Regulating the hole transfer from CuWO4 photoanode to NiWO4 electrocatalyst for enhanced water oxidation performance

The electrocatalyst coupling with CuWO4 has resulted in a comparable or worse performance when compared to the bare CuWO4. This work attempts to address this challenge by coupling CuWO4 with NiWO4 electrocatalyst that can form a Type-II 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 by adding Cu(NO3)2 and Ni(NO3)2 precursors to obtain the CuWO4/NiWO4 composite with common anions. A high surface-to-volume ratio, perfect interface lattice match, suitable energy level alignment, and high electrocatalytic activity were exhibited in the composite. These characteristics led to a 100 mV negative shift on the onset potential compared to the pure CuWO4 photoanode. Moreover, it featured a 0.7-fold higher photocurrent density than that of the pure CuWO4 photoanode. Only 9% of photocurrent density decreased after 4 h of photo-irradiation, demonstrating excellent photostability. Our mechanism study demonstrated that NiWO4 could act as a semiconductor to form a Type-II heterojunction with CuWO4, promoting hole transfer from the CuWO4 valence band to the NiWO4. Meanwhile, the NiWO4 effectively injects the separated holes into the water solution as a promising electrocatalyst, thus enhancing the overall water splitting performance. This work provides an important design consideration by focusing on the corrected level alignment and lattice match for developing the CuWO4/electrocatalyst system to work effectively.