Quinolinediol Molecule Electrode and MXene for Asymmetric Supercapacitors with Efficient Energy Storage

Asymmetric supercapacitors (ASCs) need positive and negative electrodes to produce a larger redox peak position difference to achieve a higher energy density. Here, 2,8-quinolinediol (QD) is adopted to modify reduced graphene oxide (rGO) and prepare an organic molecule electrode (OME), in which the Faraday reaction occurs in a more positive potential range. The electrochemical tests show that the optimized OME (QD/rGO-0.75) releases a high special capacitance (371 F g(-1) at 5 mV s(-1)) and exhibits an excellent rate capability (86.8% of the initial value at a scanning rate multiple of nearly 20 times). Meanwhile, an MXene (Ti3C2Tx) with a relatively negative potential is prepared. QD/rGO-0.75 and Ti3C2Tx are, respectively, used as positive and negative electrodes to assemble an ASC. The measurements indicate that the assembled ASC is able to store charge within a wide voltage window of 1.6 V in the 1 M H2SO4 electrolyte and exhibit better energy storage performance. Furthermore, the device delivers an excellent cycling stability (83.5%, over 10,000 cycles). The two series-connected devices can light 37 red light-emitting diodes, indicating their potential application.