Insulator-Transition-Induced Degradation of Pyrochlore Ruthenates in Electrocatalytic Oxygen Evolution and Stabilization through Doping

Abstract

Ru-based pyrochlores (e.g., Y₂Ru₂O_7−δ) are promised to replace IrO₂ 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 Y₂Ru₂O_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 Y₂Ru₂O_7−δ due to its inner “perfecting” lattice induced by continuous atom rearrangement. Therefore, a stabilization strategy of the Ir-substituted Y₂Ru₂O_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 4d³ (with the state of e_g′^↑↑a_1g^↑ e_g⁰) and Ir 5d⁶ (e_g′^↑↓↑↓a_1g^↑↓ e_g⁰) 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 Y₂Ru₂O_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.