Design, synthesis and electrochemical performance of a phosphazene–coumarin based organic–inorganic hybrid for high-energy supercapacitor applications

The development of high-performance electrode materials is crucial for advancing next-generation supercapacitors. Using a straightforward synthesis approach, a novel Schiff base derived from an organic-inorganic hybrid phosphazene-coumarin system, 7,7′,7″,7″‘,7″“,7″“‘-(((1E,1′E,1″E,1″‘E,1″“E,1″“‘E)-(((1,3,5,2 l5,4l5,6 l5-triazatriphosphinine-2,2,4,4,6,6-hexayl)hexakis(oxy))hexakis(benzene-4,1-diyl))hexakis(methaneylylidene))hexakis(azaneylylidene))hexakis(4-(trifluoromethyl)-2H-chromen-2-one), Cpz-O-7-ACSB was designed and synthesized in two steps. This involved the reaction of hexachlorocyclotriphosphazene (HCCP) with 4-hydroxybenzaldehyde, subsequently followed by a reaction with 7-amino-4-trifluoromethylcoumarin in ethanol. Carbonization with carbon nanotubes (CNTs) resulted in the formation of the Cpz-O-7-ACSB@Cp-CNT composite, which demonstrated significantly improved electrochemical performance. This process was subsequently followed by activation with potassium hydroxide (KOH) as an activator. Fourier Transform Infrared (FT-IR) spectroscopy, Nuclear Magnetic Resonance (NMR), Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA) were used to characterize the structure and properties of Cpz-O-7-ACSB. Cpz-O-7-ACSB@CNT shows a high specific capacitance of 182 F g⁻¹ at 0.9 A g⁻¹ in 6 M KOH, with 84.58% retention after 2000 cycles, demonstrating excellent electrochemical durability. The asymmetric Cpz-O-7-ACSB@Cp-CNT device performs significantly better than its symmetric counterpart, making it a promising candidate for next-generation high-energy, high-power supercapacitors.