Xin Zhao

This tutorial review provides a brief summary of recent research progress on carbon-based electrode materials for supercapacitors, as well as the importance of electrolytes in the development of supercapacitor technology. The basic principles of supercapacitors, the characteristics and performances of various nanostructured carbon-based electrode materials are discussed. Aqueous and non-aqueous electrolyte solutions used in supercapacitors are compared. The trend on future development of high-power and high-energy supercapacitors is analyzed.

Chemically modified graphene and polyaniline (PANI) nanofiber composites were prepared by in situ polymerization of aniline monomer in the presence of graphene oxide under acid conditions. The obtained graphene oxide/PANI composites with different mass ratios were reduced to graphene using hydrazine followed by reoxidation and reprotonation of the reduced PANI to give the graphene/PANI nanocomposites. The morphology, composition, and electronic structure of the composites together with pure polyaniline fibers (PANI-F), graphene oxide (GO), and graphene (GR) were characterized using X-ray diffraction (XRD), solid-state 13C NMR, FT-IR, scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). It was found that the chemically modified graphene and the PANI nanofibers formed a uniform nanocomposite with the PANI fibers absorbed on the graphene surface and/or filled between the graphene sheets. Such uniform structure together with the observed high conductivities afforded high specific capacitance and good cycling stability during the charge−discharge process when used as supercapacitor electrodes. A specific capacitance of as high as 480 F/g at a current density of 0.1 A/g was achieved over a PANI-doped graphene composite. The research data revealed that high specific capacitance and good cycling stability can be achieved either by doping chemically modified graphenes with PANI or by doping the bulky PANIs with graphene/graphene oxide.

Graphene is an emerging carbon material that may soon find practical applications. With its unusual properties, graphene is a potential electrode material for electrochemical energy storage. This article highlights recent research progress in graphene-based materials as supercapacitor electrodes. With a brief description of the working principle of supercapacitors, research progress towards the synthesis and modification of graphene-based materials, including graphene oxide, fullerenes, and carbon nanotubes, is presented. Applications of such materials with desirable properties to meet the specific requirements for the design and configuration of advanced supercapacitor devices are summarized and discussed. Future research trends towards new approaches to the design and synthesis of graphene-based nanostructures and architectures for electrochemical energy storage are proposed.

The oxygen reduction reaction (ORR) is one of the most important electrochemical reactions in energy conversion and storage technologies, such as fuel cells and metal–air batteries.

An asymmetric supercapacitor (ASC) was fabricated using reduced graphene oxide (RGO) sheets modified with ruthenium oxide (RGO–RuO2) or polyaniline (RGO–PANi) as the anode and cathode, respectively. The ASC exhibited a significantly improved capacitive performance in comparison with that of the symmetric supercapacitors fabricated with RGO–RuO2 or RGO–PANi as the electrodes. The improvement was attributed to the broadened potential window in an aqueous electrolyte, leading to an energy density of 26.3 W h kg−1, about two-times higher than that of the symmetrical supercapacitors based on RGO–RuO2 (12.4 W h kg−1) and RGO–PANi (13.9 W h kg−1) electrodes. In addition, a power density of 49.8 kW kg−1 was obtained at an energy density of 6.8 W h kg−1.