The stability of different types of platinum surfaces in the presence of chloride was evaluated by applying a potential of 1.2 V vs reversible hydrogen electrode while the associated mass change in the Pt electrode was monitored with an electrochemical quartz crystal microbalance. The platinum metal surfaces based on the particles and films show a large difference toward dissolution when exposed to small amounts of chloride. While an electrodeposited platinum metal film showed no degradation in a sulfuric acid solution containing 10 ppm of chloride, an electrode made from a fuel cell catalyst (50 wt % Pt/C) lost 10% of its platinum content over a 24 h period when exposed to a sulfuric acid solution containing 10 ppm of chloride. At a chloride concentration of 20 ppm, the onset potential of the Pt oxide formation increased ∼200mV compared to an electrode in a chloride-free solution. The degradation of nanoparticles thus appears to be much more significant than for the electrodeposited platinum electrodes.

No abstract

Carbon corrosion rates were measured for four types of polymerelectrolyte membrane (PEM) electrode assemblies (MEAs) during shut-down air purging and start-up. The corrosion rates were measured at different purge rates, temperatures, and relative humidities. The highest amount of carbon corrosion occurs when gases are humidified and when using low flow rates for the air purging during shut-down and low hydrogen flow during start-up. Dry conditions give the highest rates of corrosion during shutdown when comparing the same flow rates of hydrogen and air, while humid conditions gives the highest rate of corrosion during start-up when comparing the same flow rates of hydrogen and air.

Experimental design has been applied to study PEMFC performance and durability as a function of operating conditions. Two levels of relative humidity, clamping pressure and back pressure have been systematically applied to an ON/OFF load cycle. Effluent analysis of fluoride and sulfate has been performed to correlate the emission rates to the durability observed. Background effluent levels for fuel cell test rigs were also assessed. Fluoride emission rates increases with time. The rates are higher for the experiments with back pressure, but they do not correlate well with voltage losses. High initial emission rates of sulfur are observed. After flushing with humidified inert gas, the emission rates decline but are sustained at high rates compared to fluoride. Sulfate emission rates are higher for experiments with high humidification levels. The total mass of sulfur released is higher than expected from the ionomer equivalent weight.

not Available.