Exceptionally Robust Face-Sharing Motifs Enable Efficient and Durable Water Oxidation.

Corner-sharing oxides usually suffer from structural reconstruction during the bottleneck oxygen-evolution reaction (OER) in water electrolysis. Therefore, introducing dynamically stable active sites in an alternative structure is urgent but challenging. Here, 1D 5H-polytype Ba5 Bi0.25 Co3.75 FeO14-δ oxide with face-sharing motifs is identified as a highly active and stable candidate for alkaline OER. Benefiting from the stable face-sharing motifs with three couples of combined bonds, Ba5 Bi0.25 Co3.75 FeO14-δ can maintain its local structures even under high OER potentials as evidenced by fast operando spectroscopy, contributing to a negligible performance degradation over 110 h. Besides, the higher Co valence and smaller orbital bandgap in Ba5 Bi0.25 Co3.75 FeO14-δ endow it with a much better electron transport ability than its corner-sharing counterpart, leading to a distinctly reduced overpotential of 308 mV at 10 mA cm-2 in 0.1 m KOH. Further mechanism studies show that the short distance between lattice-oxygen sites in face-sharing Ba5 Bi0.25 Co3.75 FeO14-δ can accelerate the deprotonation step (*OOH + OH-  = *OO + H2 O + e- ) via a steric inductive effect to promote lattice-oxygen participation. In this work, not only is a new 1D face-sharing oxide with impressive OER performance discovered, but also a rational design of dynamic stable and active sites for sustainable energy systems is inaugurated.