Ning Sun, Dongdong Zhang, Yifei Li, Yang Qin, Xinyu Xie, Guowei Liu, Pengda Ye, Xiangjiang Dong, Gongjin Xu, Lei Lian, Peng Wei, Lijia Zhou, Yucheng Huang, Jing Zhou, Jihao Zhang, Ruxanda Mireanu, Qingyu Kong, Ying‐Rui Lu, Zhiwei Hu, Ming Lei, Kai Huang, Xiang Li, Runze Yu
ABSTRACT Surface reconstruction governs the activity and stability of oxide‐based electrocatalysts in alkaline hydrogen evolution reaction (HER), yet its structural origins remain unclear. Here, we show that tuning the connectivity of RuO 6 octahedra in BaRuO 3 perovskites modulates reconstruction thermodynamics, with the balance between corner‐ and face‐sharing units determining the formation of amorphous surface Ru x O y layers. Increased corner‐sharing weakens lattice cohesion and promotes early Ba/Ru dissolution and amorphization, whereas excessive face‐sharing suppresses reconstruction. The 6H phase, featuring a balanced connectivity motif, undergoes moderate, self‐activating reconstruction that preserves bulk stability. In situ Raman spectroscopy reveals rapid Ru–O rearrangement producing an amorphous Ru x O y shell with accelerated OH * turnover and interfacial water reorganization. Density functional theory (DFT) shows that reconstructed Ru x O y domains redistribute interfacial charge, strengthen Ru 4 d –O 2 p orbital hybridization, lower the water‐dissociation barrier, and optimize hydrogen‐binding energetics. These features account for the outstanding performance of AC‐6H (the activated 6H‐BaRuO 3 is denoted as AC‐6H), achieving 11 mV at 10 mA cm −2 and sustaining 150 h at 200 mA cm −2 . This work establishes octahedral‐connectivity engineering as a platform for directing reconstruction and designing high‐performance HER catalysts.