Ultrafine NiCo₂S₄ Nanosheets for Bifunctional Catalysis of Oxygen Reduction and Oxygen Evolution

Developing transition-metal sulfides with optimized surface structures shows great potential for boosting both oxygen reduction (ORR) and oxygen evolution (OER) reactions but remains challenging due to the lack of effective synthesis strategies. This limitation results in a suboptimal performance for most reported transition-metal sulfide catalysts. Herein, NiCo2S4 ultrafine nanosheets (NCS-SP) were obtained through conducting vulcanization treatment over nickel–cobalt hydroxide nanosheets (NiCo–OH) prepared in advance via a clean solvothermal synthesis, during which sulfur powder was employed as the sulfur source. NCS-SP integrates multiple catalytic advantages simultaneously, including the morphology structure of ultrafine nanosheets, excellent hydrophilia, abundant oxygen vacancies, and stable spinel structure, endowing NCS-SP to be an excellent bifunctional catalyst for ORR and the OER, with a smaller potential difference (ΔE) than Pt/C + RuO2. The work may not only highlight the significance of multistrategy synergy on improving catalytic performance but also pave the way for developing cost-effective and efficient bifunctional catalysts.