Ti3C2Tx quantum dot-modified Ti3C2Tx nanosheets freestanding films for flexible solid-state pseudocapacitors

MXenes with high conductivity, good stickiness, excellent flexibility and hydrophilicity are widely used as electrode materials for supercapacitors, but its limited active sites led to a restricted electrochemical performance, which limits the development of MXenes. Herein, Ti3C2Tx nanosheets modified by Ti3C2Tx quantum dots (TCQDs-TCNs) heterodimensional hybrid material were succeeded to be produced with a one-pot protected microwave hydrothermal method. The prepared TCQDs-TCNs nanocomposites retain the merits of Ti3C2Tx nanosheets, such as excellent flexibility and high conductivity. Meanwhile, the tailored ultra-fine sized Ti3C2Tx quantum dots expose more active sites, leading to the greatly enhanced electrochemical properties. The prepared freestanding TCQDs-TCNs-2 heterodimensional hybrid electrode has a high flexibility, with an excellent capacitance 2202 mF cm−2 at 3 mA cm−2, which surpasses the most previously reported MXenes-based electrodes, owing to the synergistic effect of TCQDs and TCNs. Additionally, the assembled symmetric solid-state pseudocapacitor exhibits an outstanding areal energy density (90.33 μWh cm−2) when the areal power density is 450 mW cm−2. What's more, the pseudocapacitor is still maintained an excellent capacity retention (84 % after 10 000 charge–discharge cycles) and displays almost no loss on the capacitance performance under mechanical deformations, suggesting its high flexibility and robust mechanical stability. This method opens up the possibility of exploiting a variety of advanced materials for storing energy.