Being clean and abundant, green hydrogen is touted to be one of the essential ingredients for the sustainable energy mix of the future. Yet, there’s an invisible yet big problem. It’s a gas with a low volumetric energy density. This makes its storage, transport, and operation complicated and expensive. But what if we could store hydrogen as a solid … on the cheap? A start-up1 may have a solid technology that could speed up the energy transition. Spoiler: It’s so good it was banned!

How do you get solid hydrogen?

Hydrogen is a key driver for heavy-duty e-mobility applications like buses, trucks, trains and ships. That’s because these large-scale vehicles require an amount of energy that batteries can’t provide yet. However, a fuel cell doesn’t need to be recharged like a battery as long as you can supply hydrogen. The major advantages of fuel cell electric vehicles (FCEVs) are a longer driving range and a lower refueling time compared to batteries.2 This makes hydrogen an ideal fuel for long-distance transport.

But there’s still a problem. How do you store a high load of hydrogen safely and cheaply on board? Storing hydrogen as a gas requires high-pressure containers which are both costly and more difficult to keep safe. Alternatively, you can compress it and turn it into a liquid. However, hydrogen starts boiling off at -252.8°C (-423°F)3, and if you want to keep it in a liquid phase you need to cool it down and chuck it into a cryogenic tank, which is expensive to maintain.

Compared to storing its liquid molecule, the solid storage of single atoms would incorporate a larger amount of hydrogen into a small volume. Plus, this approach wouldn’t require high pressure or freezing temperatures, which makes it more cost-effective. This would be a low-cost way of increasing the driving range of hydrogen-powered electric vehicles, which could then compete with fossil-fueled cars … and maybe even battery electric vehicles.

That’s why a great deal of research has been done on solid-state hydrogen storage applications.4 Normally, you can bind hydrogen to a metallic compound through two common processes. We’re talking about ad-sorption, when the hydrogen molecule or its single atoms gently link up with a solid surface … that surface is referred to as the ad-sorbent. Another option is ab-sorption. In this case, the hydrogen atoms go through the surface and bind to the internal structure of the ab-sorbent. In both cases, you end up with what’s called a metal hydride.5

However, the startup Plasma Kinetics has come up with a slightly different solution. As touted on their website, this is a 3-prong zero-carbon technology which is doing multiple jobs: capture, storage and delivery. Apparently, this pot of gold (or hydrogen I guess I should say) has a higher energy capacity and lower cost than a lithium ion battery. And you can recharge it in 5 minutes. The company said they ab-sorbed the hydrogen from air onto a light-activated nano-scale film, which is 10 times thinner than a human hair. This hydrogen sponge can trap the gas at low temperature and pressure, which translates into a lower cost. Then you just need to put a spotlight on the film to take some hydrogen out. That sounds amazing, right? And a little oversimplified? Let’s try to get a more solid grasp on this tech.

Light-activated hydrides

First, where did this idea come from? Back in 2009, Plasma Kinetics introduced their Light Activated Energy Storage (LAES) technology to the U.S. Department of Energy, who first defined it as transformational. However, they then transformed their opinion a little while later to label it as disruptive. Apparently, their technology provides an energy source that falls under the US national security umbrella.6 For that reason, the US government restricted Plasma Kinetics patent until 2017, which slowed down their progress. The company received explosive news when they found out that their business activity was limited by the International Traffic in Arms Regulations (ITAR).7 In other words, they can’t sell their tech for missile fuel applications, which wasn’t their target anyway.

So, what’s all the fuss about it? Plasma Kinetics designed a nanophotonic filter that captures hydrogen onto an internal graphite-based structure at atmospheric pressure and ambient temperature. The device could extract metric tons per day of 99.99% pure hydrogen directly from smokestacks and gas streams and turn it into a solid state. How is that possible?

The secret behind this unbelievable invention seems to lie within the material used. A multilayer shape-memory alloy (SMA), which is basically an alloy that remembers its shape once it’s changed. Typically, you can mold this material at low temperature and get it back to its original shape by heating it. While it might sound like plastic, SMAs are just a mix of two metallic compounds like nickel and titanium.8

Two common examples of SMA applications are mechanical actuators and medical stents.9 As for Plasma Kinetics’ SMA, you have magnesium in it. This alkaline-earth metal is also a core component of chlorophyll, the substance used by plants to perform photosynthesis.10 That’s the reason why the company’s material interacts with light. This property is the key difference when you compare light-activated hydrides to standard metal hydrides.

