Non-catalytic, instant iridium (Ir) leaching: A non-negligible aspect in identifying Ir-based perovskite oxygen-evolving electrocatalysts

The large-scale application of proton exchange membrane water electrolysis technology requires the development of high-performance oxygen evolution electrocatalysts with as little iridium (Ir) as possible. Ir-based double perovskite oxides (A2B'IrO6; A = alkaline, alkaline-earth, or rare-earth elements; B' = transition metal or rare-earth elements) represent a class of oxides with great potential to replace the commercial catalyst IrO2. However, the structural evolution of Ir-based double perovskite oxides in electrolytes is incompletely understood, and foundational knowledge of the design principle of the “ideal” material is lacking. In this work, we report the unexpected phenomenon of instant Ir leaching from Ir-based double perovskite oxides in acid under non-catalytic conditions and discuss the implications of this phenomenon for mechanism investigation and material identification. Some well-known Ir-based double perovskite oxides, such as Ba2PrIrO6 and Sr2YIrO6, undergo instantaneous Ir leaching when they come into contact with acidic electrolytes. The Ir-leaching process is found to be non-persistent and non-thermodynamically determined, and its extent is correlated with the leaching of other B'-site elements in the perovskite oxides. Based on this observation, we revisit the Ir dissolution-precipitation process for surface IrOx formation during the perovskite-electrolyzed oxygen evolution reaction, emphasizing the non-negligible role of Ir species owing to acid corrosion in the electrolyte. Finally, we modify a screening protocol for low-Ir oxygen evolution electrocatalysts and propose an instant acid corrosion test as an indispensable process to evaluate the structural stability of potential catalysts.