| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 100 === The detail introduction of graphene-based materials and their fabricating routes are summarized in Chapter 1. Chapter 2 introduces the basic theory and literature review about proton exchange membrane fuel cells and supercapacitors. The experimental methods and procedures are descripted in Chapter 3.
The physicochemical properties of aggregated GS are similar to that of graphite, their performances are significantly worse than expected. In Chapter 4, a simple approach was designed to enhance the utilization (i.e., enlarging electrolyte-accessible surface area) of GS and to improve the capacitive performances by combining 1D CNTs and 2D GS. In addition, dependence of the microstructure and capacitive performance on the composition of GS-CNT composites is systematically investigated by varying the weight ratio of reduced GO to CNTs. The specific capacitance of GS-CNTs-9-1 (326.5 F/g at 20 mV/s) is much higher than that of GS material (83 F/g). Furthermore, the energy and power densities of GS-CNTs-9-1 are as high as 21.74 Wh/kg and 78.29 kW/kg, respectively exhibiting that the hierarchical graphene-CNT architecture provides remarkable effects on enhancing the capacitive performance of GS-based composites.
In Chapter 5, a simple, efficient and practical approach to fabricate a novel hierarchical a-MnOx/GS-CNT composite which contains a homogeneous ultrathin a-MnOx nanoflower film with slender nanopetals was designed to approach the full utilization of electroactive materials through combing a simple solution-assembled process and the cost-effective electrochemical deposition technology. The utilization of a-MnOx on the desired 3D hierarchical a-MnOx/GS-CNT composite (specific capacitance of MnOx, CS,Mn = 1200 F g1) is much-higher than that of a pure a-MnOx electrode (CS,Mn = 233 F g1). Futhermore, at the CV scan rate = 200 mV s1, the specific energy and specific power of a-MnOx/GS-CNT are respectively as high as 46.2 Wh kg1 and 33.2 kW kg1, revealing that this 3D hierarchical a-MnOx/GS-CNT electrode delivers energy and power densities well above those of electrochemical capacitors (ECs) in current state-of-the-art
In chapter 6, an approach was designed to enhance the utilization of GS-based materials and to improve the electrocatalytic performances of Pt nanoclusters by combining 1-D CNTs and 2-D GS. Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes to form a 3-D hierarchical structure which enhances the utilization of GS-based composites. The specific electrochemically active surface area (SECSA) and specific double-layer capacitance (CS,DL) of Pt/GS–CNTs (127.9m2/g, 171.3 F/g) are much higher than those of Pt/GS (105.4m2/g, 104.7 F/g) and Pt/CNTs (51.5m2/g, 37.1 F/g), respectively, revealing the synergistic effects between GS and CNTs on enhancing the electrochemical activity of Pt nanoparticles and electrolyte-accessible surface area.
In Chapter 7, an integrated approach is proposed to fabricate N-doped GS with pyridinic-N and graphitic-N as the main functional groups (ca. 88% in nitrogen structures) and high surface area through combining molecular functionalization, ultrafast thermal expansion-exfoliation, and covalent transformation steps. The exceptional performances of N-doped GS for the oxygen reduction reaction are attributable to the following reasons: (i) The highly porous architectures of N-doped GS possess higher electrolyte-accessible surface area, especially the nitrogen active sites, leading to a much higher electrochemical activity. (ii) Annealing at high temperatures thermally reduces GO and induces bond formation between aromatic nitrogen molecules and GS, resulting in the formation of highly crystalline N-doped GS. (iii) The N-doped GS prepared in this work contains high percentages of pyridinic- (49.8%) and graphitic-N sites (38.2%), is promised for the 4-electron transfer ORR. Hence, this work offers a promising route for fabricating N-doped GS, a typical metal-free electrocatalyst.
Finally, the main contributions of this dissertation and further feasibility works are summarized in Chapter 8.
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