|Protective chromium-nitride surface layer. Click to enlarge.|
The Department of Energy has awarded $4.5 million to Oak Ridge National Laboratory (ORNL) and its partners to further the development of nitrided metallic bipolar plates for automotive PEM fuel cells. The award is a follow-on to an earlier $1.65-million project designed to demonstrate the potential for metallic bipolar plates to meet 5,000-hour durability goals at a cost of <$6/kW.
The first project ended in September 2006; the follow-on will begin in 2007, and last for two years.
In addition to ORNL, which is developing the nitridation surface treatment, partners include the National Renewable Energy Laboratory (NREL); Los Alamos National Laboratory; GenCell, makers of bipolar-plate fuel cells; Arizona State University; and Allegheny Ludlum Corp.
Metallic bipolar plates are an alternative to carbon-composite bipolar plates and are preferred by many automobile companies. The key issue with metallic plates, however, is developing corrosion-resistant and low-contact-resistant materials while offering the potential for low-cost production.
The goal of the follow-on project is to scale up and to demonstrate the technological and economic viability of thin-stamped metallic bipolar plates protected by a thermally nitrided surface treatment.
In this approach, an electrically-conductive and corrosion-resistant chromium-nitride surface layer is formed on the bipolar plate component by heating a specially designed bipolar plate alloy to high temperatures in a nitrogen-containing environment.
The process results in a surface conversion, and is not a deposited coating. The high process temperature favors the reaction of all metal surfaces, eliminating pin-hole defects. The process is also amenable to complex geometries, such as those in the bipolar plate. This allows the plates to be stamped and then nitrided—an established and low-cost approach.
The project work will include optimization of an inexpensive iron-chromium base alloy composition and nitridation process; characterization of the bipolar plates; and demonstration of the optimized bipolar plate stamping and nitridation processes and subsequent plate testing in a fuel cell stack.
|GenCell bipolar plate cell.|
GenCell has developed a proprietary sheet metal bipolar separator plate, current collector and electrodes—the discrete components of a fuel cell. The GenCell product nests sheet metal bipolar plates with thin walls and high surface area.
The company will receive $1.25 million of the grant to advance these stamped metallic bipolar plates and to provide the plate and stack architecture designed to meet cost and weight targets set by the DOE.