Zinc Ion-Induced Assembly of Crystalline Carbon Dotswith Excellent Supercapacitor Performance

Crystalline carbon dots (Cdots) with a size of 3.2 ± 1.0 nm have been assembled into three-dimensional crystalline structures via complexation between Cdot surface functional groups (especially phosphate) and zinc ions (Zn2+). We attempt to understand the unprecedented crystalline nature in the Cdot assembly using spectroscopic and microscopic techniques. Experimental evidences suggest that the addition of Zn2+ to the crystalline Cdot dispersion resulted in a template-free controlled growth of orthorhombic hopeite structures over the surface, which further assisted in initiating an assembled crystalline Cdot system. Importantly, crystallinity in the Cdot assembly helped in improving the electrochemical performance and charge storage ability of electrodes significantly. Finally, the so-generated crystalline assembly was successfully applied toward the fabrication of Cdot-based supercapacitor electrodes with excellent specific capacitance (743.2 F/g) and high energy density (20 W h kg–1 at 110 W kg–1).