Lesson video

Hello, my name's Dr.

Warren and I'm so pleased that you can join me for today's lesson on fuel cells.

It's a final lesson in the electrolysis unit.

We're going to work through this lesson today together.

I'm here to support you all the way, especially through the tricky parts.

Our learning outcome for today's lesson is I can describe how a hydrogen fuel cell works and compare one to a chemical cell.

Here are our keywords.

Fuel cell, a device that produces a voltage when supplied with a fuel and oxygen.

National Grid, the network that connects all the power stations in the country to make sure that everywhere has access to electricity.

Fossil fuel, a fuel that formed over millions of years from dead remains of organisms. You may wish to pause the video now and copy down these keywords and definitions so that you can refer to them later on during the lesson.

In today's lesson, we have two learning cycles.

The first one is on fuel cells and in the second learning cycle, we are going to compare different types of fuel cells.

So let's get started with our first learning cycle and learn about fuel cells.

A fuel cell is a device that produces a voltage when supplied with a fuel and oxygen.

We have different types of fuel cells.

So this image shows a methanol fuel cell.

Methanol is a fuel and it works when it's mixed with oxygen.

And in this car engine, we have a hydrogen fuel cell.

So there the fuel is hydrogen, and again, it's mixed with oxygen.

Fuel cells work like electric cells and batteries, with a main difference, they don't run down and they don't need recharging.

Fuel cells are used to produce a voltage and they do have a wide range of applications and we're seeing more and more of them.

So for example, hydrogen fuel cells are used for transportation, and in some places you'll find trains powered by hydrogen fuel cells.

You'll also find buses in many cities that are powered by a hydrogen fuel cell.

And even now we get an aeroplane that's been tested with hydrogen fuel cells.

So hydrogen fuel cells are definitely something that all sorts of different transportation are looking at for the future.

So what's it all about? Well, first of all, a fuel cell will produce a voltage.

To do that, we need a constant supply of fuel, for example, hydrogen, and we need oxygen or air, 'cause remember air contains 20% of oxygen.

In a hydrogen fuel cell, hydrogen and oxygen are used to produce a voltage and the product is water.

So the chemical reaction is simply hydrogen plus oxygen gives water and we can write that as a symbol equation, 2H2 plus O2 gives 2H2O.

When this reaction happens, energy is released from the reaction and the voltage produced can push a current around a circuit and that's what makes it into a cell.

Another advantage is water is the only product which doesn't pollute and it's not a greenhouse gas.

So that's my transportation, trains, buses, planes, and cars are all looking towards hydrogen fuels to see if that will be a cell that we can use more in the future.

So quick check for understanding, what is the word equation for the overall reaction in a hydrogen fuel cell? Is it A, B, C, or D? Well done if you chose D, hydrogen plus oxygen gives water.

Let's have a look at the different parts of a hydrogen fuel cell.

So the image you can see now is a hydrogen fuel cell and we're gonna go through it bit by bit.

So to start off with, we have a source of hydrogen and that flows into the hydrogen fuel cell.

Now the hydrogen can come from two different places, it's either produced from the electrolysis of water, which takes energy in itself or it's extracted from fossil fuels.

And we'll talk a little bit more about fossil fuels later on in the lesson.

So the first point for hydrogen fuel cell is we need a good consistent supply of hydrogen that can be tapped into the cell.

And when it goes in, the first thing that it will come up to is the anode.

I remember from previous learning that an anode is a positively-charged electrode.

Between the two electrodes, we have our electrolyte and there's also a membrane there that allows some ions to flow in and out.

So remember, our electrolyte is a source of ions that are free to move, and the cathode is the negatively-charged electrode, the other side of the electrolyte.

So it's all kind of quite compact.

Now, on the other side, we have oxygen that flows in and it flows into the tank on the side of the cathode.

Again, we need a good supply of oxygen, and for most of the time that oxygen is extracted directly from the air.

And then, at the end of the reaction, water is produced so we need an outlet, we need somewhere for that water to go.

So those are all the main features and parts of a fuel cell.

