Highly dispersed Co nanoparticles decorated on N−doped defective carbon nano−framework for hybrid Na−Air battery
Efficient and low−cost bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of vital importance in energy conversion. Herein, an excellent highly dispersed Co nanoparticles decorated on N−doped defective carbon nano−framework (Co−N−C) derived from ZnCo bimetal organic framework (bi−MOF) is reported. A high specific surface area originated from zinc evaporation facilitates adsorption and desorption of oxygen, which promotes the accessibility of catalytic sites. The abundant Co−N−C species act as strong bridging bonds between Co nanoparticles and carbon materials which facilitates the interface electron transfer. The Co−N−C−0.5 (0.5 represents the molar ratio of Zn in the initial ZIF−67) exhibits a low overpotential gap of 0.94 V due to the amount of active sites (e.g. N−doped defective carbon and CoNx/Co set) and fast interface electron transfer. In addition, the hybrid Na−air battery with Co−N−C−0.5 materials displays low voltage gap of 0.31 V and high roundtrip efficiency of 90.0% at the current density of 0.1 mA·cm2. More importantly, the hybrid Na−air battery indicates fantastic cyclability for charging and discharging due to its stable structure. Our results confirm Co−N−C materials derived from bi−MOF as an alternative to high−cost Pt/C catalyst for ORR and OER activities in metal−air batteries.