Constituent-tunable ternary CoM _2x Se _2(1−x) (M = Te, S) sandwich-like graphitized carbon-based composites as highly efficient electrocatalysts for water splitting

Herein, we fabricated two groups of component-tunable sandwich-like CoTe2xSe2(1-x) and CoS2ySe2(1-y) graphitized carbon-based composites. Due to the synergistic effect between the sandwich-like structures and anion-doping, CoTe2xSe2(1-x) and CoS2ySe2(1-y) demonstrated attractive catalytic performance towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. After optimizing the composition, we found that sandwich-like Co(Te0.33Se0.67)2 possesses optimal OER properties, with a low Tafel slope (44 mV dec-1), a small η10 (272 mV) and eminent stability for 50 h; meanwhile, the Co(S0.72Se0.28)2 catalyst presents attractive HER performance, featuring a minimum Tafel slope (80 mV dec-1) and a low η10 (106 mV) in alkaline media. Additionally, density functional theory (DFT) calculations confirmed that ΔGH* of the Co(S0.72Se0.28)2 catalyst (0.182 eV) is closest to zero. Therefore, an alkaline electrolyzer was fabricated using Co(Te0.33Se0.67)2 as the anode and Co(S0.72Se0.28)2 as the cathode; it manifested striking catalytic activity and favorable stability for overall water splitting. This is the first time that the effects of different dopants (Te and S atoms) and doping contents on the electrocatalytic performance of CoSe2 were explored towards overall water splitting. Also, this research provides a new pathway for the fabrication of ternary dianion transition metal dichalcogenides as admirable electrocatalysts for water splitting.