Fuel Cell Technologies
There are five different major fuel cell technologies. UTC Power is the only manufacturer with experience working with all five. A fuel cell type is determined by the composition of the electrolyte in the middle of the fuel cell. An explanation of each type of fuel cell and its attributes are below:
- Phosphoric Acid Fuel Cells (PAFCs)
- Proton Exchange Membrane Fuel Cells (PEM)
- Alkaline Fuel Cells
- Solid Oxide Fuel Cells (SOFCs)
- Molton Carbonate Fuel Cells (MCFCs)
Phosphoric acid fuel cells (PAFCs)
Phosphoric acid fuel cell technology is proven and reliable for on-site combined heat and power (CHP) applications. PAFCs are highly efficient - a total efficiency of 90 percent is achievable when the process heat produced by the fuel cell is fully utilized. They are a relatively new fuel cell technology, with development beginning in the 1960's (compared to solid oxide and molten carbonate fuel cells, which trace their development back to the 1930's and 1950's respectively). PAFCs were the first fuel cells commercialized for stationary applications and have benefited from 20+ years of field experience, technology improvements and cost reduction. UTC Power's stationary fuel cell power plants - from the first generation model produced in 1991 to the latest generation PureCell system (the Model 400) released in 2009 - use PAFC technology.
Proton exchange membrane (PEM) fuel cells
PEM fuel cells, also known as polymer electrolyte membrane fuel cells, deliver high power density and offer the advantages of low weight and volume compared to other fuel cells. These fuel cells also operate at relatively low temperatures, around 175°F, which allows them to start quickly (less warm-up time), making them particularly well suited for transportation applications (such as automobiles and fleet vehicles), materials handling equipment (such as forklifts), and for backup power.
Alkaline fuel cells (AFCs)
One of the oldest fuel cell types, alkaline fuel cell power plants were initially developed by UTC Power for the Apollo missions. An updated version was produced and is still in use to provide electrical power and potable water in today's Space Shuttle fleet. These power plants use a porous matrix saturated with potassium hydroxide for the electrolyte. AFCs are very efficient, reaching efficiencies of 60% in space applications. However, AFCs are susceptible to carbon contamination, so they require pure hydrogen and oxygen. This characteristic limits the terrestrial applications of the technology
Solid oxide fuel cells (SOFCs)
Solid oxide fuel cells use a thin sheet of hard, non-porous ceramic compound as the electrolyte. SOFCs operate at very high temperatures — around 700 - 800°C, which results in a long startup time compared to other technologies. They can achieve electrical efficiencies over 50% and total system efficiencies of 65-70% if their heat is recaptured for co-generation purposes. The combination of brittle materials and high operating temperatures has limited the durability of SOFCs.
Molten carbonate fuel cells (MCFCs)
Molten carbonate fuel cells use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO2) matrix. These systems are large and operate at very high temperatures (in the range of 650°C). They are very efficient when the heat produced is used for co-generation. However, because the electrolyte used in MCFC fuel cells is corrosive, their durability is limited.