FUEL CELL

What is Fuel Cell A 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.

Construction and Working A fuel cell consist of following parts: Two electrodes(Anode and Cathode) Two catalyst layer An electrolyte The two electrodes sandwiched around an electrolyte. Their is an catalyst layer between electrodes and electrolyte.

Types of Fuel Cells Fuel Cells are of following types : Proton Exchange Membrane Fuel Cell Alkaline Fuel Cell Direct Methanol Fuel Cell Phosphoric Acid Fuel Cell Molten Carbonate Fuel Cell Solid Oxide Fuel Cell Microbial Fuel Cell Zinc Air Fuel Cell

Proton Exchange Membrane F C (PEM)

PEMFC PEMFC operated at low temperature of 50 to 100 °C. Efficiencies of PEMs are in the range of 40–60%. Reactions At 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.

Alkaline 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. Reactions At Anode: At Cathode

Direct 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 120-190°F. Reactions At Anode At Cathode Overall reaction

Phosphoric 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. Reactions At the Anode: At the Cathode: Overall reaction:

Molten 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 + CO3 H2O + CO2 + 2e- At the cathode: l/2O2 + CO2 + 2e- CO3 The overall cell reaction: H2 + l/2O2 + CO2 H2O + CO2

Solid Oxide Fuel Cell Solid 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 + H2 H20

Microbial Fuel Cell Microbial 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 as MFCs could be installed to wastewater treatment plants. The bacteria would consume waste material from the water and produce supplementary power for the plant. C12H22O11 + 13H2O ---> 12CO2 + 48H+ + 48e

Zinc Air Fuel Cell In 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- 2 OH- O2 + 4H+ + 4e- 2 H2O Overall Cell Reaction: CH4 + 2O2 CO2 + 2H2O

From 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. Reforms Enzymes Solar- and Wind- powered generation

Hydrogen Safety Hydrogen is safe due to following factors: Hydrogen's carbon fiber composite tanks Hydrogen 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.

Applications of Fuel Cells Stationary Telecommunication Wastewater Treatment Plants Transport Portable power Micro Power

Benefits 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 costs Benefits 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.

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