Enhancing MXene-based supercapacitors: Role of synthesis and 3D architectures

MXene has been the limelight for studies on electrode active materials, aiming at developing supercapacitors with boosted energy density to meet the emerging influx of wearable and portable electronic devices. Despite its various desirable properties including intrinsic flexibility, high specific surface area, excellent metallic conductivity and unique abundance of surface functionalities, its full potential for electrochemical performance is hindered by the notorious restacking phenomenon of MXene nanosheets. Ascribed to its two-dimensional (2D) nature and surface functional groups, inevitable Van der Waals interactions drive the agglomeration of nanosheets, ultimately reducing the exposure of electrochemically active sites to the electrolyte, as well as severely lengthening electrolyte ion transport pathways. As a result, energy and power density deteriorate, limiting the application versatility of MXene-based supercapacitors. Constructing 3D architectures using 2D nanosheets presents as a straightforward yet ingenious approach to mitigate the fatal flaws of MXene. However, the sheer number of distinct methodologies reported, thus far, calls for a systematic review that unravels the rationale behind such 3D MXene structural designs. Herein, this review aims to serve this purpose while also scrutinizing the structure–property relationship to correlate such structural modifications to their ensuing electrochemical performance enhancements. Besides, the physicochemical properties of MXene play fundamental roles in determining the effective charge storage capabilities of 3D MXene-based electrodes. This largely depends on different MXene synthesis techniques and synthesis condition variations, hence, elucidated in this review as well. Lastly, the challenges and perspectives for achieving viable commercialization of MXene-based supercapacitor electrodes are highlighted.