High Power Density Fuel Cell Stack Development For Automotive Applications

Ric Pow Ballard Power Systems Inc.

9000 Glenlyon Parkway Burnaby, British Columbia

Michael Reindl and Werner Tillmetz Dornier GmbH department FOEE D-88039 Friedrichshafen Germany

Canada V5J5J9

Introduction

This paper describes the joint development by Daimler-Benz and Ballard Power Systems of a high power-density fuel cell stack and its demonstration in a 6-passenger Minivan.

Background

The PEM fuel cell is generally recognized as a promising candidate to realize society's objectives of ultra low and zero-emission vehicles. Ballard Power Systems has been working on the development of the PEM fuel cell since the mid eighties, and by 1993 had reached a level of technology represented by the Mk 5 stack. This technology enabled interested parties to get some experience with fuel cell operation and to gather test results. The Mk 5 was not optimized for power density, efficiency, durability, or cost and it was recognized that new generations of fuel cells would be required for commercial applications.

In 1993, Daimler-Benz and Ballard commenced joint development of a high power-density fuel cell stack for the automotive application, which was given the name "Mk 7." The first phase of the program targeted demonstration in a passenger vehicle within 4 years. The objective was to produce technology that is compact enough to power a car, is capable of operating in an automotive environment, and has adequate transient response to fulfill typical automotive duty cycles. The development of the technology to a level where it is commercially competitive with other environmentally acceptable alternatives to the internal combustion engine will be the topic of future phases.

The first task was the integration of the existing Mk 5 technology into a commercially available vehicle, which was given the name NECAR, for New Electric Car. The purpose was to provide a working platform to collect experience in the operation of a motive fuel cell power plant, and learn about the requirements for technology advancement. It also provided assurance that the technology is viable for the application, and that with development, can meet the requirements of the commercial automotive market.

Mk 7 Fuel Cell Stack

The major objective of development of the Mk 7 stack was a dramatic increase in power density. Analysis of practicable fuel cell systems for the car indicates that the power density of the fuel cell stack must be at least five times greater than the Mk 5, which was the state of the art at the beginning of the project. In addition, it was desired that the fuel cell be capable of operating on reformed methanol, in preparation for future applications. The longevity target for the fuel cell was at least 1000 hours to enable demonstration and collect experience. This represents a balance between the need to test large numbers of designs, and operating conditions, and the eventual need for 3000-5000 hours in a commercial product. Other requirements included operation on reduced air and reactant flows, pressures, and humidification to optimize overall system performance, and

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