Sodium Tartrate-Assisted Synthesis of High-Purity NiFe 2 O 4 Nano-Microrods Supported by Porous Ketjenblack Carbon for Efficient Alkaline Oxygen Evolution.

Herein, a simple two-step synthetic method was developed for the synthesis of NiFe 2 O 4 nano-microrods supported on Ketjenblack carbon (NiFe 2 O 4 /KB). A sodium tartrate-assisted hydrothermal method was employed for the synthesis of a NiFe-MOF/KB precursor, which was then pyrolyzed under N 2 at 500 °C to yield NiFe 2 O 4 /KB. Benefiting from the presence of high-valence Ni 3+ and Fe 3+ , high conductivity, and a large electrochemically active surface area, NiFe 2 O 4 /KB delivered outstanding OER electrocatalytic performance under alkaline conditions, including a very low overpotential of 258 mV (vs RHE) at 10 mA cm -2 , a small Tafel slope of 43.01 mV dec -1 , and excellent durability in 1.0 M KOH. Density functional theory calculations verified the superior alkaline OER electrocatalytic activity of NiFe 2 O 4 to IrO 2 . While both catalysts possessed a similar metallic ground state, NiFe 2 O 4 offered a lower energy barrier in the rate-determining OER step (*OOH → O 2 ) compared to IrO 2 , resulting in faster OER kinetics.