BMW Z3 exhaust. Image: Ben Smith/Shutterstock
A new breakthrough could lead to clean fuels from carbon dioxide or water powering cars and homes.
A collaborative study involving scientists from Trinity College Dublin (TCD) has managed to squeeze a fourfold boost with cerium oxide, a catalyst used in clean energy.
The study also involved scientists from Stanford University, SLAC National Accelerator Laboratory, Lawrence Berkeley National Laboratory and the University of Pennsylvania.
‘Whether we stretched or compressed the ceria, we found that the strained films showed a fourfold increase in oxygen capacity, which is pretty huge’
– MAX GARCÍA MELCHOR
Published today (18 May) in the scientific journal Nature Communications, the scientists were able to achieve the breakthrough using cerium oxide, or ceria, a spongy material commonly used in catalytic converters, self-cleaning ovens and various green-energy applications, such as fuel cells and solar water splitters.
“Ceria stores and releases oxygen as needed, like a sponge,” said Will Chueh, assistant professor of material science and engineering at Stanford, and a faculty scientist at SLAC.
“We discovered that stretching and compressing ceria by a few percent dramatically increases its oxygen storage capacity. This finding overturns conventional wisdom about oxide materials and could lead to better catalysts.”
Colourised transmission electron microscopy of ceria ultra-thin film reveals that individual atoms (shown as dots) shift under intense pressure. Image: Sang Chui Lee
Ceria helps to remove air pollutants from vehicle exhaust systems, essentially taking oxygen from poisonous nitrogen oxide to create harmless nitrogen gas. It then releases stored oxygen and converts lethal carbon monoxide into benign carbon dioxide.
Studies have shown that squeezing and stretching ceria causes nanoscale changes that affect its ability to store oxygen. In particular, it has been suggested that stretching ceria would increase its capacity to store oxygen, whereas compressing it would decrease this capacity.
Surprise results
Assistant professor in the School of Chemistry at TCD, Max García Melchor. Image: TCD
To test this prediction, the research team grew ultra-thin films of ceria, each just a few nanometres thick, on top of substrates made of different materials. This process subjected the ceria to enormous stress, equal to 10,000 times the Earth’s atmosphere, and caused its molecules to separate and squeeze together, at a distance of less than one nanometre.
Typically, materials such as ceria relieve stress by forming defects in the film – but atomic-scale analysis revealed a surprise. Analysis of the position of individual atoms showed that the films of ceria remained stretched or compressed without any defects – allowing the stress to remain in full force.
The researchers then used the brilliant beams of x-ray light produced at Lawrence Berkeley National Laboratory’s Advanced Light Source along with supercomputers to measure the impact of stress under real-world conditions.
“Whether we stretched or compressed the ceria, we found that the strained films showed a fourfold increase in oxygen capacity, which is pretty huge,” said Max García Melchor, assistant professor in the School of Chemistry at TCD.
Melchor said that there are a lot of potential applications for this, in using catalysis to improve the efficiency of energy conversion and storage, including in green-energy technologies.
“We hope that we may use this discovery to develop new clean fuels from carbon dioxide or water to power our cars and homes, for example.”
