NaCl-assisted Ni(SeO₃)·xH₂O/NC synthesis as high-performance co-catalyst for highly efficient photocatalytic hydrogen evolution

Rapid recombination hinders the optimal photocatalytic hydrogen evolution reaction (PHER) performance of titanium dioxide (TiO₂). Herein, a hydrated nickel selenite/nitrogen-doped carbon (Ni(SeO₃)·xH₂O/NC) was combined with TiO₂ to achieve high PHER performance by varying the amount of sodium chloride (NaCl) during the synthesis of Ni(SeO₃)·xH₂O/NC. The addition of NaCl change the morphology of Ni(SeO₃)·xH₂O/NC from a dense layer into a highly transparent and lace-like layer. Ni(SeO₃)·xH₂O/NC exhibits a narrow band gap (0.7–1 eV), with the optimized 0.5Ni(SeO₃)·xH₂O/NC exhibits the lower band gap of 0.75 eV and also suppressed recombination. Combining with TiO₂ narrowed the band gap of composite from 3.27 eV to 3.12 eV and decreased charge-transfer resistance. Consequently, 0.5Ni(SeO₃)·xH₂O/NC/TiO₂ achieved an exceptional PHER activity at 16,832 µmol·g^–1 (4208 µmol·g^–1·h^–1), which further enhanced to 56,081 µmol·g^–1 (14,020 µmol·g^–1·h^–1) by the addition of platinum. 0.5Ni(SeO₃)·xH₂O/NC/TiO₂ demonstrated good stability over 16 h, with performance restored upon the addition of fresh methanol. This strategy provides a simple approach to producing a co-catalyst by NaCl addition during synthesis for high PHER performance.