Scientists at the University of California Santa, Santa Cruz (UCSC) have developed a new method to efficiently generate hydrogen from water at ambient temperatures using aluminium and gallium.
Aluminium is an excellent candidate material for this purpose because the highly reactive metal easily reacts with the oxygen molecules in water to release hydrogen gas. But the pure form of the metal is so reactive that it instantly reacts with air to create a coating of aluminium oxide on its surface, meaning it cannot react with water.
That is where gallium comes in. Gallium is liquid at slightly above room temperature and it removes the aluminium oxide coating that forms on the bare metal, allowing it to be in direct contact with the water and react with it. The reaction of aluminium and gallium with water to produce hydrogen gas is already common scientific knowledge but the new technology features innovations that bring it closer to practical applications.
According to the researchers, previous such studies mostly focused on using aluminium-rich composites. But they discovered that using a gallium-rich mixture led to an unexpectedly high rate of hydrogen production. This discovery was made by co-author Isai Lopez, who is a student of Bakthan Singaram, the co-corresponding author of the paper.
“After the process, we could easily recover 95 per cent of Gallium that was used, without optimisation. The only other product that was formed was Alumina [Aluminium Oxide], which can be used for many other applications,” Scott Oliver, co-corresponding author of the research article, told indianexpress.com over email.
This is important because gallium is an expensive and rare mineral. Alumina has many applications including in spark plugs, abrasion-resistant tiles and cutting tools.
Due to the new proportion of the composite, not only was gallium removing the aluminium oxide coating, but it was also separating the aluminium into nanoparticles, which helped speed up the reaction. The researchers found that a 3:1 ratio of gallium and aluminium in the composite was the optimum ratio for the highest hydrogen production. Further, the composite is very easy to form. The researchers created it by manually mixing small amounts of aluminium into gallium.
While it remains to be seen whether this technology can be scaled up to produce hydrogen in commercial quantities, the researchers are optimistic. “It should be possible to scale up the technology to industrial levels of production. We were only limited by our apparatus to measure the hydrogen volume and the campus limits on hydrogen. Scale-up will require control of mixing the alloy but the reaction is spontaneous once the water is added,” added Oliver.
The worldwide push for electric vehicles has largely focused on battery electric vehicles (BEVs), which typically use lithium-ion batteries to store electricity that can be used to propel the vehicle using electric motors. An alternate technology involves the use of “hydrogen fuel cells” to generate electricity from hydrogen and use that to power the vehicle.
Hydrogen fuel cell vehicles present some advantages over BEVs—they can be refuelled with hydrogen as fast as a conventional vehicle can be refilled with fossil fuels. Also, they reduce dependence on minerals like lithium and cobalt, which are used to produce lithium-ion batteries.
But the use of hydrogen also comes with a major disadvantage. According to the US Department of Energy, a majority of the world’s hydrogen gas production comes from reforming fossil fuels like natural gas. And producing hydrogen using electricity from renewable sources is an energy-intensive process. New technologies like the one produced by the UCSC could remove this barrier to large-scale hydrogen fuel adoption.
Update (10.57 AM, September 14, 2022): The article has been updated to attribute the discovery of using a gallium-rich mixture to Isai Lopez and Bakthan Singaram.