Polypyrrole-coated copper@graphene core-shell nanoparticles for supercapacitor application.

The performance of supercapacitors strongly depends on the electrochemical characterizations of electrode materials. Herein, a composite material consisted of polypyrrole (PPy) and multilayer graphene-wrapped copper nanoparticles (PPy/MLG-Cu NPs) is fabricated on a flexible carbon cloth (CC) substrate via two-step synthesis process for supercapacitor application. Where, MLG-Cu NPs are prepared on CC by one-step chemical vapor deposition (CVD) synthesis approach; thereafter, the PPy is further deposited on the MLG-Cu NPs/CC via electropolymerization. The related material characterizations of PPy/MLG-Cu NPs are well investigated by scanning electron microscopic (SEM), high resolution transmission electron microscopy (HR-TEM), Raman spectrometer and X-ray photoelectron spectroscopy (XPS); the electrochemical behaviors of the pertinent electrodes are studied by cyclic voltammogram (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) measurements. The flexible electrode with PPy/MLG-Cu NPs composites exhibits the best specific capacitance of 845.38 F g-1 at 1 A g-1, which is much higher than those of electrodes with PPy (214.30 F g-1), MLG-Cu NPs (6.34 F g-1), multilayer graphene hollow balls (MLGHBs; 52.72 F g-1), and PPy/MLGHBs (237.84 F g-1). Finally, a supercapacitor system consisted of four PPy/MLG-Cu NPs/CC electrodes can efficiently power various light-emitting diodes (i.e., red, yellow, green, and blue lighs), demonstrating the practical application of PPy/MLG-Cu NPs/CC electrode.