Insulator‐transition‐induced Degradation of Pyrochlore Ruthenates in Electrocatalytic Oxygen Evolution and Stabilization through Doping

Abstract Ru‐based pyrochlores (e.g., Y 2 Ru 2 O 7−δ ) are promised to replace IrO 2 in polymer electrolyte membrane (PEM) electrolyzers. It is significant to reveal the cliff attenuation on the oxygen evolution reaction (OER) performance of these pyrochlores. In this work, we monitor the structure changes and electrochemical behavior of Y 2 Ru 2 O 7−δ over the OER process, and it is found that the reason of decisive OER inactivation is derived from an insulator transition occurred within Y 2 Ru 2 O 7−δ due to its inner “perfecting” lattice induced by continuous atom rearrangement. Therefore, a stabilization strategy of the Ir‐substituted Y 2 Ru 2 O 7−δ is proposed to alleviate this undesirable behavior. The double‐exchange interaction between Ru and Ir in [RuO6] and [IrO6] octahedra leads the charge redistribution with simultaneous spin configuration adjustment. The electronic state in newly formed octahedrons centered with Ru 4 d 3 (with the state of e g ′ ↑↑ a 1 g ↑ e g 0 ) and Ir 5 d 6 ( e g ′ ↑↓↑↓ a 1 g ↑↓ e g 0 ) relieves the uneven electron distributions in [RuO6] orbital. The attenuated Jahn–Teller effect alleviates atom rearrangement, represented as the mitigation of insulator transition, surface reconstruction, and metal dissolution. As results, the Ir‐substituted Y 2 Ru 2 O 7−δ presents the greatly improved OER stability and PEM durability. This study unveils the OER degradation mechanism and stabilization strategy for material design of Ru‐based OER catalysts for electrochemical applications.