Revisiting Tractable Strategies to Determine the Activity/Inactivity of Electrocatalysts towards O2/•OH Production

Abstract

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 IrO2, RuO2, SnO2-Sb, and Boron doped diamond (BDD) electrodes toward H2O 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, SnO2-Sb, IrO2 and RuO2, 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.