Nanostructured core-shell cobalt chalcogenides for efficient water oxidation in alkaline electrolyte

In water splitting, oxygen evolution reaction (OER) requires most active and stable electrocatalysts to overcome their sluggish kinetics thereby improving the device efficiency. In this research work, we developed nanocarbon protected cobalt sulfide, selenide and telluride (core-shell Co₉S₈@NC, CoSe@NC and CoTe@NC) using solvent and catalyst free auto-pressurized (Swagelok) solid-state thermolysis method and introduced as active and stable OER electrocatalysts in alkaline electrolyte. In 1 M KOH aqueous solution, the nickel foam supported Co₉S₈@NC shows the highest OER activity with an overpotential of 288 mV at 10 mA cm⁻², which is 33 and 68 mV lower than that of CoSe@NC and CoTe@NC electrocatalysts, respectively. In addition, the Co₉S₈@NC exhibits small Tafel slope of 65 mV dec⁻¹ calculated from the low current density region (10 mA cm⁻²) and increases to 120 mV dec⁻¹ at high current densities region (100 mA cm⁻²). All three electrocatalysts show good stability with negligible potential loss at a static OER current density of 10 mA cm⁻². The obtained results with electrochemical active surface area revealed that the thin carbon layer coating controls nanostructure formation together with liable utilization and strong protection of active sites from the harsh electrolyte conditions, thereby providing constructive activity and stability.