Phosphoric acid fuel cells (PAFCs) consist of an anode and a cathode made of a finely dispersed platinum catalyst on carbon and a silicon carbide structure that holds the phosphoric acid electrolyte. They are quite resistant to poisoning by carbon monoxide but tend to have lower efficiency than other fuel cell types in producing electricity. However, these cells operate at moderately high temperatures of around 180ºC and overall efficiency can be over 80% if this process heat is harnessed for cogeneration.
Phosphoric Acid Fuel Cells have a liquid phosphoric acid electrolyte, are suited for medium to large-scale stationary combined heat & power, and require hydrogen as a fuel. This hydrogen is usually generated by reforming light hydrocarbon fuels such as natural gas.
Phosphoric acid fuel cells are the most mature fuel cell technology, with over 200 units installed and currently operating in banks, hotels, hospitals and police stations. Whilst still requiring hydrogen, PAFC technology has the additional benefit in that is it more tolerant to impurities, in particular reformed hydrocarbon fuels. PAFC technology operates at between 150ºC and 220ºC with an electrical efficiency of between 37% & 42% – this rises to 85% with co-generation (CHP/CCP)
Anode Reaction: 2 H2 »» 4 H+ + 4 e–
Cathode Reaction: O2(g) + 4 H+ + 4 e– »» 2 H2O
Overall Cell Reaction: 2 H2 + O2 »» 2 H2O