Molten-Salt-Assisted Fabrication of Defect-Rich 2D/3D Nitrogen-Doped Carbon with Embedded Co Nanoparticles for High-Performance Rechargeable Zn–Air Batteries with a High Open-Circuit Voltage

Porous transition metal-based nitrogen-doped carbon materials are considered promising bifunctional electrocatalysts for the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) to improve the practical performance of rechargeable metal–air batteries. In this work, utilizing the sealing effect of a molten salt, defect-rich N-doped carbon supported embedded Co nanoparticles (NPs) with a unique two-dimensional/three-dimensional (2D/3D) cross-linked structure (Co@CLNC) was fabricated by a facile one-pot salt-assisted pyrolysis of a cobalt-based zeolite imidazole framework. Density functional theory (DFT) calculations revealed that the synergistic effect of Co NPs boosts the catalytic activity of Co–Nx active sites through reducing the energy barriers of the rate-determining steps, the desorption of *OH for the ORR and the transformation of *OH to *O for the OER. The as-prepared Co@CLNC manifests a larger specific surface area and remarkable OER/ORR bifunctional electrocatalytic activity with a high ORR half-wave potential of 0.84 V. A homemade Zn–air battery using Co@CLNC as the air electrode catalyst demonstrates excellent performance with a high open-circuit voltage of 1.526 V, a peak power density of 166 mW cm–2, and a high energy efficiency of greater than 59.8%, with a low charging voltage of less than 2 V during the 600-cycle stability test.