Proton Exchange Membrane (PEM) fuel cells are the most versatile of all fuel cell types. This versatility is due to their high power densities, modular construction, relatively low operating temperature (between 40°C and 100°C) and the solid polymer electrolyte.
The electrolyte used in PEM is poly-perfluorosulphonic acid and the electrochemical reaction at the anode and cathode is as follows:
Anode reaction: H2 → 2H+ + 2e-
Cathode reaction: O2 + 4H+ + 4e- → 2H2O
Advantages of PEM fuel cells
Some fuel cell technologies are only applicable to certain applications. PEM technology is suitable to a very wide range of applications for the following reasons:
Robust PEM cells contain a solid (rather than liquid) electrolyte and so are less sensitive to shock and vibration than other fuel cell types. As a result, PEM technology is better suited to portable and motive applications.
High power density PEM fuel cells have a higher power density than all other fuel cell types and therefore can be more compact. As a result they are more suitable for applications where lower volume or weight are critical factors.
Lower cost of fabrication PEM fuel cells operate at relatively low temperatures (typically 80°C and lower). As a result, less exotic materials can be used making PEM cells more suitable for mass market applications.
Rapid load following capability PEM fuel cells can vary their output quickly to meet shifts in power demand and are suited for applications where quick start-up and high power quality is required. This responsiveness is important, not only for the demands of transport applications and the need for acceleration/deceleration etc. but also for stationary applications such a residential CHP (combined heat and power).
Efficient A PEM fuel cell system can exceed 90% overall efficiency when in CHP mode, with electrical efficiency typically around 50%. This compares to 35% efficiency for central electricity generation plants and around 20% for a typical automotive internal combustion engine.
Applications of PEM fuel cells
PEM fuel cells have the potential for application in all forms of power generation, including:
The first viable electric alternative to the internal combustion engine for vehicles, e.g. cars, motorbikes, buses, locomotives, forklifts, light aircraft and UAVs.
On board auxiliary power units (APUs) for land and air transportation.
Decentralised power generation for industrial and domestic applications.
Portable generation systems for domestic, industrial, military and maritime application.
Small scale power packs for remote, unattended and military application.
General battery replacement/displacement.
