Batteries and Fuel Cells

Question 1

What are batteries?

Answer 1

Batteries are types of electrochemical cell which provide electricity to power things

Question 2

What type of batteries are rechargeable?

Answer 2

Lithium batteries

Question 3

Give a type of lithium cell battery

Answer 3

One type of lithium cell battery is made up of a lithium cobalt oxide electrode and a graphite electrode. The electrolyte is a lithium salt in an organic solvent

Question 4

What are the half-equations in a lithium battery

Answer 4

1. Li ——- Li+ + e-
2. Li+ + CoO2 + e- —– Li+[CoO2]-

The Li+/Li half-cell has more negative E value so goes in the direction of oxidation (backwards)

Question 5

What are the reactions which happen in a lithium battery when the battery supplies power?

Answer 5

At the negative electrode:

Li —– Li+ + e-

At the positive electrode:

Li+ + CoO2 + e- —– Li+[CoO2]-

Question 6

How do you recharge lithium batteries?

Answer 6

To recharge batteries, a current is supplied to force electrons to flow in the opposite direction around the circuit and reverse the reaction

Question 7

What is the difference between chemical cells and fuel cells?

Answer 7

In most cells the chemicals that generate the electricity are contained in the electrodes and the electrolyte that form the cell. In a fuel cell the chemicals are stored separately outside the cell and fed in when electricity is required

Question 8

Give one example of a fuel cell

Answer 8

One fuel cell is the alkaline hydrogen-oxygen fuel cell, which can be used to power electric vehicles

Question 9

How do alkaline hydrogen-oxygen fuel cells work?

Answer 9

Hydrogen and oxygen gases are fed into two separate platinum-containing electrodes. The electrodes are separated by an anion-exchange membrane that allows anions (OH-) and water to pass through it, but not hydrogen and oxygen gas. The electrolyte is an aqueous alkaline (KOH) solution

Question 10

Give the two half equations in an alkaline hydrogen-oxygen fuel cell

Answer 10

Hydrogen is fed to the negative electrode. The reaction is:

2H2 + 4OH- —– 4H2O + 4e-

Oxygen is fed to the positive electrode. The reaction is:

O2 + 2H2O + 4e- —– 4OH-

Question 11

How do the electrons flow through an alkaline hydrogen-oxygen fuel cell?

Answer 11

The electrons flow from the negative electrode through an external circuit to the positive electrode. The OH- ions pass through the anion-exchange membrane towards the negative electrode.

The overall effect is that H2 and O2 react to make water

Question 12

What are the advantages of using fuel cells in cars?

Answer 12

1. They are more efficient - they convert more of their available energy into kinetic energy to get the car moving. Internal combustion engines waste a lot of their energy producing heat
2. The waste product is water, so there are no toxic chemicals to dispose of and no CO2 emissions from the cell itself
3. Fuel cells don’t need to be recharged like batteries - as long as hydrogen and oxygen are supplied the cell will continue to produce electricity

Question 13

What is the downside of using fuel cells in cars?

Answer 13

1. You need energy to produce hydrogen and oxygen. They can be produced from the electrolysis of water but this requires electricity - this is generated from burning fossil fuels
2. Hydrogen is highly flammable so it needs to be handled carefully when being stored and transported