And finally, once we've got our hydrogen and our oxygen flowing in and everything's working, a voltage is used to light up the bulb and we can see that, or it can be used to power whatever is connected into the electric circuit.

So in a hydrogen fuel cell, the hydrogen is oxidised, electrochemically, to produce water.

So we're back to this idea again of oxidation because we're talking about electrons.

Energy is released from the reaction and a voltage produced that can push a current around the circuit.

So very, very similar to our previous learning about electric cells.

So what is actually happening? Well, at the anode, are positively-charged electrode.

Hydrogen atoms are being oxidised to become hydrogen ions.

The electrons produced are then taken by the anode.

We can write a half equation as we've done in previous learning, H2 goes to 2H+ plus 2E-.

So that's the first thing to think about, we'll think about kind of how the cell works by going round the cell.

Hydrogen comes in, the atoms are oxidised to become hydrogen ions, the electrons are taken by the anode, which we can now see on the diagram.

Those electrons then pass around the wire to the cathodes, so you can think about those electrons going up through that wire around to the cathode.

But the hydrogen ions, they move through the membrane into the electrolyte and go towards the cathode.

Positively-charged ions are going to be attracted towards the more negatively-charged cathode.

Okay, a quick check for understanding, true or false.

In a hydrogen fuel cell, the hydrogen is reduced at the anode.

True or false? Well done if you chose false.

That's the correct answer.

Now let's have a look at the reason why.

Is it A, hydrogen loses electrons to form hydrogen ions so it's oxidised at the anode, or B, hydrogen gas is formed at the anode? Well done if you chose A.

In all of these fuel cells, we are talking about electrons moving and being transferred.

So hydrogen loses electrons to form hydrogen ions, so it's oxidised at the anode.

So let's think about now what happens to the cathode? So at the cathode, the electrons and the hydrogen ions react with oxygen molecules.

So we've got our oxygen coming into the cell, we've got our hydrogen ions, they've now gone through the electrolyte and they're at the cathode, and the electrons have gone round the circuit, they're now on the cathode, they react with the oxygen molecules and water is formed.

The oxygen has been reduced, and we can write the half equation, O2 plus 4H+ plus 4E- gives 2H2O.

The water molecules leave the fuel cell by the outlet.

And as that happens, we have found in this reaction energy is released.

And that is why we have, that is where the energy has come from in that reaction.

So let's just do a quick summary of what happens in a hydrogen fuel cell.

First of all, hydrogen comes into the cell.

It is then oxidised at the anode.

The voltage pushes the electrons around the circuit.

A voltage is created between the electrodes, the H+ ions and the electrons react with oxygen to produce water and energy is released.

So that tells you, in a nice summary, how the hydrogen fuel cell works.

Let's look at the half equation for the reaction at the anode.

We have hydrogen gas coming in, it's oxidised, so H2 goes to 2H+ plus 2E-.

The half equation for the reaction at the cathode is O2 plus 4H+ plus 4E- gives 2H2O.

If we combine the two equations, the two half equations, we'll get the overall reaction.

So remember when we combine half equations, we look to see what can be cancelled out and we find on each side of the equation we have 4H+ and 4E-.

We can cancel those out and we end up with 2H2 plus O2 gives 2H2O, which is our reaction that takes place during a hydrogen fuel cell.

So quick check for understanding, why is the chemical reaction between oxygen and hydrogen used in a fuel cell? Is it A, to produce a voltage, B, to produce water, or C, to produce a temperature change? Well done if you chose A.

The whole purpose of that reaction in a fuel cell is to produce a voltage.

That is the correct answer.

The reaction does produce water, but if we wanted to produce water, we wouldn't use a fuel cell if that's what we were only interested in.

Okay, so that brings us to our first task.

So we've got some questions here, we'd like you to work through them.

First of all, what is a fuel cell? Then we've got a fuel cell, we'd like you to label it.

Question three, write a word equation for the overall reaction that takes place in a hydrogen fuel cell.

B, complete the half equations that take place at the electrodes and try and tell us why hydrogen fuel cell is seen as unpolluting.

