Metal Air Fuel Cells: Try and Try Again

June 11, 2006 – Vol.11 No.12

METAL AIR FUEL CELLS : TRY AND TRY AGAIN.

They seem so simple. They work pretty much as advertised. Yet a number of companies - Metallic Power, Evionyx, Aluminum Power, Green Volt, to name a few - tried to commercialize metal-air fuel cells (MAFCs) and failed. Why did they fail?

First let’s see how they work

Simply put, metal air fuel cells are electrochemical batteries that have the ability to be refueled with fresh, unoxidized metals, particularly because of their low weight, aluminum, magnesium or zinc.

(The most basic form of metal air fuel cells are hearing aid batteries available in drug stores, but they’re disposable, not refuelable.)

Technically metal air fuel cells are a series of galvanic cells where the dissolving metal (the fuel) can be replenished, thus refueled.

In operation metal fuel (which has a dual purpose as an electrode) oxidizes in a series of individual cells in an air-rich bath of electrolyte. Another electrode, the cathode, makes up the other side of each cell. As the metal fuel oxidizes (aka corrodes or dissolves) a small electric current is available between oxidizing metal and the cathode. The metal fuel electrode is also known as a sacrificial anode.

To jazz things up a bit the metal fuel is sometimes in pellet form so it can be pumped in and out of each cell - thus refuel it. The other, non-corroding electrode, the cathode, is often a carbon membrane which allows air into each cell but won’t let the electrolyte out, thus it too has a dual purpose. The fuel pellets are recyclable by either melting them down or chemically removing the oxidized material from each pellet.

If the technology is so simple why have so many failed?

Mostly lack of interest at a time when hydrogen was at the forefront of energy-for-the-future investment. But also there were operational issues with the technology. For one, once the reaction starts - the metal fuel begins to corrode - it’s difficult to stop. Further while its relatively easy to pump fresh clean metal pellets into each small cell, it’s hard to get the pellets out again.

Still MAFCs are a possibility and new companies keep trying. After all they’re emission free, have long run times and the fuel is endlessly recycled with any source of power - including renewables.

Alchemy Enterprises is working with NASA’s Jet Propulsion Labs (JPL) and Cal Tech on an MAFC that uses magnesium as fuel. The company has contracted New Zealand motor-coach builder DesignLine to build a bus powered by an MAFC. The company, too, has announced good test results for magnesium fuel in testing at JPL, but wasn’t too specific about the tests. The company says the DesignLine bus should be ready for testing in about a year. (That seems very hopeful.)

Power Air Corporation has been working on a zinc-fueled back-up power generator that could be used indoors or out.

The company has announced that it is collaborating with Schrader Bridgeport International to build, test and commercialize the zinc-air device. Schrader is a division of Tomkins which owns a number of brand-name auto part suppliers such as Gates (belts) and Trico ( wiper blades).

Visit DesignLine at http://www.designline.co.nz/ Alchemy at http://www.alchemy-energy.com/ and Power Air at http://www.poweraircorp.com/