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Low elution materials for Fuel Cells Renew energy and storage

Summary

  • Fuel cells (FCs) are next-generation batteries that generate electricity by reacting hydrogen with oxygen to produce water.
  • Although fuel cells pose some practical challenges, including high costs and the need for infrastructure installations, they have the key advantage of being a clean technology—in the sense that their use generates no CO2 emissions—and are expected to find many applications in both automobile and stationary uses.
  • Materials for FCs must offer low ion elution, resistance to hydrolysis, and high heat resistance.
  • Asahi Kasei recommends our XYRONTM 500H modified polyphenylene ether (m-PPE) resin for use in fuel cells.

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What are fuel cells?

Operating principles and practical advantages of fuel cells

Fuel cells are batteries that generate electricity by reacting hydrogen with oxygen to produce water. Fuel cells offer the potential to assist in reducing the use of carbon by serving as a basic means of hydrogen utilization, thus helping to realize the much-discussed hydrogen societies of the future.

 

Hydrogen energy has the key advantage of being clean: its use generates no carbon-dioxide emissions. Hydrogen allows storage in the form of secondary energy, is highly energy-efficient, and may be used to generate heat or electric power. Although energy is required to produce hydrogen, the potential to make effective use of reusable energy sources, underutilized energy sources, or excess power resources suggests that fuel cells may accelerate the transition to the low-carbon societies of the future.

In fuel cells, the hydrogen that constitutes the fuel is supplied externally, and the electrical energy obtained by causing this hydrogen to react electrochemically with atmospheric oxygen is extracted in the form of electric power. In principle, fuel cells generate power by reversing the process of water electrolysis. When hydrogen atoms come into contact with the fuel electrode (negative electrode), they release electrons and become hydrogen ions. The released electrons flow to the air electrode (positive electrode), generating an electric current. Meanwhile, hydrogen ions generated at the fuel electrode proceed through an electrolyte to recover electrons at the air electrode by combining with oxygen to form water.

Structure of a fuel cell. Source: Produced by Asahi Kasei based on the website of the Agency for Natural Resources and Energy within Japan’s Ministry of Economy, Trade and Industry

Structure of fuel cells

The section of a fuel cell in which electrical energy is generated is called the stack. The stack consists of multiple cells, layered one atop the other; each cell contains a separator providing a flow pathway for hydrogen and oxygen and a membrane electrode assembly (MEA) consisting of catalyst layers, electrolyte layers, gas diffusion layers, and a sealing structure.

Four types of fuel cells and their unique characteristics

Fuel cells may be classified into four categories, each with characteristic behavior in areas such as power-generation efficiency and operating temperature, based on the type of electrolyte used.

 

  • Phosphoric-acid fuel cells (PAFCs)
    In PAFCs, the electrolyte consists of a separator immersed in an aqueous solution of phosphoric acid. Cells of this type have an extensive track record of operation in environments such as factory co-generation systems, but they suffer from the drawback of high cost due to the use of platinum catalysts.

 

  • Polymer-electrolyte fuel cells (PEFCs)
    PEFCs use ion-exchange membranes as electrolytes. Although PEFCs are expensive due to the use of platinum catalysts, their low operating temperatures—ranging from room temperature to around 90°C—and potential for miniaturization make them well-suited for a range of applications, including as stationary household cells, automobile cells, or portable cells.

 

  • Molten-carbonate fuel cells (MCFCs)
    MCFCs use carbon ions as fuel and molten carbonates as electrolytes. These cells have high operating temperatures, on the order of 700°C, and offer promise for use as backup or substitute cells in settings such as thermoelectric power plants and factory power generators.

 

  • Solid-oxide fuel cells (SOFCs)
    SOFCs use zirconia-based ceramic electrolytes. Although they have the highest operating temperatures of all fuel cells, ranging from 700 to 1,000°C, they also exhibit the highest power-generation efficiency and do not require platinum catalysts, making them relatively inexpensive. SOFCs are also being developed for use as household fuel cells.

Uses of fuel cells

Applications of fuel cells may be divided into two categories: automobile and stationary. Initiatives to promote the adoption of fuel cells are currently being actively pursued both by governments and the private sector, and the present day may prove to be the decisive moment that determines whether or not fuel cells achieve substantial popularity going forward.

Automobile applications

The primary automobile applications of fuel cells are in fuel-cell electric vehicles (FCEVs) and industrial vehicles such as buses, trucks and forklifts.

In general, there remain a number of challenges to be addressed—including high costs and the need for infrastructure investments such as hydrogen stations—and the practical utility of FCEVs is currently being evaluated. In contrast, forklifts and similar vehicles based on fuel cells have already begun to find broad adoption.

Indeed, because forklifts only operate within the restricted spatial area of a factory or warehouse, they require only minimal infrastructure investment; moreover, FCEVs require only a few minutes to be charged with enough hydrogen to operate for several hours, increasing operating efficiency compared to conventional vehicles. Beyond forklifts, fuel cells are also being considered for use in trains, boats, and large commercial vehicles such as buses or trucks that travel between fixed points.

Stationary applications

Stationary fuel cells may be installed as distributed power supplies or backup generators for households, factories, stores, data centers, and other facilities, and are expected to provide power in a wide range of settings. In Japan, residential fuel cells are ahead of commercial and industrial fuel cells, with more than 300,000 units in use to date. Indeed, Japan is far ahead of other nations in promoting the spread of stationary fuel cells. Aspirations for the future include not only further cost reductions but also practical tests of efforts to stabilize the power grid by using fuel cells in concert with the power-generation cycles of renewable energy plants.

Properties required for materials used in fuel cells

As noted above, fuel cells use hydrogen and oxygen to generate electric power. For this reason, fuel-cell stacks are typically surrounded by various peripheral components including ducts, pipes, connectors, and tools such as hydrogen-cycling pumps and compressors that transport large quantities of air to stacks.

 

Because the presence of excess ions may obstruct the transfer of electrons and create risks of malfunction, these peripheral components must be made from materials featuring low ion elution.

 

An additional requirement is that materials be resistant to hydrolysis at high temperatures to avoid problems associated with hydrolysis or thermal degradation due to the water and heat produced as byproducts of power generation.

Asahi Kasei’s Recommended Solutions

XYRON™ 500H modified polyphenylene ether (m-PPE) resin

Asahi Kasei recommends our XYRON™ 500H modified-Polyphenylene Ether (m-PPE) resin as a material for peripheral components of fuel-cell stacks.

Features of XYRON™ 500H

  • Unreinforced, flame-retardant
  • Low elution:
    Minimal elution (of ions, oligomers, etc.) from resin; highly regarded by users.
  • Resistant to hot water and acid:
    Outstanding resistance to hot water and acid; physical properties remain essentially stable even after submersion for extended durations.

Components for fuel cells

For more information, please contact us.

In addition to our XYRONTM 500H modified-Polyphenylene Ether (m-PPE) resin, we offer other materials and grades with extensive track records. For more information, please contact us via the links below.


Please contact us to ask any questions, discuss any concerns, and request samples.

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