Wednesday, March 30, 2005

UI Researcher Builds Membraneless, All-Liquid Fuel Cell

A little older than usual, I let this New Scientist article pass me by without commenting on it last week. University of Illinois at Urbana/Champaign researcher Paul Kenis has discovered an ingenious method for reducing the cost of fuel cell membranes: eliminating them altogether. His fuel cell is the first alkaline unit ever.
His system exploits a phenomenon known as "laminar flow", where tiny streams of liquid become so viscous they do not mix when squeezed past one another.

"The concept of a membraneless fuel cell is a great idea, because between 20% and 40% of the cost of a fuel cell is the membrane," says chemist Shelley Minteer at the University of St Louis in Missouri, US.


In the past, fuel cells have been made up of two chambers, one housing the liquid fuel that produces protons and supplies electrons to the anode, the other containing an oxygen-water mixture, which absorbs electrons.

The polymer membrane separating the chambers is punctured by tiny pores that allow protons through but are small enough to stop the larger methanol and oxygen molecules from diffusing across.

The problem is that using these membranes means that all fuel cells must be based on the exchange of acidic protons. Because alkaline hydroxide ions are much bigger than protons, there are no membranes that can allow the hydroxide ions through without also causing mixing between the two chambers, explains Kenis. "The membrane limits the chemistry of the fuel cell," he says. But he insists that alkaline fuel cells are nevertheless more efficient.

So he decided to do away with the membrane altogether. Kenis realised that if he shrank the chambers down to about 0.25 millimetres and ensured that the liquids were always moving, the two could flow past each other and would not mix, even with no separating a membrane. And they would still allow the diffusion of protons or hydroxide ions from one side of the cell to the other.

The 3 cm X 3 cm X 0.1 mm unit he has built already is powering a small fan, though it is not as efficient as other existing fuel cells. Kenis says the problem is caused by a lack of dissolved oxygen in water. He claims to have a solution for this, but won't divulge it until his patent is completed.