Mechanistic Aspects of the Electrocatalytic Oxygen Evolution Reaction over Ni−Co Oxides

The electrocatalytic oxygen evolution reaction (OER) presents the key transformation in electrochemical water‐splitting majorly determining energy efficiency and economics of hydrogen generation. In this study, the kinetics of the OER over Ni‐Co oxide structured by KIT‐6 templating and non‐structured Ni‐Co oxide catalysts in alkaline solution have been investigated aiming for insight with regard to the respective kinetically relevant surface reactions. Steady‐state Tafel plot analysis and electrochemical impedance spectroscopy (EIS) were used to determine kinetic parameters, Tafel slopes and the order of reaction. A dual Tafel slope behavior was observed for both catalysts. Tafel slopes of ca. 40 and 120 mV dec‐1 and 90 and 180 mV dec‐1 at low and high overpotentials appear for structured and non‐structured Ni‐Co oxide, respectively. A reaction order of unity was observed for structured Ni‐Co oxide, while non‐structured Ni‐Co oxide possessed a fractional reaction order in the high overpotential region. The kinetics of OER over structured Ni‐Co oxide were governed by Langmuir adsorption with the rate‐limiting step after primary adsorption of surface intermediates. In contrast, non‐structured Ni Co oxide obeyed the Temkin adsorption isotherm condition with the primary adsorption step being rate‐limiting.