Available and Cheap Methodology for Accurate Onset Potential and Tafel Slope Determination of Earth-Abundant Water Oxidation Electrocatalysts

Abstract

To date, a plethora of electrocatalysts for the Oxygen Evolution Reaction (OER) have been proposed. For evaluating their electrocatalytic behaviour the determination of the onset potential and Tafel slope in each studied electrolyte are key parameters.[1] Nevertheless, this evaluation becomes particularly problematic for first-transition metal catalysts as well as by the use of electroactive collectors whose redox peaks overlap the onset potential and hinder the correct determination of Tafel slope.[2] A usual solution to solve this problem is the in-situ determination of generated oxygen by mass spectrometry.[3]However, this in-situ determination is very expensive and only available in few laboratories. To overcome these limitations, coulovoltammetric response obtained from cyclic voltammetry allow a quantitative separation in the same potential range of the charge consumed by reversible (redox peak) reactions and the charge consumed by the irreversible reaction: the oxygen release. Accordingly, by means of quantifying the irreversible charges for different anodic potential limits is possible the unambiguous determination of both, the onset potential and the Tafel slope values isolating the catalyst redox contributions. To demonstrate the use of this technique, the onset potential and the Tafel slope for three benchmark electrocatalysts based on first-transition metal: a layered double hydroxide, a Prussian blue analogue and a β-Layered hydroxide were determined.[4] This study evidence the potential of coulovoltammetry as a straightforward and powerful tool for the investigation of electrocatalytic performances.