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USC team finds Li-Al nanoparticles produce hydrogen from water with high rate and yield; potential for industrial scaling

27 June 2014

Aluminum and water react exothermically to form aluminum hydroxide and hydrogen; this basic property has lured numerous researchers interested in generating hydrogen from the aluminum-water reaction for modern transportation systems for at least 35 years. (Earlier post.) However, among the barriers to the practical application of this reaction are the low reaction rate and poor yield.

Now, results of large quantum molecular dynamics (QMD) simulations by a team at the University of Southern California suggest that alloying aluminum particles with lithium to produce hydrogen from water can produce orders-of-magnitude faster reactions with higher yields. Their paper is published in the ACS journal Nano Letters.

Metals such as Al can be used in renewable energy cycles. In a two-step thermochemical cycle, an exothermic reaction between metal and water produces hydrogen gas, followed by endothermic reduction of the metal-oxide product assisted by solar energy to regenerate metal fuel. One potential application of this technology is on-board hydrogen production for hydrogen-powered vehicles, but conventional metal−water reaction kinetics is not fast enough to make such on-demand hydrogen production commercially viable. Previous experimental and theoretical works suggested that remarkable reactivity of “superatoms” (i.e., clusters consisting of a magic number of Al atoms) with water may solve this problem.

… While this superatomic design achieves high reaction rates in nanometer-size clusters, unfortunately, it does not scale up to larger particle sizes of industrial relevance. For larger particles, surface atoms begin to lose acid−base distinction that originates from local geometrical differences on nanocluster surfaces. More seriously, formation of an inert oxide or hydroxide layer associated with the hydrogen-production reaction protects the metal core and thereby stops the reaction incomplete. This leaves a large fraction of Al atoms unreacted, leading to low yields. Radically new design principles are thus needed for scalable high-yield H2 production.

—Shimamura et al.

In the study, the USC team performed large QMD simulations on a parallel supercomputer consisting of 786,432 processors to provide spatially and temporally resolved reaction dynamics of LinAln particles at the atomic resolution (n = 30, 135, and 441). The total numbers of atoms involved in the simulation were 606, 4,836 and 16,611, respectively, for the Li30Al30, Li135Al135, and Li441Al441 systems.

Master.img-001
(a) The 16,611-atom system, where cyan, green, white, and red spheres represent Li, Al, H, and O atoms, respectively. (b) Hydrogen production rate as a function of temperature (red circles with error bars), where the blue line is the best fit to the Arrhenius equation. Credit: ACS, Shimamura et al. Click to enlarge.

A total of 1, 4, and 19 H2 molecules were produced from water using Li30Al30 within 10 ps at temperatures 300, 600, and 1500 K (26.85 ˚C, 326.85 ˚C and 1,226.85 ˚C), respectively. The reaction rate was drastically higher than Aln (n is between 12 and 55), for which no H2 production was observed at 300 and 600 K within a similar time frame.

The LinAln particles also appear to have overcome the problem of formation of a passive oxide or hydroxide coating layer on the particle surface, which prohibits reaction of the inner Al core with water—i.e., the aluminum core remains unreacted. This is one of the key barriers in aluminum-water technology.

The USC team found a high yield of H2 production reactions from water using LinAln particles, with no Al atom remaining unreacted at the end of the simulation. By contrast, most of the Aln particles remained unreacted.

The team determined that the abundance of neighboring Lewis acid−base pairs is a key nanostructural design element through which water-dissociation and hydrogen-production require very small activation energies. These reactions are facilitated by charge pathways across Al atoms that collectively act as a “superanion” and a “surprising” autocatalytic behavior of bridging Li−O−Al products.

Furthermore, they found, the dissolution of Li atoms into water produces a corrosive basic solution that inhibits the formation of a the reaction-stopping oxide layer on the particle surface, thereby increasing the yield.

These atomistic mechanisms not only explain recent experimental findings but also predict the scalability of this hydrogen-on-demand technology at industrial scales.

—Shimamura et al.

