Surface engineering of 2D MOF to construct high-density Co9S8 nanoparticles supported on nitrogen doped carbon for efficient oxygen evolution reaction

Transition metal sulfides and their hybrids are promising alternative to precious metal catalyst for the oxygen evolution reaction (OER). Herein, the high-density Co9S8 nanoparticles (NPs) embedded in N-doped carbon has been prepared by using surface-engineered zeolitic imidazolate framework-9 (ZIF-9) nanosheets as precursor. The surface of ZIF-9 was modified with TAA, which is able to create chemical barrier and prevents metal from aggregation in the subsequent pyrolysis, thus making small Co9S8 NPs densely anchored on carbon layers. Arising from the unique structure, Co9S8@NC affords an optimized electronic structure and rich effective reactive sites for OER. As expected, Co9S8@NC exhibits small overpotential of 264 mV at 10 mA cm−2, low Tafel slope of 68.4 mV dec−1, and superior stability for alkaline OER (0.1 M KOH). The electrolysis cell, which was equipped with Co9S8@NC cathode and Pt/C anode, shows low water splitting voltage of 1.58 V at 10 mA cm−2 in 1.0 M KOH. This work employs an efficacious surface engineering strategy to design metal sulfide-based electrocatalysts for enhancing OER performance.