Polymer electrolyte membrane fuel cell electrode studies: Modeling and experiments

A series of fundamental studies on fuel cell electrodes has been reported in this dissertation to better understand the fuel cell electrode and electrode-membrane-assembly (MEA). These studies include: use of reference electrode in monitoring fuel cell electrode polarization; study of the oxygen reduction reaction (ORR) at simulated fuel cell environment; and a microscopic fuel cell porous electrode model.; Potential measurement with a reference electrode in the PEM fuel cell or other thin electrolyte cell could be inaccurate because both current distribution and potential profile are affected by electrodes misalignment and different electrode kinetics. It has been shown that the overpotential measurement error in PEM fuel cells could be as high as 60% even with practicable ohmic compensation. However for PEM fuel cells with identically sized electrodes, such measurement error could be minimized by using a two-reference-averaging method.; A micro band electrode technique has been developed and has been proved by mathematical model and experiments to be an effective tool to study the oxygen reduction reaction at the metal/polymer electrolyte interface at various temperature and relative humidity. This technique was applied to the investigation of the oxygen reduction on Pt interfaced with H3PO4 doped PBI at elevated temperature and various relative humidities. Tafel plots obtained by this technique are linear over 4 orders of magnitude in kinetic current density. Both kinetic parameters and mass transport parameters are comparable to those of the Pt/H3PO4 system under similar conditions reported in the literature. Investigations of the influences of H3PO4 doping level and electrolyte water content on ORR suggest that the proton transfer is the rate determining step under elevated temperature and low relative humidity.; A pseudo 3D, multi-phase microscopic fuel cell electrode model is reported in this dissertation. The simulated IR free polarization curve fits the experimental data without adjusting any parameters used in the model. The model has been used to evaluate the effects of porous electrode structure, the catalyst loading, and the amount of electrolyte in catalyst layer on electrode performance. It has also been used to evaluate the assumptions used in other porous electrode models.