Electrochemical Impedance and Surface Charge Dynamics in Alkaline Oxygen Evolution on NIFE-Based Electrocatalysts

Abstract

Nickel-based catalysts are widely explored for the oxygen evolution reaction (OER) in alkaline media, yet variations in reported activity and kinetic parameters remain a challenge. This study investigates NiFe-based electrocatalysts synthesized via hydrothermal deposition, assessing their OER performance through electrochemical impedance spectroscopy (EIS) and chronoamperometry under varying alkaline conditions. We demonstrate that the charge transfer resistance (R_ct) and double-layer capacitance (C_dl) significantly influence the reaction kinetics, leading to variations in the apparent Tafel slope. At low overpotentials, a near-ideal slope of ~35 mV/dec is observed; however, higher polarization induces deviations due to surface charge accumulation, diffusion limitations, and bubble formation. Unlike conventional Tafel analysis, our approach highlights the role of electrochemical surface area (ECSA) and interfacial charge redistribution in modulating catalytic activity. Additionally, in situ Raman spectroscopy reveals hydroxide adsorption dynamics as a critical factor governing reaction efficiency. Our findings suggest that analyzing impedance behavior alongside conventional kinetic models provides a more comprehensive understanding of OER activity and mitigates misinterpretation arising from non-kinetic effects.