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–N_x 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.