(589g) Investigating Metal Dissolution of Calcium Iridium Oxide during Long-Term Oxygen Evolution Reaction in Acid

Studies on iridium-based perovskites for the oxygen evolution reaction (OER) in acid have shown that A-site alkali metal leaching creates surface polymorphs that may be responsible for high activity. In parallel, minimal dissolution of B site iridium during OER is correlated with high catalytic stability; however, long-term stability remains a critical challenge because degradation can be driven by oxidation or dissolution in harsh acidic conditions. Therefore, understanding the driving force for and effects of metal dissolution from catalytic materials during a range of operating conditions is crucial to unraveling degradation mechanisms of materials during long-term operation.

In this work, we focus on Ca₂IrO₄ to understand how materials respond to an expanded range of operating potentials and low pH levels. Inductively coupled plasma-mass spectrometry (ICP-MS) is used after extensive chronoamperometry tests to monitor Ir leaching at different stages during both catalyst activation and degradation phases. We observe higher Ir dissolution upon exposure to the more oxidizing potentials, but results for pH are less straightforward. Dissolution results indicate that Ca₂IrO₄ may have different stability regimes in pH 0 and 1 compared to pH 2 under the same applied potentials that ultimately result in various catalytic behaviors. In addition, substrate instability from glassy carbon oxidation contributes to overall electrode instability and limits necessary charge transport to the catalyst. Comparative stability studies on glassy carbon and gold substrates provide insights to the various degradation mechanisms at play. X-ray photoelectron spectroscopy (XPS) provides critical insights to dynamics of substrates and catalysts after various electrochemical stability testing protocols. Using a combination of electrochemical and spectroscopic tools, we aim to provide an understanding of the material degradation for future catalyst design with balanced activity and long-term stability.