Hierarchical porous yolk-shell Co-N-C nanocatalysts encaged ingraphene nanopockets for high-performance Zn-air battery
Yisi Liu, Zongxu Li, Shizhu Wang, Jinnan Xuan, Dongbin Xiong, Lina Zhou, Jianqing Zhou, Jun Wang, Yahui Yang, Yue Du
Abstract
The rational design and preparation of promising cathode electrocatalysts with excellent activity and strong stability for metal-air batteries is a huge challenge. In this work, we innovate an approach of combining solvothermal with high-temperature pyrolysis utilizing zeolitic imidazolate framework (ZIF)-8 and ZIF-67 as the template to synthesize a novel hybrid material of hierarchical porous yolk—shell Co-N-C polyhedron nanocatalysts engaged in graphene nanopocket (yolk—shell Co-N-C@GNP). The obtained catalyst exhibits prominent bifunctional electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the alkaline condition, in which the half-wave potential is 0.86 V for ORR, and the over-potential for OER is 0.42 V at 10 mA·cm−2. The rechargeable aqueous Zn-air battery fabricated with yolk—shell Co-N-C@GNP cathode deliveries an open circuit voltage (OCV) of 1.60 V, a peak power density of 236.2 mW·cm−2, and excellent cycling stability over 94 h at 5 mA·cm−2. The quasi-solid-state Zn-air battery (ZAB) using yolk-shell Co-N-C@GNP displays a high OCV of 1.40 V and a small voltage gap of 0.88 V in continuous cycling tests at 2 mA·cm−2. This work provides a valuable thought to focus attention on the design of high-efficient bifunctional catalysts with hierarchical porous yolk—shell framework and high-density metal active sites for metal-air battery technologies.