Fuel Cells
Fuel cells generating efficient electricity and heat
Fuel Cells are regarded by many to provide a tangible alternative to an oil based economy. Newform Energy has undertaken many years of research into the viability of Hydrogen and fuel cells and have an in depth knowledge of fuel cell systems.
The Fuel Cell market is evolving at pace with economic solutions for energy storage promised in the near future. There are several systems available at present primarily for UPS and stand alone applications with companies offering solutions for applications of just a few watts to mega watts.
How they work
A fuel cell contains an anode and a cathode insulated by an electrolyte between them. Hydrogen is supplied to the anode while oxygen is supplied to the cathode. The two gases try to join, but because of the electrolyte, the hydrogen atom splits into a proton and electron allowing the proton to pass freely through the electrolyte whilst the electron takes a different route, creating an electric current before recombining with the hydrogen and oxygen, creating a molecule of water. This chemical process generates electrical and thermal energy with 100% pure water as its only by-product.
There are five main categories of fuel cell:
PEM's (Proton Exchange Membranes) operating temp 40 - 80 ºC. They are being developed primarily for automotive use however there are cost benefits associated with this technology as the membranes used are generally made from fluorinated sulfonic acid polymer or similar polymers and therefore lend themselves to mass manufacture. There low running temperature also makes them ideal for use for domestic applications.
One downside to this technology is that they are very susceptible to impurities in the hydrogen gas they run on and there life span can be seriously reduced if other chemicals such as CO2, sulfur and ammonia are present.
AFC (Alkaline Fuel Cell) operating temp 65 - 220 ºC. These fuel cells have excellent perform when using pure hydrogen and oxygen compared to other fuel cells.
Due to the necessity for pure gasses and the removal of any CO and CO2 from the system these systems are largely cost prohibitive.
PAFC (Phosphoric Acid Fuel Cell) operating temp 150 -220ºC. This type of fuel cell has had the most success in the field with up to 30 years lifespan. They are more durable than the PEM's and are not as effected by the possible presence of impurities, however development of these has slowed in favor of PEM's due to their mass manufacturing potential.
Although PAFC have enjoyed much success in the field the highly corrosive nature of phosphoric acid requires the use of expansive materials in there construction.
MCFC (Molten Carbonate Fuel Cell) operating temp 600-700ºC. MCFC are highly efficient with up to 60% efficiency possible. They are cheaper to produce than most fuel cells and have the capability on running on certain hydrocarbons making them attractive for system integration into existing power distribution networks.
The main challenge for these fuel cells include a corrosive and mobile electrolyte and higher stack temperatures promote material problems, impacting mechanical stability and stack life.
SOFC (Solid Oxide Fuel Cell) operating temp 600-700ºC. SOFC have many applications including stationary power generation, mobile power and auxiliary power for vehicles and specialty applications including uses in space exploration. These fuel cells have the longest continuous development period, starting in the late 1950's. The electrolyte is solid therefore the cell can be cast in various shapes and the solid construction of the unit cell alleviates any corrosion problems. The materials used in the construction of these cells are modest in cost and have been shown to show power densities close to those of PEM's. SOFC offer the same resistance to impurities as MOFC and for this reason can be used with many hydrocarbons and due to their high operating temperature offer the potential to be used for cogeneration purposes greatly increasing there overall efficiency. When recovering the heat in this manner operating efficiencies of >80% can be achieved with a nominal operating efficiency of >50%.
The high operating temperatures of these cells has its drawbacks and results in difficult fabrication processes. Thermal cycling can lead to degradation of the cell and reduction in the useful life of the cell.
For a downloadable PDF containing more information about Fuel Cells click here.
