Gallium is platinum's new best friend

Researchers at the University of New South Wales Sydney and the Royal Melbourne Institute of Technology recently made a groundbreaking discovery in the use of platinum. By adding just a pinch of this high-priced precious metal to gallium, they created a liquid-metal catalyst with the potential to significantly extend the Earth's reserves of this valuable metal.

Platinum is generally very effective as a catalyst but is only used when it is absolutely needed at the industrial scale due to its extreme cost, with most catalysis systems involving platinum also having high ongoing energy costs to operate.

When platinum is in its solid state, which is anything below its melting point of 1,700 degrees Celsius (2,732 degrees Fahrenheit), it takes roughly 10% of this precious metal for a carbon-based catalytic system to function.

With its price topping $1,000 per ounce, this is often not an affordable ratio when manufacturing catalytic components and products for commercial sale.

This could change, however, as Australian researchers have discovered that by using trace amounts of liquid platinum combined with liquid gallium, they were able to create cheap and highly efficient chemical reactions at low temperatures, opening a pathway to dramatically reduce carbon emissions in crucial industries – industries such as ammonia synthesis in fertilizer production, which accounts for just over half of the greenhouse gas emissions in the agricultural economic sector, according to the EPA.

The team, including members of the Australia Research Council Centre of Excellence in Exciton Science and the ARC Centre of Excellence in Future Low Energy Technologies, combined platinum with liquid gallium – which has a melting point low enough to liquify in the palm of your hand – to find that the platinum becomes soluble.

In other words, the platinum melts without firing up a hugely powerful industrial furnace.

For this mechanism, processing at an elevated temperature is only required at the initial stage, when platinum is dissolved in gallium to create the catalysis system. Despite this initial firing, roughly five times less heat is required for roughly an hour or so to produce the liquified platinum that remains a liquid at room temperatures.

"If you're working with iron and steel, you have to heat it up to make a tool, but you have the tool and you never have to heat it up again," said contributing author Jianbo Tang of UNSW. "Other people have tried this approach but they have to run their catalysis systems at very high temperatures all the time."

With this new method, using their platinum-gallium catalyst, the researchers used a ratio of less than 0.0001 platinum to gallium. Yet even more remarkably, was that the resulting system proved to be over 1,000 times more efficient than its solid-state rival (the one requiring around 10% platinum to function).

Because it is a liquid-based system, it is evidently more reliable, adding more advantages to this recent breakthrough.

Solid-state catalytic systems eventually clog up and stop functioning; however, that does not happen with liquid platinum-gallium. Like a water feature with a built-in fountain, the liquid mechanism constantly refreshes itself, self-regulating its effectiveness over a period of time and avoiding the catalytic equivalent of pond scum building up on the surface.

"From 2011, scientists were able to miniaturize catalyst systems down to the atomic level of the active metals," said lead author Arifur Rahim of UNSW. "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."

It was found that the mechanism is also versatile enough to perform both oxidation and reduction reactions, in which oxygen is provided or taken away from a substance, respectively.

"The catalytic atoms anchored onto a solid matrix are immobile," Rahim added. "We have added mobility to the catalytic atoms at low temperature by using a liquid gallium matrix."

Turns out, the secret ingredient was gallium all along.

Using advanced computational chemistry and modeling, colleagues at RMIT were able to identify that platinum within liquid gallium never becomes solid, right down to the level of individual atoms.

"What we found is that two platinum atoms never came into contact with each other," said Exciton Science Research Fellow Nastaran Meftahi. "They were always separated by gallium atoms. There is no solid platinum forming in this system. It's always atomically dispersed within the gallium."

Surprisingly, gallium is the driving force behind the chemical reaction, acting under the influence of the platinum atoms within close proximity.

"The platinum is actually a little bit below the surface and it's activating the gallium atoms around it," added Exciton Science Associate Investigator Andrew Christofferson of RMIT. "So the magic is happening on the gallium under the influence of the platinum. But without the platinum there, it doesn't happen. This is completely different from any other catalysis anyone has shown, that I'm aware of."

With the potential to dramatically reduce the cost and content of platinum use, while it may not fall in value, perhaps gallium will see a spike as industries begin to experiment with their own platinum-gallium blends.

The findings were published in the journal "Nature Chemistry."