(82b) Acidic Oxygen Evolution Reaction Activity-Stability Relationships in Ru-Based Pyrochlores

To enable seasonal grid-scale energy storage and decarbonize industrial hydrogen production, proton exchange membrane (PEM) electrolyzer catalysts must have long-term operational stability and high activity. Ru-based oxygen evolution reaction (OER) catalysts have the potential to improve electrolyzer efficiency today, but fast degradation has thus far rendered them unsuitable for commercial applications. Incorporating Ru into metal oxide structures such as perovskites (ARuO₃) and pyrochlores (A₂Ru₂O₇), where A is typically a rare-earth or alkaline-earth metal, has shown promising improvements in OER activity and stability relative to RuO₂.

In this work, we combine experimental and theoretical techniques to explore a series of A₂Ru₂O₇ (A = Y, Nd, Gd, Bi) catalysts with a range of physical and electronic properties to assess the influence of the A-site on OER activity and stability in acidic electrolyte. Ultimately, all A₂Ru₂O₇ investigated showed greater activity and stability relative to a RuO₂ standard, and even achieved stability comparable to Ir mixed metal oxide catalysts. Activity was assessed using cyclic voltammetry, revealing a strong dependence on the A-site cation. Stability was assessed using chronoamperometry while simultaneously monitoring catalyst dissolution with inductively coupled plasma mass spectrometry (ICP-MS) to determine the S-number (mol O₂ evolved/mol Ru dissolved). We found the most active catalyst (Nd₂Ru₂O₇) was also the least stable, while the other A-site elements (Y, Gd, Bi) exhibited similar stability despite differences in activity.

To gain a more fundamental understanding of the OER activity and stability relationship, the pyrochlores were characterized extensively using x-ray absorption spectroscopy (XAS), x-ray diffraction (XRD), and scanning electron microscopy (SEM). Dissolution thermodynamics were also assessed using density functional theory (DFT)-derived Pourbaix diagrams. Our findings indicate that tuning structural and electronic properties of Ru-based catalysts can influence OER performance in acidic electrolyte, and the insights gained will aid the design of next-generation OER catalysts with enhanced stability.