Abstract
Understanding the pathways of oxygen evolution reaction (OER) and the mechanisms of catalyst degradation is of essential importance for developing efficient and stable OER catalysts. Experimentally, a close coupling between OER and catalyst dissolution on metal oxides is reported. In this work, it is analysed how the microkinetic network structure of a generic electrocatalytic cycle, in which a common intermediate causes catalyst dissolution, governs the interplay between electrocatalytic activity and stability. Model discrimination is possible based on the analysis of incorporated microkinetic network structures and the comparison to experimental data. The derived concept is used to analyse the coupling of OER and catalyst dissolution on rutile and reactively sputtered Iridium oxides. For rutile Iridium oxide, the characteristic activity and stability behaviour can be well described by a mono-nuclear, adsorbate evolution mechanism and the chemical type of both competing dissolution and rate-determining OER-step. For the reactively sputtered Iridium oxide surface, experimentally observed characteristics can be captured by the assumption of an additional path via a low oxidation state intermediate, which explains the observed characteristic increase in OER over dissolution selectivity with potential by the competition between electrochemical re-oxidation and chemical dissolution.
Highlights
Understanding the pathways of oxygen evolution reaction (OER) and the mechanisms of catalyst degradation is of essential importance for developing efficient and stable OER catalysts
The analysis indicates that dissolution via a chemical reaction step is associated with either a constant or increasing OER over dissolution selectivity
The derived concepts are applied to analyse the coupling of OER and catalyst dissolution on rutile and reactively sputtered Iridium oxide surfaces
Summary
Understanding the pathways of oxygen evolution reaction (OER) and the mechanisms of catalyst degradation is of essential importance for developing efficient and stable OER catalysts. For various noble metal oxide surfaces as well as some Iridium-based perovskites, a constant ratio between oxygen evolution and catalyst dissolution rates has been reported, at different conditions of applied potential, pH or electrolyte composition[2,5,6,8]. Iridium accommodating an oxidation state of +3 under oxygen evolution has been reported in different studies supported by XPS11 and X-ray absorption spectroscopy (XAS)[12] Connecting both online inductively coupled plasma mass spectrometry (ICP-MS) and online inductively coupled plasma mass spectrometry (ICP-MS) and online electrochemical mass spectrometry (OLEMS) to a scanning flow cell (SFC) setup, Kasian et al.[4] proposed a two-pathway dissolution mechanism, assuming a second dissolution path via an OER-intermediate with Iridium in oxidation state +3. EIS methods were used for deriving corrosion models of various different metals such as iron or copper[21,22,23]
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