Shaping a Doped Perovskite Oxide with Measured Grain Boundary Defects to Catalyze Bifunctional Oxygen Activation for a Rechargeable Zn-Air Battery.

Symmetry broken configurations within a long-range atomic arrangement exhibit new physical properties, and distinctive strategies are needed to resuscitate the localized symmetry by introducing measured defects, which can be attractive in displaying enhanced catalytic activities for energy applications. Our hypothesis is validated by introducing lattice defects due to the strain originating from a slightly higher doped grain boundary (GB) than at the interconnected grains of perovskite oxide. When Pd is doped at the B-site of ABO ₃ -type La _0.7 Sr _0.3 CoO _3-δ , a marginally higher ionic radius of Pd ⁴⁺ than Co ³⁺ enables partial deportation of Pd ⁴⁺ to the GB. Consequently, the GB unit cell is relatively expanded with a higher interplanar spacing, as observed by microscopic analysis. When the Pd concentration is increased, oxygen vacancy sites are reduced and both metallic Pd and PdO _x are exsolved at the perovskite oxide surface. With the Pd/Co ratio of 0.05, the defects originating from the Pd-modulated GB can be maximized to 1.29 ± 0.21% which enhances the bifunctional O ₂ activation ability by lowering the combined overpotential of oxygen evolution and reduction reactions (OER/ORR) to 0.91 V, duly corroborated by computational studies. The fabricated rechargeable Zn-air battery has a specific capacity of 740 mA·h/g _Zn (851 mW·h/g _Zn ) when discharge is performed at 10 mA/cm ² . Galvanostatic charge-discharge cycling with a 1 h cycle time shows 60 h stable performance. The OER/ORR bifunctional activity is found to be strongly correlated to the repositioned lattice symmetry at the perovskite GB.