Question: what is the Best way to extract and to store hydrogen then insert it in to a fuel cell to create a non pollutant fuel source?

Hello! I’m Suze, friend of Jen and fellow Geek Princess, over from the Energy Generation Zone. I’m working on photocatalytic water splitting, but I’ll get to what that means in a moment. Hydrogen is, in my opinion, a good way forward, and not just because I’m writing my PhD thesis on the topic 😉 It burns cleanly, to make water as a ‘waste’ product, as opposed to fossil fuels, which release carbon dioxide into the atmosphere, and contribute to global warming.

So, we’ve got quite a lot of water on this lovely planet of ours, and hydrogen is made up of two atoms of hydrogen and one atom of water. If we try and ‘split’ this through the process of two ‘half reactions; that make up one whole balanced reaction, we can get hydrogen (H2, two hydrogen atoms making a molecule) and oxygen (O2, two oxygen atoms making a molecule). Now, obviously if we were to work backwards from H2 and O2, we’d have hydrogen peroxide. Great for hair bleaching, but we don’t have as much of that around to play with, so we need to balance our equation, therefore if we get two molecules of water, we can have two molecules of hydrogen and one molecule of oxygen after we split them, and everything balances.

All sounds pretty good, but water isn’t energetically that easy to split. It takes a lot of energy to make it separate into hydrogen and oxygen, and so att the moment, water splitting reactions take place by shoving a whole load of electricity through the water. This is called electrolysis. ‘-lysis’ just means breaking, and electro- means with electricity, so electrolysis is the breaking of a molecule, using electricity as an energy source. All sounds great, but the problem here is where the electricity itself is coming from, and that is by burning fossil fuels. They carry on polluting the atmosphere, so the purpose of making hydrogen for use as a fuel is lost!

What I’ve been working on is a way to split water molecules using sunlight. Now, I’m sure you’ve had a drink of water during daylight hours before, and haven’t seen any bubbles of explosive gases evolving from your drink! The reason is because, as I mentioned earlier, it is energetically very hard to split water. It requires a lot of energy, and it can’t make use of the sunlight energy itself. What we need then is something that can catch the energy from the sun, and pass it onto the water molecules.

For tis purpose, I use something known as a semiconductor photocatalyst. It is a semicondutor, which means that it is in between an insulator (like rubber, which takes LOADS of energy for it to do anything) and a conductor (which doesn’t need much energy at all to get the electrons within it moving around carrying charge). The semiconductor that I am using is titanium dioxide. You might not have heard of it, but it’s a white powder that’s in loads of things, from suncream to paint. The energy that it takes to get the electrons moving in titanium dioxide is 3.2 eV (electron volts. Using a bit of maths and physics by a guy called De Broglie, we can work this energy out as a wavelength of light. 3.2 eV equals 380 nm (nanometers – tiny! Even smaller than me!). You know when you pass light through a prism, or sunshine goes through raindrops and you get a rainbow, you can see the rainbow of colours? Each colour has its own energy associated with it, and its own wavelength. The blue end has a shorter wavelength, and the red end has a longer wavelength. The energy of light is inversely proportional to its wavelength, so a short blue wavelength of light has more energy than a longer red wavelength of light.

380 nm of light is actually in the blue end of the rainbow, and is actually in the ultra-violet region. Light in this end is very powerful, and this is what can cause skin cancer if we sit in direct sun for too long. Although we can’t see all of these colours in sunshine normally, we see them in rainbows, and this is actually why the sky looks blue to us – but that’s a different story altogether!

So, back to our story. This UV-light hits the titanium dioxide, and has the right energy to excite a negatively charged electron to its conduction band, which is when it has enough energy to move around. This electron travels to the surface of the titanium dioxide, and attacks the water molecule, reducing it to hydrogen. As the charge on the titanium dioxide is out of balance, the hole that is left behind is effectively a lack of negative charge, or a positive hole. This hole can also move to the surface as electrons fill in the gap, and this oxidises water molecule to create oxygen. As a result, we get hydrogen and oxygen being produced. The titanium dioxide is speeding up a reaction that involves light, and that is why it is known as a photocatalyst (photo- means light, and -catalyst is something that speeds up a reaction, but is never used up). The set-up that my group has devised means that the hydrogen and oxygen come off the titanium dioxide from different areas, and so we are able to easily collect the two gases without having to separate them.

So, once we’ve made out hydrogen and collected it, we need to store it in order to take it to where it is needed. Hydrogen can be cryogenically cooled (which means sort of freezing it down so that the gas molecules turn into a really tightly packed liquid), which would be good as you can get a denser liquid hydrogen, and can carry more in one go however, the cost of cooling something like that is huge, and so the cost of the hydrogen fuel would increase. So, the best way so far is to compress the gas into canisters or huge cylinders, and transport it that way. There is a whole area dedicated to hydrogen storage, where it could be stored within chemicals, without losing any of its energy, as it is so important if we are to embrace hyrogen as our future sustainable energy.

Once transported, an appropriate fuel cell would be able to burn the hydrogen cleanly, producing water. As the hydrlgen came from water, we have a complete cycle of energy, and so this method is known as a sustainable energy, as it can always be kept, and will never run out. The energy created in burning the hydrogen would be able to power a motor in a fuel cell, which would then be able to run appliances, cars, etc.

I’ve mentioned cars because, remember earlier I said how electricity is made by burning fossil fuels? How then can electric cars be good for the environment, unless the electricity is make from a sustainable or renewable energy source?! It’s an issue that I have with the idea of electric cars, but just my own rantings and ramblings! Hopefully people will realise this soon though!

So there we have it. A cheap, clean, renewable method of making hydrogen, and burning it in a fuel cell. If you have any questions, do give me a shout!

Team Cobalt, this is EnGen Suze signing off. Muchos love! 🙂

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