MEAs

The main purpose of this work was to study and develop electrode materials for proton exchange fuel cells and characterize the performance of a laboratory cell.
Essentially this work is divided in three parts:
1. Principles and fundaments
The first part is constituted by the three first chapters, where a revision about the principles and theoretical fundaments about fuel cells is made. In the first chapter is detached the history of the cells, basic principles, aspects related with the thermodynamics and kinetics of chemical reactions, the several kinds of cells, procedures of production and storage of hydrogen. The second chapter contains considerations about porous electrodes and the theoretical fundaments of the gaseous diffusion in the electrodes. The third chapter lean over the proton exchange membranes, properly the working mechanisms of the membranes, namely the management of the water in the electrodes/membrane and the theoretical models witch characterize the several fuel cell components.
2. Electrodes for fuel cells
The main purpose of this work was to develop methods for the preparation and the characterization of the electrode materials. In the fourth chapter synthesis protocols were developed for the support materials for the electrodes and the gas diffusion layer. In both processes it is explained how to regulate the quantity of PTFE that the electrode should contain to maximize the performance of the fuel cell. A sequential thermic treatment was established to apply in the carbon materials soaked in PTFE emulsions in order to cause an effective splitting of the PTFE in carbon clothe fibres. In the fifth chapter the carbon clothes were characterised, using the optical microscopy, measuring the hidrophobicity, measuring the gas diffusion and measuring the resistivity. In the different cells were calculated the several overvoltages, as well as the kinetic and thermodynamic parameters that compose them.
3. Study of the performance of segmented fuel cell
In the sixth chapter of the study it was adopted the segmentation of the electrode by partial machination/plotting of the canals in the collector of the cathode plate. It was possible to partially isolate blocks of electrodes with golden copper segments. This approach of the current collection allows the measure the current distribution in the fuel cell of polymeric electrolyte. Relatively to the known studies, this technology wasn’t previously explored for the measurement of the current distribution in real prototypes fuel cells, such as current gas collectors belonging to the stack of PSI, employed in Volkswagen Bora prototype.
Thus, each segment of the cathode can be seen as a monitoring sensor and proof of the local activity of the cathode. It is also useful to have an idea of the local conductibility in the membrane. In the experiments described in the sixth chapter, some relevant comments will be made, according to the specific components and the operational conditions. The design of the cell and the specific operational circumstances are technologically relevant for the experimental diagnostic. This work pretends most of all to present a new and effective diagnostic tool to evaluate the performance of the cell.