Bifunctional N-doped copper sulfide/oxide cathode for zinc-air battery operable in both aerobic and anaerobic environments

Abstract

Recently, demands for rechargeable energy storage systems, such as secondary Li-ion battery, have remarkably increased. Especially, the zinc-air battery (ZAB) is one of promising energy storage systems because zinc metal is quite stable compared to lithium metal in ambient conditions and it is abundant on Earth. One critical issue for operating ZAB is the requirement of an efficient and stable air cathode for the reversible oxygen reduction and evolution reactions (ORR & OER). Herein, we introduce nitrogen-doped copper sulfide (N-CuS) as a bifunctional ORR/OER air cathode. Although pristine CuS has oxygen reduction catalytic activity, nitrogen atoms doped in CuS lattice facilitate not only active sites but also electrochemical conductivity. As a result, ZAB using N-CuS air cathode reveals superior electrochemical capacity (1.20 V vs. Zn/{\rm Zn}^{2+} at 1\ mA\ {\rm cm}^{-2}) compared to when using pristine CuS. In addition, unlike conventional ZAB systems, the redox reaction concerning Cu in N-CuS ensures the effective electrochemical charge/discharge properties even in anaerobic conditions.