Aqueous Electrolyte Asymmetric Supercapacitors Based on the 5-Hydroxyindole Molecule Electrode and MXene with Efficient Energy Storage

It is a suitable tactic to boost energy density, which extends the difference between the redox peak positions of positive and negative electrodes. In this paper, an organic molecular electrode (HIN@rGO) based on 5-hydroxy indole (HIN) non-covalently anchored on graphene is reported, which is used as the positive electrode of asymmetric supercapacitors (ASCs) to enlarge the voltage window. The HIN@rGO-0.5 displays an outstanding specific capacitance of 519 F g–1 at 5 mV s–1 and high capacitance retention of 85.6%, even if the scan rate is increased to 100 mV s–1. What is more, it is observed that the Faraday reactions of HIN@rGO occur in the range of more positive potential. The MXene (Ti3C2Tx) is a two-dimensional titanium carbide, which has been prepared as the counterpart electrode to match the HIN@rGO-0.5. The voltage window of the constructed ASC (HIN@rGO-0.5//Ti3C2Tx) is extended to 1.6 V. The device can deliver an excellent energy density of 32.5 W h kg–1 along with the power density of 640 W kg–1 and show 90.5% of capacitance retention after 10,000 cycles, which is originating from the two electrodes exhibiting a good synergistic matching effect in terms of charge and kinetics during the electrochemical reaction. To verify the application potential, two devices (HIN@rGO-0.5//Ti3C2Tx) connected in series can light up to 58 LEDs.