Copper–Azolate Framework Coated on g-C₃N₄ Nanosheets as a Core–Shell Heterojunction and Decorated with a Ni(OH)₂ Cocatalyst for Efficient Photoelectrochemical Water Splitting

A novel photoanode was designed using the Cu–azolate framework (CuAF) and g-C 3 N 4 as a core–shell nanocomposite (g-C 3 N 4 @CuAF) decorated with a Ni(OH) 2 cocatalyst. The band structure of the g-C 3 N 4 @CuAF composite presented a heterojunction of staggered-gap type II. The transfer of photogenerated electrons and holes to relative low-energy bands of CuAF and g-C 3 N 4 prevents their recombination so that the photocurrent density of g-C 3 N 4 @CuAF photoanode significantly increased compared to that of CuAF photoanode. The Ni(OH) 2 cocatalyst loaded on the photoanodes provided a facile path for photogenerated holes to split water molecules. The photoconversion efficiency of the g-C 3 N 4 @CuAF/Ni(OH) 2 photoanode was 6 times greater than that of the pristine CuAF. The photovoltage of 290 mV for the g-C 3 N 4 @CuAF/Ni(OH) 2 photoanode compared to 189 mV for the CuAF/Ni(OH) 2 photoanode indicates its deeper band bending. The g-C 3 N 4 @CuAF/Ni(OH) 2 photoanode is stable under continuous light irradiation for 1 h.