Plasma-assisted synthesis of hierarchical defect N-doped iron-cobalt sulfide@Co foam as an efficient bifunctional electrocatalyst for overall water splitting

Developing noble-metal-free bifunctional electrocatalysts at an effective cost and with a high catalytic ability for hydrogen production via water-splitting is imperative, although a great bottleneck remains. Herein, we present a plasma engraving strategy to synthesize N-doped CoFeS on cobalt foam with a multi-interface and defect hierarchical structure. The N-doped CoFeS was synthesized using an ion exchange method to prepare the CoFe LDH precursor, followed by sulphidation and plasma-assisted engraving in nitrogen gas. The N-doped CoFeS requires an overpotential of 230 mV for the OER and 26 mV for the HER to reach a current density of 10 mA cm(-2). It also shows an excellent catalytic activity towards overall water splitting, which requires a low voltage of 1.61 and 1.80 V to achieve a current density of 10 and 50 mA cm(-2), respectively, in 1 M KOH. The super-catalytic properties can be attributed to the interface and defect structure, which induces a high intrinsic activity, a superior transfer coefficient, and abundant active sites. This work presents a novel approach to prepare noble-metal-free electrocatalyst with plenty of interface and defect sites for overall water splitting.