Single-step synthesis of core-shell diamond-graphite hybrid nano-needles as efficient supercapacitor electrode

Single-step synthesis of core-shell diamond-graphite hybrid electrodes is demonstrated by a mere variation of CH4 concentration (CC) in the microwave growth plasma. The excellent electrochemical stability of diamond and high surface area/electrical conductivity of graphite make the hybrid electrode suitable for supercapacitor application. The supercapacitor study of the hybrid electrode is carried out using both aqueous and redox species contained electrolytes. A brilliant supercapacitor performance (specific capacitance 0.19 F cm−2) with high energy and power density and remarkable electrode retention (96% after 10,000 cycles) is obtained and discussed in the light of different electrochemical techniques such as cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The supercapacitor performance is explained by analyzing the microstructural evolution of diamond films from a well-faceted geometry dominated with pure diamond phase to an entirely different needle-like structure having diamond-graphite mixed phase. The CC-dependent phase transition is confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy study. Finally, the core-shell structure of the hybrid nano-needles is confirmed by transmission electron microscopy investigations. [Display omitted]