Electrodeposited nanostructured flakes of cobalt, manganese and nickel-based sulfide (CoMnNiS) for electrocatalytic alkaline oxygen evolution reaction (OER)

The nanostructured flakes of cobalt, manganese, nickel-based sulfide (CoMnNiS) were synthesized by facile electrodeposition technique on Ni foam, for electrocatalytic water splitting. Growth of interconnected flake-like, surface morphology of CoMnNiS was evaluated from field emission scanning electron microscopy (FE-SEM), and its formation has been corelated to metal ion denudated layer (MIDL) theory. Electrocatalytic activities, oxygen/hydrogen evolution were tested in 1 M KOH electrolyte. Oxygen evolution reaction (OER) results revealed a Tafel slope of 48 mV/dec, and overpotential of 371 mV@10 mA/cm² with an exchange current density of 0.33 mA/cm² (from geometrical surface area). On the contrary, hydrogen evolution reaction (HER) activity exhibited a Tafel slope of 101 mV/dec, and overpotential of − 226 mV@10 mA/cm² with an exchange current density of 0.13 mA/cm². Stability of CoMnNiS electrocatalyst was tested for 21 h. duration, which demonstrates an efficiency of 48 and 56% for OER and HER process, respectively. These electrocatalytic results are attributed to the presence of electrochemical species (multiple oxidation states of Co, Mn, i.e., Co⁺³/Co⁺², and Mn⁺²/Mn⁺³/Mn⁺⁴) on the sample surface, as evidenced from X-ray photoelectron spectroscopy (XPS). Thus, the electrodeposited CoMnNiS nanostructure proves to be an effective electrocatalyst in alkaline reaction for OER due to its ease of synthesis, performance, and stability.