Designing nitrogen-enriched heterogeneous NiS@CoNi2S4 embedded in nitrogen-doped carbon with hierarchical 2D/3D nanocage structure for efficient alkaline hydrogen evolution and triiodide reduction

Fabrication of efficient non-precious electrocatalysts with hierarchical nanostructures and the desired compositions is highly desirable to enhance the catalytic activity and stability for hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR). This work proposes a zeolitic imidazolate framework (ZIF) template-based strategy to generate sulfide embedded in nitrogen-doped carbon with a hierarchical 2D/3D nanocage structure. ZIF-67, as a sacrificial template, is first etched to form 2D/3D NiCo layered double hydroxide/2-Methylimidazole (NiCo LDH/MeIm) and then converted to CoNi2S4 nanoparticles embedded in nitrogen-doped carbon (CoNi2S4/NC) through one-step sulfurization and pyrolysis. When a core-shell ZIF-8@ZIF-67 is designed as a template for the generation of Ni@NiCo LDH/MeIm, the obtained NiS@CoNi2S4/NC not only retains the unique 2D/3D nanostructure but also has a high N content, abundant active sites, larger specific surface area, and hierarchical pore distribution. NiS@CoNi2S4/NC mediates an overpotential of 126 mV at 10 mA cm-2 and a Tafel slope of 47.2 mV dec-1 in the alkaline HER. The solar cell equipped with NiS@CoNi2S4/NC as the IRR catalyst achieves a high cell efficiency of 7.96 %. NiS@CoNi2S4/NC shows durably high HER and IRR activity. This controllable synthetic strategy provides a valuable support for developing efficient catalysts in electrocatalytic energy conversion systems.