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Go with the flow

ElecTrans talks with University of Glasgow Regius Chair of Chemistry Leroy Cronin about the technology behind a new hydrogen flow battery

A team from the University of Glasgow in Scotland has developed a new energy storage method that could potentially reduce electric vehicle (EV) charging times down to seconds.

The new energy storage system uses a nano-molecule that can store electric power or hydrogen gas, creating a new type of hybrid energy storage system that can be used as a flow battery or for hydrogen storage.

ElecTrans spoke to developer and designer of the storage system Professor Leroy Cronin at the University of Glasgow about the new technology.

“We’ve been able to take electrical energy and store the energy, the electrons, in a liquid, in a nanocluster,” Cronin explained. “This nanocluster is very small so you can put a lot of it in the solution and it can absorb a lot of charge, a bit like charging up a battery.”

A flow battery works when two charged liquids, stored in two different circuits, pass close to one another, separated only by a thin membrane. Electrons can flow through this membrane, which in turn makes an electrical charge.

The University of Glasgow’s flow battery is able to use their nano-molecule-filled fluid either to produce electricity to run the fuel cell or release the energy in the form of hydrogen.

“In a flow system, we can take the charge out as electrical power, or, if we add a catalyst, we can remove the power out as hydrogen gas,” Cronin said.

Fun with tungsten
The University of Glasgow’s flow battery utilises a tungsten oxide nano-molecule dissolved in water, with bromine and hydrogen bromide running in the opposite loop of the flow battery. Each molecule contains 18 tungsten atoms, each of which is capable of holding a single electron.

“That is a massive increase on the number of electrons that molecules in most batteries can store. Normally it’s just one or two, so we’ve increased that almost by an order of magnitude,” Cronin explained.

At present, the liquid has an energy density of around 255 watt hours per litre. This is comparable to lithium-ion batteries, which have an equivalent energy density of around 250-700 watt hours per litre.

It is also around five times more than the energy density of a vanadium system, which is the main flow battery system used commercially at the moment.

“We should be able to increase this by up to another four to five times and perhaps even break the 1,000-watt hour per litre barrier, but we haven’t proven that yet,” Cronin added.

In order to get this extra energy storage, it would require a new type of battery. “Basically, it’s like a fuel cell, but a fuel air battery, and what we’ve got to do is just validate the system and make the prototype,” Cronin said.

A fuel air battery utilises a pure metal anode, while the cathode is air, which is likely to be dissolved in a liquid electrolyte.

“We haven’t yet proven that we can get the extra increase in charge, but if we can, then it’s a game-changer again,” Cronin said. “Even as it works right now, it’s a significant increase on what is possible.”

Speed up
The fluid can be recharged by running it over some electrodes, and a battery using this technology can be refuelled by adding more charged fluid. This means that an EV utilising the nano-molecule could be refuelled at the same speed as a conventional fossil fuel vehicle.

“This removes a lot of the barriers to the adoption of electric vehicles,” Cronin said. “People fear it’s going to take too long to charge an EV, and if it only has to take a few seconds to recharge them like refuelling a car, then I think the broad appeal could be huge.”

ElecTrans asked Professor Cronin how easily he thought his energy storage could be adapted to fit existing technology and infrastructure.

He pointed out that EVs could theoretically replace their existing batteries with ones based on the University of Glasgow’s technology.

“Because it’s a liquid, we should be able to use some of the liquid-handling infrastructure we already have,” Cronin said. “But I don’t know what the difference between the viscosity of our material is likely to be compared with, say, petrol.

“I’m guessing that our material will be a little more viscous and that will obviously make things more difficult, but in principle, it should be possible to move the material around as a liquid, and that liquid-handling infrastructure already exists.”

Although the technology is still in its early stages, it is a promising improvement on existing flow battery technology, with room to grow as well. Cronin said that additional funding would be needed to develop it fully.

“I need to go and validate the next steps in terms of getting the performance matrix, working out the capital expenditure required to build the batteries, and maybe an electric car company to partner with to license the technology and generally to make sure the technology is as good as it can be, and then also to think about economic models that may result from this change.”

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