Dynamics and Chemical - Mechanical Coupling in PEM Fuel Cells

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Intellectual Merit: Fuel cells have been identified by the US government as an essential element of the hydrogen economy to reduce demand for fossil fuels and improve the environment. Polymer electrolyte membrane (PEM) fuel cells operate at low temperatures and are best suited for automotive applications. PEM fuel cells must have a rapid dynamic response over a broad range of environmental and load conditions reflecting driving conditions. The fundamentals of fuel cell dynamics and control addressed in this project are necessary to make PEM fuel an economically viable technology for automotive applications.An "idealized" PEM fuel cell was developed by the PI to examine fuel cell dynamics. The model fuel cell is a one-dimensional differential reactor with uniform, independently controllable, well-defined gas phase compositions at the anode and cathode. The model fuel cell can be thought of as two stirred tank reactors (STR) coupled by a membrane, hence the name the STR PEM fuel cell. The one-dimensional structure of the STR PEM fuel cell greatly simplifies the dynamic response to changes in system parameters, and is the basic differential element for scaling and modeling the performance of larger complex fuel cell reactor systems. Preliminary studies with the STR PEM fuel cell have shown the polymer electrolyte membrane is a reservoir for water, and the membrane resistance and mechanical properties depends on the water inventory in the membrane. Changes in the operating parameters of the PEM fuel cell, such as the external load resistance or the fuel cell temperature, alter the balance between water production and water removal changing the membrane water activity in the membrane. Extensive parametric studies of PEM fuel cell dynamics over a broad range of operating conditions will be pursued. Dynamic measurements of the chemical and mechanical properties of polymer electrolyte membranes will complement the fuel cell studies. Broader Impacts: Fuel cells are of great interest as one of the most promising technologies for the commercial development of the "hydrogen economy," which is of high priority for environmental and political reasons. The research outlined in this project could advance the efficient and robust operability and control of PEM fuel cells. The program addresses fundamental issues associated with the dynamics of water management and changes in operating conditions including variable load. The dynamics of PEM fuel cells have not been previously addressed. The data and models developed from the work outlined here will serve as a basis for systems engineering of PEM fuel cell systems.