Mxenes for Zn-based energy storage devices: Nano-engineering and machine learning

Zn-based rechargeable energy devices showed more advantages, including safety, abundance, and high volumetric/gravimetric capacities. MXenes have been evaluated as valuable emerging 2D materials due to their thermal/chemical stabilities, conductivities, flexible mechanical properties, and unique topological features. However, the recent trends in MXenes for Zn-based rechargeable energy devices have rarely been reviewed. This review article presents a comprehensive summary of the latest developments in the design and synthesis of MXene materials intended for utilization as electrodes in Zn-based energy storage devices. Specifically, the focus is on their application in Zn-ion supercapacitors, Zn-ion batteries, Zn-air batteries, and Zn-halide batteries. Firstly, we have deliberately discussed the synthesis of MXenes by summarizing the latest reported techniques but giving the weightage of the initial synthetic methods. Further, the discussion on nano-engineering of active sites revealed that surface termination followed by defect engineering is an emerging strategy to improve the performance of MXenes. The role of machine learning in the synthesis of MXenes is also summarized by establishing the structural activity relationship. In the next section and sub-sections, we have outlined the recent advances in the MXenes as electrode materials for Zn-based energy storage devices. Each section is arranged according to the synthesis strategies to clarify the structural activity relationship in each sub-section and provide a suitable basis for the researchers to design and synthesize targeted materials instead of conventional hit-and-trial methods. Finally, concluding remarks and future perspectives are discussed to offer new directions in targeted MXenes synthesis for energy storage devices.