The document summarizes fuel cells and provides details about phosphoric acid fuel cells (PAFC). It states that fuel cells directly convert the chemical energy of a fuel into electricity through an electrochemical reaction with oxygen without combustion. PAFC were an early commercial type of fuel cell that uses phosphoric acid as an electrolyte and operates at 150-200°C. The document describes the basic components and chemical reactions of PAFC and compares them to polymer electrolyte membrane fuel cells.