University of RochesterDept. of Chemical Engineering
University of Rochester
General MotorsSample Preparation and Imaging Methods
Samples for this work were taken from a fresh fuel cell membrane-electrode assembly (MEA) and a corroded MEA with measured carbon weight loss of about 12%. Each sample was prepared in two ways; the first preparation was intended for low magnification thickness analysis in an environmental SEM with a thermionic emission source, the second preparation was intended for high magnification in a field emission SEM for carbon structural analysis.
Thickness measurements were done on samples fixed in epoxy and then polished to expose a cross section of the MEA. The samples were then sputter coated with gold-palladium and placed in an environmental SEM with a tungsten filament thermionic electron source. Micrographs were taken using a back scattered electron detector, cathode thickness measurements were done using the built in analysis software.
Structural imaging could not be done on the samples fixed with epoxy because the delicate carbon structure in the cathode was polluted with the epoxy. Instead, samples were prepared utilizing a simple freeze fracture method. The samples were first fixed between two clamps then dipped in liquid nitrogen for approximately 30 seconds. Tension was then applied to the sample resulting in a fracture which exposed a clean cross section of the cathode electrode. These samples were then imaged using a Zeiss-Leo DSM982 SEM with a tungsten field emission electron source. Micrographs were taken using the in lens secondary electron detector and x-ray microanalysis was done using energy dispersive x-ray spectroscopy.