Ni-Fe-S Supported on Mo-Based Mxene (Mo2CTx) As a High-Performance Bifunctional Electrocatalyst for Rechargeable Zinc–Air Batteries

Abstract

Rechargeable Zn-air batteries are a promising alternative to lithium-ion batteries due to their high theoretical energy density (1350 Wh kg−1), low cost, and environmental benefits. To meet the growing demand on renewable power for electric vehicles and sustainable goals, inexpensive and efficient bifunctional catalysts with both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities have recently garnered a great interest in energy conversion fields. MXene, a rising family of two-dimensional (2D) materials, particularly Mo2CTx, has been identified as a promising electrocatalyst supporter. The tunable surface chemistry, atomic thickness, and high surface area of the MXene architecture reduce the reaction barrier by enhancing the conductivity, exposing active sites and increasing the reaction rate in charge transfer and gas/ion diffusion process. Therefore, with coexistence of MXene platform, favorable reaction conditions can be created to facilitate the catalyst's performance.In this study, a novel bifunctional electrocatalyst of Ni-Fe sulfide uniformly embedded in a Mo-based MXene (Mo2CTx) sheet structure is designed for Zn-air battery applicaiton. Surface characterization shows that 2-D Mo2CTx nanosheets can be successfully fabricated by hydrothermal etching method. The deposition of Ni-Fe sulfide nanocatalysts onto Mo2CTx MXene nanosheets exhibits excellent electrochemical performance, which is attributed to the enhanced intrinsic activity due to rapid electron transfer from MXene, abundant functional groups on the surface to lower the reaction activity energy. In addition, the architecture of MXene support provides a large specific surface area, high porosity, good conductivity and highly exposed active sites. When using MXene supported Ni-Fe-S nanocatalysts as the electrode materials for Zn-air battery application, a high peak power density at 107.24 mW cm−2 with superior cycle stability within 200h is obtained. Moreover, the possible mechanisms on energy storage is also proposed. These results clearly indicates the successfully development of an exciting bifunctional electrocatalyst for electrochemical energy conversion applications.