Rapid determination of a number of trace elements in zinc sulfate electrolyte is essential for adequate plant process control. As a basis for an on-stream monitoring system, differential pulse polarography and differential pulse anodic stripping voltammetry at a hanging drop mercury electrode have been investigated, using conventional and computercontrolled instrumentation, for the determination of Cd, Cu, Pb, Sb, Co, Ni, TI, and As. Cd and Cu were determined directly In the zinc sulfate solution down to 10 µg/l., and Sb to a similar low level after addition of concentrated hydrochloric acid. Pb, Co, Ni, Tl, and As were determined after addition of appropriate reagents in some cases; however, these determinations are generally better suited to higher concentration levels than for Cd, Cu, and Sb.Successful operation of electrolytic zinc plants depends critically on the purity of the cell feed, both for product purity and for high current efficiency in the deposition stage (1-4); therefore, reliable analytical data are very important to the economics of the process. Over the years, reasonable process control has existed (2, 5-9) by virtue of manual sampling and
Materials for constructing low-temperature fuel cell batteries must be carefully selected not only to resist attack by corrosive electrolytes, but also to avoid poisoning of catalysts. Very few systematic studies of fuel cell catalyst poisoning have been published. Witherspoon and Adams (1) studied a Rh-Pd hydrogen anode catalyst and found that cupric and ferrous ions in solution and a surfactant (Triton x 100) caused some loss of activity, while sulfide ion caused severe poisoning. Terry (2) reports that short life of hydrogen-air cells was attributable to poisoning from sulfur in molded rubber cell frames. Cathro (3) has found that platinum-based formaldehyde anodes fail rapidly in the presence of copper and silver ions in acid solution. Workers at Esso Research and Engineering (4) found that copper poisoned methanol anodes, but that aluminum had no effect.Active catalysts for the oxidation of both methanol and formaldehyde have been developed in this laboratory (5, 6) and tested successfully for long periods in small-scale fuel cells. Early versions of larger cells and batteries were less successful, showing poor performance and short life, and it was evident that anode catalysts were becoming poisoned by impurities in solution. The experiments described below were undertaken to determine the undesirable impurities and their sources and to investigate possible substitutes. ExperimentalEach test was performed using a covered 2 liter glass pot cell. Five holes in the cover contained leads to the working and counterelectrodes, a probe leading out to a mercury/mercurous sulfate reference electrode, a glass-sheathed immersion heater, and a glass thermistor pocket. Anode catalyst (approx 150 mg of Pt-ReSn) was electrodeposited onto a gold-plated expanded tantalum or niobium disk of 13 cm~ nominal area to form the working electrode. The counterelectrode was platinum gauze, and was surrounded by a glass tube to prevent evolved hydrogen reaching the working electrode. The solution was maintained at 60~ and agitated by the use of a magnetic stirrer unit. The working electrode was supplied with a current of 0.SA (38 mA/ cm 2) from an external source. The fuel used was formaldehyde (0.3 _ 0.15M) dissolved in 2M sulfuric acid electrolyte. A few experiments were also performed with methanol (approx 1.0M) as fuel. Results were generally similar to those with formaldehyde.The procedure for each test was to run the electrode for 50 or more hours to allow it to reach a steady potential, then to introduce a sample of the material to the pot. Where possible, size and physical form of the samples were selected to correspond with the maximum exposure likely in a practical battery. Working electrode potential was recorded daily, and any poisoning effect was detected by the resulting rise in potential. Corrections for IR drop were determined by a simple interruption technique. Results and DiscussionOne electrode was tested for several hundred hours in a solution free of impurities, using reagent-grade formaldehyde. The potential rema...
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