A coulometric titration of fluoride ion has been developed in which the supporting electrolyte consists of a sodium perchlorate solution in acetic anhydride containing a small amount of acetic acid. The fluoride is titrated as a base in this solvent with an accuracy of 2 to 3 parts per thousand. Perchloric acid is generated with 1 00% titration efficiency at a mercury
The anode and cathode reactions that accompany the passage of current through solutions of sodium perchlorate in acetic anhydride-acetic acid mixtures have been elucidated. Hydrogen gas and acetate ion are formed at the cathode. Hydrogen and acetylium ions are formed at the anode. The acetylium ion condenses with the acetic anhydride to form basic products that effectively remove hydrogen ion from the solution. The occurrence of the condensation reaction causes coulometric generation of hydrogen ions at platinum anodes to be less than 100% efficient. COULOMETRIC acidimetric titrationA of bases in which the supporting electrolyte consists of sodium perchlorate in an acetic anhydride-acetic acid solution has been described (11), and the results of titrations of a number of inorganic weak bases have been reported (10). These experiments showed that perchloric acid could be generated electrolytically a t a mercury anode with 100% titration efficiency. Attempts to match this generation efficiency with a platinum anode in the same supporting electrolyte resulted in maximum achievable current efficiencies of 95%. Since all of the electrode reactions that could reasonably be expected to occur at a platinum electrode in this solvent correspond to 100% current efficiency for hydrogen ion generation, the present study was undertaken to elucidate the anodic and cathodic reactions that occur when current is passed through acetic anhydride-acetic acid solutions. EXPERIMENTAL Reagents.Except for sodium perchlorate, all chemicals were commercial products of the highest purity and were used without further purification.
Fuel cells with NaLiCO3 electrolyte contained in a porous MgO matrix have been operated at 650~ on synthetic, "realistic" fuels containing combinations of H2, CO, CO2, H20, and N2. A mixture of air and CO2 was used as the oxidant. Hydrogen reacted nearly reversibly when a completely oxidized state of the electrode was avoided. No reversible oxidation of CO was observed, and current-time data confirmed that electrode oxidation occurred preferentially. H2 and CO were oxidized at oxidized electrodes with 0.6v activation polarization. Carbon deposition from the disproportionation of CO occurred even during the oxidation of H2. The disproportionation can be prevented by addition of H20 or CO2.The molten carbonate fuel cell has been and continues to be under intensive investigation and development (1-11). Rejection of CO2 by the electrolyte and high operating temperatures of 500~176give promise of practical operation on impure hydrogen and less reactive carbonaceous fuels. Distinct advantages are the reversibility of the silver oxygen electrode and the efficient dissipation of heat at a useful level. Disadvantages are slow starting and the severe testing of materials by the hot, corrosive environment. Considering that these factors are not overruling or can be overcome, there remain problems such as carbon deposition and low anode activity for CO. The objectives of this work were to examine the behavior of realistic fuel gases, especially impure H2 with CO2, to develop a working hypothesis of the anode reactions in order to discover and, if possible, remove limitations on cell performance, and to find an electrode catalyst for efficient oxidation of CO. Since CO is present in or formed from all fuel gases (even pure H2) in the molten carbonate cell, efficient operation will require that CO be consumed at a cell voltage near that of H2. ExperimentalExperimental cells were disk-type similar to those described by Trachtenberg (I1). A binary electrolyte of the composition LiNaCO3 was contained in a porous MgO matrix. Electrodes were of the porous diffusion type formed from silver powders sintered or brazed to silver flame-sprayed areas on either side of the MgO disk. In most cases a dual porosity electrode was prepared by sintering layers of--80 ~100 mesh and--20 -t-40 mesh silver powders at 850~176 for 1 hr in a nitrogen atmosphere. The sintered structures were 2 in. diameter and weighed from 10 to 15g.Anode catalysts were incorporated both by electroplating and as mixed or enclosed powders. Electroplating was performed "internally" by first soaking the porous Ag electrode in the plating solution and then cathodizing it in a similar solution without the reducible metal salt. To overcome limitations on the amount and kind of catalyst which could be introduced by electroplating and the inability to sinter electrode structures containing more than a few per cent of refractory materials, an enclosed powder structure was used. Either a ring of sintered Ag or an Ag gauze basket was filled with a mixture of powdered silver and c...
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