Understanding the Enhancement Mechanism of A-Site-Deficient LaxNiO3 as an Oxygen Redox Catalyst

Lanthanide perovskite oxides have attracted much attention as an oxygen reduction and evolution catalyst because of their high chemical stability and composition adjustability. A defect strategy has been applied to enhance their electrocatalytic activity with the modulation of the crystal/electronic structure. However, the intrinsic roles of the defects, particularly A-site vacancies, are poorly understood. Herein, we prepare LaxNiO3 with various ratios of A-site vacancies by a facile nonstoichiometric strategy, which has boosted the dual-function catalytic activity of LaNiO3. More importantly, the enhancement mechanism of A-site-deficient LaxNiO3 as an oxygen redox catalyst has been unveiled. Induced vacancy defects on the A sites raise a compression strain in the NiO6 octahedron, exerting a positive enhancement on Ni-O covalency. Furthermore, the e g electron filling in the active cation Ni and the overlapping state of Ni 3d-O 2p hybridization have also been optimized, in which renovation will further boost the catalytic ability of oxygen redox processes. This work not only clarifies the intrinsic roles of A-site deficiency in the structure and electrocatalytic activities of perovskite oxides but also presents some insights into the design and exploration of high-activity catalysts by cation defect modulation.