A multifunctional cobalt iron sulfide electrocatalyst for high performance Zn–air batteries and overall water splitting

Abstract

Developing a highly efficient, inexpensive, and robust catalyst with multifunctional activity is pivotal and central to regenerative greener metal–air batteries and fuel cells. However, it is still a big challenge to achieve the integration of three functions in a single catalyst. Herein, we report a facile, template-free and scalable strategy to synthesize nanorod embedded wheat-grain CoFe(3:1)S₂ in conjunction with nitrogen-containing carbon by a simple single-step hydrothermal reaction. The synthesized catalyst demonstrates remarkable pH-universal hydrogen evolution activity and requires only 98, 117, and 123 mV overpotential in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS to achieve a current density of 10 mA cm⁻². The optimized catalyst also exhibits a remarkable bifunctional oxygen activity and when CoFe(3:1)S₂ is used as an air cathode, it demonstrates a very high peak power density of 387 mW cm⁻² and energy density of 1008 W h kg⁻¹ with prolonged cycling stability. Besides, a water electrolyzer assembled using a CoFe(3:1)S₂ based anode and cathode affords a current density of 10 mA cm⁻² at a low cell potential of 1.584 V. When two Zn–air batteries are connected in series, they successfully powered overall water splitting, manifesting the feasibility of CoFe(3:1)S₂ for various energy conversion and storage systems.