Ordered macroporous design of sacrificial Co/VN nano-heterojunction as bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

Abstract

• •Ordered macroporous design of sacrificial Co/VN nano-heterojunction was developed. • •VN act as sacrificial OER promoter converting Co into active Co 3 O 4 /CoOOH species. • •The Co/VN electrode exhibits excellent performance in rechargeable zinc-air batteries. The development of efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) bifunctional electrocatalysts is essential for rechargeable zinc-air batteries (ZABs). Herein, an ORR/OER bifunctional pre-catalyst consists of Co/VN heterojunction supported by N-doped carbon (NC) with three-dimensionally ordered macroporous (3DOM) architecture was fabricated. The VN was introduced as sacrificial promoter to facilitate the oxidization and self-reconstruction of Co into Co 3 O 4 and CoOOH during OER process, which acts as the real active OER component. On the other hand, the Co-decorated N-doped carbon is the active species for ORR reaction. Meanwhile, the 3DOM structure design also provides a large specific surface area and exposes rich active sites. Benefiting from those advantages, the Co/VN@NC exhibits good activity and stability towards ORR and OER reactions comparable with commercial catalysts. Moreover, density functional theory calculations confirmed that Co 3 O 4 and CoOOH exhibit higher adsorption energy for OH – and present an exothermic reaction in the OER process, which is beneficial to OER reaction. The ZABs using Co/VN@NC as bifunctional catalyst exhibits a high specific capacity of 775.68 mAh g −1 under 10 mA cm −2 and ultralong charge–discharge cycle life about 200 h at 20 mA cm −2 . This work provides a new strategy of using sacrificial heterojunction for the development of efficient and durable bifunctional oxygen electrocatalyst.