Herein, we successfully developed a positive electrode material (PD/rGOs). The Faraday reaction of the optimized PD/rGO-0.5 occurs at approximately 0.4 V. In order to maximize the voltage window of asymmetric supercapacitor (ASC), MXene served as the negative electrode. The assembled ASC achieves a remarkable energy density of 36.8 Wh kg⁻¹, demonstrating exceptional energy storage performance.

Abstract

An efficient approach to increase the energy density of supercapacitors is to prepare electrode materials with larger specific capacitance and increase the potential difference between the positive and negative electrodes in the device. Herein, an organic molecular electrode (OME) is prepared by anchoring 1,10-phenanthroline-5,6-dione (PD), which possesses two pyridine rings and an electron-deficient conjugated system, onto reduced graphene oxide (rGO). Because of the electron-deficient conjugated structure of PD molecule, PD/rGOs exhibit a more positive redox peak potential along with the advantages of high capacitance-controlled behaviour and fast reaction kinetics. Additionally, the small energy gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) leads to increased conductivity in PD/rGO. To assemble the asymmetric supercapacitor (ASC), a two-dimensional metal carbide, as known as MXene, with a chemical composition of Ti₃C₂T_x is selected as the negative electrode due to its exceptional performance, and PD/rGO-0.5 is employed as the positive electrode. Consequently, the working voltage is expanded up to 1.8 V. Through further electrochemical measurements, the assembled ASC (PD/rGO-0.5//Ti₃C₂T_x) achieves a remarkable energy density of 36.8 Wh kg⁻¹. Remarkably, connecting two ASCs in series can power 73 LEDs, showcasing its promising potential for energy storage applications.