The new framework may lead to the creation of cleaner, more sustainable, and nontoxic batteries, and other sources of chemical power. The research was published in an early online edition of the Proceedings of the National Academy of Sciences.
This is a cartoon depicting how the ionic liquid molecules arrange in electrically charged interfaces (not to scale). The green shading represents the 99.98 percent of the molecules that exist in a neutral state, the blue shapes represent positive ions and the red shapes represent negative ions. The reaction shown above the cartoon illustrates the fact that the molecules can exist in two states: a neutral ionic liquid molecule (99.98 percent of the molecules) and separated positive (blue) and negative (red) ions (0.02 percent of the molecules).
Credit: Matthew Gebbie
"I think this framework would provide a nice strategy to begin discussions toward batteries utilizing ionic liquids," said graduate student researcher Matthew Gebbie, first author of the paper, "Ionic liquids behave as dilute electrolyte solutions."
An electrolyte is a compound that is dissolved in a solution –– usually water –– in order to separate the individual, charged atoms of the compound. Take, for example, sulfuric acid dissolved in water to provide the free ions that create the charge given off by automotive batteries. Electrodes pick up the positively and negatively charged ions and deliver the current where it's needed to start the car or power electrical components.
But, despite the abundance of ions and a free-flowing environment, ionic liquids have never lived up to their promise of delivering the same kind of energy as currently available electrolytes, like sulfuric acid. Their conductivity is just not as high, said the scientists.
Using a surface forces apparatus, a device developed in the Israelachvili lab that can measure forces between surfaces to the sub-nano scale, the researchers analyzed the interactions of the charges in an ionic liquid –– how the surfaces attract or repel each other, the effective voltage of the liquid, and the ions' interactions with each other, as well as with the electrodes that are meant to pick up or discharge, and thereby conduct their charges.
They found that the ions in the ionic liquids are "stickier" than previously thought.
"They're bound to each other, and it's related to a complex property of any liquid or material, called the dielectric constant, which is the measure of how much you would expect charges to be free," explained Israelachvili. In fact, the somewhat-overlooked dielectric constant, which is a measure of how well charged particles stick to each other in a liquid, plays a larger role in the conductivity of ionic liquids than was previously assumed. Instead of the estimates of 50 percent separation that have been made, the experiments with the surface forces apparatus yielded a less than 0.02 percent separation between ions for typical ionic liquids.
"The connection that nobody had made before that emerged from our work was that it's not enough just to know how sticky the ions are to each other in a vacuum; you need to account for all the other billions of ions that surround any two ions in the liquid state," said Gebbie.
With that parameter taken into account along with the materials' dielectric constant, said the scientists, it became possible to come up with a simple equation that can quantitatively predict the number of free –– effectively separated –– ions that are present in ionic liquids.
"It's so simple. It really captures the physics of what's going on, but it's also simple enough to be used for predictive purposes," said Gebbie, adding that the group is now in active discussions with potential collaborators to refine and improve the equation.
The research has wide implications. With the formula, it would be possible to design an ionic liquid with particular desired properties, instead of performing countless trial-and-error tests or experiments. To date, over a million combinations of positive and negative ions have been identified that can be mixed together to form an ionic liquid, according to the researchers. To further blend these liquids to find, change, or add properties, the number of possible combinations shoots up to about 1018, or a trillion trillion potential combinations.
Not only could efficient charge-conducting ionic liquids be found in a shorter amount of time, but other properties could also be incorporated via molecular fine-tuning, such as less toxicity, reduced corrosiveness, or increased biodegradability.
"An electric vehicle has to have a very large battery. So if that very large battery is based on something that's acid, then you have a large compartment of acid. In an accident, if you had a nonflammable, nontoxic ionic liquid, then at least you could take some of that risk out of the equation," said Gebbie.
Sonia Fernandez | EurekAlert!
New study from the University of Halle: How climate change alters plant growth
12.01.2018 | Martin-Luther-Universität Halle-Wittenberg
Disarray in the brain
18.12.2017 | Universität zu Lübeck
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy