Hydrogen Energy promises to be a major player in the transport of the future

Professor David Book delivered his inaugural lecture in March 2015

IMG_0976Queuing at a filling station could become a thing of the past if new-generation hydrogen-fuelled cars take to the road. Innovative research being carried out by Professor David Book could see drivers refuelling their vehicles at home.

David, who is Professor of Energy Materials in the School of Metallurgy and Materials, is a world-leading expert on hydrogen energy and storage. In his recent Inaugural Lecture, entitled ‘Hydrogen energy – using materials to purify, compress and store H2’, he explained how hydrogen promises to be a major player in the transport of the future, as it can be combined with oxygen from the air in a fuel cell to produce electricity, with only water vapour as the exhaust gas.

‘However, for hydrogen to become a ubiquitous energy carrier – that can be used, for example, for zero-emission transport and helping balance the electricity grid – we need to be able to produce low-cost, low-carbon hydrogen; develop low-cost, durable fuel cells, and be able to effectively store, purify and compress hydrogen,’ says David, who is head of Birmingham’s Hydrogen Materials Group.  

David’s starting point, in the late 1990s, was exploring how hard magnetic materials interacted with hydrogen and, later, how hydrogen interacts with materials in general – namely, how it changes the microstructure, causing the material to behave differently.

More recently, David – who gained his Master of Engineering degree in materials engineering at Birmingham in 1990 – has focused his research interests on using hydrogen as a clean, renewable energy source, in particular for vehicles.

There is a debate now about how best to move energy around and how best to store it. There are certain applications where we need to store more energy in smaller spaces with lighter weight than lithium batteries will allow us – and one of those is cars.

Hybrid electric vehicles (HEVs) are now mass-produced – the best known being the Toyota Prius – and battery electric vehicles (BEVs) have also hit the road with the introduction, in 2010, of the all-electric Nissan LEAF. But there remain several obstacles to overcome if electric cars are going to be parked on every street corner. One problem is their limited battery life: BEVs have a mileage range of only about 100, compared to 300 for a diesel car.

Now, car companies in Japan and Korea have turned their attention to fuel cell vehicles (FCVs), in which hydrogen is stored in 700 atmosphere tanks.  ‘Many things about FCVs are wonderful, but there are a few problems,’ explains David, who spent several years studying and lecturing at Tohoku University in Japan before returning to Birmingham. ‘FC batteries are still very expensive, and also storing hydrogen is a bit tricky.’

At present, hydrogen is stored in on-board tanks. They are pretty big and the hydrogen is in there as a high-pressure gas, at 700 atmospheres. So although it works, the tank takes up a lot of space; it’s an inconvenient shape and in the long-term, car companies are wondering what customers are going to think about 700 atmospheres of gas. So the hope is that we can find a material that will absorb hydrogen.

David and his group are working on these technical challenges – searching for new types of hydrogen-absorbing materials: lighter-weight hydrides (materials that sit inside the metallic structure, acting like a sponge) that might allow both the size of the tanks and the hydrogen pressure to be reduced; metal hydrides that can be used in compact devices to compress hydrogen up to 100s of atmospheres, and metal membranes that only allow hydrogen to pass through, thereby protecting the polymer electrolyte membrane (PEM) fuel cell from damaging impurities. As with so many challenges, however, overcoming one obstacle can create another.

'Metal hydrides work wonderfully well in absorbing large amounts of hydrogen, but they’re really heavy: You can shrink the size of your tank, but that doesn’t reduce the weight. So we’re looking at using lighter metals or light non-metals. Magnesium, for example, is a light metal and for certain compositions will absorb a lot of hydrogen, but you have to heat it up a bit to get the hydrogen in and out.'

This is also the case when you use what we and our colleagues in Chemistry call complex hydrides. So for the longer-term, we’re hoping these kinds of materials could be very promising. But if hydrogen fuel cell cars are going to take off in the mass market, and we want smaller cars, there’s more urgency for smaller tanks and we would also like pressure lower than 700 atmospheres.

David is also looking at ways to efficiently and safely re-fuel hydrogen cars – possibly at home. At present, mechanical compressors are used, and although they work, they take up a lot of space, are noisy and expensive to maintain.

We’ve been working on a metal hydride compressor. One of the things about hydrogen is that it will go in at different pressures, so we’ve created different compositions where it is possible to put low-pressure hydrogen into the system and build it up by the absorption of heat so that high-pressure hydrogen comes out. We have a system in our lab and the compressor is quiet, apart from the sound of the valves going on and off, and works nicely.

David and his team are halfway through a collaborative EPSRC project with Nottingham and Loughborough universities to design a home refuelling system.

‘Public filling stations are being set up in the UK, but in the near- to medium-term, there might not be many around, especially outside large cities, so home filling stations could be the way to go,’ says David.

Notes:

• Professor David Book delivered his inaugural lecture in March 2015