Structure and defect dual-engineering of cobalt oxides for low-temperature Zn-air batteries

The exploration of bifunctional electrocatalysts with high catalytic activity and long-term durability for low-temperature Zn-air batteries (ZABs) is an ongoing challenge. Here, quintet-shelled hollow spheres, P-doped multi-layer Co3O4 (PM-Co3O4), with enriched oxygen vacancies are prepared by thermally induced mass relocation and a simple phosphating process. Various advanced characterizations reveal P anion-induced effects on internal electronic structure and local coordination environment. The finite element method elucidates that the complex multi-layer spherical nanostructure is conducive to the transport and diffusion of OH− and O2. Benefiting from its unique structural features and abundant oxygen vacancies, the well-designed PM-Co3O4 presents small reversible oxygen overpotential for catalyzing oxygen reduction/evolution reactions. Accordingly, the fabricated low-temperature ZABs based on PM-Co3O4 as air-cathode exhibit high power density (20.8 mW·cm−2) and long-term stability (over 600 cycles) at the ultra-low temperature of −40 °C, outperforming state-of-art Pt/C+IrO2-based ZABs. Furthermore, the dynamic evolution mechanism of cobalt oxide catalysts during ZAB operation is elucidated. This work provides a guideline to design efficient electrocatalysts with regulated electronic configurations and exquisite nano-/microstructures for ZABs under extreme working conditions.