Constituent-tunable ternary CoM2xSe2(1−x) (M = Te, S) sandwich-like graphitized carbon-based composites as highly efficient electrocatalysts for water splitting

Abstract

Herein, we fabricated two groups of component-tunable sandwich-like CoTe_2xSe_2(1−x) and CoS_2ySe_2(1−y) graphitized carbon-based composites. Due to the synergistic effect between the sandwich-like structures and anion-doping, CoTe_2xSe_2(1−x) and CoS_2ySe_2(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(Te_0.33Se_0.67)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(S_0.72Se_0.28)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 ΔG_H* of the Co(S_0.72Se_0.28)₂ catalyst (0.182 eV) is closest to zero. Therefore, an alkaline electrolyzer was fabricated using Co(Te_0.33Se_0.67)₂ as the anode and Co(S_0.72Se_0.28)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.