One-step synthesis of heterostructured cobalt-iron selenide as bifunctional catalyst for overall water splitting

Transition metal selenide catalysts have been identified as suitable materials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) as a result of their high electrical conductivity, large surface area, and tunable electronic structure to generate clean hydrogen through electrocatalytic water splitting. In this work, we report the fabrication of cobalt-iron selenide nanoparticles to form a heterostructured Co-Fe Selenide catalyst through a one-step hydrothermal process. The fabricated Co-Fe Selenide shows an improved performance toward HER in both acidic and alkaline electrolyte as compared to individual CoSe₂ and FeSe₂ catalysts. The HER activity of Co-Fe Selenide, at a current density of 10 mA cm⁻², generates an overpotential of 129 and 142 mV, a Tafel slope of 47 and 46 mV dec⁻¹ in both acidic and alkaline electrolytes, respectively. Furthermore, the catalyst exhibits an OER activity with an overpotential of 270 mV at a current density of 10 mA cm⁻² with a small Tafel slope (78 mV dec⁻¹) in alkaline electrolyte. Moreover, a symmetric water electrolysis cell assembled using Co-Fe Selenide on carbon cloth as both anode and cathode in alkaline electrolyte achieves a cell voltage of 1.68 V at a current density of 10 mA cm⁻² with strong stability for 9 h. This outcome renders Co-Fe Selenide as a low-cost material for efficient HER and OER activity and as a potential replacement to noble metal catalysts for overall water splitting devices.