Yong Gao, Yunyun Xu, Lingjie Yuan, Zhenwen Yu, Mengyue Liu, Ruize Xu, Kun Chang*, Yinlong Zhu*, Zhong-Shuai Wu*

Advanced Materials, 2026, accepted.

An Ir,La-MCOδ catalyst featuring Laoct-Iroct units with adjacent bridging and Ir z-axis oxygen vacancies was developed, achieving over 1550 h of PEM water electrolysis at 1 A cm-2 with an ultralow Ir loading of only 0.12 mg cm-2. The mechanistic origin of the durable catalytic activity of Ir,La-MCOδ was investigated, further revealing an oxygen-vacancy-mediated water-derived oxygen-hydroxyl coupling mechanism.