The synergy of photodeposited CoNi co-catalysts for the photocatalytic performance of C₃N₄/CdS nanosheets: Optimized Gibbs free energy and Co-S bridging bonds

Transition metal co-catalysts exhibit considerable potential in the photocatalytic water splitting process, but their limited activity and poor stability inhibit their extensive application, and therefore effective schemes are required to further enhance their co-catalytic performance. In this article, 2D/2D C3N4/CdS heterogeneous photocatalysts are first synthesized, and then CoNi alloyed NPs are selectively loaded on their CdS nanosheets by a convenient photodeposition method. The CoNi loading amount and Co/Ni ratio are adjusted by the photodeposition time and precursor Co2+/Ni2+ ratio, respectively. Meanwhile, Co-S bonds are formed between CdS and CoNi NPs. Their optimal hydrogen evolution rate can reach up to 2936.65 μmol g-1 h-1, which is higher than that of C3N4/CdS with Co, Ni or Pt as co-catalysts (i.e. 844.59, 2385.96 and 2486.66 μmol g-1 h-1), respectively. The enhanced photocatalytic performance should be due to the following three points: (1) the formation of the 2D/2D C3N4/CdS heterojunction; (2) the optimized Gibbs free energy of the CoNi co-catalysts; (3) the formation of Co-S bonds between CoNi and CdS. Our work provides a cost-effective scheme to exploit stable and efficient photocatalysts.