Hierarchical cobalt sulfide with vertical in-plane edge structure for enhanced electrocatalytic oxygen evolution reaction

Highlights: • A direct growth of hierarchical Co_1-xS/Co₉S₈ nanostructure was formed and characterized. • It exhibited remarkable OER activity with Tafel slope of 30 mV per decade. • A possible catalytic mechanism of such hierarchical cobalt sulfide was put forward. Transition metal-based sulfides are hopeful nonprecious eletrocatalysts for enhanced oxygen evolution reaction (OER). Compared with noble-metal based materials, such transition metal-based sulfides have been widely investigated in catalysis and energy storage, which can be easily controlled into various morphology due to their various valences. However, it is still a challenge to engineer transition metal-based sulfides of 3D nanostructure with rich edges. In this work, hierarchical cobalt sulfide nanocomposites (HCSN), with the vertical growth of Co₉S₈ nanosheets on horizontal Co_1-xS nanoplates, were fabricated via simple one-pot synthesis. Due to adequate exposed-edge planes, the HCSN exhibited remarkably catalytic property for OER with low overpotential of 275 mV at a current density of 10 mA cm⁻², a low Tafel slope of 30 mV/decade and excellent stability. By investigating the chemical states before and after OER, the possible catalytic mechanism was provided. This work may provide a simple and efficient method to prepare hierarchical metal sulfides for electrocatalytic OER.