Additive-Free Ti3C2Tx MXene/Carbon Nanotube Aqueous Inks Enable Energy Density Enriched 3D-Printed Flexible Micro-Supercapacitors for Modular Self-Powered Systems

Abstract

3D-printed Ti₃C₂T_x MXene-based interdigital micro-supercapacitors (MSCs) have great potential as energy supply devices in the field of microelectronics due to their short ion diffusion path, high conductivity, excellent pseudocapacitance, and fast charging capabilities. However, searching for eco-friendly aqueous Ti₃C₂T_x MXene-based inks without additives and preventing severe restack of MXene nanosheets in high-concentration inks are significantly challenging. This study develops an additive-free, highly printable, viscosity adjustable, and environmentally friendly MXene/carbon nanotube (CNT) hybrid aqueous inks, in which the CNT can not only adjust the viscosity of Ti₃C₂T_x MXene inks but also widen the interlayer spacing of adjacent Ti₃C₂T_x MXene nanosheets effectively. The optimized MXene/CNT composite inks are successfully adopted to construct various configurations of MSCs with remarkable shape fidelity and geometric accuracy, together with enhanced surface area accessibility for electrons and ions diffusion. As a result, the constructed interdigital symmetrical MSCs demonstrate outstanding areal capacitance (1249.3 mF cm⁻²), superior energy density (111 μWh cm⁻² at 0.4 mW cm⁻²), and high power density (8 mW cm⁻² at 47.1 μWh cm⁻²). Furthermore, a self-powered modular system of solar cells integrated with MXene/CNT-MSCs and pressure sensors is successfully tailored, simultaneously achieving efficient solar energy collection and real-time human activities monitoring. This work offers insight into the understanding of the role of CNTs in MXene/CNT ink. Moreover, it provides a new approach for preparing environmentally friendly MXene-based inks for the 3D printing of high-performance MSCs, contributing to the development of miniaturized, flexible, and self-powered printable electronic microsystems.