Bifunctional sulfur-doped cobalt phosphide electrocatalyst outperforms all-noble-metal electrocatalysts in alkaline electrolyzer for overall water splitting

Sulfur-doped CoP (S:CoP) nanoparticles are synthesized as a noble metal-free electrocatalyst via a novel and eco-friendly thiourea-phosphate-assisted solvothermal route. When used as a bifunctional electrocatalyst for the hydrogen and oxygen evolution reactions from water splitting in an alkaline solution, the electrode exhibits excellent activity and stability outperforming noble mental-based Pt/C, IrO2, and reported non-noble metal-based electrocatalysts. Density functional theory calculations indicate that the excellent performance is attributable to the improved charge-transfer characteristics of the S:CoP nanoparticles owing to their modified electronic structure. It also increases the number of exposed active sites especially on the conductive substrates. A bifunctional S:CoP catalyst-based alkaline electrolyzer for overall water splitting exhibits a stable current density of 100 mA/cm2 at an overvoltage of 0.55 V during a long-term operation; this performance is superior to that obtained from all-noble metal electrolyzer with a Pt/C cathode and an IrO2 anode.