“We don’t need any energy input, and the hydrogen is bubbling like crazy. I’ve never seen anything like it,” said Professor Scott Oliver of UCSC, describing a new powder of aluminum and gallium nanoparticles that generates H2 when placed in water – even seawater.
Aluminum by itself oxidizes rapidly in water, removing O from H2O and releasing hydrogen as a by-product. This is a short-lived reaction, however, as in most cases the metal quickly reaches a thin, microscopic layer of aluminum oxide that seals it in and ends the pleasure.
But UC Santa Cruz chemistry researchers say they’ve found a cost-effective way to get things done. Gallium has long been known to remove the aluminum oxide coating and hold the aluminum in contact with water to continue the reaction, but previous research has shown that aluminum-heavy combinations have limited effect.
So when chemistry/biochemistry professor Bakthan Singaram discovered student Isai Lopez was toying with aluminum/gallium hydrogen production in his kitchen at home, there didn’t seem to be anything particularly special about the idea. .
“He wasn’t doing it in a scientific way, so I set him up with a graduate student to do a systematic study,” Singaram said. “I thought it would make a good thesis for him to measure the hydrogen production of different ratios of gallium and aluminum.
When Lopez decided to expand the experiment to test gallium-rich mixtures, things got a little weird. Hydrogen production exploded, and the team began trying to figure out why these mixtures behaved so fundamentally differently.
After electron microscopy and X-ray diffraction studies, they realized that the most efficient mixture, three parts gallium to one part aluminum, did indeed do something that the lower ratios did not. Not only did the gallium dissolve the aluminum oxide, but it also caused the aluminum to separate into nanoparticles and kept them separated.
“The gallium separates the nanoparticles and prevents them from aggregating into larger particles,” Singaram said. “People have struggled to make aluminum nanoparticles, and here we produce them under normal atmospheric pressure and room temperature conditions.”
With the aluminum so finely separated, its surface area is maximized and the reaction with water was spectacularly efficient, extracting 90% of the theoretical maximum amount of hydrogen possible for a given amount of aluminum. In a study published in ACS nanomaterialsthe researchers report that a single gram of their gallium-aluminum alloy rapidly releases 130 ml of hydrogen when placed in water.
Remarkably, the water source also does not need to be clean.
“Any available water source can be used,” the study states, “including sewage, commercial beverages, or even seawater, without generation of chlorine gas.”
Now, yes, gallium is expensive. But researchers say it can be fully recovered at the end of the process and used with fresh aluminum to create more of this remarkable hydrogen-producing alloy. Indeed, the creation of the alloy is extremely easy in itself; one simply mixes the gallium manually with aluminum, including aluminum foil or used cans, in the correct ratio.
“Our method uses a small amount of aluminum, which ensures that everything dissolves in the majority of the gallium as discrete nanoparticles,” Oliver said. “This generates a much larger amount of hydrogen, almost complete compared to the theoretical value based on the amount of aluminum. It also facilitates the recovery of gallium for reuse.
The team has filed a patent application on the process and is beginning to examine how it will evolve commercially.
So what are we looking at here? Well, it’s effectively a solid-state way to store and release hydrogen – remarkably, the third hydrogen storage powder we’ve written about in the past two months, if ever. Hydrogen is an important fuel that will be needed in some applications during the decarbonization race, but it is notoriously difficult and expensive to compress into a gas, or cryogenically condense into a liquid, for storage and transportation.
A hydrogen storage powder, on the other hand, is much easier and cheaper to handle, which can change the cost of working with hydrogen so drastically that new applications become viable. That’s why Deakin’s mechanical-chemical ball milling process and EAT’s Si+ silicon powder were so important.
And why this lead from UCSC could also be so important. This stuff looks extremely easy to make and even easier to use for hydrogen production. It will keep and travel well for at least three months if stored in cyclohexane gas. The fact that it works in seawater is extremely significant; access to clean water is not the kind of thing you would want to bet a volume business on to get ahead. The fact that gallium can be collected and recycled in the process will help reduce costs. And the fact that the reaction happens at ambient pressures and temperatures means you can get by with less equipment at the sharp end of the whole operation where you actually need the hydrogen.
So how does it compare to these other two powders? Well, the figures provided at least allow us to guess. If you’re treating this material as a hydrogen storage medium, the key metric is probably mass fraction: for a given mass of powder, how much hydrogen can you extract? Well, if one gram of gallium-aluminum powder produces 130 ml, or 5.4 mmol of hydrogen, that hydrogen would weigh 0.00544 grams.
This is a mass fraction of 0.544%. Not much chop, really; EAT’s Si+ powder is probably the stuff to beat at this point, at least on this metric, claiming a mass fraction of 13.5%. Of course, there are many other considerations when you’re talking about a commercial cycle of transporting and releasing energy – especially one that isn’t fussy about water quality – so there are certainly still opportunities for this new powder to make a contribution.
The research is published in the journal ACS nanomaterials.
Source: University of Santa Cruz