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ALKALINE CELL

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Alkaline Fuel Cells (AFC) Alkaline fuel cells (AFC) are one of the most developed technologies and have been used since the

mid-1960s by NASA in the Apollo and Space Shuttle programs. The fuel cells on board thesespacecraft provide electrical power for on-board systems, as well as drinking water. AFCs are amongthe most efficient in generating electricity at nearly 70%.

Alkaline fuel cells use an electrolyte that is an aqueous (water-based) solution of potassium hydroxide(KOH) retained in a porous stabilized matrix. The concentration of KOH can be varied with the fuelcell operating temperature, which ranges from 65C to 220C. The charge carrier for an AFC is thehydroxyl ion (OH-) that migrates from the cathode to the anode where they react with hydrogen to

produce water and electrons. Water formed at the anode migrates back to the cathode to regeneratehydroxyl ions. Therefore, the chemical reactions at the anode and cathode in an AFC are shownbelow. This set of reactions in the fuel cell produces electricity and by-product heat.

Anode Reaction: 2 H2 + 4 OH- => 4 H2O + 4 e

- Cathode Reaction: O2 + 2 H2O + 4 e- => 4 OH- Overall

Net Reaction: 2 H2 + O2 => 2 H2O One characteristic of AFCs is that they are very sensitive to CO2that may be present in the fuel or air. The CO2 reacts with the electrolyte, poisoning it rapidly, andseverely degrading the fuel cell performance. Therefore, AFCs are limited to closed environments,such as space and undersea vehicles, and must be run on pure hydrogen and oxygen. Furthermore,molecules such as CO, H2O and CH4, which are harmless or even work as fuels to other fuel cells,are poisons to an AFC.

On the positive side, AFCs are the cheapest fuel cells to manufacture. This is because the catalyst

that is required on the electrodes can be any of a number of different materials that are relativelyinexpensive compared to the catalysts required for other types of fuel cells. AFCs are not being considered for automobile applications. Their sensitivity to poisoning, which

requires use of pure or cleansed hydrogen and oxygen, is an insurmountable obstacle at the presenttime. Conversely, AFCs operate at relatively low temperatures and are among the most efficient fuelcells, characteristics that would enable a quick starting power source and high fuel efficiency,respectively.

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ADVANTAGES OF ALKALINEADVANTAGES OF ALKALINE

CELLCELL

Portable

More long-lasting

Longer than the dry cell Voltage produced is more constant

Voltage of 1.5V

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DISADVANTAGES OF ALKALINE

CELL

Expensive

Not rechargeable

May leak