Mesoporous Hollow Nested Nanospheres of Ni, Cu, Co-Based Mixed Sulfides for Electrocatalytic Oxygen Reduction and Evolution

Nanostructured thiospinel-based transition metal sulfides with high-density active sites hold great application potentials as non-noble electrocatalysts. In this paper, high-performance bifunctional oxygen electrocatalysts of well-designed Ni, Cu, Co-based mixed sulfides, which combine two highly active thiospinels of NiCu2S4 and CuCo2S4, have been prepared successfully through solvothermal reaction, calcination, and the following sulfurization. The products of Ni, Cu, Co-based mixed sulfides present unique hollow structures with mesopores, in which several nanoparticles-assembled hollow nanospheres of 30–50 nm in thickness are nested one by one, forming multishell morphologies. Benefiting from the synergistic effect from combined NiCu2S4 and CuCo2S4 and the well-designed hollow structures with large electroactive surfaces/interfaces and efficient mass transportation, the obtained Ni, Cu, Co-based mixed sulfides exhibit remarkable electrocatalytic activities and excellent long-term durability toward not only oxygen reduction reaction (ORR) but also oxygen evolution reaction (OER). Regarding the overall oxygen-based electrocatalytic performance, the mixed sulfides present an extremely low potential difference (0.73 V) between the ORR and OER in KOH electrolyte, delivering significant superiority to their oxide counterparts and the commercial catalyst of Pt/C, as well as most of the oxygen bicatalysts reported recently. Therefore, the obtained Ni, Cu, Co-based mixed sulfides hold great promise as low-cost bifunctional catalysts with high efficiency for oxygen-based advanced energy storage systems.