Unraveling the Mechanism of Self-Repair of NiFe-Based Electrocatalysts by Dynamic Exchange of Iron during the Oxygen Evolution Reaction

Understanding the mechanism of catalyst surface evolution during the continuous oxygen evolution reaction (OER) process is critical to optimize the stability. Here, by detailed insights into the activity and stability variations of NiFe-based catalysts including the NiFe alloy and NiFe layered double hydroxides (NiFe-LDH) for the OER, we reveal that NiFe-based electrocatalysts possess the ability to repair themselves during the OER in an alkaline medium via the balance of dynamic Fe exchange between catalysts and electrolytes. When the concentration of Fe leached from the NiFe-based catalyst into the electrolyte reaches a moderate level, a sufficient amount of Fe can be readsorbed onto the surface of the reconstituted NiFe oxyhydroxide, resulting in a balance between the repair and loss rates. In situ Raman experiments reveal that Fe doping in Ni-based catalysts can inhibit the excess oxidation of Ni; and the surface-adsorbed Fe species can be strongly adsorbed to the formed NiOOH layer in the OER, which further improves and stabilizes the activity of NiFe-based catalysts. This dynamic stability is further analyzed by isotope-labeled differential electrochemical mass spectrometry and theoretical calculation, which showed that the adsorption of Fe on the NiFe oxyhydroxide can promote the weak-bonding oxygen from adsorbed Fe(OH)x as a priority participant in the O2 formation through the lattice oxygen mechanism, reducing the loss of inner lattice oxygen of the NiFe-LDH structure and realizing self-repairing of activity. This work provides a more in-depth analysis of the actual OER self-repair ability of NiFe-based catalysts in alkaline media.