A novel photoanode was designed using the Cu–azolate framework (CuAF) and g-C3N4 as a core–shell nanocomposite (g-C3N4@CuAF) decorated with a Ni(OH)2 cocatalyst. The band structure of the g-C3N4@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-C3N4 prevents their recombination so that the photocurrent density of g-C3N4@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-C3N4@CuAF/Ni(OH)2 photoanode was 6 times greater than that of the pristine CuAF. The photovoltage of 290 mV for the g-C3N4@CuAF/Ni(OH)2 photoanode compared to 189 mV for the CuAF/Ni(OH)2 photoanode indicates its deeper band bending. The g-C3N4@CuAF/Ni(OH)2 photoanode is stable under continuous light irradiation for 1 h.

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