Design, optimization and dynamic studies of proton exchange membrane fuel cells (PEMFC) using detailed models.

摘要

Proton exchange membrane fuel cells (PEMFC) are currently in an advanced state of development with promising applications for stationary and portable power generation. In spite of this, even today, there are several critical issues that researchers are trying to address and resolve. The aim of 'the research performed during this' work was to address systems engineering aspects of PEMFC design and operation. These include optimization using steady state models and transient studies using detailed dynamic models. Detailed models that take into consideration modeling of reaction and transport processes that occur inside PEM fuel cells were developed. A two-dimensional steady state model was validated using experimental data. Subsequently, the steady state model was used for optimizing cathode catalyst layer design parameters. The dynamic cathode model was used to study transient characteristics of various transport and electrochemical phenomena. In addition, the dynamic model was used to predict spatial variations of partial pressure and dissolved concentration of oxygen inside cathode catalyst layer. Such predictions are useful in identifying regions of transient operation that could lead to problems such as oxygen starvation inside the cathode catalyst layer. The dynamic model can be used for systems engineering studies such as control and diagnostics.; As a part of the dynamic simulation studies using the cathode dynamic model, transient characteristics of the various transport and electrochemical phenomena are studied. Model based chronoamperometry and chronopotentiometry studies are performed to investigate the interactions among the various phenomena and the limiting mechanisms under various operating modes. Dynamic response of the current to step changes in the voltage under chronoamperometry and that of the voltage to step changes in the current under chronopotentiometry are found to be significantly different. Moreover, it was also observed through simulations that the dynamics in the output variables are strongly influenced by the operating cathode voltage. Results from chronoamperometry studies were used to highlight the problem of oxygen starvation, which is also reflected by the magnitude of the oxygen excess ratio or stoichiometric ratio. Results from the step tests in chronopotentiometry studies show that the response of the voltage to changes in the inputs such as current and air flow rate is nonlinear. (Abstract shortened by UMI.)