HT-PEM technology

High-temperature polymer electrolyte membrane (HTPEM) fuel cells are one of a number of different fuel cell technologies being developed and marketed today, including, low-temperature PEM (LTPEM), solid-oxide (SOFC), and alkaline fuel cells (AFC).

The membrane/electrolyte material is one of the main elements that categorizes fuel cells. It is the membrane assembly which often dictates the fuel quality, operating temperature range, durability and preferable applications of a fuel cell. HTPEM fuel cells are based on the use of polybenzimidazole (PBI) membranes doped with phosphoric acid for proton conduction. It is this membrane construction which allows HTPEM to operate at temperatures above that of the more common LTPEM. The Nafion membranes, used in LTPEM, rely on liquid water for proton conduction, thus limiting operation to approx. 80ºC.

The operating temperature range of 100-180ºC (130-170ºC recommended) for HTPEM is one characteristic which gives many advantages. It leads to:

• Higher tolerance to impurities such as CO. Up to 5% CO is manageable, depending on the corresponding hydrogen concentration. This makes operation on reformate systems without large gas clean-up systems a reality.
• Simple system designs, since the fuel cell can be air-cooled, with a combined cathode supply and cooling circuit. This minimizes the balance of plant components and complicated control systems, increasing system efficiency while at the same time decreasing system volume.
• Increased reaction kinetics, improving performance.
• High-quality waste heat which can be used effectively in CHP systems.
   

In the larger picture, there are some practical issues which are also avoided through the use of HTPEM fuel cell systems:

• The high CO tolerance makes the combination of HT-PEM fuel cells with reformer systems a realistic option. This means the use of fuel cells in everyday applications need not wait for the implementation of pure hydrogen production, transport and storage infrastructure.
• Pre-heating times for HTPEM vary greatly depending on the method used (minutes to multiple hours), but the system can be hibernated and be ready to operate instantly (with backup power systems) if required or can easily be inserted into hybrid systems where batteries can supply the initial power requirements.
• Atmospheric air is the preferred cathode supply and will always be readily available. The limitation of requiring pure oxygen or at least purified air, as with alkaline fuel cells, does not exist with HT-PEM.