(Invited) Benchmarking Oxygen Evolution Reaction Activity and Stability of Unsupported and Supported IrO x Nanoparticles

High investments and operational cost of proton-exchange membrane water electrolysers (PEMWE) devices are partly due to that of their constituting materials. In this context, research efforts are dedicated to minimize the content in iridium (Ir) used to electrocatalyze the oxygen evolution reaction (OER) at the anode. One possible materials’ strategy is to support iridium oxide nanoparticles (IrO x NPs) on a corrosion resistant support, such as antimony-doped (ATO), niobium-doped (NTO) or tantalum-doped (TaTO) tin oxide [1,2]. However, the Gibbs-Thompson effect, which controls the electrochemical stability of nanomaterials casts a doubt on the long-term relevance of this approach. To tackle these issues, we built a library of 18 supported and unsupported IrO x catalysts and established their stability number values using inductively-coupled plasma mass spectrometry (ICP-MS) and electrochemistry. Our results provide quantitative evidence that supported IrO x nanocatalysts are more active towards the OER but less stable than unsupported micrometer-sized catalysts. A large part of this instability comes from the metal oxide support which, by degrading, results in IrO x NPs being detached or electrically-disconnected (loss of doping element). In this respect, TaTO supports revealed substantially more stable than ATO supports [2]. Another reason for the drop in OER performance over the long term comes from the fact that IrO x NPs contain mixed valences including Ir atoms in (+III) oxidation state, which are highly active towards the OER but also prone to dissolve [1,3]. Similar to what was observed on extended surfaces, we report that mild thermal annealing (450°C) leads to lower Ir atom dissolution rate. Overall, the best compromise between OER activity and stability was obtained for unsupported porous IrO x microparticles after mild thermal annealing under air at 450°C [4]. Ackowledgements This work was supported by the French National Research Agency in the frame of the MOISE project (grant number ANR-17-CE05-0033). References F. Claudel, L. Dubau, G. Berthomé, L. Solà-Hernandez, C. Beauger, L. Piccolo, F. Maillard, ACS Catal . 9 (2019) 4688-4698. S. Abbou, R. Chattot, V. Martin, F. Claudel, L. Solà-Hernández, C. Beauger, L. Dubau, F. Maillard, ACS Catal. 10 (2020) 7283-7284. M. Scohy, S. Abbou, V. Martin, B. Gilles, E. Sibert, L. Dubau, F. Maillard, ACS Catal . 9 (2019) 9859-9869. C. Daiane de Ferreira, F. Claudel, V. Martin, R. Chattot, S. Abbou, I. Jiméne