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SDK Develops Bipolar-Type Carbon Separators for PEFCs

Published on 2009-07-28. Author : SpecialChem

Showa Denko K.K. (SDK) has developed new technologies to produce low-cost carbon separators that will increase output density of polymer electrolyte fuel cells (PEFCs). Specifically, SDK has established technologies to produce carbon separators with lower cost and lighter weight by making substantial changes in the process and raw materials. At the same time, SDK has achieved an increase of around 30% in output density compared with PEFCs made earlier by SDK on a trial basis. These technical developments have been supported by the New Energy and Industrial Technology Development Organization (NEDO).

PEFCs generate power through chemical reactions of hydrogen and oxygen, contributing to the reduction of CO2 emissions and enabling the production of compact and lightweight cells. Thus, PEFCs are expected to be widely used as power sources for vehicles, mobile devices and homes. While PEFCs consist of unit cells connected in a series, separators are used to divide each cell, completely separate and control the flows of hydrogen and oxygen gases, and efficiently conduct electricity generated by the cells. To increase the use of PEFCs, we need to develop separators with high mechanical strength, corrosion resistance and productivity in addition to high gas-barrier and high conductivity characteristics.

To achieve high mechanical strength and conductivity of separators, SDK has established a technology to bond two boron-added carbon sheets with high precision by heating a specialty adhesive resin. Based on this technology, SDK has developed a new "bipolar-type" carbon separator that integrates the anode side (along which the hydrogen gas flows), the cathode side (along which the oxygen gas flows), and cooling-water channels (for removal of heat resulting from chemical reactions). Compared with our conventional carbon separators that are bonded with auxiliary parts, the new "bipolar-type" carbon separators have the following advantages:
  1. The packing process for sealing the cooling-water channels between the two separator sheets can be eliminated.
  2. The contact resistance involving two separator sheets can be reduced to 1/10 or less.
  3. The wall thickness can be reduced to approximately 0.1 mm as a result of the integrated structure and accompanying reinforcement effect.
  4. Gas diffusion can be facilitated by longstanding hydrophilic treatment, which encourages drainage of water (resulting from chemical reactions) from the separator surface.

Due to the above advantages, the output of PEFCs can be increased by around 30% compared with conventional types. Furthermore, SDK has developed a new collector (an electrode for taking out electric current from both ends of the cells laminated in a series), based on press molding of proprietary graphite with high conductivity and packing property. The new collector has conductivity equal to that of a sintered-carbon-based collector, and is lower in cost than collectors based on precious-metal-plated metallic sheets or sintered carbon sheets. Thus, the new collector has partially been adopted in PEFCs for home use.

Under the Passion Extension business plan for 2009 and 2010, SDK is stepping up its R&D efforts pertaining to environmental-protection and energy-conservation technologies to meet increasing social demand.

SDK will continue developing and commercializing components for PEFCs, fully utilizing its rich stock of inorganic/metal and organic chemical technologies.

Source: SDK

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