Fuel cells fire up handhelds

High-performance handheld electronic devices such as smart phones, video/music players, multi-functional PDAs and RFID tag readers require longer usage times than power sources currently provide. Traditional battery technologies are not keeping pace with these demands.

Direct methanol fuel cells (DMFC) offer several advantages over lithium-ion batteries. Methanol, otherwise known as methyl alcohol or wood alcohol, is a colorless liquid commonly used in antifreeze for windshield washer fluid. It is lighter than water and weighs far less than a lithium-ion, making it a better option for portable electronics. A DMFC provides longer usage between charges, increasing run time between charges by two to 10 times over the status quo of current battery technologies. And when a charge is needed, a DMFC fuel refill can be easily swapped into place without interruption of power.

Moreover, methanol is inexpensive and widely available. A gallon of methanol, enough to power a cell phone for about 10 years, costs only US$10. A DMFC converts chemical energy into electricity via oxidation of methanol.

Fuel-cell power packs include a fuel refill, methanol-feed subsystem, fuel cell and electronics circuits. The feed in a methanol-powered option might include a valve, pump, pipes, filters or orifices on a very small scale, much like one would find in a desktop inkjet print head.

Traditional DMFC systems, also known as active systems, include a condenser, fans, pumps and fluid-mixing circuits to dilute the methanol as it is fed to the anode side of the fuel cell. The fuel cell is akin to a chemical sandwich with layers of catalysts and membranes between an anode and a cathode layer.

A more simplified approach is offered by what is called passive DMFC technology. When methanol is introduced into the cathode (entry) site of the DMFC, a chemical reaction occurs and the byproducts are CO2 and water. In a passive DMFC, the water required for the process on the methanol side is transferred internally within the fuel cell from the site of water generation on the air-side of the cell. This internal flow of water takes place without the need for any pumps, complicated re-circulation loops or other plumbing.

A passive design requires the DMFC platform to manage water in a way that obviates the need for condensing the vapor from the cathode exhaust, then storing and mixing it with methanol to maintain an accurate concentration of methanol and water at the anode.

A small battery is often added to the DMFC system to serve peak demands of the device. This hybrid approach lets the DMFC operate at its optimal level that keeps pace with the continuous power of the device.

The passive design leads to fewer components and a smaller DMFC power pack that could fit onto the back of a PDA or cell phone. Because components might require power to operate, having fewer components yields longer usage time.

And having fewer components leaves more space for methanol. Every cubic centimeter of space for methanol means another 2 to 3 hours of usage while the fuel cell provides 0.5 watt of power on average to a device. By comparison, one cubic centimeter's worth of typical battery allows about 30 to 60 minutes of usage time.

Finally, with a better power pack and a spare fuel refill or two, there are no more AC cubes to pack and carry, no more international adapters to pack and carry, no more car chargers, no more searching for an electrical outlet and no more waiting for a charge.

Becerra is vice president of strategic planning and alliances at MTI MicroFuel Cells. He can be reached at juan.becerra@mechtech.com.

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