So if you can pause the video, have a go at the question, and then when you're ready, we'll have a look at the answer together.

Let's have a look at the answer to question one.

What is a fuel cell? A fuel cell is a device that produces a voltage when supplied with oxygen and a fuel.

So well done if you got that right, and you may have given an example of hydrogen being the fuel, that's fine as well.

Let's have a look at our actual diagram and see if we can label it.

Well, A is a hydrogen, that's where our hydrogen gas goes in.

B is our anode, C is our electrolyte.

D is where the water comes out, so it's our water outlet, or water.

E is our cathode, and F is oxygen.

So very well done if you've got all of those labels correct.

Question three, our word equation.

Well that is hydrogen plus oxygen gives water.

There's no other products.

Well done if you got that.

For our half equations, H2 plus 2H+ plus 2E- it's the reaction that takes place at the anode.

So well done if you got that correct.

For the other half equation which will take place at the cathode, we have O2 plus 4H+ plus 4E- gives 2H2O.

So very well done if you've got all of those answers correct, that's excellent work.

Let's have a look at our last question.

Question four, why is a hydrogen fuel cell seen as unpolluting? Well, it only produces water, which is not harmful and it's not polluting.

It doesn't produce carbon dioxide, which is a greenhouse gas, or any other pollutants.

So that's why the hydrogen fuel cell is seen as unpolluting and it's why transportation is having a look at using it, seeing if it will be viable for all transportation in future to be run on fuel cells.

So that brings us to the end of our first learning cycle on fuel cells.

And now we're gonna move on to have a look at different types of fuel cells.

So in our second learning cycle, we're gonna look at comparing fuel cells.

Hydrogen fuel cells offer a potential alternative to rechargeable cells and batteries.

So in this part of the lesson we're gonna have a look at some of the advantages and disadvantages of a hydrogen fuel cell compared to other cells.

So first of all, there's quite a lot of advantages of hydrogen fuel cells and these include there is a good supply of oxygen and hydrogen gas and one of the places we can get that from is from water around us from electrolysis, as well as oxygen from the air.

Water is the only product, so again, that is an advantage because it's not a pollutant.

No greenhouse gases, so no carbon dioxide or any other particulates or any other pollutants are formed during the reaction.

Again, this is a really good advantage when we're thinking about climate change.

There are simple devices that have a long life compared to other types of cells because there are no moving parts in it.

And at the end of their life they're very easy to dispose of.

So hydrogen fuel cells do have a lot of advantages, but they also have quite a few disadvantages.

And one of the main disadvantages is hydrogen is a gas and gases need a lot of storage space, much more space is needed than in other cells, and then we sometimes have to start thinking about pressurising that gas to make it a smaller space.

So storage is definitely a disadvantage.

Another problem with hydrogen is it's dangerous to store because it's explosive, when mixed with oxygen, if a spark gets to that supply, then there's a massive danger that everything will explode.

Hydrogen used in fuel cells can be extracted from fossil fuels, such as methane.

Now the disadvantage of this source of hydrogen is carbon dioxide, a greenhouse gas may be produced in the process.

So if hydrogen, for example, is extracted from methane gas, CH4, we do get carbon dioxide produced.

So we are making a clean hydrogen fuel cell, but en route, we are actually producing some greenhouse gases, which has to be a disadvantage.

The other disadvantage is hydrogen produced by electrolysis is often powered by the National Grid.

So that may use renewable energy source of wind power, or solar power, or tidal power, but it also may be taking some power from the National Grid that has come from a fossil fuel.

We don't always know.

So hydrogen fuel cells, where they have a lot of advantages, they also have quite a lot of disadvantages as well.

So let's just think about a fossil fuel for a moment because that's a fuel that's formed over millions of years from the dead remains of organisms and I'm sure you are familiar with the different types of fossil fuel.

We have coal, we have crude oil, and we have natural gas.

The main issue with these are, first of all, fossil fuels are finite.

They are non-renewable sources of energy.

