C5 FUEL CELLS AND RECHARGEABLE BATTERIES

C.5.1 Describe how a hydrogen-oxygen fuel cell works.

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.

C.5.1 Describe how a hydrogen-oxygen fuel cell works.

What is the half reaction occurring at the anode?

A: 2H2(g) + 4OH- (aq) → 4H2O (I) + 4e-

What is the half reaction occurring at the cathode?

A: O2 (g) + 2H2O(I) + 4e-   →    4OH- (aq) After cancelling, what is the overall

reaction? A: 2H2 (g) + O2 (g)   →  2H2O (I)  

C.5.1 Describe how a hydrogen-oxygen fuel cell

works. You also need to know the half reactions

in acidic conditions: Anode: 2H2(g) → 4H+(aq) + 4e-

Cathode: O2 + 4H+ + 4e- → 2H2O

C.5.2 Describe the workings of rechargeable batteries.

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.

C.5.2 Describe the workings of rechargeable batteries.

What is the reaction happening at the anode?

A: Pb(s)+SO42-(aq) → PbSO4(s) + 2e-

What is the reaction happening at the cathode?

PbO2(s) + 4H+(aq) + SO42-(aq) + 2e-

→ PbSO4(s) + 2H2O(l) Overall reaction? Pb(s) + PbO2(s) + H2SO4(aq) → 2PbSO4 +

2H2O

C.5.2 Describe the workings of rechargeable batteries.

The battery is then recharged using an alternator when the car is running.

2PbSO4(s) + 2H2O(l) → Pb(s) + PbO2(s) + 2H2SO4(aq)

C.5.2 Describe the workings of rechargeable batteries.

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) + H2O(l) + e- → Ni(OH)2(s) + OH-(aq) Overall reaction? Cd(s) + 2NiO(OH)(s) + 2H2O(l) → Cd(OH)2(s) +

Ni(OH)2(s)

Help your Earth!! 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.

C.5.2 Describe the workings of rechargeable batteries.

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.

C.5.3 Discuss the similarities and differences between fuel cells and rechargeable batteries.

SimilaritiesBoth devices convert chemical energy into

electricalBoth have redox reactions taking place at the

anodes and cathodes.

C.5.3 Discuss the similarities and differences between fuel cells and rechargeable

batteries.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.