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Highlights in Chemical Technology

Chemical technology news from across RSC Publishing.



Breakthrough for metal cation-free alkaline fuel cells


08 January 2007

Cheap and effective fuel cells are achievable using alkaline anion-exchange membranes, according to a UK chemist. The technology offers the potential to produce power more efficiently and cleanly than combustion methods.

A more detailed schematic of the anion exchange membranes

Fuel cells operate like batteries but they do not run down or require recharging. They produce energy electrochemically rather than by combustion and are far less polluting than traditional energy sources. They consist of an anode and a cathode with a polymer electrolyte membrane in between.

John Varcoe, from the University of Surrey, has been developing alkaline anion-exchange membranes (AAEM) for many years. AAEM fuel cells are similar to the highly studied proton-exchange membrane (PEM) fuel cells but the membranes are designed to transport hydroxide ions instead of protons. AAEMs are less expensive to make than PEMs and can be used with cheaper electrodes.

Varcoe studied the effect of humidity on the ionic conductivity of AAEMs. He found that at high humidity levels, the membranes were good conductors, which was not previously thought to be the case.

'Ionic conductivity is the membrane property that directly affects fuel cell performance, whilst the humidity of the fuel and oxidant gases is a critically important operational parameter,' he explained.

Varcoe also showed that AAEMs conduct well in the absence of metal hydroxide salts, an essential component in traditional alkaline fuel cells. The metal cations react with alcohol fuels producing metal carbonate precipitates that decrease the performance of the fuel cell. This result represents a significant breakthrough, Varcoe said.

"At high humidity levels, the membranes were found to be good conductors, which was not previously thought to be the case"
Lin Zhuang, an expert in the field of AAEMs from Wuhan University, China, agrees. 'Although there are still some disadvantages of this kind of membrane, Varcoe's work represents a milestone in the development of alkaline membrane fuel cells,' he said.

The next challenge for Varcoe is to develop electrodes specifically designed for AAEM fuel cells to optimise their performance.

Joanne Thomson

References

Investigations of the ex situ ionic conductivities at 30 C of metal-cation-free quaternary ammonium alkaline anion-exchange membranes in static atmospheres of different relative humidities
J R Varcoe, Phys. Chem. Chem. Phys., 2007
DOI: 10.1039/b615478f