Aluminum itself oxidizes rapidly in water, stripping oxygen from the water and releasing hydrogen as a by-product. But it was a short-lived reaction because, in most cases, the metal quickly formed an extremely thin coating of aluminum oxide, sealing it in, ending the reaction.
But chemistry researchers at UC Santa Cruz say they’ve found a cost-effective way to keep the reaction going. Gallium has long been known to remove the aluminum oxide coating, allowing the aluminum to come into contact with water to continue the reaction, but previous studies have found that the combined effect of aluminum weight is limited.
So when chemistry/biochemistry professor Bakthan Singaram found out that student Isai Lopez was at homekitchenWhen playing with aluminum/gallium hydrogen production, the idea doesn’t seem to be anything special. “He didn’t do it in a scientific way, so I assigned him a graduate student to do a systematic study,” Singaram said. “I think it would be a good senior thesis for him to measure the hydrogen output of different ratios of gallium and aluminum.”
Things got a little weird when Lopez decided to expand the experiment to test a mixture of heavy gallium. The production of hydrogen began to increase rapidly, and the team set out to try to figure out why the mixtures behaved so differently. After studying electron microscopy and X-ray diffraction, they realized that the most effective mixture, three parts gallium and one part aluminum, did show something that the lower ratio didn’t. Gallium not only dissolves the aluminum oxide, it also separates the aluminum into nanoparticles and keeps them separate.
“Gallium separates the nanoparticles so they don’t aggregate into larger particles,” Singaram said. “People have been working hard to make nanoparticles of aluminum, and here we are producing them at normal atmospheric pressure and room temperature.”
Because the aluminum is so finely separated, its surface area is maximized, and the reaction with water is surprisingly efficient, pulling out 90% of the theoretical maximum amount of hydrogen for a given amount of aluminum. In a study published in the journal ACS Nanomaterials, the researchers report that when one gram of their gallium-aluminum alloy is placed in water, 130 milliliters of hydrogen is rapidly released.
It is worth noting that the water source also does not need to be clean. “Any available water source can be used, including wastewater, commercial beverages, and even sea water, and will not produce chlorine,” the study said.
Gallium is expensive, however. But the researchers say it could be fully recovered at the end of the process and used with new aluminum to create more of this remarkable hydrogen-producing alloy. In fact, the alloy itself is very easy to make; one simply mixes gallium and aluminum (including used foil or cans) together in the correct proportions by hand.
“Our method uses a small amount of aluminum, which ensures that it all dissolves into most of the gallium as discrete nanoparticles,” Oliver said. “This produces a large amount of hydrogen, which is almost complete compared to the theoretical value based on the amount of aluminium. It also makes the recovery of gallium easier to reuse.”
The team has filed a patent for the process and has begun researching how to scale it up for commercial use.
So what are we seeing here? This is actually a solid-state way of storing and releasing hydrogen — notably, the third hydrogen storage powder ever written in the past few months. Hydrogen is an important fuel, necessary in some applications in the race to decarbonize, but it is notoriously difficult and expensive to compress into a gas, or cryogenically condense into a liquid for storage and transport .
Hydrogen storage powders, on the other hand, are easier to handle and cheaper, and have the potential to dramatically change the cost of using hydrogen, making new applications feasible. That’s why Deakin’s mechanochemical ball milling process and EAT’s Si+silicon powder are so important.
This advance at UC Santa Cruz could also be such a big deal. This thing sounds very easy to make and easier to use for hydrogen production. It can be stored and transported well for at least three months if stored in cyclohexane gas. The fact that it works in sea water is very important; getting clean water is not the kind of thing you want to bet on in your future business. The fact that gallium can be collected and recycled into the process will help keep costs down. Also, the reaction is carried out at ambient pressure and temperature, which means less equipment can be used at the very end of the entire operation, since hydrogen is actually required.
So how does it measure up compared to the other two powders? The numbers provided by the researchers allow us to at least guess. If you think of this stuff as a hydrogen storage medium, the key metric might be mass fraction: how much hydrogen can you get for a given mass of powder? If one gram of gallium aluminum powder produces 130 milliliters or 5.4 mmoles of hydrogen, then the weight of hydrogen is 0.00544 grams.
This is a quality score of 0.544%. EAT’s Si+ powder is probably the most popular substance at this stage, at least on this metric, with a claimed mass fraction of 13.5%. Of course, when talking about commercial energy transport and release cycles, there are many other considerations — especially not being picky about water quality — so there’s certainly still a chance this new powder can contribute.
The study was published inACS Nanomaterials” magazine.