A Highly Stable MXene Aqueous Conductive Ink for Inkjet Printing Flexible Microsupercapacitors

Recently, MXene-based microsupercapacitors (MSCs) prepared by inkjet printing have attracted great attention due to their potential applications in portable and wearable electronics. Although the aqueous MXene inks are more eco-friendly than their organic counterparts, their practical applications seriously suffer from the poor stability of MXene in water. In this work, a high-stability aqueous ink is developed by grafting sodium dodecyl sulfate (SDS) onto the surface of MXene. The SDS molecules firmly adsorb on MXene in a parallel configuration through electrostatic interactions and hydrogen bonding, thereby inhibiting the agglomeration of MXene nanoflakes and protecting the defective sites from water and oxygen. Thus, the dispersion and structural stabilities of the SDS-MXene ink are substantially promoted compared with those of the pristine MXene ink. The lifetime constant of the SDS-MXene ink is estimated to be 157.3 days, while that of the pristine MXene ink is only 22.1 days. Furthermore, the interdigital electrodes are prepared on the flexible polyethylene terephthalate substrates by inkjet printing using a home printer, with a high resolution (150 μm), high conductivity (1091 S/cm), and controllable thicknesses. The assembled MSCs using the SDS-MXene ink shows greatly enhanced electrochemical performance than that of the devices using the pristine MXene ink, with the volume capacitances increasing from 177 F/cm³ to 714.3 F/cm³, which is mainly attributed to expanded ion transport channels, increased active sites, and maintained high conductivity. Besides, the MSCs derived from the ink aged for 60 days still have a similar performance to that of the device from the fresh ink. Finally, the MSCs also show impressive flexibility and an adjustable voltage window. The present work provides a basic formula of a highly stable aqueous MXene ink, which can be further modified to match the manufacturing requirements of different electronic devices such as sensors, batteries, and electric circuits.