5 A Fuel Cell Converts Chemical Energy to Electrical Energy HydrogenAir or OxygenLoadAnodeCathodeElectrolytee-Gas Diffusion LayerGas Diffusion LayerH+CatalystCatalyst
6 The Electrical Energy is in the form of DC voltage The voltage is usually between 0.5 and 1.0 volts DC (direct current).Several fuel cells are connected together in series to obtain higher voltages 25—100 volts.These fuel cells connected in series are called stacks.The fuel cell stacks still give DC voltage.
7 An Inverter is used to change the DC voltage to AC voltage (alternating current). Direct Current (DC) has a voltage that is always in one direction.DC voltage is the kind of voltage that comes from a battery.Alternating Current (AC) has a voltage that varies from positive to negative 60 times/second (50 times/second in Europe).Normal household current is AC.
9 Each type of fuel cell is particularly suited to certain applications: PEM: most versatile, used for portable power, transportation, and stationary powerDMFC: used for portable powerSOFC: primarily used for stationary power, in development for transportation (e.g. semi trucks)MCFC: power plantsAFC: power and water production for space vehicles (e.g. Apollo and Space Shuttle spacecrafts), in development for more general usePAFC: stationary power, power plants
10 Each type of fuel cell has particular advantages and disadvantages PEM & DMFC: solid construction, low temperature, sensitive to impurities, can only be used with hydrogen or methanol.SOFC: can be used with many fuels, doesn’t require precious metal catalysts, solid, rugged, very high temperature, expensive materials.MCFC: can be used with many fuels, efficient, doesn’t require precious metal catalysts, high temperature, very corrosive electrolyte.AFC: most efficient medium for oxygen reaction - high performance, doesn’t require precious metal catalysts, sensitive to carbon dioxide, caustic medium.PAFC (phosphoric acid fuel cell): same electrochemical reactions as PEM, but not as sensitive to impurities in the fuel, very corrosive.
11 Advantages PEM & DMFC: solid construction, low temperature SOFC: can be used with many fuels, doesn’t require precious metal catalysts, solid, rugged, very high temperature (high enough for power generation)
12 AdvantagesMCFC: can be used with many fuels, efficient, doesn’t require precious metal catalysts, high temperature (high enough for power generation)AFC: most efficient medium for oxygen reaction - high performance, doesn’t require precious metal catalystsPAFC (phosphoric acid fuel cell): same electrochemical reactions as PEM, but not as sensitive to impurities in the fuel
13 DisadvantagesPEM & DMFC: low temperature (low grade energy), must have pure hydrogen.SOFC: very high temperature, expensive materials.MCFC: liquid, high temperature , very corrosive electrolyteAFC: liquid, sensitive to carbon dioxide, caustic medium, low temperature (low grade heat)PAFC: liquid, very corrosive, low temperature, (low grade heat)
14 Typical fuel cells run on hydrogen and oxygen Methane, methanol, and other hydrogen containing compounds can be reformed to make hydrogen.Air is usually used instead of pure oxygen.
17 Source: Thampan, PEM Fuel Cell as a Membrane Reactor
18 PEM or DMFC Fuel Cell Components CCM (Catalyst Coated Membrane): Proton-conducting membrane plus 2 electrodesGDL (Gas Diffusion Layer): Carbon cloth or paper with carbon particle filler and TeflonAnode and Cathode plate: Graphite, carbon composite or metal with machined or stamped ‘flow field’Gaskets and seals: seals around edge of structure
20 MCFC ComponentsAnode is a highly porous sintered nickel powder, alloyed with chromiumElectrolyte is a liquid in a lithium—Aluminum Oxide matrixCathode is a porous nickel oxide material doped with lithium.
21 AFC Components Electrodes: >porous (and catalyzed) graphite electrodes>semi-permeable, Teflon coated carbonmaterial>heavily catalyzed as compared with othertypes of fuel cellsElectrolyte: potassium hydroxide (KOH) solution retained in a porous stabilized matrix
22 PAFC ComponentsElectrodes: porous carbon containing Pt or its alloys as catalystsElectrolyte: liquid phosphoric acid in Teflon-bonded silicon carbide matrix