Batteries & Fuel cells





 

Disposable batteries

ChemistryAnode (−)Cathode (+)Nominal voltage
(V)		Specific energy
(MJ/kg)
Zinc–carbonZnMnO21,20,13
Alkaline (zinc–manganese dioxide)ZnMnO21,150.4–0.59
Lithium (lithium–iron disulphide) LiFeS2LiFeS21,51,07
Zinc–airZnO21,11.59
Silver-oxide (silver–zinc)ZnAg2O1,50,47

Rechargeable batteries

Chemical compoundsCell voltage
(V)		Specific energy
(MJ/kg)
NiCd1,20,14
Lead–acid2,10,14
NiMH1,20,36
NiZn1,60,36
AgZn1.86-1.50,46
Lithium ion4,2-3.60,46

Thermal efficiency - Fuel cells

Fuel Cell TypeOperating TemperatureSystem OutputEfficiencyApplications
Alkaline (AFC)90–100oC
(194–212oF)		10kW–100kW60–70% electric• Military
• Space
Phosphoric Acid (PAFC)150–200oC
(302–392oF)		50kW–1MW
(250kW module typical)		80–85% overall with combined heat and
power (CHP) (36–42% electric)		• Distributed generation
Polymer Electrolyte Membrane or Proton Exchange Membrane (PEM)*50–100oC
(122–212oF)		<250kW50–60% electric• Back-up power
• Portable power
• Small distributed generation
• Transportation
Molten Carbonate (MCFC)600–700oC
(1112–1292oF)		<1MW
(250kW module typical)		85% overall with CHP (60% electric)• Electric utility
• Large distributed generation
Solid Oxide (SOFC)650–1000oC
(1202–1832oF)		5kW–3 MW85% overall with CHP (60% electric)• Auxiliary power
• Electric utility
• Large distributed generation
The table indicates the thermal efficiency for various types of fuel cells based on the higher heating value for hydrogen.

Gibbs free energy - Fuel cells

Form of water productTemp oC∆g ̄f kJ/moleMax EMFEfficiency limit
Liquid25-237,21.23V83 %
Liquid80-228,21.18V80 %
Gas100-225,31.17V79 %
Gas200-220,41.14V77 %
Gas400-210,31.09V74 %
Gas600-199,61.04V70 %
Gas800-188,60.98V66 %
Gas1000-177,40.92V62 %
The table above indicates the amount of free energy by applying Gibbs function at various states.