Sunday, March 21, 2021
Fuel cells
LO’s:
1. To recall in the cells and batteries.
2. To describe how a fuel cell works.
3. To evaluate the strengths and weaknesses of fuel cells for
given uses.
Keywords:
Fuel cell, non-rechargeable,
hydrogen fuel cell
Hook/Starter:
Cloze test
“Cells and batteries”
Starter
(Hook)
cells and batteries
recall
Insert the gaps
with the words
form the left
side box.
Starter – Hook (answers)
Electric Current
Here’s a battery (a “cell” really) powering a lightbulb:
+
-
e-
How does the cell work?
e-
A “battery” is technically a combination of cells.
How cells are made
Basically, cells are made out of chemicals:
Carbon rod with
metal cap cathode
Manganese oxide
Ammonium
chloride
(electrolyte)
Zinc casing anode
In other words, a battery is basically two DIFFERENT metals
in contact with an electrolyte. The voltage produced by the
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cell depends
on the type of metals and electrolyte.
Alkaline vs Rechargeable Batteries
In non-rechargeable
batteries the chemical
reactions stop when one of
the reactants has been used
up. Alkaline batteries are
non-rechargeable.
In rechargeable batteries
the chemical reactions are
reversed using an external
electric current.
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Questioning
•
•
Cells contain chemicals which react to produce electricity.
(a) Why can a rechargeable cell be recharged?
The chemical reaction is reversible
• (b)
1.
Give two factors that affect the voltage produced by a cell.
1. Type of electrode
2.
2. Concentration of electrolyte
Think –Pair-Share
Current vehicle technology uses fossil fuels or battery
power.
What problems are associated with using fossil fuels and
batteries?
Hydrogen Fuel Cells
Fuel cells are supplied by an external
source of fuel (e.g. hydrogen) and
oxygen or air.
In a hydrogen-oxygen fuel cell,
hydrogen and oxygen are used to
produce a voltage. Water is the only
product.
The fuel is oxidised electrochemically
within the fuel cell to produce a
potential difference.
Stretch: Write a balanced equation for the
overall reaction in a hydrogen-oxygen fuel cell.
2 H2 + 02  2H20
1.
Two separate reactions happen, one on each side of the fuel cell.
On one side, hydrogen
molecules lose electrons
and form hydrogen ions:
2H2 → 4H+ + 4e-
The two products reach the
other side of the cell,
hydrogen ions through a
membrane and electrons
through the electrical
circuit.
2.
On the other side,
hydrogen ions react with
oxygen molecules and
electrons to form water:
4H+ + O2 + 4e- → 2H2O
Task: Watch the video and complete
the table on the worksheet.
Hydrogen fuel cells
Advantages
1.
2.
3.
Disadvantages
Task: Watch the video https://www.youtube.com/watch?v=MQG87a8EwzY
and complete the table on the worksheet.
Hydrogen fuel cells
Advantages
1.
2.
3.
Disadvantages
The only exhaust from fuel-cellpowered vehicles would be water
vapour.
There are no natural reservoirs of
pure hydrogen; it must be extracted
from compounds such as natural gas or
water.
A hydrogen-oxygen fuel cell is an
electrochemical cell – that is, it
converts chemical energy in fuels
directly to electrical energy.
Hydrogen is very difficult to store and
transport in a vehicle unless it is
compressed to thousands of pounds
per square inch (psi).
They are very light.
When natural gas (basically methane, a
lightweight molecule made of carbon and
hydrogen) is exposed to steam under high
temperatures in the presence of a
catalyst, it frees the hydrogen. However,
the process itself also produces
substantial amounts of CO2.
How fuel cells work
Fuel Cells
Fuel cells work by using the
reaction between hydrogen
and oxygen to produce an
electric current:
1) The hydrogen atom loses
an electron (this is called
“oxidation”)
2) They then pass through
the electrolyte
3) The oxygen atoms gain two
electrons each
(“reduction”).
The whole
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process is called a “redox” reaction.
Exam Style question
1 . Some cars are powered by hydrogen fuel cells.
(a)
What type of energy is released by hydrogen fuel cells?
chemical
electrical
light
(b) Owners of cars powered by fuel cells buy hydrogen from hydrogen filling stations.
Figure 2 shows how the number of hydrogen filling stations in the UK is expected to
increase up to the year 2030
Suggest the total
number of hydrogen
filling stations
expected in 2028.
900
2. The number of hydrogen filling stations will still be very low compared with the number
of petrol filling stations.
• Suggest one reason why.
little demand/few hydrogen cars/changeover from petrol to hydrogen will take time
Plenary
Task: Complete the
mind map using
information
Fuel cells from
board and from your
books