The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Fuel cells are useful as a power source for electric vehicles and other applications. An exemplary fuel cell has a membrane electrode assembly (MEA) with catalytic electrodes and a proton exchange membrane (PEM) formed between the electrodes. Water is generated at the cathode electrode based on the electrochemical reactions between hydrogen and oxygen occurring within the MEA. Gas diffusion media plays an important role in PEM fuel cells. Generally disposed between catalytic electrodes and flow field channels that introduce reactant gases into the fuel cell, the gas diffusion media provide pathways for reactant to diffuse to the electrode and pathways for removal of the product water, electronic conductivity, and heat conductivity, as well as mechanical strength needed for proper functioning of the fuel cell.
During operation of the fuel cell, water is generated at the cathode based on electrochemical reactions involving hydrogen and oxygen occurring within the MEA. Efficient operation of a fuel cell depends on the ability to provide effective water management in the system. For example, the diffusion media prevent the electrodes from flooding (i.e., filling with water and severely restricting O2 access) by removing product water away from the catalyst layer while maintaining reactant gas flow from gas flow channels of the bipolar plate through to the catalyst layer.
Fuel cell stacks can contain a large number of fuel cells depending on the power requirement of the application. For example, typical fuel stacks have up to 400 individual fuel cells and more. Because the fuel cells in the stacks operate in series, a weakness or poor performance in one cell can translate into poor performance of the entire stack. For this reason, it is desirable for every fuel cell in the stack to operate at high efficiency.
Typical manufacturing steps for gas diffusion media include manufacturing a carbon fiber paper, impregnating the paper with resin or a mixture of resin and fillers, molding the impregnated paper, and carbonization or graphitization of the resin-impregnated carbon fiber paper. The steps of manufacturing paper and impregnation are continuous, while the molding, carbonization and graphitization steps may be either batch or continuous.
Because typical fuel stacks contain so many individual fuel cells, it is important for the manufacturing process of the diffusion media to have a high degree of reliability. Improvements in the manufacturing process that reduce cost, simplify the process, or enhance performance of the media are thus desirable.