The electrocatalytic behavior of "inactive" (Boron Doped Diamond (BDD), SnO 2 -Sb and PbO 2 ) 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 (H 2 O ads , • OH ads , • O ads , • OOH ads , and O 2ads ) involved in the OER. It is found that the rate-controlling step on SnO 2 -Sb (≤2.14 V), PbO 2 (≤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 O 2ads which on its turn promotes the O 2 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. In the last decades, the OER mechanism has turned out be of significant importance for environmental applications related to wastewater treatment, particularly those involving the destruction of toxic and/or recalcitrant organic compounds, using "inactive" catalysts.1-9 Under this context, active anodes contain transition elements on their surfaces with intermediate oxidations states, which enhance the OER and the partial oxidation of the contaminants; while inactive anodes favor the mineralization of the organic compounds throughout an indirect mechanism involving a strong oxidizing mediator (• OH radicals).10 Concerning inactivity, the boron doped diamond (BDD) is the state-of-the-art catalyst, since it possesses a unique role toward the formation of hydroxyl radicals.11-14 Nevertheless, overcoming its inherent high cost and manageability remain as main challenges to achieve an adequate operation at industrial levels. An intense research combining the best characteristics to electrochemically enhance • OH formation has resulted in the proposal of materials containing PbO 2 (β phase) and SnO 2 , with multiple variations during synthesis conditions. [1][2][3]12,[15][16][17] However, although the applications of these catalysts have been successful toward the electrocombustion of different organic compounds, their fundamental chemistry, rate-controlling steps and interactions occurring during the occurrence of• OH generation have not been fully understood. Most computa...

The measurement of the electroactivity of anode materials toward the generation of hydroxyl radicals or oxygen evolution from water oxidation is overriding to develop novel catalysts with tuned electrocatalytic applications. Thus, this work experimentally revisits chemical and electrochemical characterization techniques with the aims of establishing a comparison of the electrochemical performance of typical IrO 2 , RuO 2 , SnO 2 -Sb, and Boron doped diamond (BDD) electrodes toward H 2 O oxidation under feasible experimental conditions, and highlighting those conditions where variability cannot be removed. Tafel slopes corrected for ohmic resistance and active areas are 127, 175, 42, 48 mV dec −1 for BDD, SnO 2 -Sb, IrO 2 and RuO 2 , respectively; while in the same order, the onset potential for water oxidation is: 2.49, 2.29, 1.47, 1.38 V vs SHE, measured at a current density of 0.5 mA cm −2 . Additionally, a new interpretation is presented for the analysis of electrochemical impedance spectroscopy (EIS), and its connection with the OER mechanism: in the potential zone where Tafel is applicable is possible to appreciate the dielectric properties of the substrate for non-active anodes and elucidating the variation in the rate-determining step of water oxidation. EIS results suggest the possibility to use the time-constant associated with this stage as a parameter of the active or non-active behavior of the above electrodes. The advantages and drawbacks of different trapping molecules used to detect the • OH generation in electrocatalysis is discussed. The photoluminescence of coumarin could be used as a fast and reliable method for the evaluation of the electrocatalyst activity toward the • OH production.