Enhanced electrochemical properties of cellular CoPS@C nanocomposites for HER, OER and Li-ion batteries

CoPS/Co4S3 Heterojunction with Highly Exposed Active Sites and Dual-site Synergy for Effective Hydrogen Evolution Reactions

Cobalt phosphosulphide (CoPS) has recently been recognized as a potentially effective electrocatalyst for the hydrogen evolution reaction (HER). However, there have been no research on the design of CoPS-based heterojunctions to boost their HER performance. Herein, CoPS/Co4S3 heterojunction was prepared by phosphating treatment based on defect-rich flower-like Co1-xS precursors. The high specific surface area of nanopetals, together with the heterojunction structure with inhomogeneous strain, exposes more active sites in the catalyst. The electronic structure of the catalyst is reconfigured as a result of the interfacial interactions, which promote the catalyst's ability to adsorb hydrogen and conduct electricity. The synergistic effect of the Co and S dual-site further enhance the catalytic activity. The catalyst has overpotentials of 61 and 70 mV to attain a current density of 10 mA cm-2 in acidic and alkaline media, respectively, which renders it competitive with previously reported analogous catalysts. This work proposes an effective technique for constructing transition metal phosphosulfide heterojunctions, as well as the development of an efficient HER electrocatalyst.

Solid-state synthesis of single-phase nickel monophosphosulfide for the oxygen evolution reaction

High-performance and cost-effective nonprecious-metal catalysts are essential for the next-generation oxygen evolution reaction (OER). However, the electrocatalysis of the OER during water splitting is often carried out by using noble metal catalysts, such as RuO₂ or IrO₂ with high-cost and limited stability. Herein, we reported a successful synthesis of a ternary nickel monophosphosulfide (NiPS) compound via a simple solid-state route and further investigated its electrocatalytic performances for water oxidation. It is found that the NiPS electrocatalyst exhibits good OER performance in 1.0 M KOH solution, i.e., achieving a current density of 20 mA cm^-2 at an overpotential of 400 mV and a Tafel slope of 126 mV dec^-1, comparable to commercial benchmark RuO₂. The ternary NiPS electrocatalyst for the OER is superior to its binary counterparts, i.e., Ni₂P and NiS. Density functional theory (DFT) calculations combined with ex situ XPS were performed to obtain further insights into the intrinsic catalytic mechanism of NiPS, and their results clearly revealed that the instability of the NiO intermediate during the OH* → O* process and the easy oxidation of the (PS)^3- anion favoring the formation of hydroxyl-based species (i.e., Ni(OH)₂/NiOOH) on the surface of the catalyst, which plays a crucial role in facilitating the OER activity. Furthermore, we creatively extended this method to the fabrication of heteroatom substituted catalysts and a new quaternary CoNiP₂S₂ compound was successfully synthesized for the first time in the same way. The structural properties and electrocatalytic performance towards the OER for CoNiP₂S₂ (e.g., 20 mA cm^-2 at 376 mV) are also systematically investigated in this work.