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Published byDaniela Goodsell Modified over 9 years ago
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Fuel cell: A device that converts chemical energy into electrical energy. In the hydrogen- oxygen fuel cell, both cathode and anode are made of porous carbon with platinum or palladium. The electrolyte solution used is KOH or NaOH.
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What is the half reaction occurring at the anode? A: 2H 2 (g) + 4OH - (aq) → 4H 2 O (I) + 4e - What is the half reaction occurring at the cathode? A: O 2 (g) + 2H 2 O(I) + 4e - → 4OH - (aq) After cancelling, what is the overall reaction? A: 2H 2 (g) + O 2 (g) → 2H 2 O (I)
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You also need to know the half reactions in acidic conditions: Anode: 2H 2 (g) → 4H + (aq) + 4e - Cathode: O 2 + 4H + + 4e - → 2H 2 O
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Rechargeable batteries are like voltaic cells. Except that you can add electricity to make the reaction go the other way. Lead-acid batteries are used in cars. Sulfuric acid is the electrolyte. The anode is made of lead plates, the cathode is made of lead(IV) oxide plates.
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What is the reaction happening at the anode? A: Pb(s)+SO 4 2- (aq) → PbSO 4 (s) + 2e - What is the reaction happening at the cathode? PbO 2 (s) + 4H + (aq) + SO 4 2- (aq) + 2e - → PbSO 4 (s) + 2H 2 O(l) Overall reaction? Pb(s) + PbO 2 (s) + H 2 SO 4 (aq) → 2PbSO 4 + 2H 2 O
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The battery is then recharged using an alternator when the car is running. 2PbSO 4 (s) + 2H 2 O(l) → Pb(s) + PbO 2 (s) + 2H 2 SO 4 (aq)
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Nickel-cadmium batteries are used as lightweight batteries (AA, AAA, etc.) KOH is used as an electrolyte. The reaction at the anode? Cd(s) + 2OH-(aq) → Cd(OH)2(s) + 2e- Reaction at the cathode? NiO(OH)(s) + H 2 O(l) + e - → Ni(OH) 2 (s) + OH - (aq) Overall reaction? Cd(s) + 2NiO(OH)(s) + 2H 2 O(l) → Cd(OH) 2 (s) + Ni(OH) 2 (s)
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Cadmium is an extremely toxic heavy metal, so when disposing of rechargeable batteries, make sure you dispose of them (just like any battery) in a special drop-off for batteries.
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Lithium ion batteries are used in products such as cell phones and laptops. It typically contains a graphite anode, and a metal oxide cathode. The electrolyte is a lithium salt.
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Similarities Both devices convert chemical energy into electrical Both have redox reactions taking place at the anodes and cathodes.
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Differences Fuel cells convert energy and rechargeable batteries store energy. Fuel cell requires a constant supply of reactants. Batteries have stored chemical energy and provide energy until they are used up. Batteries can be recharged. A fuel cell does not need recharging, but needs a continuous supply of fuel. The electrodes in fuel cells are made of inert materials. Fuel cells are more expensive than batteries.
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