Gallium: A catalyst for the green future
Metal Tech News - November 13, 2023
Last updated 11/13/2023 at 12:05pm
Liquid metal again displays an almost magical ability to become a catalyst for lowering CO2 in the atmosphere
A liquid metal with semiconductor properties that make it an essential ingredient in next-generation smartphones, telecommunication networks, and solar technologies, gallium already lives at the edge of science fiction and science reality. Working at this threshold, Australian scientists are demonstrating that gallium may also be a major catalyst for the green energy future.
Working behind the scenes to create rubbers, plastics, paper, and other products that we use every day, catalysts are metals or metal compounds that facilitate and accelerate chemical reactions without participating in the reaction.
Using gallium as a medium, a research team from the University of Sydney and University of New South Wales has created a liquid metal catalyst that could greatly reduce the carbon dioxide footprint of chemical manufacturing.
"Our method offers an unparalleled possibility to the chemical industry for reducing energy consumption and greening chemical reactions," said Professor Kourosh Kalantar-Zadeh, head of the University of Sydney's School of Chemical and Biomolecular Engineering.
While much of the global focus on reducing CO2 going into the atmosphere has been on obvious emitters such as vehicles and the generation of electricity, several industrial sectors of the global economy are also major contributors. This includes the production of chemical products such as plastics, fertilizers, and fuels, which account for nearly 15% of global CO2 emissions and climbing.
"It's expected that the chemical sector will account for more than 20% of emissions by 2050," said Kalantar-Zadeh. "But chemical manufacturing is much less visible than other sectors – a paradigm shift is vital."
A liquid gallium-nickel catalyst developed by an Australian team of scientists led by Kalantar-Zadeh could substantially lower the energy required for these chemical processes, and thus the CO2 emitted by them.
Gallium super catalyst
While the chemical sector and the catalysts that enable it are largely unseen, they are an essential part of modern life. From beer and cheddar cheese to laundry detergent and plastic jugs, catalysts are an essential part of modern life.
Traditionally, these chemical processes use platinum, palladium, aluminum, nickel, and other metals or metal compounds as catalysts. The reason why these chemical processes tend to emit so much CO2 is because they require temperatures sometimes exceeding 1,000 degrees centigrade (1,800 degrees Fahrenheit), which translates to a lot of energy.
If these catalysts were liquid at near room temperature, however, they could do their work without so much energy input and CO2 output.
"Theoretically, they can catalyze chemicals at much lower temperatures – meaning they require far less energy," Kalantar-Zadeh said.
Gallium's melting point happens to be 86.5 degrees Fahrenheit, which means the heat from your hand is enough liquify it. While this liquid metal is not inherently a catalyst, it has the uncanny ability to take on catalytic properties of metals that are.
The primary reason for this is that the catalytic atoms floating around in liquid gallium are more randomly arranged and have greater freedom of movement than they do when they are solid. This allows them to easily come into contact with, and participate in, chemical reactions.
To create a near-room-temperature catalytic fluid capable of turning cooking oil into useful chemicals, the Australian research team dissolved high-melting-point nickel and tin in a gallium-based liquid metal.
"By dissolving nickel in liquid gallium, we gained access to liquid nickel at very low temperatures – acting as a 'super' catalyst. In comparison solid nickel's melting point is 1,455 degrees centigrade (2,650 degrees Fahrenheit)," said Junma Tang, who works jointly at the University of Sydney and University of New South Wales. "The same effect, to a lesser degree, is also experienced for tin metal in liquid gallium."
The metallic catalysts were dispersed in the gallium-based liquid metal at the atomic level.
"So, we have access to single atom catalysts," said Arifur Rahim, senior author of a scientific paper on the findings published in Nature Nanotechnology and DECRA Fellow at the University of Sydney's School of Chemical and Biomolecular Engineering. "Single atom is the highest surface area accessibility for catalysis which offer a remarkable advantage to the chemical industry."
With this liquid metal super catalyst, the scientists were able to break down canola oil molecules into smaller organic chains, including propylene, a high-energy fuel that is often used in clothes, outdoor furniture, automotive parts, boats, and a wide range of other products.
The researchers said their formula could also be used for other chemical reactions by mixing metals using low-temperature processes.
"It requires such low temperature to catalyze that we could even theoretically do it in the kitchen with the gas cooktop – but don't try that at home," Tang said.
More liquid metal catalysts
This is not the first time the Australian research team has transformed gallium into a liquid metal catalyst capable of lowering the amount of CO2 in the atmosphere.
In 2021, a 24-member team led by Kalantar-Zadeh and Tang mixed nano-sized silver rods into gallium to create a catalyst able to break atmospheric CO2 down to its constituent parts – oxygen and carbon.
"We are very hopeful that this technology will emerge as the cornerstone of processes that will be internationally employed for mitigating the impact of greenhouse emissions," Kalantar-Zadeh said at the time.
In a paper detailing this technology, the researchers estimate that it will cost about $100 per metric ton to convert CO2 into oxygen and a saleable carbon flake product that could be used in batteries or carbon fiber materials for high-performance products like aircraft, racing cars, and luxury vehicles.
LM Plus, a startup created with support from the University of New South Wales and seed investment from Uniseed, hopes to make this liquid metal CO2 scrubber a reality.
"What we are working towards now is to raise funds to build a larger size proof-of-concept for this system to work within a 40-foot container – the size of a truck trailer – that could ultimately help industrial sites immediately capture any CO2 emissions and convert them," said Paul Butler, a director at LM Plus.
The Australian research team created yet another liquid-metal catalyst in 2022 that is thousands of times better at scrubbing CO2 from industrial exhaust than solid-state platinum.
"To keep the single atoms separated from each other, the conventional systems require solid matrices to stabilize them. I thought, why not use a liquid matrix instead and see what happens," said Rahim.
This pondering led to the discovery of a process to create a metal that enjoyed the liquidity of gallium and the catalytic properties of platinum.
Even more remarkably, at a ratio of less than 0.0001 platinum to gallium, this new liquid metal alloy is 1,000 times more efficient than a solid-state catalyst with around 10% platinum.
The liquidity of the gallium-platinum alloy offers yet one more advantage – it is self-cleaning.
Like a water fountain, the liquid mechanism constantly refreshes itself, self-regulating its effectiveness over time and avoiding the catalytic equivalent of pond scum building up on the surface.
As it turns out, platinum lends its catalytic abilities to gallium, a driving force behind the reaction.
"The platinum is actually a little bit below the surface and it's activating the gallium atoms around it," said Andrew Christofferson, an Exciton Science associate investigator that worked on the project. "So, the magic is happening on the gallium under the influence of the platinum. But without the platinum there, it doesn't happen."
Others have picked up on this magic, including a team at the University of California Santa Cruz that has demonstrated that gallium and aluminum can be used as a catalyst that separates water into oxygen and hydrogen at room temperature and without any energy inputs. The hydrogen produced could be used as zero-carbon emitting fuel.
China restricts exports
Gallium's seemingly magical properties could make the liquid metal a major catalyst for the green future.
One potential setback, however, is that China accounts for roughly 98% of the gallium produced globally. Earlier this year, the communist nation put export restrictions on gallium that require state authorization before any of this futuristic tech metal can be shipped out of the country.
Gallium is currently selling for $766 per kilogram, a 157% increase over the $298/kg selling price in January 2020.