according to the kind of electrolyte used , fuel cells are categorized into five types : phosphoric acid fuel cell -lrb- pafc -rrb- , molten carbonate fuel cell -lrb- mcfc -rrb- , solid oxide fuel cell -lrb- sofc -rrb- , polymer electrolyte fuel cell -lrb- pefc -rrb- , and alkaline fuel cell -lrb- afc -rrb- .