β- and γ-NiFeOOH electrocatalysts for an efficient oxygen evolution reaction: an electrochemical activation energy aspect

Measuring experimentally the activation energy (E_a) of the oxygen evolution reaction (OER) is very important to understand the OER mechanism and to develop efficient electrocatalysts. However, few studies concerning E_a measurements are reported to support theoretical predictions. Herein, we prepared nickel foam (NF) supported β-NiFeOOH, β-NiOOH, γ-NiFeOOH, and γ-NiOOH and compared their OER performances. β-NiFeOOH exhibits an exceptionally high activity, with an overpotential (η) of 196, 245 and 257 mV to yield a current density of 10, 50, and 100 mA cm⁻², respectively. We measured E_a of the OER on different catalysts and established the E_avs. η relationship. The activation energy at zero-overpotential and the overpotential at zero-activation-energy on β-NiFeOOH/NF are the lowest (89 kJ mol⁻¹ and 350 mV), revealing the key origin of its high activity. This work provides the first experimental evidence for the high OER activity of Fe-doped NiOOH catalysts from the aspect of electrochemical activation energy.