(116a) Influence of a-Site Cation on the Dynamic Restructuring of Ru-Based Pyrochlores Under Acidic Oxygen Evolution Conditions

Electrochemical water splitting using proton exchange membrane electrolyzers is a promising technology for sustainable electrochemical energy conversion and storage. However, their widespread commercial adoption is hindered by several challenges, including the sluggish kinetics of the anodic oxygen evolution reaction (OER; 2H₂O → O₂ + 4H⁺ + 4e^-; E⁰ = 1.23 V vs. RHE) leading to high overpotential losses. Choice of catalytic materials is constrained due to the highly corrosive cell environment. Among the precious 4d/5d transition metal oxides, RuO₂ exhibits superior intrinsic activity but suffers from relatively low stability. One strategy to enhance electrochemical stability of the Ru-based electrocatalysts is to incorporate active cations of Ru into a mixed metal oxide framework (i.e. A₂B₂O₇, B = Ru). While OER activity is linked to bulk oxide properties like Ru 4d-O 2p orbital overlap, the fundamental factors governing catalyst stability remain unclear.

In this work, we investigate A-site composition effects on the overall electrochemical performance of Ru-based pyrochlores under acidic OER conditions. A series of pyrochlores with varying lanthanide A-site cations (A = Pr, Nd, Sm, Eu, Gd) are synthesized. Characterization techniques such as X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and Raman spectroscopy reveal structural differences induced by A-site variation. Electrochemical performance is assessed through cyclic voltammetry (CV) and chronopotentiometry (CP), while intrinsic stability is quantified using the stability number (S-number), which relates the charge passed during OER to cationic dissolution measured via inductively coupled plasma mass spectrometry (ICP-MS). Additionally, pH-dependent studies during electrochemical cycling are conducted to evaluate whether dynamic changes under OER conditions alter the reaction mechanism. Our findings indicate that while the OER mechanism remains unchanged across all oxides, variations in metal-oxygen bond strength and redox properties of the oxide influence the extent of restructuring and cation dissolution impacting the overall OER stability of the oxides.