3D printed MXene-based films and cellulose nanofiber reinforced hydrogel electrolyte to enable high-performance flexible supercapacitors

Abstract

3D-printed MXene electrodes hold great promise for the development of next-generation electrochemical devices, offering improved performance, customization, and design flexibility. To this end, it is crucial to improve the 3D printability of MXene ink and address the restacking phenomenon of MXene nanosheets. Herein, a hybrid ink consisting of MXene, cellulose nanofibers (CNFs), and multiwalled carbon nanotubes (MWCNTs) is developed and then printed into high-fidelity, customized, freestanding electrodes using a controlled direct-ink-writing technology. The incorporation of hydrophilic CNFs and highly conductive MWCNTs not only effectively enhances the rheology properties of MXene ink, but also bridges the horizontally aligned MXene nanosheets, resulting in a more integral internal structure and increased interlayer spacing of MXene. Consequently, the 3D-printed flexible electrode exhibits stable conductivity, enhanced surface area accessibility, improved wettability, and excellent electrochemical performance. Furthermore, a cellulose nanofiber/polyacrylamide (CNF/PAM) hydrogel electrolyte is fabricated by in situ radical polymerization. By covering the CNF/PAM hydrogel electrolyte on two 3D printed interdigitated electrodes, we successfully fabricate a flexible interdigitated supercapacitor, which delivers a high energy density of 21.7 μW h cm⁻² at 0.3 mW cm⁻². The findings of this work provide valuable insights into formulating MXene-based inks for 3D printing of next-generation flexible supercapacitors.