Joined: 16 Mar 2004
|Posted: Fri Aug 28, 2009 9:38 am Post subject: Ion Jelly Could Satisfy Appetite for Greener Batteries
|You've likely heard of strawberry jelly, mint jelly and even royal jelly. Now Portuguese chemists have created what they call an ion jelly that could make a range of electrochemical devices, including batteries, fuel cells and solar cells, cheaper and more environmentally friendly.
A cube of ion jelly - a flexible mixture of gelatine and an ionic liquid (Image: S Barreiros)
The jelly is made by dissolving gelatine in an ionic liquid – a solution made up entirely of negatively and positively charged ions.
Ionic liquids conduct electricity and are generally very stable, non-flammable and non-volatile. That makes them attractive as environmentally friendly replacements for materials normally used as the electrolytes that separate the positive and negative electrodes in electrochemical devices, such as batteries.
But such electrolytes must usually be solid. And turning ionic liquids into solid form, by combining them with polymers or nanotubes, is challenging and expensive.
Ion jelly could be the answer, say scientists led by Susana Barreiros from the New University of Lisbon.
Ion jelly was a chance discovery made while mixing a range of natural polymers, including gelatine, into ionic liquids.
Gelatine is derived from the fibrous protein collagen, found in the skin, bones and tendons of animals. And as anyone who has ever made jelly will know, it dissolves in hot water into a solution that sets into jelly when cooled.
Barreiros and her colleagues found that exactly the same thing happens when gelatine dissolves in ionic liquids. "All of a sudden, we had arrived at something we were not trying to achieve, a material with very interesting properties," she said.
The researchers immediately showed that ion jelly conducts electricity, although only around half as well as the parent ionic liquid.
But this was enough to use in simple circuits and even to manufacture a small electrochemical device – ion jelly electrolyte carries current to a transparent sheet that changes from clear to opaque when electric current is applied (see image, bottom right).
The researchers are currently experimenting with different "flavours" of ion jelly, made using different ionic liquids, and say it should be possible to match the performance of existing, less stable, electrolytes.
James Wishart works with ionic liquids at the US Department of Energy's Brookhaven National Laboratory. He envisages a range of uses for ion jellies.
"Because of their jelly-like properties, these materials fill a gap between electrolyte solutions and [existing] rubbery ionic liquid/nanotube/polymer composites," he says.
"They have applications in flexible devices and in disposable sensors with low environmental impact," he adds.
Journal reference: Chemical Communications (DOI: 10.1039/b811647d) .
Source: New University of Lisbon via http://www.newscientist.com/article/dn14975