Copper doped cobalt sulfide hollow polyhedron as efficient bifunctional catalysts for overall water splitting: An experimental and theoretical study

The development of highly active bifunctional electrocatalysts holds immense significance for achieving efficient overall water splitting. In this work, we successfully synthesize a novel Cu-doped cobalt sulfide hollow polyhedron through an ion-exchange-assisted solvothermal strategy. This catalyst exhibits excellent bifunctional electrocatalytic performance for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Experimental characterization combined with density functional theory (DFT) calculations reveals a synergistic enhancement mechanism. Cu doping promotes surface reconstruction into the formation of active cobalt oxyhydroxide species, which significantly boosts the density of active sites, optimizes the adsorption energetics of reaction intermediates, reduces the energy barrier of rate-determining steps, and activates the lattice oxygen mechanism (LOM). As a result, it facilitates enhanced OER kinetics. The optimized catalyst, designated as CCS - 2, achieves low overpotentials of 132 mV for HER, outperforming its undoped counterpart by approximately 14 %. For OER, it attains an overpotential of 279 mV, surpassing IrO₂ by about 18 %. When deployed in a two-electrode electrolyzer, the CCS-2 || CCS-2 system reaches a current density of 10 mA cm⁻² at a very low cell voltage of 1.63 V, comparable to the noble-metal benchmark Pt/C || IrO₂ (1.62 V). These findings demonstrate the great potential of CCS-2 as a highly efficient bifunctional electrocatalyst for practical water splitting applications. Moreover, they offer valuable insights into innovative design principles for advancing bifunctional water-splitting electrocatalysts.