Multicomponent 3d-Metal Nanoparticles in Amorphous Carbon Sponge for Electrocatalysis Water Splitting

Design and understanding of complex material systems represent an intriguing pursuit for chemical research and could lead to functional materials with superior performance and new applications. Here, a highly porous amorphous carbon sponge incorporating uniformly dispersed multicomponent 3d-metal nanoparticles was prepared from heterometal cluster-based metal–organic frameworks (MOFs) of [M3(bpt)2(DMF)2(H2O)2] (M = Fe2+, Co2+, and Ni2) through controllable structural transformation under mild temperature. The octahedral coordination geometry of metal ions in the [M3(COO)6] nodes is highly versatile and compatible with various metal ions, thus rendering the metal mode as an ideal platform to assemble mono-, bi-, and trimetallic clusters as precursors for heterometallic nanoparticles. A mild temperature of 400 °C was found to be optimal to produce NiCoFeOx@C-400, featuring extremely small particles as low as 5 nm in diameter, high-content amorphous carbon, and coexistence of different metal oxide phases covering M3O4, M2O3, and MO besides the metal alloy nanoparticles. In contrast, higher annealing temperatures of 600 and 800 °C lead to aggregated particles above 100 nm, low-content and dense graphitized carbon, and simple oxide phases. The presence of heterometals, multicomponent synergism, rich heterojunctions, phase boundaries, and porous carbon promotes mass transport and contributes to the prominent electrocatalyst performance of NiCoFeOx@C-400, which is better than that of bi/monometallic species and high-temperature derivatives. When coated on nickel foam, NiCoFeOx@C-400 realizes small overpotentials of 253 and 84 mV for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, and can work with a cell voltage of merely 1.63 V for durable overall water splitting, under a current density of 10 mA cm–2 using 1 M KOH as the electrolyte. This study presents an efficient strategy to prepare and expand chemically complex systems for energy conversion application.