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June 27, 2014 in Hydrogen, Hydrogen Production, Water | Permalink | Comments (25) | TrackBack (0)

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We badly need a cheap mean of producing plenty of hydrogen gas for cars and truck. When gonna we have cheap hydrogen without any pollution. Since then I must rely on my cheap dodge neon 2005 that still drink a lot of costly polluting gasoline. We should fine goverments and car manufacturers and big oil, im not responsible of pollution and economic distress because I know that hydrogen should be the future and im saying it.

Hydrogen has been falsely long known as the magic fuel. Hydrogen must be produced from water with another source of energy which is fossil fuel or electricity from any source. There is no large source of nearly pure hydrogen except the Sun and it is too expensive. Any hydrogen on earth is also expensive especially that made from aluminium and water. Much electricity is used to make aluminium and is better stored in batteries for use in electric vehicles. There is no extra hydropower in the world for making aluminum for fuel. Sodium is a more compact and easier to produce fuel than aluminum. Sodium sulphur batteries could be modified to fuel cells or flow batteries for nearly direct use and are cheaper than hydrogen fuel cells.

The combined hydraulic hybrid technologies of Artemis and INNAS NOX could reduce fuel consumption to half of present for all types of motor vehicles at no higher costs than present transmissions; so hydrogen and fuel cells and biofuels are not necessary or economical. ..HG..

Reducing liquid fuel consumption for 1B to 2B ICEVs by up to 50% would only extend the availability of non-renewable fuels by a few decades.

GHGs, climate changes and associated ill-effects would still be major unsolved problems, specially when the total world fleet goes from 1B to 2+B.

The world has to progressively switch to cleaner vehicles and clean sustainable energy sources. Electricity is ideal and H2 is a good storage medium for extended range vehicles. Short and mid-range light vehicles and domestic energy storage could use lower cost more efficient batteries.

Harvey,

Previously you said we had 50 years of oil, if you reduce consumption by half you now have 100 years. We know fossil fuels are finite, so increasing mileage while blending synthetic and bio synthetic fuels with refined product makes sense.

That gives us time to transition, at the present sales of about 0.1% EV, we will need all the time we can get to improve batteries and fuel cells. Saying we should not make fuels because it will delay adoption of EV makes as much sense as jumping out of a plane without a parachute based on the idea that we will think of something on the way down, we will be forced to.

Ah but can the CLIMATE handle another 50-100 years of us burning oil?

This is why you make bio synthetic fuel, the plant absorbs carbon while it grows. I certainly don't advocate burning more coal for 100 years to charge EVs.

Its an interesting use of Al-Li alloy to generate hydrogen but the process is inefficient and costly. No data on recycling Al alloy either. Its better to invest in recycleable Al air battery. Israeli start up Phinergy has demonstrated 330 km car using Al air battery. Partnership and investment from Alcoa make them very credible.

Given the hype about hydrogen, I'm surprised that its advocates haven't suggested mining Jupiter yet.

The reaction of water with aluminum is VERY exothermic, meaning a lot of the energy in the metal is lost as heat and never appears as hydrogen.  I once calculated how much energy that was, but I can't find that now.

@SJC.

Good observations but ground vehicles are not the only users of fossil and bio-fuels? The world do not have to use dirty CPPs. There are many other clean energy sources.

@ai_vin.

Yes, a very import point that too many posters would like to ignore.

More efficient lower cost ways will soon be found to extract huge quantities of H2 from water, store, transport and use it. It is an excellent clean and very abundant energy medium.

Good point, EP , re. the inefficiency of metal to H2.
A better and more efficient H2 carrier would be hydrocarbons, in either gaseous or liquid form, thus allow easy pipeline transportation. Adding GHG-free H2 to waste biomass during pyrolysis will allow incorporation of these H2 much more efficiently and cheaply to produce gasoline, diesel, and jet fuels that do not require new infrastructure. ICEV and HEV are getting more and more efficient.

I think the sodium amide process may clinch ammonia as the preferred carrier for hydrogen.  At 17.6% H2 by weight, it beats the 11% for water even before adding in the burden of aluminum.

