A facile one-step printing process by 3D micro-extrusion affording binder-free thermally reduced graphene oxide (TRGO) based electrochemical capacitors (ECs) that display high-rate performance is presented. Key intermediates are binder-free TRGO dispersion printing inks with concentrations up to 15 g L −1 . This versatile printing technique enables easy fabrication of EC electrodes, useful in both aqueous and non-aqueous electrolyte systems. The as-prepared TRGO material with high specifi c surface area (SSA) of 593 m 2 g −1 and good electrical conductivity of ≈16 S cm −1 exhibits impressive charge storage performances. At 100 and 120 Hz, ECs fabricated with TRGO show time constants of 2.5 ms and 2.3 ms respectively. Very high capacitance values are derived at both frequencies ranging from 3.55 mF cm −2 to 1.76 mF cm −2 . Additionally, these TRGO electrodes can be charged and discharged at very high voltage scan rates up to 15 V s −1 yielding 4 F cm −3 with 50% capacitance retention. Electrochemical performance of TRGO electrodes in electrolyte containing tetraethyl ammonium tetrafl uoroborate and acetonitrile (TEABF4-ACN) yields high energy density of 4.43 mWh cm −3 and power density up to 42.74 kW cm −3 , which is very promising for AC line fi ltering application and could potentially substitute state of the art electrolytic capacitor technology.

Here, this study reports a novel single‐step preparation of graphene functionalized by redox‐active nitroxyl radicals, a promising electrode material, without the requirement of graphite oxidation. Key feature of this concept is the Diels‐Alder [4+2] cycloaddition of dispersed graphene (DG), which has been obtained by shear‐induced solution exfoliation of graphite and functionalized maleimides as dienophiles. The redox‐active organic radical 2,2,6,6,‐tetramethylpiperdinyl‐1‐oxyl (TEMPO) is covalently attached by cycloaddition of DG with either N‐(1‐oxyl‐2,2,6,6,‐tetramethyl‐4‐piperidinyl)‐maleimide (TEMPO‐MI), or N‐(2,2,6,6‐tetramethyl‐piperidinyl)‐maleimide (TEMP‐MI), and subsequent oxidation. Successful product formation could be confirmed by high field Electron Paramagnetic Resonance (EPR) spectroscopy. Temperature‐dependent reaction monitoring by time‐resolved EPR in conjunction with Raman spectroscopy and elemental analysis results in an optimum cycloaddition temperature of 130 °C, at which 2.2 wt% TEMPO‐MI has been incorporated. However, owing to the limited thermal stability of TEMPO‐MI at temperatures above 100 °C, as again verified by EPR spectroscopy, the route via TEMP‐MI and subsequent oxidation is favored. Cyclovoltammetric evaluation of TEMPO‐functionalized graphene shows a reversible redox potential of +0.65 V as measured against Ag/AgCl, similar to that of TEMPO in solution. Hence, organic radical functionalized graphene derived by cycloaddition shows great potential for an easy production of electrodes that aim toward applications in organic energy storage devices.