Co/N nanoparticles supported on a C3N4/polydopamine framework as a bifunctional electrocatalyst for rechargeable zinc-air batteries

Metal N-doped carbons (M–N–C) and specifically cobalt-based N-doped carbons (Co–N–C) have attracted extensive attention as suitable multifunctional catalysts. Their high catalytic activity, originating from the strong coupling effect of Co with N, lead to the formation of active sites with suitable binding energies for promoting the discharging and charging reactions. Herein, we propose the synthesis of an efficient bifunctional electrocatalyst (ZIFCNDA) prepared by the introduction of Co ions during the polymerisation of dopamine, which lead to the direct doping of a carbon framework and the localized growth of Co-based MOFs polyhedrons, generating Co-based nanoparticles (Co NPs) upon pyrolysis. The C3N4-controlled polydopamine growth formed thin graphitized carbon nanosheets which can facilitate the transfer of electrons to the catalytically active sites. The ZIFCNDA catalyst was able to efficiently catalyse both the oxygen reduction (ORR) and oxygen evolution (OER) reactions). The ZAB containing the developed catalyst presented a stable discharge voltage of 1.1 V at a high current density of 10 mA cm−2 with higher stability and longer cycle life compared to their counterparts constructed using Pt/C and Ir/C in air–cathode. This study illustrates a platform to enhance the catalytic activity of the ORR and OER catalyst via promoting the formation of well distributed cobalt active sites, achieved due to the insertion of cobalt ions during the polymerization process of dopamine, instead of on a previously prepared framework and their application for rechargeable metal–air batteries