The origin of high electrochemical stability of iridium oxides for oxygen evolution

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 12; no. 31; pp. 2317 - 2326
• Main Authors: Ding, Yunlong, Liu, Wenwen, Xu, Zirui, Duan, Zhiyao
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 06.08.2024
• Subjects: Anodic dissolution; Anodizing; Catalysts; Dissolution; Electrochemistry; Iridium; Oxidation; Oxygen evolution reactions; Reaction kinetics; Reconstruction; Relativistic effects; Rutile; Surface stability
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d4ta02494j

Understanding the dissolution mechanism of oxygen evolution reaction (OER) catalysts is essential for designing efficient and stable electrolyzers. Iridium oxide (IrO 2 ), the most stable single oxide OER catalyst, represents an ideal subject for investigating and decoding the secrets of electrochemical stability under high anodic potentials. Using constant-potential DFT calculations, we reveal that the exceptional stability of IrO 2 originates from a highly activated surface reconstruction step. Compared with Ru reconstruction on RuO 2 (110), which occurs readily (<1 eV) via a water oxidation induced mechanism, Ir reconstruction cannot be facilitated with concerted water oxidation, imposing a significantly higher barrier (>2 eV). We further illustrate that the distinct Ir reconstruction kinetics stems from the inherent stability of Ir 4+ in the rutile phase - a consequence of relativistic effects, which makes the oxidation of Ir 4+ unfavorable even at highly anodic potentials. Instead, the formation of a high-energy surface-adsorbed IrO 4 precursor is required before further oxidation can occur to form soluble IrO 3 or IrO 2 (OH) species. Our findings suggest that stabilizing the relative stability of rutile Ru 4+ with respect to that of higher oxidation states could be a working strategy for the design of stable Ru-based OER catalysts. The exceptional stability of IrO 2 is attributed to the highly activated Ir reconstruction due to the inherently stable Ir 4+ in the rutile phase, which hinders the facile water oxidation induced reconstruction mechanism as in Ru dissolution.