A Simple Route to Porous Graphene from Carbon Nanodots for Supercapacitor Applications

Abstract

A facile method to convert biomolecule‐based carbon nanodots (CNDs) into high‐surface‐area 3D‐graphene networks with excellent electrochemical properties is presented. Initially, CNDs are synthesized by microwave‐assisted thermolysis of citric acid and urea according to previously published protocols. Next, the CNDs are annealed up to 400 °C in a tube furnace in an oxygen‐free environment. Finally, films of the thermolyzed CNDs are converted into open porous 3D turbostratic graphene (3D‐ts‐graphene) networks by irradiation with an infrared laser. Based upon characterizations using scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and Raman spectroscopy, a feasible reaction mechanism for both the thermolysis of the CNDs and the subsequent laser conversion into 3D‐ts‐graphene is presented. The 3D‐ts‐graphene networks show excellent morphological properties, such as a hierarchical porous structure and a high surface area, as well as promising electrochemical properties. For example, nearly ideal capacitive behavior with a volumetric capacitance of 27.5 mF L−1 is achieved at a current density of 560 A L−1, which corresponds to an energy density of 24.1 mWh L−1 at a power density of 711 W L−1. Remarkable is the extremely fast charge–discharge cycling rate with a time constant of 3.44 ms.

Synthesis Strategies of Porous Carbon for Supercapacitor Applications

“…Kaner et al proposed a mechanism for the graphene formation during CO 2 laser scribing. Carbon dots absorb CO 2 laser energy which is very close to the absorbance of sp 3 CC, thus breaking the chemical bonds between CC and forming sp 2 ‐dominated carbon dots (Figure 15c) 231. The carbon dots then self‐assembled into porous long‐range turbostratic graphene nanodomains.…”

“…c) Proposed LSG formation mechanism by laser scribing of carbon quantum dots. Reproduced with permission 231. Copyright 2018, Wiley‐VCH.…”

Silica‐assisted urea‐formaldehyde‐based carbon microspheres with enhanced supercapacitor performances as electrode

“…Owing to the hierarchical porous structure, the electrochemical properties of all SUFCM series have been significantly improved. Porous structure can not only effectively shorten the distance of electrolyte ions to the sample but also make electrolyte ions contact with active sites both of which increase the specific capacitance of the samples …”

Graphene a promising electrode material for supercapacitors-A review

“…107 Thus, the main future challenge will be optimization of integrated flexible graphene-based supercapacitors with other electronic devices to attain an efficient and valuable multifunctional system. The self-powered hybrid systems with multifunctional have attracted a considerable interest in future development of supercapacitors in high flexibility to be combined with other energy devices such as nano-generators, solar cells, and LIBs.…”