Yeah, but CH4 contains even more H2 by weight and even much more energy than NH3. No other H2 carrier can beat CH4 at 25% by wt.

Yes, but use of CH4 generally converts it to CO2, which is then dumped.  CO2 is expensive to recover from the atmosphere, while N2 is dirt cheap.

You use the carbon from reforming natural gas to H2 to create synthetic fuels, rather and putting it into the atmosphere. Going from natural gas to DME to diesel requires more carbon and now you have it.

I thought the point was to stop using natural gas, period.

Question: Would adding "GHG-free H2 to waste biomass during pyrolysis" reduce the amount of biochar produced? I ask because biochar is under investigation as an approach to carbon sequestration to produce negative carbon dioxide emissions. Biochar thus has the potential to help mitigate climate change. Independently, biochar can increase soil fertility, increase agricultural productivity, and provide protection against some foliar and soil-borne diseases. Biochar is a stable solid, rich in carbon and can endure in soil for thousands of years.

ai vin,

Cool Planet produces a lot of bio char because that is how their process works. I advocate adding more H2 to make more fuels. There is a market for fuels, they are still looking for customers to buy billions of tons of biochar.

@ai-vin,
Pyrolysis releases a lot of CO2 and biochar, the proportion of the latter can be controlled, but some biochar will be inevitable. The addition of H2 will reduce or eliminate CO2 release, but not affecting biochar proportion much.

Production of biochar is a very expensive way to increase soil fertility, which is exactly what proponents seem to want. You'll find that soil liming, fungal development, and NPK are far more effective at increasing soil fertility and a biome of carbon sequestration than trying to dig in carbon. the idea of tillage and adding compost to a depth of six or so inches is that you would do it as LITTLE AS POSSIBLE -- maybe as little as once in 20 years, and use deep root dry cropping to eliminate tillage.

In fact control burns are the only practical way to deal with dessicated, dry rotting and vine infested forests, which emit vast amounts of methane and NOx, while not pulling their weight in carbon reabsorbtion. We can't seriously chop down every tree and late season hay stand in order to char them!

@ SJC

BP has recently confirmed that Oilcos will be pumping Oil for another 53.8 years. It may turn out to be 85+ years or till the end of the current century? The last drops will cost more to extract.

Fossil, bio and nuclear energies will progressively be replaced with unlimited, lower cost, clean renewable energy sources. It will be done without competing with food production.

Due to the huge funds involved, the transition will take many decades. The move has started and will gain speed as clean energy storage cost is reduced and as the ill effects of increasing GHG is better known.

Harvey,

You have to look at what happens between now and then. If oil goes to $200,$300,$400 per barrel and oil exporters have all the customers in Asia they want, the supposed EV/FCV revolution will not mean much.

It will take decades to even make a difference with the present low sales of EVs. Even IF the sales increase you will not replace 1 billion cars with EVs in the next 40 years. Get realistic and practical about a transition. Bio synthetic fuels using crop waste will not affect food, land nor water.

This is the kind of solution we NEED for the next 40 years. Gasify biomass like corn stalks and synthesize gasoline, diesel and jet fuel. It is a realistic and rational option for us to obtain "sustainable mobility", which is the purpose of this site.

The typical lifespan of a vehicle is on the order of 15-20 years.  If anything is certain, it's that today's vehicle fleet WILL be replaced over the next 40 years, likely 2 and possibly 3 times over.

The development of biowaste-solar-wind synthetic fuels can proceed in parallel to the growth of PEV's and FCV's since many people will resist change and will continue to buy ICEV's. Better to not put all eggs in one basket.

Synthetic fuels from RE may already be cost-competitive with deep sea oil or artic oil, so eventually it will make economic sense to make the fuels on the surface and not having to dig real deep while the cheap oil sources are being depleted.

Burning more and more fossil and bio fuels thereby creating larger climate changes (and the quick rise of djihadism) are the major problems we may be facing in the not too distant future.

It is much like cigarette smoking. You cannot just slow down (it doesn't work), you have to stop.

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