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Chemical reactions occur trillions of times every second in our world, from photosynthesis in plants, ammonia production in industry and the combustion of petrol in our cars. These reactions all need energy, sunlight, heat or electricity to get started or to keep going.
This is where the research of Dr Peter Sherrell, an Elizabeth & Vernon Puzey Research Fellow in the Department of Chemical Engineering at the University of Melbourne, comes in. Dr Sherrell is working to design new catalysts; small molecules or materials that lower the amount of energy needed for a reaction without being used up themselves. These catalysts make reactions cheaper, faster and more efficient.
Helping reactions out
Researchers have been trying to design new and better catalysts for a long time – tailoring their chemistry, shape and size to come up with catalysts that can dramatically speed up the reaction. But many challenging reactions critical for a transition to a green future – such as water oxidation, carbon dioxide reduction or ammonium reduction – still require more help (or energy) to proceed. This help normally comes from sunlight (photo-catalysts), electrical energy (electro-catalysts) or both (photo-electro-catalysts).
The problem here is with electro or photo-electro-catalysis the stored energy within these green fuels (for example hydrogen or ammonium) is often not much more than the electrical energy needed to make them.
This means we need to figure out a way to get rid of this need for electricity, so scaleable future fuel production is possible. A simple way to engineer this is to harvest energy from the environment, from a solar cell, wind power or water flow and hook it straight up to the catalyst. However, this approach – with separated energy source and catalyst – doesn’t lend itself to use at an industrial scale, simply due to energy losses.
Footsteps to fuel
Dr Sherrell is doing something different. He’s taking the energy from mechanical motion – the flow of water, a gust of wind, the step of the foot – to provide that extra help. The effect he’s exploiting is called the piezoelectric effect, the conversion of mechanical-to-electrical energy. This piezoelectric effect is powerful, producing up to 10x more driving force than the energy from the sun.
Dr Sherrell has already tackled energy reduction in piezoelectric polymers themselves. By combining nanomaterials (just 5 atoms thick) with piezoelectric polymers, his team has shown the electrical energy to make these piezoelectric energy harvesters can be reduced from up to 10,000,000 V per m to 0.
This means piezoelectric energy harvesters can be made with virtually no electrical energy, making electricity from mechanical motion cheap and easy to access. The team has explored 3D printing meaning devices like this could be easily molded to an insole of a shoe to harvest energy just by walking down the street!
Combining these low energy technologies will enable green fuel & energy to be produced from anything from the pressure of water flowing through a pipe to cars driving along the road. The same technology is expected to find its way into existing industries, breaking down contaminants in industrial process water and helping to mitigate toxic contamination.
There’s so much to be excited about in this fascinating research, but it’s not all smooth sailing – and part of that is by design.
Piezoelectricity is only generated when force changes - for example a foot pressing down or stepping away – not while someone is standing still, so figuring out how to smooth out the energy generated is critical.
The trick to this is engineering the connection between the piezoelectric and catalytic material from both an electrical and mechanical perspective. Think of this as the difference between connecting the materials by twisting two wires together (unpredictable and prone to failure) and through the controlled connection by adding some solder (safe, stable, and predictable).
By studying this interface between piezoelectric and catalytic materials Dr Sherrell is building a general toolbox for energy harvesting that is directly coupled to a catalyst making more efficient and low energy pathways to drive chemical reactions.
First published on 19 October 2021.
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