Effects of Processing Conditions on the Physical and Electrochemical Properties of Carbon Aerogel Composites
- PDF / 386,108 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 91 Downloads / 266 Views
properties. Results of these effects on the materials properties and their electrochemical capacitive behavior are reported. EXPERIMENTAL Carbon aerogel/carbonpaper composites - The preparation of composite electrode materials containing RF aerogels integrated into a commercial carbon paper has been described before [9]. In general, resorcinol (1,3 dihydroxybenzene) and formaldehyde were mixed in a 1:2 molar ratio, respectively. Deionized/distilled water was added as the diluent and sodium carbonate as the base catalyst. A porous carbon paper (0.127-mm thick, Lydall Technical Papers, Rochester, NH) was soaked with the catalyzed-RF solution and placed in between two glass plates. The impregnated sample was cured at room temperature, 50'C and 85°C successively for one day each at the various temperatures. The cured composite was then soaked in a copious amount of acetone and subsequently dried at room temperature. Care had to be taken to assure that the pore water was adequately exchanged with acetone. Finally, the RF/carbon paper composite was heat treated at 1050'C in a nitrogen atmosphere for two hours to pyrolyze the RF component. Table 1 lists several monolithic and composite samples and their characteristics. Conventional high-density monolithic and composite RF materials (samples M 1, M2 and C 1) were prepared with RF concentrations between 50-70% weight per volume (w/v) using a molar ratio of resorcinol to catalyst (sodium carbonate) of 200. A number of the carbon aerogel composite materials were commercial products obtained from Ocellus, Inc. (San Carlos, CA). These materials were prepared in a similar procedure as described above except with modified formulation and drying steps. The solvent (acetone) exchange step was eliminated in this case and the pore fluid (water) was dried directly at ambient conditions. The concentration of resorcinol-formaldehyde was varied between 50 to 70% weight per volume (w/v) at a constant resorcinol to catalyst molar ratio. After curing and drying, the resulting RF composites were then pyrolyzed under an inert atmosphere using a temperature ramp of 8 to 13 hours duration, depending on the final pyrolysis temperature (between 600 and 1050'C.) Electrode materials were then tested directly without any additional treatment. Electrochemical capacitancemeasurements - Electrochemical studies were performed using a 64-channel Maccor battery tester. Experiments were done using circular (4.5-cm diameter) Teflon cells. The two identical 1.5-cm diameter electrodes were separated by 2 pieces of Whatman fiberglass filter papers (934-AH). Nickel foils were used as current collectors in sodium hydroxide (5M KOH) electrolytes. The whole assembly is sandwiched between 2 Teflon plates and held together by 0.6-cm diameter Teflon screws. Electrolyte filling was accomplished via three successive evacuation (2 psi) and pressurization (24.5 psi) stages in approximately 30 minutes. The assembly and testing of aqueous cells were carried out under ambient conditions. The charge/discharge experiments we
Data Loading...
