A fuel cell has been proposed as a clean, efficient and environmentally responsible energy source for various applications. Individual fuel cells can be stacked together in series to form a fuel cell stack. The fuel cell stack is capable of supplying a quantity of electricity sufficient to provide power to an electric vehicle. In particular, the fuel cell stack has been identified as a desirable alternative for the traditional internal-combustion engine used in modern vehicles.
One type of fuel cell stack is known as a proton exchange membrane (PEM) fuel cell stack. The typical PEM fuel cell includes three basic components: a cathode, an anode, and an electrolyte membrane. The cathode and anode typically include a catalyst such as platinum or other suitable material for facilitating the electrochemical fuel cell reaction. The electrolyte membrane is sandwiched between the cathode and the anode. Porous diffusion media, such as carbon paper and the like, are generally disposed adjacent the anode and the cathode and facilitate a delivery and distribution of reactants, such as hydrogen gas and air, thereto.
The hydrogen gas supplied to the fuel cell reacts electrochemically in the presence of the anode to produce electrons and protons. The protons pass through the electrolyte membrane to the cathode where oxygen from the air reacts electrochemically to produce oxygen anions. The oxygen anions react with the protons to form water as a reaction product. The electrons are conducted from the anode to the cathode through an electrical circuit disposed therebetween. The electrical circuit allows the fuel cell stack to be used as an electrical power source.
The electrolyte membrane, electrodes, and diffusion media are disposed between a pair of fuel cell plates and sealed, for example, with a subgasket. The subgasket typically has an elongate bead seal formed thereon that provides a substantially fluid tight seal of the fuel cell. Each fuel cell plate has an active region to which the gaseous reactants are delivered for distribution to the electrodes. The fuel cell plate also includes a feed region configured to deliver the gaseous reactants from a supply source to the active region.
In known fuel cell stacks, the diffusion media and the seal of the subgasket are spaced apart to accommodate manufacturing tolerances and to avoid overlapping the diffusion media and the seal. An overlapping of the diffusion media and the seal is known to result in an undesirable leakage of gaseous reactants. The spaced apart diffusion media and seal, however, form a gap that permits a quantity of the reactants to bypass the active area of the fuel cell plates in a phenomenon known as “reactant bypass flow”. The reactant bypass flow is wasteful since the reactant is not directed to the active region of the fuel cell stack where the electrochemical fuel cell reaction takes place. The reactant bypass flow may also have an undesirable impact on durability, reliability, and performance of the fuel cell stack, particularly at low stoichiometric ratios of the reactants when a reactant starvation may occur.
There is a continuing need for a subgasket that militates against wasteful reactant bypass flow in a fuel cell stack. Desirably, the subgasket causes a higher percentage of the reactant to flow to the active regions of the fuel cell stack, and optimizes a durability, reliability, and performance of the fuel cell stack under a low stoichiometric ratio of the reactants.