Question: Hello, I watched the RI Christmas Lectures, and in the 3rd lecture Dr Tara Shine was talking about how we can use hydrogen as a renewable source of energy and how it can replace fossil fuels and electric power. As this is such a good source of energy, why isn't it used to power transport and other things?

Michael Nolan answered on 29 Jan 2021:

Great question Nathan!
Tara was correct – hydrogen is a really important fuel and energy source for the future. When you burn it in a fuel cell you make electric current and water. No pollution or CO2! You can use it in place of natural gas and there is work happening to replace some of the natural gas in our pipelines with a mix of gas and hydrogen.

There are a couple of issues with hydrogen at present that prevent its use as an energy carrier.
First is that it is hard to find on earth as hydrogen gas – being so light it diffuses away rather easily. So hydrogen is tied up in water, methanol or other molecules with carbon-hydrogen bonds. So you have to get the hydrogen out of those molecules (which itself takes energy).
Second is storing hydrogen. It is a flammable gas (Hindenburg Airship disaster) and needs to be pumped under very high pressure to be stored and transported.
These are two challenges that are not easy (or cheap) to overcome.

However!

We are making progress on both.
You can use (sun)light and a catalyst (which promotes the chemical reaction without being used up) to break water into hydrogen and oxygen. Water is stable of course, but if you put an electric current through water in the presence of platinum you break it up – electrolysis. Ideally we would use light as this is freely or will be cheaply available. With the right catalyst you can make the chemistry which breaks water into oxygen and hydrogen take place and collect the hydrogen

For storage there are two interesting options. First is to convert the hydrogen into a compound with a metal, such as magnesium hydride (MgH2) which can be stored and transported. Magnesium is cheap and easy to work with. You can also use porous materials (these are like solid sponges) that are full of holes and channels into which hydrogen molecules sit and are stored. The last option is my favourite, which is to convert the hydrogen together with carbon monoixde into methanol which is a liquid and can be used as a liquid fuel itself or broken down to produce hydrogen. It’s easy to store and transport

Lots of work to do, but we know where we want to go