Inkjet Printing Transparent and Conductive MXene (Ti₃C₂T_x) Films: A Strategy for Flexible Energy Storage Devices

MXene is a generic name for a large family of two-dimensional transition metal carbides or nitrides, which show great promise in the field of transparent supercapacitors. However, the manufacturing of supercapacitor electrodes with a high charge storage capacity and desirable transmittance is a challenging task. Herein, a low-cost, large-scale, and rapid preparation of flexible and transparent MXene films via inkjet printing is reported. The MXene films realized the sheet resistance (Rs) of 1.66 ± 0.16 Mω sq-1 to 1.47 ± 0.1 kω sq-1 at the transmissivity of 87-24% (λ = 550 nm), respectively, corresponding to the figure of merit (the ratio of electronic to optical conductivity, σDC/σOP) of ∼0.0012 to 0.13. Furthermore, the potential of inkjet-printed transparent MXene films in transparent supercapacitors was assessed by electrochemical characterization. The MXene film, with a transmittance of 24%, exhibited a superior areal capacitance of 887.5 μF cm-2 and retained 85% of the initial capacitance after 10,000 charge/discharge cycles at the scan rate of 10 mV s-1. Interestingly, the areal capacitance (192 μF cm-2) of an assembled symmetric MXene transparent supercapacitor, with a high transmittance of 73%, still surpasses the performance of previously reported graphene and single-walled carbon nanotube (SWCNT)-based transparent electrodes. The convenient manufacturing and superior electrochemical performance of inkjet-printed flexible and transparent MXene films widen the application horizon of this strategy for flexible energy storage devices.