Hierarchical Porous Double-Shelled Electrocatalyst with Tailored Lattice Alkalinity toward Bifunctional Oxygen Reactions for Metal–Air Batteries

Increasing both catalytic site accessibility and intrinsic activity of multishelled materials is critical to boost its efficiency for bifunctional oxygen electrocatalysis and initiate its application in metal–air batteries. Herein, a hierarchical porous double-shelled (Mg,Co) 3 O 4 electrocatalyst with controllable Mg substitution is synthesized via a proposed in situ coordinating process. The hierarchical porosity optimizes the availability of active sites and broadens diffusion channels for oxygen species. Meanwhile, Mg substitution greatly increases electrical conductivity and realizes novel insight of tailoring lattice alkalinity. Specifically, Mg substitution positively influences oxygen electrocatalysis by inducing lattice buffer zones that promote hydroxyl detachment from nearby catalytic sites. As a result, the final hybrid of (Mg,Co) 3 O 4 encapsulated in N-doped graphitized carbon affords superior bifunctional oxygen electrocatalytic activities, outperforming state-of-the-art noble-metal benchmarks. When serving as an air electrode in Zn–air batteries, a low charge–discharge gap and long-term cyclability for over 200 h are realized in ambient air.