Inkjet-printed flexible MXetronics: Present status and future prospects

Over the past several years, atomically thin two-dimensional carbides, nitrides, and carbonitrides, otherwise known as MXenes, have been expanded into over fifty material candidates that are experimentally produced, and over one hundred fifty more candidates that have been theoretically predicted. They have demonstrated transformative properties such as metallic-type electrical conductivities, optical properties such as plasmonics and optical nonlinearity, and key surface properties such as hydrophilicity, and unique surface chemistry. In terms of their applications, they are poised to transform technological areas such as energy storage, electromagnetic shielding, electronics, photonics, optoelectronics, sensing, and bioelectronics. One of the most promising aspects of MXene's future application in all the above areas of interest, we believe, is reliably developing their flexible and bendable electronics and optoelectronics by printing methods (henceforth, termed as printed flexible MXetronics). Designing and manipulating MXene conductive inks according to the application requirements will therefore be a transformative goal for future printed flexible MXetronics. MXene's combined property of high electrical conductivity and water-friendly nature to easily disperse its micro/nano-flakes in an aqueous medium without any binder paves the way for designing additive-free highly conductive MXene ink. However, the chemical and/or structural and hence functional stability of water based MXene inks over time is not reliable, opening research avenues for further development of stable and conductive MXene inks. Such priorities will enable applications requiring high-resolution and highly reliable printed MXene electronics using state-of-the art printing methods. Engineering MXene structural and surface functional properties while tuning MXene ink rheology in benign solvents of choice will be a key for ink developments. This review article summarizes the present status and prospects of MXene inks and their use in inkjet-printed (IJP) technology for future flexible and bendable MXetronics.