| The search for alternative energy generation/conversion technologies is a necessity due to the limited availability of fossil fuels, cost and environmental impact of current technologies. Polymer electrolyte membrane fuel cells (PEMFCs) are an exciting prospect to replacement of current energy technologies. The main deterrents to widespread implementation are cost, durability, and freeze performance. The research presented focuses on cathode catalyst durability aspects, specifically during automotive potential cycling conditions.;The dominant mechanism responsible for catalyst degradation is still a matter of some debate with three possibilities still being considered---particle growth via Ostwald ripening, particle growth via coalescence and particle detachment from the support. A possible source of contention is the use of different testing conditions during accelerated stress tests (ASTs) leading to very different phenomena and conflicting results. The work presented probed the effect of the upper potential limit (UPL) for potential square waves on commercially available noble metal catalyst and detected carbon support corrosion when voltages higher than 1.0 V were used. Based on the available literature, DOE specified targets for PEMFC performance, and the results from this study, it was determined that a square or isosceles trapezoid (using a scan rate of 300 mV/s) with an UPL of 0.95V should be used during ASTs.;The investigation involved a variety of electrochemical techniques including cyclic voltammetry, thin film rotating disk electrode, and electrochemical quartz nanobalance, at ambient conditions in liquid electrolyte (0.1 M HCLO 4), which was monitored for platinum content using inductively coupled plasma mass spectroscopy. Results show a dependence of active surface loss with UPL, an increase in measured platinum dissolution above 1.1 V, and a difference in mass profile due to oxide formation at high UPLs. A surface loss dependence on size and support were also observed, as well as an effect due to voltage clipping. |
