Implementing iridium oxide (IrO x) nanocatalysts can be a major breakthrough for oxygen evolution reaction (OER), the limiting reaction in polymer electrolyte membrane water electrolyser devices. However, this strategy requires developing a support that is electronically conductive, is stable in OER conditions, and features a large specific surface area and a porosity adapted to gas-liquid flows. To address these challenges, we synthesized IrO x nanoparticles, supported them onto doped SnO 2 aerogels (IrO x /doped SnO 2), and assessed their electrocatalytic activity towards the OER and their resistance to corrosion in acidic media by means of a flow cell connected to an inductively-coupled mass spectrometer (FC-ICP-MS). The FC-ICP-MS results show that the long-term OER activity of IrO x /doped SnO 2 aerogels is controlled by the resistance to corrosion of the doping element, and by its concentration in the host SnO 2 matrix. In particular, we provide quantitative evidence that Sb-doped SnO 2 type supports continuously dissolve while Tadoped or Nb-doped SnO 2 supports with appropriate doping concentrations are stable under acidic OER conditions. These results shed fundamental light on the complex

Advanced materials are needed to meet the requirements of devices designed for harvesting and storing renewable electricity. In particular, polymer electrolyte membrane water electrolyzers (PEMWEs) could benefit from a reduction in the size of the iridium oxide (IrOx) particles used to electrocatalyze the sluggish oxygen evolution reaction (OER). To verify the validity of this approach, we built a library of 18 supported and unsupported IrOx catalysts and established their stability number (S-number) values using inductively-coupled plasma mass spectrometry and electrochemistry. Our results provide quantitative evidence that (i) supported IrOx nanocatalysts are more active towards the OER but less stable than unsupported micrometer-sized catalysts, e.g. commercial IrO2 or porous IrOx microparticles; (ii) tantalum-doped tin oxides (TaTO) used as supports for IrOx nanoparticles are more stable than antimony-doped tin oxides (ATO) and carbon black (Vulcan XC72); (iii) thermal annealing under air atmosphere yields depreciated OER activity but enhanced stability; (iv) the beneficial effect of thermal annealing holds both for microand nano-IrOx particles, and leads to one order of magnitude lower Ir atom dissolution rate with respect to non-annealed catalysts; (v) the best compromise between OER activity and stability was obtained for unsupported porous IrOx microparticles after thermal annealing under air at 450°C. These insights provide guidance on which material classes and strategies are the most likely to increase sustainably the OER efficiency while contributing to diminish the cost of PEMWE devices.