No abstract

Developing efficient and low-cost bifunctional oxygen reduction/evolution reaction (ORR/OER) electrocatalysts is incredibly desired for the large-scale commercial application of zinc−air batteries. Hierarchical NiCo 2 O 4 hollow rectangular nanobars (NiCo 2 O 4 HRNBs) with ultrathin nanosheets were synthesized via the template-directed methodology, followed by sequential etching and annealing treatments. The NiCo 2 O 4 HRNBs with advanced features of a hierarchical hollow nanoarchitecture and a high surface area expose more reaction sites and provide ample mass diffusion pathways. Meanwhile, the abundant and accessible oxygen vacancies on the surface of NiCo 2 O 4 HRNBs can significantly accelerate the reaction kinetics of adsorbed oxygencontaining species. As a result, the as-obtained NiCo 2 O 4 HRNBs deliver an outstanding bifunctional electrocatalytic performance, which generates a positive half-wave potential of 0.81 V for ORR (reaching Pt/ C) and a current density of 10 mA cm −2 at a low potential of 1.59 V for OER (surpassing Pt/C) and robust stability in alkaline electrolytes. Expectedly, the rechargeable zinc−air batteries assembled by as-obtained NiCo 2 O 4 HRNB cathodes demonstrate superior battery performance with a large specific capacity of 724.6 mA h g Zn −1 at a current density of 10 mA cm −2 , a high power density of 117.6 mW cm −2 , and long-term cycle stability with a slight increase in polarization over an entire 200 h test, showing potential application in the field of new-generation rechargeable batteries.

No abstract

Co3O4@NiCo2O4double-shelled nanocages with hierarchical hollow structure and oxygen vacancies provide efficient reactive sites and charge/mass transport environmen, demonstrating excellent bifunctional oxygen electrocatalytic performance.