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Safe Hydrogen Receives Funding to Complete Pumpable Hydride Slurry Project

Pouring the hydride slurry.

Safe Hydrogen, LLC. of Lexington, Mass has been awarded $308,000 from the Massachusetts Renewable Energy Trust SEED Program (Sustainable Energy Economic Development), a division of the Massachusetts Technology Collaborative (MTC), to complete a three-year, $2.4-million DOE project designed to determine the functionality, cost and efficiency of Safe Hydrogen’s pumpable hydride slurry.

Safe Hydrogen has developed a pumpable magnesium-hydride-based fuel that releases hydrogen as needed.

A pumpable fuel rich in hydrogen would eliminate several key road blocks to wide spread adoption in transportation, including distribution infrastructure and storage safety and efficiency.

The slurry, both before and after yielding the hydrogen, is not flammable, safe to handle, easy to store and can use current pumps and tanks used for diesel fuel, gasoline or water. The slurry is reacted with water to produce the hydrogen required. The metal hydroxide byproduct is captured and recycled.

The slurry consists of a finely ground light-metal hydride, protected by mineral oil and suspended by dispersants to keep the particles from settling out of the suspension. (Safe Hydrogen originally developed the concept using lithium hydride, but is further developing it with magnesium.)

The oil forms a protective coating around the hydride particles that slows the movement of water toward the particle.

This protective coating allows the hydride to be safely handled and stored in the air without absorbing moisture from the air. It also slows the kinetics of the reaction allowing the development of reaction vessels to mix the hydride with water for releasing hydrogen.

A prototype on-board hydrogen generator developed earlier by Safe Hydrogen consists of storage vessels for the hydride slurry and a small amount of water, pumps for both the slurry and the water, a mixing reactor, a heat exchanger, and a hydroxide storage tank.

The reactor is a tube with an auger/mixer running through it. Hydride slurry and water are pumped into the reactor at one end, and moved and mixed by the auger/mixer. Excess water is evaporated, absorbing and carrying the heat of reaction out of the reactor with the hydrogen.

Hydrogen and water vapor are separated from the hydroxide product in the head of the hydroxide tank. The water vapor is condensed in the heat exchanger. Condensed water is returned to the water circuit and hydrogen is delivered to the fuel cell.

In the current project, which began in 2004, Safe Hydrogen is targeting developing a MgH2 slurry with an energy density of 3.9kWh/kg and 4.8kWh/L and a mixing system to use MgH2 slurry meeting 2kWh/kg and 1.5kWh/L system targets.

Slurry production and hydroxide recycling are also part of the project.


One unit of slurry, according to the company, carries the potential of generating twice as much volume of hydrogen (at about the same weight) as one unit of cryogenically cooled liquid hydrogen. Liquid hydrogen is a proven method of storing hydrogen, but it takes substantial energy to liquefy the hydrogen and there is continual boil off of hydrogen during storage. Slurry, on the other hand, is stored at normal temperature and normal pressure.



Jesse Jenkins

So, the next question would be what are the energy losses of this H2 storage option and how do these compare to compression and liquidification?

This is an intruiging option for H2 storage and distribution...


Can someone translate this into layman's terms?


Instead of hard to store gas or frozen hydrogen, you store it by mixing it with "sludge" Now it can be easily pumped into cars by anyone and no need for expensive hydrogen cells.

Few questions, how do you recycle the metal that is created by converting sludge into hydrogen? And yes, like said above how much energy is wasted. (although if it si completely made with clean energy, then a small waste of conversion energy would be ok I guess....)


Very broadly, a hydride is a binary chemical compound between hydrogen and another element. A metal hydride decomposes when heated, releasing the hydrogen.

It's a bit like a sponge, except much more solid and stable.

To use metal hydride as a solid hydrogen storage mechanism in a vehicle you need to be able to recharge it with hydrogen gas or swap it out (canister-like)--the latter not very convenient for a car.

You can also use a hydride in a slurry--a suspension of ground-up solid hydride in a liquid. Such a chemical slurry uses reaction with water to release the hydrogen, and that's what Safe Hydrogen is doing.

So in this vision of hydrogen storage, rather than using compressed gas or liquid hydrogen storage on a car, or using a solid hydride storage system that requires recharging form gaseous hydrogen, you use the slurry -- which could be pumped into your car just about the way we pump liquid fuels now.

Assuming they get the system components down to a reasonable size, it's a way to avoid having to build up additional refueling infrastructures and systems to support hydrogen fueling.

That said, there are other elements and processes that would have to be in place -- a system and process for removing the reaction byproduct from the car (magnesium hydroxide), and systems for reconstituting the hydride slurry. All of which would factor into the overall analysis of the effectiveness of the system, as Jesse points out above.

On the regeneration side, it's a carbo-thermic reduction process, i.e., relying on carbon and heat. The company earlier envisioned regeneration being performed in centralized plants much like refineries using technologies synergistic with blast, aluminum reduction, and glass furnaces. The metal hydroxide (the byproduct) and carbon are fed to a radiant reduction reactor where they are heated to high temperatures. During this reaction, hydrogen and carbon monoxide are released and the metal is melted.

Hydrogen and carbon monoxide are separated from the metal and from each other. Carbon monoxide is put through a shift reaction to form carbon dioxide and hydrogen. The hydrogen is used to produce electric power and new metal hydride. The CO2 is captured for sequestration.

There is a more detailed description in the first document under Resources above.

Part of this three-year project is working through an efficient mechanism for such carbo-thermic regeneration.

Roger Arnold

I first heard about this process a couple of years ago. I thought then that it would be a great way to provide range and fast refueling for small electric vehicles where clean and quiet operation, rather than cost of fuel, was the dominant consideration.

I was thinking, in particular, of snowmobiles for ski areas and upscale winter playgrounds. Trail bikes for park rangers and tour vehicles for national parks would be other examples. But neither fuel cell technology, nor Safe Hydrogen's production capacity were really mature enough for commercial use at that time.

Still seems like a natural market, however. Anybody have a few million dollars they'd like to invest?


Hey Mike, but if you're using heat and carbon to regenerate MgH2, with a CO2 release (even if a sequestration occur), what's the bennefit? I can't say much, but I believe such proccess doesn't have a nice efficiency and, besides, if you use carbon/coal resulting in CO2, where is the 'renewable energy issue' in it? Not much different from today coal thermal plants then.

They could use some form of electrolysis process to regenerate the MgH2 from Mg(OH)2 (is this the byproduct?), because such processes can be easily sustained with electricity, which can be made out from solar power of wind power plants, which are very clean and would be actually renewable.


You can't regenerate magnesium with carbon; magnesium will burn in an atmosphere of carbon dioxide.  You have to do it electrolytically.

The hydride in this case is something like magnesium hydride, MgH2.  It reacts with water:  MgH2 + H2O -> MgO + 2 H2.  The losses in the regeneration might not be as bad as the recent proposal to react pure metal with steam to make hydrogen (much worse than 50%, IIRC).  Links in the comments here.

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