| Carbon material has many outstanding features, such as abundant source,rich reserve, low cost, good conductivity, large specific surface area and so on.So, it has become the promising renewable electrode material in sustainable energy storage and conversion devices. Among these devices, there are always some electrochemical reactions, occuring at solid/liquid/gas interface, for example, oxygen reduction reaction (ORR). Additionally, although no redox reactions exsit in the electrochemical double layer capacitor, it still involves the reversible adsorption/desorption of ions on the surface of electrode.Therefore, the electrode with advanced unique structure should be developed to meet the further demand in practical application. In this paper, according to the innovative approach and structural design, we synthesize the micro/nanostructure carbon-based electrode material, aiming at solving the problems during preparation and use process of electrode material, especially graphene-based carbon and biomass porous carbon material. The main contents and conclusions about this work are as follows:1. By the modified Hummers' method, we prepared the graphene oxide(GO) nanosheets with large size and numbers of oxygen-containing functional groups. The GO with above features can be used as a shape-directing agent and is beneficial to fabricating relevant graphene-based carbon material.2. Under the protection of poly diallyldimethylammonium chloride(PDDA), a electrochemical catalyst was prepared using GO as the substrate and [Ag(NH3)2]+ solution by hydrothermal reaction. Meaningfully, the agglomeration of graphene and Ag nanoparticles were successfully avoided during the liquid-phase synthesis process. In the catalyst, Ag nanoparticles of about 5.7 nm evenly disperse on the surface of approximate single-layer reduction graphene oxide (RGO). The resultant, Ag-PDDA-RGO, shows the excellent ORR performance in the alkaline media. When it is used as oxygen reduction cathode in the electrolysis of sodium carbonate, the average cell voltage is just 1.48 V. Compared with 2.53 V of cell voltage in the conventional hydrogen evolution electrolysis, up to 41.5% of electrical energy is saved.3. Although the content of Pt has been reduced in non-precious metal ORR catalysts, it suffers from the performance instability and secondary pollution. So it is necessary to develop a sandwich-like graphene-based material as the metal-free electrochemical catalyst. If so, it can reduce the content of graphene, avoid the agglomeration of graphene, enrich the pore structure of graphene-based material and lower the cost of catalyst. We synthesized the N-doped graphene/carbon composites with a sandwich-like structure by using low cost and nontoxic glucose as the carbon source and ethylenediamine (EDA) as the nitrogen source. After high-temperature pyrolysis, the catalyst had a well-ordered three dimensional network and porous pore structure. Besides, the percentage of graphene is about only 4.9%in this graphene/carbon composites. Importantly, the catalyst has the specific surface area of 1510.83 m2 g-1 and exhibits the good ORR activity, comparable to that of Pt/C.4. In view of the single-type active site and limited accessible active surface area in almost metal-free catalysts, we develop a novel type of graphene-based electrocatalyst with advanced micro/nanostructure and multiple active sites. During the preparation process, the environment-friendly starch was used as the carbon source and urea was the nitrogen source. The carbon/graphene/carbon material was synthesized using GO as shape orientation reagent. Then, the sandwich-like graphene-based electrocatalyst decorated by Fe and S was prepared by high-temperature pyrolysis.Meanwhile, the three-dimensional porous pore structure was obtained without the activation reagent (corrosive KOH). The test results show the catalyst owns the onset potential of 0.95 V, half-wave potential of 0.83 V and 4e selection pathway in alkaline solution due to the synergistic effect of multiple active sites, and its ORR activity is better than commercial Pt/C. Furthermore,it also shows the competitive performance in acid media.5. After the factors which can affect the structure of catalyst were studied deeply, we chose the cauliflower of unique structrue as the carbon precusor and 2-imidazolidinone was the nitrogen source to prepare the N-doped porous cauliflower carbon. It is noteworthy that the catalyst with open and three-dimensional porous structure was obtained by a facile one-step prolysis procedure including two temperature-rise stage. The electrochemical results show the N-doped porous carbon has a high specific capacitance of 311 F g-1,excellent rate performance and long-term stability in 6 M KOH. In addition, it exhibits the high energy density and power density in the assembled symmetric supercapacitor. |
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