They will run out eventually, but the real problem is when fossil fuels are burnt to produce the energy that is needed to power things, they produce also carbon dioxide gas and other pollutants that are harmful to the environment.

So that is why we are trying to move away from fossil fuels.

The National Grid, well this is a network that contains all the power stations in the country to make sure that everybody has access to electricity.

And the electricity supplied is a mixture from non-renewable sources as well as renewable sources.

Once the electricity is produced, we can't distinguish from the source it comes from.

So we may have our fossil fuel power station, which could be a gas-powered station, or a coal-powered station alongside offshore wind, which is renewable and clean, and solar, which also is renewable.

In the National Grid, we can't distinguish which type where our electricity has come from.

So again, if we're trying to use clean renewable energy, it can be difficult when we are taking from the National Grid.

Quick check for understanding, which of the following are disadvantages of using a fuel cell? So we're looking at disadvantages.

A, water is the only product, B, hydrogen gas is explosive, C, fossil fuels are sometimes used to produce hydrogen, and D, they are simple devices that last a long time? Well done if you chose B, hydrogen gas is explosive, so storage is a problem, and sometimes fossil fuels are used to produce the hydrogen in the first place.

Again, a disadvantage.

So well done if you've got both of those right.

So we've talked about transportation, about buses and trains and cars being powered by hydrogen fuel cells.

Well, spacecrafts are as well.

And here we've got an image produced by NASA of a spacecraft going off into space.

There are some additional advantages when using hydrogen fuel cells in space.

For example, the water produced can be used for drinking water.

So when that water is tapped off on the hydrogen fuel cell, it can be piped into storage containers, which can then be used for drinking water or for other purposes with onboard the spacecraft.

Also, the water produced can then be electrolyzed to replace the hydrogen and oxygen using solar cells, which convert light from the sun into electricity.

So if you imagine that the spacecraft is in space perhaps at the international space station and they are running low on hydrogen fuel, what they can then do is use their solar cells and the water produced and reverse that reaction.

So they have got hydrogen and oxygen ready for their journey back home.

We talked a little bit earlier about the fact there are many different types of fuel cells being developed as people see this as a potential future way of powering things, devices.

For example, we have the methanol fuel cell here.

The overall reaction is methanol plus oxygen gives carbon dioxide and water.

And there we have our balanced symbol equation.

When compared to a hydrogen fuel cell, there are some advantages.

For example, methanol is a liquid so it's easier to store than hydrogen and that is a big issue, especially if you're thinking about transportation.

The disadvantage of course is carbon dioxide, a greenhouse gas, is produced in the normal methanol fuel cell reaction.

So it is a greenhouse gas producer.

Quick check for understanding.

Using a methanol fuel cell is considered to be less harmful to the environment than using a hydrogen fuel cell.

Would you say that is true or false? Well done if you chose false.

Now why? Is it A, both cells produce water as a byproduct, so using either of them does not harm the environment, or B, a methodol cell also produces carbon dioxide, which is a greenhouse gas? A or B? Well done if you chose B.

A methanol cell also produces carbon dioxide, which is a greenhouse gas.

So what we're gonna do now is we're gonna evaluate the use of rechargeable battery.

For example, a lithium ion battery, and lithium ion batteries are often used in cars as well as electrical devices.

So the advantages are, first of all, it can be recharged many times, it can be recycled at the end of the life, and it reduces the use of resources.

But there's also some disadvantages.

First of all, they can catch fire and there has been cases that have hit the news headlines where certain types of mobile phone batteries have caught fire, which obviously isn't very safe.

They release toxic chemicals on disposal.

So we really have to think about how the batteries are disposed at the end of their life.

They have a finite life as eventually they will no longer be able to be recharged.

And again, I know this happened to one of my phone batteries after I'd used it and used it and used it, eventually there was no more charge left.

So I'd plug it in but it wouldn't recharge and they are very expensive to manufacture in the first place.

So the lithium ion battery does have some good advantages but also some disadvantages.

So cars, I mean these run on batteries, electric cars can be powered by a hydrogen fuel cell or rechargeable batteries such as the lithium ion battery.

