The PEMFC, also known as the solid polymer fuel cell (SPFC), is different from most other fuel cell types as its electrolyte consists of a layer of solid polymer across which protons are transmitted.
It generally requires hydrogen and oxygen as its inputs, though the oxidant may also be ambient air; the input gases must be humidified.
It has a high power density, a rapid start-up and operates at low temperatures (80-100°C), due to the limitations imposed by the thermal properties of the membrane itself.
In order for the reactions to take place at the low temperatures of a PEMFC, catalysts are required; the most commonly used are platinum and other noble metals.
PEMFCs are highly sensitive to carbon monoxide, which preferentially reacts with catalyst inactivating it; this phenomenon is usually referred to as catalyst poisoning and reduces the performance by several percent for contaminant in the fuel in ranges of tens of ppm.
There are a number of companies involved in manufacturing PEMFCs. Ballard are probably the leaders, though companies such as DeNora in Italy and Siemens are progressing fast.
The main focus of current designs is transport applications, where PEMFC are attractive for several reasons:
- a solid electrolyte is safer than a molten, high temperature one:
- the heat produced by the fuel cell is not adequate for any form of cogeneration
- a fast start-up is required in vehicles
Daimler-Benz has taken a high profile in developing cars powered by Ballard fuel cells, while Toyota has recently presented vehicles that use fuel cells of proprietary design. Other car manufacturers, including General Motors and Ford, are actively engaged in similar developments.
In addition it appears that there is a possibility of using PEMFCs in small scale localised power generation, where the low temperature heat could be used for hot water or space heating. Such waste heat could also drive chiller units, thus providing opportunities for cooling and air conditioning.
If it does prove possible to use this particular type of fuel cell for both transport and power generation, then the advantages generated by economies of scale and synergy between the two markets could make the introduction of the technology easier than in other cases.
For further information contact David Hart (email: firstname.lastname@example.org) from E4tech