A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM) such as carbon fiber paper, which facilitates a delivery of reactants such as hydrogen to the anode and oxygen to the cathode. In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
It has been desirable to fabricate the fuel cell and related fuel cell components from radiation-cured structures. The formation of radiation-cured structures such as microtruss structures are described in Assignee's co-pending U.S. patent application Ser. No. 12/339,308, the entire disclosure of which is hereby incorporated herein by reference. The formation of radiation-cured fuel cell structures are further described in Assignee's co-pending U.S. patent application Ser. Nos. 12/341,062 and 12/341,105, the entire disclosures of which are hereby incorporated herein by reference.
Radiation-cured microtruss structures and methodology are described by Jacobsen et al. in “Compression behavior of micro-scale truss structures formed from self-propagating polymer waveguides”, Acta Materialia 55, (2007) 6724-6733, the entire disclosure of which is hereby incorporated herein by reference. One particular method and system of creating radiation-cured structures is disclosed by Jacobsen in U.S. Pat. No. 7,382,959, the entire disclosure of which is hereby incorporated herein by reference. Further radiation-cured structures are disclosed by Jacobsen in U.S. patent application Ser. No. 11/801,908, the entire disclosure of which is hereby incorporated herein by reference.
Typically, the radiation-cured structures are formed from radiation-sensitive materials such as radiation-curable materials and radiation-dissociable materials. The radiation-cured structure is generally formed by a method including the steps of: providing the radiation-sensitive material; placing a mask between an at least one radiation source and the radiation-sensitive material, the mask having a plurality of substantially radiation-transparent apertures formed therein; and exposing the radiation-sensitive material to a plurality of radiation beams through the radiation-transparent apertures in the mask. The apertures of the mask may be selected to provide different radiation cured structures. To form complex or multi-layered radiation cured structures, different masks having different apertures are generally sequentially applied. Undesirably, masks must be removed following radiation exposure so that further radiation-cured structure may be fabricated. Since masks typically are placed in physical contact with the radiation-sensitive material, the masks must also be cleaned after use in order to remove residual radiation-sensitive material. Although it is possible to achieve multiple radiation exposures through repeated release and application of masks, this methodology can be quite complicated and costly.
There is a continuing need for an efficient and cost effective system and method for fabricating radiation-cured structures. Desirably, the system and method provide complex radiation-cured structures without employing costly and inefficient masking techniques, processing steps, and cleaning steps.