Abstract
The development of fuel cell vehicles (FCVs) at Nissan proceeded to the level of limited customer leasing with the X-TRAIL FCV equipped with an in-house FC stack (2005- model). Subsequently, a further improved 2008-model FC stack was developed with double the power density and using only half the amount of precious-metal catalysts, thus giving the vehicle subzero startability at -20°C. For the coming stage of FCV commercialization, we have proposed the concept of a compact and low-cost FC stack (2011 model) that increases the maximum power density to 2.5 kW/L and reduces the estimated production cost to a level that comes very close to meeting the target of the DOE Hydrogen Program for the adoption of 2010 technologies. These advances were achieved mainly by improving membrane electrode assembly (MEA) performance and simplifying the FC stack structure. This paper presents an overview of the simplified structure of the new FC stack incorporating various new features: a shell-enclosed FC module and simplified configuration. This remarkable evolution of the FC stack structure was brought about by the development of various technologies: an advanced MEA, an adhesive seal, and a fastening enclosure. The advanced MEA has an integrated molded frame around it to reduce the production cost. Another benefit of the advanced MEA is the ability to build a stiff insulating shell around a FC module when the frames are bonded together with adhesive seals to form the module. As a result, the FC module can be fastened directly using steel plates uniquely shaped in both the stacking direction and the direction perpendicular to it, thereby maintaining proper compression to prevent the stacked FC modules from sliding. These improvements reduce the variety of components of the new FC stack by an estimated 75%, thus increasing the maximum power density by 30%, compared with the 2008-model FC stack.