14.2.1 - Storage cells and fuel cells Flashcards
What is a storage cell?
Can be charged by passing an electrical current through it in the opposite direction to the flow of current generated by the cells.
(Often called batteries)
What are fuel cells?
Electrochemical cells in which the chemical energy of a fuel is converted directly into electrical energy.
Name some features of a hydrogen-oxygen fuel cell.
Positive and negative electrode.
Acidic or alkaline electrolyte.
proton exchange membrane.
Hydrogen and oxygen entering with water leaving.
Under standard conditions in a commercial cells, what is the potential difference usually?
1.2 V
What metal are both electrodes in a hydrogen-oxygen fuel cell coated in and what is the function of this metal?
Platinum
Catalyses the reactions that take place at the electrodes.
With an acidic electrolyte, what are the reactions at the positive and negative electrodes?
Negative electrode: H2 = 2H+ + 2e-
Positive electrode: 0.5O2 + 2H+ +2e- = H2O
What is the function of the proton exchange membrane in a hydrogen-oxygen fuel cell?
The hydrogen ions can pass through which allows them to react with oxygen.
What is the overall equation in a hydrogen-oxygen fuel cell with both an acidic or alkaline electrolyte?
H2(g) + 0.5O2(g) = H2O(l)
What is the equation at the negative electrode and positive electrode in a hydrogen-oxygen fuel cell with an alkaline electrolyte?
Negative electrode = H2 + 2OH- = 2H2O + 2e-
Positive electrode = O2 + 2H2O +4e- = 4OH-
What are some advantages of using a hydrogen-oxygen fuel cell to produce power in fuel cells?
Offers an alternative to the direct use of fossil fuels such as petrol and diesel.
The products do not include pollutants unlike the burning of fossil fuels.
They are lighter and more efficient engines than engines that use fossil fuels.
What are some problems with the use of hydrogen-oxygen fuel cells?
Hydrogen is explosive so care needs to be taken when transported.
Compressing the gas is a risk.
Some metals absorb hydrogen gas onto surface and may react.
What is the role of the acid or alkaline electrolyte in a fuel cell?
To transfer ions
Describe one advantage of using hydrogen in fuel cells rather than burning the
hydrogen directly.
More efficient energy transfer
Explain the main advantage of using a fuel cell over the direct combustion of hydrogen.
More efficient.
Produces electricity directly.
