Salts that exist in a liquid state at room temperature could soon change the cars we drive, improve our renewable energy sources and help wean industrial chemistry off petroleum.
Hybrid vehicles constitute a significant part of the automotive market. But safety concerns about the technology that powers these cars – their batteries are more likely than standard ones to ignite – is a major hindrance to reducing the carbon emissions of road transport.
For Douglas MacFarlane, Professor of Chemistry at Monash University, the tendency of such car batteries to explode if damaged is a practical problem that he believes can be remedied by harnessing a remarkable conductive material that is much more stable. Ionic liquids, consisting of salts that have a low melting point, can be turned to diverse applications through the manipulation of their positive and negative molecules and atoms, components known as ions.
Thanks to an Australian Laureate Fellowship from the Australian Research Council (ARC), over the next five years he will continue an ambitious research program of refining these ionic liquids, leading about 30 research chemists and materials engineers.
“We develop new kinds of chemical technologies for sustainable energy applications, primarily for energy storage, but also for energy generation, such as in solar cells,” says Professor MacFarlane, whose 15 years working with ionic liquids has led to numerous patents and now a commercialised technology for cost-efficient extraction of hydrogen as a fuel source.
He explains that liquid salts, which look rather like water or alcohol to the naked eye, are more chemically manageable than salts in a solid state and have high stability that prevents them from evaporating or breaking down. They can also be used as solvents.
“We have learnt how to make these salt molecules bigger and more awkwardly shaped, so they are less able to fit together into a crystalline structure. This means their melting point comes down and they can be liquid at room temperature,” he says.
To tackle the problem of the electric cars, Professor MacFarlane and his team are developing processes using ionic liquids to improve larger batteries, currently made of lithium. Improving safety is the first goal.
“Ionic liquids aren’t flammable or explosive, so that problem goes away.”
The next stage of the process will be to develop a new kind of lithium battery that can store far more energy. “The big issue with electric vehicles, and the reason that we don’t yet have fully electric cars in our garages, is that you can’t really put enough power on board to drive further than about 150 to 200 kilometres, whereas most of us are used to 500 to 600 kilometres of range in a tank of petrol. And the reason we can’t do that is that the batteries just don’t pack enough energy.”
Because lithium is relatively scarce and therefore expensive, Professor MacFarlane’s researchers are also working on batteries made of the far more abundant element sodium.
The hope is that the higher costs for sustainable processes and products could eventually be brought low enough to rival those that use traditional fuels.
“One of the problems we face is that fossil fuels are so cheap. We are always aware that we can develop alternative, more sustainable technologies, but their economics are ultimately the big issue.”
Applications and collaborations
Professor MacFarlane’s research group at Monash is also working on solar cells that operate more like a battery than a traditional photovoltaic cell. Thanks to the stability of ionic liquids, these will also last longer – allowing more time for the user to recover costs.
But in pursuing his passion for renewable energy sources, Professor MacFarlane’s work reaches far beyond Monash. He is a leader of various Australian and international collaborations with researchers and industry.
In a venture with the University of North Carolina, he is developing complex, purpose-created salts that store energy for solar thermal power plants.
Meanwhile, his patents for a process that can produce plastics from sugarcane waste using ionic liquids as a solvent have been sold to an Australian chemical technologies company.
One of his biggest involvements is with the ARC Centre of Excellence for Electromaterials Science (ACES), a collaboration involving six Australian research organisations, including Monash. Within ACES, Professor MacFarlane leads the energy program, collaborating closely with researchers from the University of Wollongong and Deakin University, also ACES members.
Building momentum
The program’s goal is to develop hydrogen as the ultimate non-carbon fuel and store of solar energy, and its recent successes include improved ways to split the water molecule into its constituent parts of hydrogen and oxygen. Hydrogen is used in many chemical and food industries and could ultimately power vehicles and homes, but is extracted using inefficient processes and fossil fuels.
Using ionic liquids in two separate stages of the process, Professor MacFarlane and fellow researchers have made water-splitting cleaner and more efficient. The liquids are used to prepare the catalyst that triggers the water-splitting. Later in the process, the water molecule splits more efficiently if it is dissolved in an ionic liquid solution.
Parts of the water-splitting process are now working at close to the 75 per cent energy efficiency that the US Department of Energy estimates is necessary to make hydrogen production economically feasible for use as a fuel in cars.
Commercial application of this technology is imminent, with venture capital investment from Chicago-based True North Venture Partners in the US to shepherd this process through a spin-out company – AquaHydrex.
“Being able to develop hydrogen as a fuel source has been talked about since I was at school,” Professor MacFarlane says, “but has not been possible until now due to the inefficiency of the process.”
He sees this as a major step towards building commercial and scientific momentum for a clean energy future, and hopes the day will come when hydrogen is affordable enough to challenge fossil fuel use in the cars we drive.
If this were to happen, he says with satisfaction, “It would mean fossil fuels could stay in the ground.”
