2What is Fuel CellA fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity, with water and heat as its by-product. As long as fuel is supplied, the fuel cell will continue to generate power. Since the conversion of the fuel to energy takes place via an electrochemical process, not combustion, the process is clean, quiet and highly efficient – two to three times more efficient than fuel burning.
3Construction and Working A fuel cell consist of following parts:Two electrodes(Anode and Cathode)Two catalyst layerAn electrolyteThe two electrodes sandwiched around an electrolyte. Their is an catalyst layer between electrodes and electrolyte.
4Types of Fuel Cells Fuel Cells are of following types : Proton Exchange Membrane Fuel CellAlkaline Fuel CellDirect Methanol Fuel CellPhosphoric Acid Fuel CellMolten Carbonate Fuel CellSolid Oxide Fuel CellMicrobial Fuel CellZinc Air Fuel Cell
6PEMFC PEMFC operated at low temperature of 50 to 100 °C. Efficiencies of PEMs are in the range of 40–60%.ReactionsAt the Anode:At the Cathode:Overall reaction:This reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack.
7Alkaline FC(AFC)The alkaline fuel cell (AFC), also known as the Bacon fuel cell after its British inventor, is one of the most developed fuel cell technologies and is the cell that flew Man to the Moon.Alkaline fuel cells use potassium hydroxide (KOH) as the electrolyte and operate at 160°F.Alkaline fuel cells can achieve power generating efficiencies of up to 70 percent.The fuel cell produces power through a redox reaction between hydrogen and oxygen.ReactionsAt Anode:At Cathode
8Direct Methanol Fuel Cell Direct-methanol fuel cells or DMFCs are a subcategory of proton-exchange fuel cells in which methanol is used as the fuel.In the DMFC, the anode catalyst itself draws the hydrogen from the liquid methanol, eliminating the need for a fuel reformer.Efficiencies of about 40% .This is operated at a temperature between °F.ReactionsAt AnodeAt CathodeOverall reaction
9Phosphoric Acid Fuel Cell Phosphoric acid fuel cells use liquid phosphoric acid as the electrolyte and operate at about 450°F.PAFCs generate electricity at more than 40% efficiency - and nearly 85% of the steam this fuel cell produces is used for cogeneration.One of the main advantages to this type of fuel cell, besides the nearly 85% cogeneration efficiency, is that it can use impure hydrogen as fuel.ReactionsAt the Anode:At the Cathode:Overall reaction:
10Molten Carbonate Fuel Cell Molten carbonate fuel cells use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert matrix, and operate at high temperatures - approximately 600°C.Molten carbonate fuel cells can reach efficiencies approaching 60 %.The electrochemical reactions occurring in the cell are:At the anode: H2 + CO H2O + CO2 + 2e-At the cathode: l/2O2 + CO2 + 2e CO3The overall cell reaction: H2 + l/2O2 + CO H2O + CO2
11Solid Oxide Fuel CellSolid oxide fuel cells use a hard, non-porous ceramic compound as the electrolyte, and operate at very high temperatures between 500 and 1,000 °C.SOFCs are suitable for stationary applications as well as for auxiliary power units (APUs) used in vehicles to power electronics.SOFCs use a solid oxide electrolyte to conduct negative oxygen ions from the cathode to the anode.The electrochemical reactions occurring within the cell are: At the anode: 1/2 O2 + 2e O At the cathode: H2 + 1/2O H2O + 2e-The overall cell reaction:l/2O2 + H H20
12Microbial Fuel CellMicrobial fuel cells use the catalytic reaction of microorganisms such as bacteria to convert virtually any organic material into fuel.It could be capable of producing over 50% efficiency.When micro-organisms consume a substrate such as sugar in aerobic conditions they produce carbon dioxide and water. However when oxygen is not present they produce carbon dioxide, protons and electrons asMFCs could be installed to wastewater treatment plants. The bacteria would consume waste material from the water and produce supplementary power for the plant.C12H22O H2O ---> 12CO2 + 48H+ + 48e
13Zinc Air Fuel CellIn a zinc air fuel cell, there is a gas diffusion electrode (GDE), a zinc anode separated by electrolyte, and some form of mechanical separators. The GDE is a permeable membrane that allows atmospheric oxygen to pass through.The electrolyte for a ZAFC is a ceramic solid that employs the hydroxyl ion, OH-, as the charge carrier. ZAFC operates at 700ºC.Anode Reaction:CH4 + H2O CO2 + 6H+ + 6e- Zn + OH ZnO + H + e-Cathode Reaction:O2 + 2H+ + 2e OH- O2 + 4H+ + 4e H2OOverall Cell Reaction:CH4 + 2O CO2 + 2H2O
14From Where Hydrogen Come There are three main methods of hydrogen generation. All three separate the hydrogen from a 'feedstock', such as fossil fuel or water - but by very different means.ReformsEnzymesSolar- and Wind- powered generation
15Hydrogen Safety Hydrogen is safe due to following factors: Hydrogen's carbon fiber composite tanksHydrogen possesses a density only 7% that of air, and has a high buoyancy so that it will rise and dissipate without wind or ventilation.If combusted, a fuel cell vehicle's hydrogen would generate less thermal energy than the comparable amount of gasoline.The hydrogen gas would also burn quicker has a burning velocity 7 times greater than natural gas or gasoline. The result could be a quick plume of fire that does not cause as much damage as a gasoline fire.
16Applications of Fuel Cells StationaryTelecommunicationWastewater Treatment PlantsTransportPortable powerMicro Power
17Benefits of Fuel Cells Benefits for Vehicles: Internal combustion engine converts about 16% of energy in gasoline to turn car’s wheels.Fuel cell efficiency 40 to 50 percent.Less maintenance costsBenefits for Our Health:Reduced local air and noise pollution, groundwater contamination.Benefits for Planet:25% human generated greenhouse gases come from transportation and fuel cells do not generate the greenhouse gases.Reduced motor oil spills.