Enhanced alkaline bifunctional electrocatalytic water splitting achieved through N and S dual-doped carbon shell reinforced Co9S8 microplates

Abstract

Developing efficient, durable, and noble-metal-free electrocatalysts is considered the Holy Grail of sustainable hydrogen production through water splitting. In light of the potential importance of carbon components in low-cost electrocatalysis, various innovative synthesis strategies offering better structural integrity and facile electronic communication between the carbon component and catalytically active component are highly sought after. In coherence with this concept, N and S dual-doped carbon-armored Co₉S₈ (Co₉S₈@NSC) nanomaterials are synthesized via an improvised solid-state pyrolysis of Co(II) and sulphanilic acid adduct. The as-obtained nanomaterials furnish a bifunctional electrocatalytic activity for overall alkaline water splitting. In particular, Co₉S₈@NSC-8 (synthesized at 800 °C) shows impressive bifunctional activity with very low overpotentials of 267 and 120 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, corresponding to a current density of 10 mA cm⁻². The catalyst supports rapid reaction kinetics for both HER and OER with respective Tafel slopes of 85 and 48 mV dec⁻¹. The full-cell measurement with Co₉S₈@NSC-8 at both electrodes demonstrates a remarkable performance towards simultaneous HER and OER production, yielding a current density of 10 and 80 mA cm⁻² at low potentials of 1.6 and 2.4 V, respectively. The degree of graphitization and the status of N and S doping in the carbon shell of Co₉S₈@NSC reasonably explain the catalytic activity they have acquired. In the long-term durability test, the catalyst retains its activity after 10 h of electrocatalysis, reflecting impeccable stability in an alkaline environment. The superior electrocatalytic activity of Co₉S₈@NSC materials is mainly attributed to a strong interfacial interaction between the Co₉S₈ cores and N,S-doped carbon shells.