Ammonia strengthened graphene/CNT-wrapped polyaniline-nanofiber composites loaded with palladium nanoparticles for coin cell supercapacitors

Supercapacitors with high specific capacitance, energy and power densities as well as high cycle stability are demonstrated in this work. A newly developed palladium nanoparticle loaded reduced graphene oxide/CNT hydrogel (rGO/CNT@Pd) was synthesized and combined with polyaniline nanofibers (rGO/CNT@Pd + PANI Nf). The prepared materials were synthesized by a hydrothermal route, simultaneously reducing graphene oxide and PdCl2. Including pre-synthesized PANI nanofibers in the process led to formation of a 3D rGO/CNT matrix incorporating PANI and effectively preventing swelling/shrinkage damage during electrochemical testing. Subsequent ammonia treatment led to strengthening of the 3D matrix which further improved supercapacitor cycling stability. Material characterizations using scanning and transmission electron microscopy as well as X-ray diffraction and Raman spectroscopy were performed and Pd nanoparticle formation and uniform distribution in the rGO/CNT hydrogel was observed. The materials were used to construct CR2032 coin cell supercapacitors and tested by 2-electrode cyclic voltammetry and galvanostatic charge-discharge with 2 M H2SO4 electrolyte. Ammonia strengthened rGO/CNT@Pd + PANI Nf exhibited excellent electrochemical performance with a specific capacitance of 611.8 F g−1 and energy and power densities of 85 Wh kg−1 and 10.2 kW kg−1 at a current of 1.5 A g−1. Ammonia treatment effectively increased the cycle life of the composite and 84.3% of capacitance was retained after 10000 charge-discharge cycles.