Electrochemical Catalyst–Support Effects and Their Stabilizing Role for IrOx Nanoparticle Catalysts during the Oxygen Evolution Reaction

Abstract

Redox-active support materials can help reduce the noble-metal loading of a solid chemical catalyst while offering electronic catalyst–support interactions beneficial for catalyst durability. This is well known in heterogeneous gas-phase catalysis but much less discussed for electrocatalysis at electrified liquid–solid interfaces. Here, we demonstrate experimental evidence for electronic catalyst–support interactions in electrochemical environments and study their role and contribution to the corrosion stability of catalyst/support couples. Electrochemically oxidized Ir oxide nanoparticles, supported on high surface area carbons and oxides, were selected as model catalyst/support systems for the electrocatalytic oxygen evolution reaction (OER). First, the electronic, chemical, and structural state of the catalyst/support couple was compared using XANES, EXAFS, TEM, and depth-resolved XPS. While carbon-supported oxidized Ir particle showed exclusively the redox state (+4), the Ir/IrO_x/ATO system exhibited evidence of metal/metal–oxide support interactions (MMOSI) that stabilized the metal particles on antimony-doped tin oxide (ATO) in sustained lower Ir oxidation states (Ir^3.2+). At the same time, the growth of higher valent Ir oxide layers that compromise catalyst stability was suppressed. Then the electrochemical stability and the charge-transfer kinetics of the electrocatalysts were evaluated under constant current and constant potential conditions, where the analysis of the metal dissolution confirmed that the ATO support mitigates Ir^z+ dissolution thanks to a stronger MMOSI effect. Our findings raise the possibility that MMOSI effects in electrochemistry—largely neglected in the past—may be more important for a detailed understanding of the durability of oxide-supported nanoparticle OER catalysts than previously thought.