Noble Metal-Free Co9S8 and NiS Composite Nanosheets for Enhanced Electrocatalytic Oxygen Evolution Reaction

Porous Ni3S2-Co9S8 Carbon Aerogels Derived from Carrageenan/NiCo-MOF Hydrogels as an Efficient Electrocatalyst for Oxygen Evolution in Rechargeable Zn-Air Batteries

Herein, we fabricate N-doped porous Ni₃S₂-Co₉S₈/carbon aerogels (Ni₃S₂-Co₉S₈/NCAs) using carrageenan/NiCo-metal-organic framework (MOF) hydrogels as the precursor via the high-temperature carbonization route with excellent electrocatalytic properties for the oxygen evolution reaction (OER). The electrochemical measurements indicate that the Ni₃S₂-Co₉S₈/NCA as a quintessential electrocatalyst exhibits excellent OER performance, which has outperformed most transition metal sulfide (TMS) catalysts in alkaline environments, as attested with a lower overpotential of 337 mV at 10 mA cm^-2 and a smaller Tafel slope of 77 mV dec^-1. Meanwhile, a Zn-air battery based on Ni₃S₂-Co₉S₈/NCA + Pt/C achieves a large power density of up to 256 mW cm^-2 (and 193 mW cm^-2), small charge/discharge voltage gap, and good cycling stability, notably better than the conventional RuO₂ + Pt/C-based Zn-air batteries. These excellent electrocatalytic properties are mainly attributed to the distinct hierarchical porous structure and interfacial synergy between the Ni₃S₂ and Co₉S₈ nanoparticle structure with rich defects, facilitating the mass transport and high graphitization degree beneficial for electron mobility. It is envisioned that the research provides a novel approach for the exploration of marine biomass as an electrocatalyst.