And we've got a picture there of a car recharging.

So there's quite a few things that we need to think about if we are going to use either a hydrogen fuel cell or a lithium ion battery in a car.

There's also some additional factors that we should consider before buying.

So the things that we've already talked about are true about the storage of the hydrogen, about it being explosive, about the lithium ion cell perhaps going on fire.

But we also need to think about the time taken to refuel or recharge, where it can be refuelled or recharged, the cost of refuelling or recharging, the range, that's how far the car will travel between refuelling and recharging, and how much the vehicle costs in the first place.

So if we're thinking of moving to an electric car, there's lots of things to consider, not just the cost of the car but how and the type of the fuel cell or the rechargeable battery, but how we can have that ongoing use day by day.

Let's have a quick check for understanding.

Which of the following are advantages of using a lithium ion battery? A, they release toxic chemicals on disposal, B, they catch fire, C, they're made for materials that can be recycled when they are no longer rechargeable, or D, they can be recharged many times? Well done if you chose C.

That is the correct answer.

And also D, they can be recharged many times.

So this brings us to our second task, Task B.

I've got a couple of questions here for you to answer.

The first question, chemical cells such as a lithium ion battery, can be used to power some vehicles.

Give one advantage of using a chemical cell to power a vehicle rather than a hydrogen fuel cell.

The second question, hydrogen fuel cells can be used to provide electricity in a spacecraft.

A, give three advantages of using a hydrogen fuel cell rather than a chemical cell in a spacecraft.

B, give three disadvantages of using a hydrogen fuel cell rather than a chemical cell in a spacecraft.

And then C, which cell would you choose if you were making a spacecraft? And can you give an explanation for your answer? So have a go at these questions, pause the video, and then when you're ready, we'll look at the answers together.

Let's have a look at the answer to question one, an advantage of using a chemical cell to power a vehicle rather than a hydrogen fuel cell.

Well, you could have said a chemical cell is easier to transport than a hydrogen fuel cell, which needs somewhere for the explosive hydrogen gas to be stored.

Of course there are other things that you could have chosen as well.

Right, question two, three advantages of using a hydrogen fuel cell in a spacecraft rather than a chemical cell.

Well, hydrogen fuel cells require no maintenance, are very, very straightforward.

Water is the only product of a hydrogen fuel cell, and it can be used for drinking water or other means on the spacecraft.

The voltage produced by a hydrogen fuel cell is constant all the time.

So all of these are advantages of a hydrogen fuel cell rather than a chemical cell in a spacecraft.

Let's have a look at some disadvantages of using a hydrogen fuel cell rather than a chemical cell in a spacecraft.

Hydrogen and oxygen must be supplied to the fuel cell.

Hydrogen is a flammable gas, which could be a real problem in space.

It's difficult to store hydrogen on the spacecraft because it is a gas and this means that we'll also have to have gas tanks to be transported.

So that, again, will take up a lot of space.

So there's some disadvantages that you could choose from.

So the question is which cell would you choose if you were producing a spacecraft? The main thing is here we want your choice linked to an explanation.

So you might say, I'll choose the hydrogen fuel cell because it provides a constant voltage and which uses water that can be used on the spacecraft.

That's a really good reason for doing that.

Or you might decide, actually, I'll choose the chemical cell because it takes up less space and you don't have to store a flammable gas.

Again, a very good reason for going to the chemical cell.

And when you're evaluating things, often, there isn't a right or a wrong, you just have to make your decision, but back it up with an explanation.

So if you've got those right, very, very well done.

Now we've come to the end of our lesson.

Let's have a look at our key learning points.

One type of fuel cell contains hydrogen that reacts with oxygen from the air to produce a voltage.

Hydrogen used in fuel cells can be extracted from fossil fuels or produced by electrolysis powered by the National Grid.

Other fuel cells exist but have other products than just water.

There are many strengths and weaknesses of fuel cells and these should be compared against other energy sources.

I've hoped that you have enjoyed today's lesson and I look forward to learning with you again very soon.