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3D-printed single-atom catalysts make making stuff easy

What if you could 3D-print a substance that turned wastewater into fertiliser, converted CO2 back into useful materials, and efficiently made hydrogen fuel out of water?

And – crucially – what if you could do it cheaply? All of this is possible, but expensive.

Now an international team of scientists has developed a simple and cost-effective technique for 3D-printing “single-atom catalysts”.

Like all catalysts, these substances make chemical reactions faster and less energy intensive.

But single-atom catalysts are particularly exciting because they’re extremely efficient, which means reactions can be done with even less energy and waste.

Single-atom catalysts are not, quite, single atoms. Instead, they’re individual metal atoms deposited onto a substance – usually a tiny solid scaffold.

Because the metal atoms are dispersed, and don’t crowd each other out, they can each do their job with maximum efficacy, turning reagent molecules into products.

“This unique advantage drives my research team to study this new kind of catalyst,” says Professor Shizhang Qiao, director of the University of Adelaide’s Centre for Materials in Energy and Catalysis, and senior author on a paper describing the research, published in Nature Synthesis.

Until now, single-atom catalysts have been very difficult and costly to make. But Qiao and colleagues have shown that it’s possible to make them with a 3D printer, in just a few minutes.

Synthesis diagram
The process for making the single-atom catalysts. Credit: Xie, F., Cui, X., Zhi, X. et al. A general approach to 3D-printed single-atom catalysts. Nat. Synth (2023).

They used a 3D bioprinter to make the scaffold.

The printing ink included natural polymers and metals.

“Among those natural polymers, most of them are commercially available,” says Qiao.

“This makes me believe that other researchers might easily pick up this process.”

Once made, researchers at the Australian Synchrotron used X-ray spectroscopy to show that the scaffolds did really have isolated atoms on them.

Person at synchrotron
Dr Bernt Johannessen at the Australian Synchrotron X-ray absorption spectroscopy beamline. Credit: ANSTO

Qiao and colleagues then tested the method by making a set of single-atom catalysts designed to convert the nitrates in wastewater into ammonia.

Ammonia is a crucial ingredient for fertilisers, pharmaceuticals, and a range of other substances. It’s also tipped to become a major energy player in the next three decades, because it can help store hydrogen fuel.

But there could be a number of other processes that the single-atom catalysts can help to make easy.

“My research group has employed various electrocatalysts in different reactions,” says Qiao.

“For example, we developed a new kind of catalyst for water splitting to produce hydrogen, carbon dioxide reduction to produce useful chemicals and fuel, oxygen reduction reaction for fuel cells, and urea-rich wastewater oxidation.

“All these applications are beneficial to renewable energy technology.”

The researchers believe single-atom catalysts could be available for the chemical engineering industry in the next decade.

“By simplifying the way catalysts are manufactured, this new technique has the potential to advance Australia’s status as a global leader in tackling the effects of climate change and help us take the lead in new techniques for making chemicals that benefit society,” says Qiao.

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