The second type of materials also rely on reversible ab-sorption for attaching the hydrogen atoms to their solid framework, but need temperatures of up 200°C (392°F) to release it.11 The company has described their device as a movie projector or CD player. Whether in a cassette, a canister, or a disc, you just need to shine a laser light on the hydrogen-filled film to release the…guest star…I mean the trapped hydrogen. That sounds spectacular but how does it actually work? During the ab-sorption cycle, the positively charged hydrogen atoms are attracted by negatively charged sites within the film’s nanopores. Because of the material photoactivity, when a laser hits the film, the light switches the polarity of the bond to positive, which frees the hydrogen atoms. That’s the big benefit with their system … the desorption process occurs without heating up the material like conventional metal hydrides do.

Con…solid…ating the future of clean energy

As of today, hydrogen is obtained using energy-intensive and high-carbon processes like natural gas reforming or electrolysis. That’s why Plasma Kinetics zero-carbon capture technology could have a massive environmental benefit for hydrogen production.

By providing a longer lasting yet lighter energy storage, the company is aiming to fuel the implementation of heavy hydrogen-powered mobile applications like boats, trucks, and electric vertical take-off and landing aircraft (e-VTOL). While hydrogen powered passenger cars aren’t likely to catch on compared to battery electric,12 the way it’s supposed to work with this tech is that you buy a hydrogen-filled disc cartridge in a convenience store. It doesn’t require special safety storage like canisters of hydrogen gas … but I’ll get to that in a minute. Once it’s empty, you return it and swap it for a fully-charged one. The actual cartridge swap in the vehicle would take just a few minutes.

Another huge market segment would be the decarbonization of energy grids. That’s because Plasma Kinetics’ device can make green hydrogen even greener. The company’s storage solution would host the surplus hydrogen created by renewable-powered electrolysis. Some of the green hydrogen could be stored without requiring compression or liquefaction. You can then feed the clean hydrogen to fuel cells to convert it back into green electricity based on demand. This would fill the gaps in the clean power supply on cloudy days or when the wind doesn’t blow, which makes our grid more flexible and resilient on renewables. Given its versatility, the film-containing canisters can be assembled wherever needed, like close to a wind farm for instance. They could serve as low-cost backup storage for remote communities or function as a mobile micro-grid for rescue operations.

Capture and storage sound very promising, but what about the hydrogen distribution? When it comes to delivery, a big plus for the Plasma Kinetics storage system is safety, as the hydrogen is carried in a non-flammable form. This means it can be shipped by any route without restrictions. Yet, the leading edge of this enlightening hydrogen trap is that you don’t need complex and costly infrastructure such as pumping stations and pipelines to spread the compressed gas around. And the system is also easily scalable from a single disc to a massive hydrogen library.

According to the company pitch deck13, by loading their containers on a single ship, they can safely move 20,000 tons of hydrogen in one trip. In energy terms, that’s enough to power 25,000 homes for a year. But how does their hydrogen storage innovation stack up to its competitors? When you compare it to lithium-ion batteries, light-activated hydrides seem to obscure them on all fronts. Besides having a higher energy density, Plasma Kinetics boasts its technology to be 17% less expensive and 30% lighter than Lithium-ion batteries for the same amount of energy stored. On the other hand, the light-activated storage unit has an efficiency of up to 70%, which is a bit lower than high-capacity batteries, ranging between 70 and 90%.

When ranking it against compressed gas systems, the battle is tighter. Although being slightly heavier than carbon-fiber tanks at around 700 bar (10,000) PSI, the solid-state hydrogen containers are much easier and safer to handle than the compressed gas vessels. Also, while Plasma Kinetic design has a lower energy density than highly pressurized storage, their materials have a lower energy cost. Based on company estimates, using one of their light-activated hydrogen trucks instead of a compressed hydrogen-powered vehicle, would save €20,000/year in fuel costs. That’s because the cost of solid-state hydrogen per kWh is 50% lower than compressed hydrogen.

To add to that, unlike the Plasma Kinetics system, a compressed gas hydrogen truck would need a refueling infrastructure worth €2.3M/station. I can hear you already, “We get it … this tech is unreal, but what’s the catch?” According to the company founder, the only drawback is that you can’t just plug your car in at home and re-charge it like you would with a conventional BEV.14 That’s because you first need to feed the stored hydrogen to a fuel cell to convert it into electricity. On top of that, while the cartridge or film can be used up to 150 times, the film is not…never ending…that’s because of deuterium, the hydrogen’s…fatter twin…which fills up the material’s nanopores. But the discs are 100% recyclable and you can even recover and sell the deuterium to cover the recycling costs.

Hydrogen will play a key role in the energy transition, but we’ll make the most out of it only with viable and efficient storage technologies. Solid-state systems like this seem to be the way forward and Plasma Kinetics is…shining a green light…at the end of the tunnel.

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Matt Ferrell
Matt Ferrell lives in the Boston area and is a UI/UX designer by trade, but has always been obsessed by technology and how it works. In 2018 he started his YouTube channel, Undecided with Matt Ferrell, where he explores sustainable and smart technologies like EVs, solar panels, and smart homes.

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