Three-dimensional Graphene Architectures:Preparation And Applications

Graphene, a two-dimensional crystal of monolayer carbon atoms tightly packed into honeycomb lattice with sp2hybridization, since its discovery, has attracted world-wide attention and research. The extraordinary electronic, optical, thermal, mechanical and chemical properties endow graphene with a wide range of applications in many areas. However, the excellent properties of graphene are usually compromised by restacking and aggregation of graphene sheets due to the strong π-π interaction and van der Waals force. In order to overcome this obstacle, one possible solution is to prepare three-dimensional (3D) graphene architectures with high conductivity, large surface area and large porosity.This dissertation launched a series of studies on the preparation of3D graphene architectures with electrochemical deposition and in-situ reduction self-assembly methods as well as their applications on fuel cell electrocatalytic electrodes, supercapacitor electrodes and environmental remediation. There are five chapters in this dissertation:in the first chapter of preface, we introduce the properties and preparation of graphene as well as existing fabrication methods and various applications of3D graphene architectures, and the investigation motivation of this dissertation; the second chapter presents the preparation of platinum nanoparticle (Pt NP) decorated3D graphene electrodes through electrochemical deposition and their improved electrocatalytic performance; the third chapter illustrates electrodeposition of porous graphene sheets on porous nickel foams and their capacitive behavior as electric double-layer capacitor electrodes; the fourth chapter demonstrates the preparation of graphene aerogels by evaporation-induced in-situ reduction method, and investigate their adsorption ability to heavy metal ions and dyes as well as selective absorption performance to organic liquids; the fifth chapter is conclusions and outlook. The main contents of chapter two to five are given below.In chapter two, we present an easy, feasible and green route to fabricate Pt NP decorated three-dimensional graphene assembled on fluorine-doped tin oxide (FTO) electrodes (Pt/3D-G/FTO) with enhanced electrocatalytic activity. The fabrication process was accomplished by preparation of3D graphene (3D-G/FTO) electrodes through electrochemical reduction of a graphene oxide (GO) suspension followed by electrodeposition of Pt NPs onto them. The Pt/3D-G/FTO electrode exhibits much higher catalytic activity and better stability for methanol oxidation compared with the electrodes prepared by electrodeposition of Pt NPs onto two-dimensional graphene sheets substrate (Pt/G/FTO) or bare FTO (Pt/FTO) under the same condition. These enhancements can be attributed to the high surface area, large void volume and high electrical conductivity as well as smaller size of Pt NPs in the hollows of the3D architecture and a large amount of ridges on it.In chapter three, we describe a facile, low-cost and green method to fabricate porous graphene/nickel foam (PG/NF) electrodes by electrochemical deposition of graphene sheets on nickel foams for the application of supercapacitor electrodes. The electrodeposition process was accomplished by electrochemical reduction of GO in its aqueous suspension. The resultant binder-free PG/NF electrodes exhibited excellent double-layer capacitive performance with high rate capability and a high specific capacitance of183.2mF cm-2at the current density of1mA cm-2. Moreover, the specific capacitance maintained nearly100%over10,000charge-discharge cycles, demonstrating a remarkable cyclic stability of these porous supercapacitor electrodes.In chapter four, we illustrate an inexpensive and mild method to fabricate graphene hydrogel by simply heating GO suspension containing sodium bicarbonate. This method demonstrates a new type of in-situ reduction-assembly approach to construct graphene hydrogel through simultaneous water evaporation and GO reduction. The freeze-dried graphene aerogel (G-Gel) shows strong adsorptivity to heavy metal ions and dyes. The thermally treated G-Gel (TG-Gel) exhibits excellent performance in recyclable selective absorption of oil and organic solvents.