Evaluating the stability of Ir single atom and Ru atomic cluster oxygen evolution reaction electrocatalysts

Single-atom catalysts (SACs) have recently emerged in electrocatalysis due to their improved electrocatalytic performance in many industrially relevant reactions. The potential application of SACs also includes oxygen evolution reaction (OER), where high anodic potentials and corrosive acidic environments narrow the choice of classical nanoparticulated electrocatalysts to scarce iridium (Ir) and ruthenium (Ru) noble metals. To date, published literature mainly focused on improving SACs activity or selectivity, while stability was rarely assessed using electrochemical methods and post-mortem characterizations. To fill this knowledge gap, we utilize an online inductively coupled plasma mass spectrometry setup (online ICP-MS) to evaluate the stability of Ir SAC and highly dispersed Ru catalysts supported by indium doped tin oxide (ITO) prepared via surface organometallic chemistry. After benchmarking with commercial IrO2 and RuO2 nanoparticulated catalysts, we validate their high activity and determine their lower stability, confirming the previously reported inverse activity-stability relationship. The observed lower stability is proposed to originate from a change in the OER mechanism from the adsorbate evolution mechanism (AEM) driven by the catalysts to the lattice oxygen mechanism (LOM) with participation of the support. This is confirmed by the increase in Tafel slope, coinciding with the dissolution onset of the ITO support. Additionally, we show that there is no effect of the commonly used backing electrodes (glassy carbon, gold foil, and boron-doped diamond) on the activity and stability. This work provides guidelines for evaluating highly dispersed atomic catalysts in future research and fundamental insights into the role of the support in their stability.