Materials for PEM Fuel Cells and System Integration
(a) Bipolar and End Plates

The bipolar/end plate forms one of the most important and costliest components of the polymer electrolyte membrane fuel cell stack (PEMFCS). The performance of the PEMFCS depends on the materials used for these plates. Graphite bipolar plates are currently being used. However due to cost restrictions, low mechanical properties and porous nature of graphite, the commercial use of graphite in fuel cells still remains a challenge. The goal of this program is to develop bipolar and end plates for PEMFCS that are economical, lightweight, corrosion resistant, and have low permeability and high electrical conductivity. Use of metallic components for bipolar/end plates has several advantages over the conventional graphite plates. Materials such as stainless steel, aluminum alloys and composites, with or without coatings are good viable options for bipolar/end plates in PEMFCS.

Presently stainless steel is being tested as material for PEMFC bipolar/end plate in actual fuel cell test conditions using fuel cell test station facilities at The University of Alabama. A two-cell prototype PEMFCS was designed, fabricated and developed at The University of Alabama. Bipolar/end plates in this stack were made of SS 316 alloy, with a modified multi-parallel fluid flow-field design (FFFD). The new design gives a more uniform distribution of reactant gases over the electrode surface. The FCS was successfully operated for over 1000 hours at constant load without any appreciable drop in voltage ( 3 mV). The efficiency of stack was measured to be 48%. Results show that around 59% of the total losses are due to contact resistance losses in the stack. Although SS alloys have high conductivity, it decreases when an oxide layer is formed on the surface due to corrosion of the plates. This effect gets more pronounced due to contact resistances when these plates are placed in PEMFCS. To inherently improve upon these contact losses, suitable heat treatment/ surface modification techniques will be used. These bipolar plates will then be tested for hydrogen permeation, corrosion and other mechanical properties using the research facilities at The University of Alabama.


(b) System Integration and Optimization of PEMFCs System

System integration software was developed for predicting stack performance, losses, and fuel and oxidant consumption. Using this software the predicted efficiency of the in-house developed PEM fuel cell stack was 53%, which matches closely with the actual efficiency (48%). Further integration of this software with gas reformer unit and power conditioner is in progress so that system performance and operation can be predicted more accurately.