Boosting oxygen electrocatalysis for flexible zinc-air batteries by interfacing iron group metals and manganese oxide in porous carbon nanowires

Abstract

The highly active and robust bifunctional non-noble electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently demanded for rechargeable metal-air batteries. Engineering heterointerfaces between metals and metal compounds is an attractive strategy for fabricating high-performance electrocatalysts. However, most reported metal/metal compound heterostructures were designed by partially converting the metal into corresponding metal compound on a one-metal basis. Herein, a facile “coordination construction-thermal decomposition” strategy is developed to construct Co/MnO heterointerface embedded in N-doped carbon nanowires by employing nitrilotriacetic acid as chelating agents to stabilize different metal ions and construct the nanowire structure. The in situ generated Co nanocrystals not only create highly conductive heterointerfaces with MnO, but also facilitate the formation of graphitic carbon as the conductive agent. The resultant Co/MnO@NC exhibits extraordinary bifunctional oxygen electrocatalytic activities and durability with a reversible oxygen overpotential of only 0.66 V. Density functional theory calculations reveal that the formation of Co/MnO heterostructure leads to optimized adsorption energy for oxygen-containing intermediates in OER and ORR. As the air-cathode, the assembled aqueous zinc-air battery (ZAB) can provide a remarkable peak power density of 146 mW cm−2 and an impressive discharge/charge stability for 400 h/600 cycles at 20 mA cm−2. The Co/MnO@NC-based quasi-solid-state ZAB also exhibits outstanding mechanical flexibility in addition to high battery performance. This strategy can be extended to prepare Fe/MnO@NC and Ni/MnO@NC electrocatalysts with other iron group elements, which paves a new way for development of efficient and robust electrocatalysts for energy conversion and storage.