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Seawater electrolysis is an attractive technique for massive green hydrogen production owing to the dominant advantages of seawater resources, namely low‐cost and limitlessness. However, the oxygen evolution reaction (OER) catalysts will be easily deactivated for severe seawater Cl− permeation and corrosion. Herein, a structural buffer engineering strategy is reported to endow the Co2(OH)3Cl with long‐term operation stability and a high OER selectivity of ≈99.6% in seawater splitting. The lattice Cl− of Co2(OH)3Cl can act as the structural buffer, whose continuous leaching during OER can leave vacancies for seawater Cl− invasion, so as to avoid catalyst deactivation. Accordingly, Co2(OH)3Cl can maintain 99.9% of its initial current density after 60 000 s operation, while that of Co(OH)2 decays by 52.7% in 7 000 s. Meanwhile, the lattice Cl− of Co2(OH)3Cl can optimize the binding energy of reaction intermediates on the neighboring OCoO site. Thus, Co2(OH)3Cl exhibits a current density of 330.5 mA cm–2 at the potential of 1.63 V versus RHE, 45.9 times higher than that of Co(OH)2. The structural buffer strategy may be applied to incorporate other metal oxides with suitable anions, and effectively boost their OER activity and stability in alkaline seawater. [ABSTRACT FROM AUTHOR]

Electric‐field‐induced strain in piezoelectric materials, which has demonstrated broad applications, usually provides about 1% strain. A giant and reversible deformation as large as ≈5% in BiFeO3 thin film induced by electrochemistry is reported, where the large lattice change is induced by electrochemical reaction through absorption and desorption of oxygen. Prior to deformation, a precursor phase with projected Fe–Fe pairs is formed first under low voltage (1 V), and then a large lattice expansion is eventually achieved under a high voltage (≈18 V), which is reversible under negative voltage. It is found that the giant strain is due to the electrochemically induced migration of oxygen ion which leads to significant out‐of‐plane lattice expansion under positive voltage, resulting in the formation of a new oxygen‐deficient phase. Interestingly, the new oxygen‐deficient phase is capable of transforming back to the pristine structure by absorbing oxygen under negative voltage. The results provide a new route to realize giant and reversible deformation in oxides by oxygen migration. [ABSTRACT FROM AUTHOR]