Dataset of the article 'Redox state kinetics in water-oxidation IrOx electrocatalysts measured by operando spectroelectrochemistry'

Data published in the article 'Redox state kinetics in water-oxidation IrO_x electrocatalysts measured by operando spectroelectrochemistry', https://doi.org/10.1021/acscatal.1c03290. Abstract: hydrous iridium oxides (IrO_x) are the best oxygen evolution electrocatalysts available for operation in acidic environments. In this study, we employ time-resolved operando spectroelectrochemistry to investigate the redox states kinetics of IrO_x electrocatalyst films for both water and hydrogen peroxide oxidation. Three different redox species involving Ir³⁺, Ir^3.x+, Ir⁴⁺ and Ir^4.y+ are identified spectroscopically and their concentrations are quantified as a function of applied potential. The generation of Ir^4.y+ states is found to be the potential determining step for catalytic water oxidation, whilst H₂O₂ oxidation is observed to be driven by the generation of Ir⁴⁺states. The reaction kinetics for water oxidation, determined from the optical signal decays at open circuit, accelerate from ~ 20 s to < 0.5 s with increasing applied potential above 1.3V vs. RHE (i.e. TOFs per active Ir state increasing from 0.05 to 2 s^-1). In contrast, the reaction kinetics for H₂O₂ are found to be almost independent of the applied potential (increasing from 0.1-0.3 s^-1 over a wider potential window), indicative of a first order reaction mechanism. These spectroelectrochemical data quantify the increase of both the density of active Ir^4.y+ states and the TOFs of these states with applied positive potential, resulting in the observed sharp turn on of catalytic water oxidation current. We reconcile these data with the broader literature while providing a unique kinetic insight into IrO_x electrocatalytic reaction mechanisms, indicating a first order reaction mechanism for H₂O₂ oxidation driven by Ir⁴⁺ states, and a higher order reaction mechanism involving the co-operative interaction of multiple Ir^4.y+ states for water oxidation.