Mechanism of oxygen reduction on platinum in netural saline and effects of interstitial fluid
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The mechanism of oxygen reduction on a platinized platinum electrode was studied in a buffered saline solution in the neutral pH region. The Tafel slope was 135 + 18 mv and the reaction orders 1.1 and 0.19 with respect to oxygen and hydrogen ion respectively. These criteria were interpreted as being consistent with a consecutive adsorption and one electron transfer rate controlling step as follows: O2 (solution)--> O2 (adsorbed) O2 (adsorbed) + e^- ---> O2^- The pH dependency is attributed to a shift in the potential of zero charge with pH in chloride solution. The factors affecting the performance of platinum activated carbon cathodes in hybrid biogalvanic fuel cells were also examined. It was found that by-products of aluminum and zinc anodes had no effect on the cathode output voltage. An artificial interstitial fluid either with or without bovine serum albumin shifted the voltage vs. current curve downwards by approximately 100 mv. These tests were performed under aseptic conditions for periods up to five days. The major cause of low in-vivo cathode voltages was attributed to mass transfer limiting conditions which were examined in-vitro in both buffered saline and artificial interstitial fluid. An automated load switching system for evaluating hybrid fuel cell characteristics is also described. The system utilizes a Linc-8 computer and Cal comp plotter to produce voltage vs. current curves from up to sixteen different anode - cathode pairs. The usefulness and limitations of the system are described.
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