Bifunctional MnO2/CNTs-Based Oxygen Catalysts with Tailored Catalytic Activity for Rechargeable Zn-Air Batteries

Abstract

Metal-air batteries, as highly effective clean energy devices, play an important role in current sustainability development. Zn-air batteries are of great interest in future power devices due to eco-friendliness, superior safety, low-cost and high theoretical energy density. Yet, it remains challenging to identify inexpensive, high-efficient and durable bifunctional catalysts to boost various reactions for Zn-air batteries. a-MnO2 exhibits 2×2 tunnels with a unique orthorhombic structure shows a higher oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) activity than other-phase MnO2. In this work, metal oxide anchored MnO2/CNTs hybrid catalysts (M-MnO2/CNTs) are developed via a facile hydrothermal process. Indeed, M-MnO2/CNTs display better catalytic activity and stability than MnO2/CNTs. The improved performance and stability are originated from (i) the novel hierarchal structure improving the mass transport, (ii) the redistribution of electrons from metal ion to MnO2 activating the Mn catalytic sites, (iii) the coupling effect from the metal oxide and MnO2/CNTs. Particularly, the overpotential (ΔE) of Co-MnO2/CNTs is low to 0.803 V, which highly approaches the referenced Pt/C+IrO2 (ΔE: 0.801 V). Accordingly, the peak power density of the Co-MnO2/CNTs-based Zn-air battery reaches 342.7 mW cm-2. The recharge Zn-air battery also exhibits good charge-discharge stability with a low voltage gap of 0.72 V for 128 hours. This work provides an effective mothed to achieve MnO2/CNTs materials with tailored catalytic activity by anchoring different metal oxides, and reveals great potential in the field of high specific energy batteries for portable electronics, electrical vehicles, and wearable devices.