 nanoplates in the presence of Cu(NO3)2 and Ni(NO3)2 precursors to obtain CuWO4/NiWO4 with common anions. Our CuWO4/NiWO4 exhibited a high interface-to-volume ratio, perfect interface lattice match, suitable energy level alignment , and high electrocatalytic activity. These characteristics led to a 100 mV negative shift on the onset potential compared to the pure CuWO4 photoanode. It also featured a 1.7-fold higher photocurrent density than that of the pure CuWO4 photoanode. Its photocurrent density decreased by only 9% after 4 h of photo-irradiation, demonstrating excellent photostability. In addition, both its electrochemical and photocatalytic characteristics indicated effective electron transfer from the NiWO4 conduction band to the CuWO4 and hole transfer from the CuWO4 valence band to the NiWO4. The catalytic effect of NiWO4 contributed effective injection of the separated holes into the water solution, thus enhancing the overall water splitting performance. Our work provides an important design considerations for the development of semiconductor/electrocatalyst system with the focus of corrected level alignment and lattice match so that the surface catalysis reaction occurring effectively.