In order to make the fuel cell stack lighter weight and more compact, the cell thickness and the number of cell stacks were reduced. This achieved the world’s highest level of volume power density at 3.1 kW/L. The reduction in cell thickness was achieved by the uniform distribution of water in the membrane electrode assembly, a reduction in the gas flow channel depth, and reduction in the membrane electrode assembly thickness. The reduction in the number of cell stacks was achieved by narrowing the gas flow channel pitch so as to enhance the power output performance per cell. Structuring the FC stack so that the gas flow channels are oriented laterally allowed the height of the fuel cell stack to be reduced while the connection bar was used as a cell retention structure, increasing the impact resistance. This enabled mounting of the fuel cell stack under the front hood. Making the fuel cell lighter weight and more compact reduced its heat mass so that the time taken to reach 50% of rated capacity when the fuel cell is at a low temperature could be shortened to one-half of the time required by a previous fuel cell. The membrane electrode assemblies that make up the cell were given a resin frame around their periphery, and squaring off their shape reduced the amount of material needed in the electrolyte membranes and diffusion layers while also increasing their continuous manufacturing productivity.
Article of Honda R&D Technical Review Vol.28 No.2 (45 - 52)