Phase- and Surface Composition-Dependent Electrochemical Stability of Ir-Ru Nanoparticles during Oxygen Evolution Reaction

The increasing scarcity of iridium (Ir) and its rutile-type oxide (IrO2), the current state-of-the-art oxygen evolution reaction (OER) catalysts, is driving transition toward use mixed Ir oxides with a highly active yet inexpensive metal (IrxM1–xO2). Ruthenium (Ru) has been commonly employed due to high OER activity although electrochemical stability in Ir-Ru nanoparticles (IrxRu1–xO2 NPs), especially at relative contents, rarely evaluated for long-term application as water electrolyzers. In this work, we bridge knowledge gap by performing thorough study on composition- phase-dependent well-defined IrxRu1–xO2 NPs prepared flame spray pyrolysis under dynamic operating conditions. As-prepared (IrxRu1–xOy) present an amorphous coral-like structure hydrous phase, which upon post-synthetic thermal treatment fully converts followed selective enrichment NP topmost surface. It was demonstrated that incorporation into RuO2 matrix drastically reduced Ru dissolution ca. 10-fold expense worsening inherent stability, regardless phase present. Hydrous IrxRu1–xOy NPs, however, were shown be 1000-fold less stable than IrxRu1–xO2, where severe leaching yielded fast convergence monometallic IrOy. For sequential start-up/shut-down protocol revealed steady-state both Ru, well key role surface species activity: minimal losses (<1 at. %) activities tested Ir0.2Ru0.8O2 equivalent those untested Ir0.8Ru0.2O2. surface, mitigates subsurface dissolution, identified origin stabilization. These results suggest Ru-rich viable electrocatalysts electrolysis, significant repercussions cost reduction.