Enhanced Activity and Stability via Fe Substitution in Lithium Nickel-Based Electrocatalyst for Oxygen Evolution Reaction in Alkaline Media

The oxygen evolution reaction (OER) is kinetically sluggish and requires a high overpotential compared to the hydrogen evolution reaction (HER) due to its four-electron transfer process. Herein, we have fabricated highly active Fe-substituted LiNiO 2 using the electrostatic spray deposition (ESD) technique as scalable electrocatalysts. With this technique, we can modify the electronic and surface structure of LiNi x Fe 1-x O 2 by controlling the amounts of Ni and Fe, where x = 0, 0.2, 0.4, 0.6, and 0.8. This substitution can modify the electronic structure of the Ni ions to more electrophilic oxidation states, resulting in the M – O step facilitation, which is considered one of the rate-determining steps in the OER. The electronic structure modification was characterized by X-ray photoelectron spectroscopy (XPS). The surface structural modulation of the electrocatalysts due to Fe substitution was analyzed by scanning electron microscopy (SEM). The OER half-cell electrochemical measurements were carried out using standard three- electrode configuration. These results elucidate that substitution of Ni by Fe increases the electrocatalytic activity significantly. The optimized electrocatalyst, LiNi 0.6 Fe 0.4 O 2 , exhibits an overpotential of 239 mV at a current density of 10 mA cm -2 and a Tafel slope of 41.49 mV dec -1 . Moreover, it exhibits excellent operational durability under continuous and dynamic operating environments without any significant performance degradation.