The Kinetic Parameters of the Oxygen Evolution Reaction (OER) Calculated on Inactive Anodes via EIS Transfer Functions:•OH Formation

The electrocatalytic behavior of "inactive" (Boron Doped Diamond (BDD), SnO2-Sb and PbO2) anodes toward the oxygen evolution reaction (OER) is evaluated using dc and ac techniques, under controlled experimental conditions (e.g. air bubbling, ohmic drop correction). Tafel slopes estimated from anodic polarization curves for all catalysts are located above 100 mV dec−1, suggesting that the rate-controlling step is similar for these materials at determined overpotentials. In agreement with the literature, it could be associated with the •OH generation since "active catalysts" displays slopes below 80 mV dec−1. A transfer function model is derived to account for the kinetic parameters of the OER mechanism for each anode, throughout its fitting to experimental electrochemical impedance spectroscopy (EIS) spectra. The model considers the kinetics of each elementary reaction and the material balances for the rates of formation of the adsorbates (H2Oads, •OHads, •Oads, •OOHads, and O2ads) involved in the OER. It is found that the rate-controlling step on SnO2-Sb (≤2.14 V), PbO2 (≤1.74 V) and BDD (2.54–2.71 V) is associated with the •OH formation, while this control is only modified when the potential becomes more positive for the oxide catalysts, thus, being determined by the production of adsorbed oxygen O2ads which on its turn promotes the O2 evolution. On the other hand, the rate-control step remains similar for BDD over the entire analyzed potential range, standing out its unique properties as inactive catalyst of the OER.