Graphene synthesis for graphene-based porous electrodes and their applications in supercapacitors

• Main Authors: Chu, Hwei-Jay, 朱慧捷
• Other Authors: Tai, Nyan-Hwa
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/40252588108921343276

博士 === 國立清華大學 === 材料科學工程學系 === 104 === In this dissertation, the studies on the graphene synthesis for graphene-based porous electrodes and their applications in supercapacitors have been investigated. Both the chemical reduced route and the chemical vapor deposition (CVD) method to synthesize graphene were used to design and fabricate the porous electrodes. The aqueous extract of Hibiscus sabdariffa L., which is inherently non-toxic, environmentally friendly and cost effective, was used as a green reducing agent to chemically reduce graphene oxide (GO). And the investigation of anthocyanins during the reduction was first studied in our work. The flexible graphene film electrodes were fabricated using the synthesized graphene as a primary material. Furthermore, over four orders of magnitude in electric conductivity were achieved with an excellent specific capacitance of 204.4 F g-1 when the graphene film electrodes were treated in a household microwave oven. Adopting an in situ construction strategy, green reduction of GO and the formation of an open porous structure are simultaneously completed in a one-pot process using an aqueous extract of another anthocyanin-containing plant, black soybean, as a green reducing agent. Graphene-based porous electrodes for supercapacitors were fabricated using the as-prepared graphene hydrogel as a primary material followed by microwave treating. Owing to the formation of uniformly dispersed nanoparticles on the graphene surface during microwave treating, both the electrical conductivity and the electroactive surface area were increased, as a consequence, the capacitance is significantly enhanced, reaching a capacitance of 268.4F g-1 at 0.1 A g-1. Three-dimensional porous polyaniline/few-layer graphene-coated active carbon fiber (PANI/FLG-coated ACF) electrodes with the unique structure, where ACFs were covered with the open porous PANI/FLG layers, were investigated. Ni networks served as the template for graphene grown by annealing the electrodeposited Ni clusters on the surface of ACFs. After CVD, FLG was synthesized on the Ni surface which was subsequently coated with PANI serving as capacitive materials and supporting layers for FLG in the construction of shell structures during Ni etching. The surface combined pultruded structure and cavity network formed with the PANI/FLG coatings, where holes on the cavity increased the electroactive surface area and facilitated penetration of the electrolyte into the cavity networks. As a result, an average specific capacitance of 400.2 F g-1 and an energy density of 61.3 Wh kg−1 at a charging current of 0.1 A g−1 over the PANI/FLG-coated ACFs electrodes were achieved. Based on the results, it is concluded that the extract of anthocyanin-containing plant can be a promising, potential, and green reducing agent for graphene synthesis. The porous graphene-based electrodes could be further improved by microwave treating owing to the naturally modification of graphene by the extract compounds. In addition, the porous PANI/FLG-coated ACFs with unique structure and good electrochemical performance could be easily designed and fabricated through the CVD method.