High fuel efficiency and clean exhaust gas are the two most important requirements in hydrazine‐air fuel cells. Four anodes of sintered nickel plaque were studied for these purposes, each one containing either cobalt, nickel, palladium, silver, or platinum as a catalyst. Exhaust gases were determined with a gas chromatograph, the consumption of hydrazine in the anolyte was analyzed chemically, and fuel efficiencies and unreacted product gases were evaluated based on these data. Consequently with the silver catalyzed electrode, 97% fuel efficiency was attained at 50 mA/cm2 at 25°C.
Due to the dissolution of the lithiated nickel oxide cathode, the life expectancy of a molten carbonate fuel cell is reduced. The use of a Li/Na carbonate electrolyte is expected to lead to a higher voltage and a longer life expectancy due to its higher ionic conductivity and its lower nickel oxide cathode solubility. Using the Li/Na electrolyte, single cells have been tested to evaluate their performance and their life expectancy. Empirical equations for these cells have been presented to determine the temperature, the CO2 partial pressure in the cathode gas, and the matrix thickness. The results prove that the life expectancy of Li/Na cells is reduced by nickel short-circuiting in comparison to Li/K cells, for which the life expectancy is many times longer. The dependence of the nickel-containing particle distribution in the matrix on the temperature has been evaluated using an image processing method. At 973 K, most of the particle distribution moves toward the anode more rapidly than at 873 K, because the rate of particle growth is lower at the higher temperature, and the particles move toward the anode due to the convection of the molten carbonate in the matrix. The initiation time for nickel short-circuiting was derived from he results of this study to explain the relationship between the shorting conductance and the volume of nickel-containing materials in the matrix porosity. Moreover, the results show that the predominant element contributing to short-circuiting is the nickel oxide, and not the metal. © 2001 The Electrochemical Society. All rights reserved.
The roles of the excess kinetic energy and the thermal ionic processes in the reaction of the 80Br from the isomeric transition of 80mBr in gaseous CH4 and CD4 were investigated using a rare gas additive. A possible isotope effect has appeared on the substitution reaction of the energetic Br atom to form CH380Br or CD380Br, but not on the thermal processes to form CH380Br and CH280BrBr or their isotopic alternatives. At a zero mole fraction of moderator, the CH380Br/CD380Br ratio for the energetic process was found to be 2.7±0.3. This is consistent with the moderator and/or probability integral isotope effects. However, in a highly moderated system the results indicated that the former effect is more important than the latter. Furthermore it can be inferred from the total pressure effects on the energetic reaction products that the excited primary products are able to decompose unimolecularly due to internal excitation.
Acid movementand performance history of a phosphoric acid fuel cell were studied using electrodes with various acid absorbancies. Acid loaded in a matrix material at the cell fabrication was absorbed by the cathode and anode. Later, acid absorbed by the anode moved through the matrix to the cathode and was carried out of the cell by the cathode gas during cell operation. An electrode with low acid absorbancy was preferable for the cathode and one with high absorbancy for the anode, which functions as an acid reservoir.Phosphoric acid fuel cells are usually fabricated by sandwiching a matrix material containing the acid between two electrodes. The electrode is composed of a porous carbon substrate and catalyst layer that consists of a carbon supported platinum catalyst and polytetrafluoroethylene (PTFE). The cell performance and history are affected by the catalyst activity, pore structure, and acid retaining ability of the matrix material, amount of the acid, cell operating conditions, etc. The cathode has already been discussed by several researchers (1-3). A design of the catalyst layer structure using two kinds of carbon support with different particle sizes has been attempted (4), and the effect of acid absorption in the catalyst layer on the electrode performance has been examined (5-6).The present study focused on investigating the effect of the electrode's acid absorbancy on the acid movement and balance in the cell, cell performance, and endurance. ExperimentalElectrode fabrication.--The electrode was made from a carbon-supported platinum catalyst with a platinum content of 10 weight percent (w/o), PTFE dispersion (D-l, Daikin Kogyo, Limited), and ribbed porous carbon substrate. Acetylene black (Denka Black, Denki Kagaku Kogyo, Limited) was used as the carbon support. The carbon substrate with a thickness of 2 mm was made using carbon fiber and phenol resin and heated at 2000~ Porosity and pore diameter of the substrate are 65% and 35 ~m, respectively. The substrate was impregnated with the PTFE dispersion and heated at 350~ for 30 min in air to give an acid repellency to the substrate. The PTFE content in the resulting substrate was 7 w/o. The catalyst layer was formed on the substrate by preparing a slurry made by kneading the catalyst and PTFE dispersion; the mixture was spread on the carbon substrate with a doctor blade method. This was followed by heating in air for 30 min at a temperature from 320 ~ to 370~ The platinum loading was 0.5 mg/cm 2. The PTFE content in the catalyst layer was varied between 30 and 70 w/o. Pore volume and distribution of catalyst layer.--Mer-cury intrusion method was used to determine the pore distribution of the catalyst layer. The sample was prepared in the same manner as described above, except that a 100 mesh nickel net was used in place of the carbon substrate. Small pieces of the sample were subject directly to the measurement, but the data were processed using the weight of the catalyst layer only. Acid absorbancy of electrode.--The acid absorbancy was defined and m...
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