Fe-Based Metal Organic Framework-Derived FeNiP/N-Doped Carbon Heterogeneous Core–Shell Structures for Oxygen Evolution

It is of great significance to explore high activity, low overpotential, and outstanding durability electrocatalysts without precious metals for oxygen evolution reaction to reduce the energy consumption in the electrolysis of water to product hydrogen. Metal organic frameworks (MOFs) with periodic structure and uniform pore distribution have been widely used as precursors for the synthesis of transition metal electrocatalysts. Herein, we first synthesized nanoscale Fe-soc-MOFs with relatively high specific surface area and in situ converted it into nickel–iron double layer hydroxide/MOF (FeNi LDH/MOF) by Ni²⁺ etching. Finally, a nickel–iron phosphide/nitrogen-doped carbon cubic nanocage (FeNiP/NC) was obtained by calcination and phosphating. FeNiP/NC with its unique core–shell structure has an overpotential of only 240 mV at a current density of 10 mA/cm² and can be continuously electrolyzed for 45 h. High catalytic activity of FeNiP/NC is mainly attributed to the action of Fe and Ni bimetals and the synergistic effect between FeNiP and N-doped porous carbon, which was confirmed by the calculation of density functional theory (i.e., Gibbs free energy). After a long period of electrolysis, FeNiP was converted to MOOH (M = Fe and Ni) and became the new active site. This study provides a feasible optimization strategy for the development of high-efficiency three-dimensional electrode materials without precious metals.