Low elution materials for Fuel CellsEnergy and storage

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.

See also: Agency for Natural Resources and Energy, Japan Ministry of Economy, Trade and Industry

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.​

See also: Agency for Natural Resources and Energy, Japan Ministry of Economy, Trade and Industry

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

   

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.

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.