26 September 2007

Best-ever power density for portable methanol
fuel cell stack shown by Polyfuel

Fuel cell membrane leader PolyFuel announced today the development of a fuel cell stack that is capable of delivering an unprecedented 500 watts per liter of stack volume, significantly advancing the state of the art for “direct methanol” fuel cells (DMFC).

The tiny stack – which easily fits in the palm of the hand – delivers a peak power of 56 watts – more than twice that needed to power a typical laptop computer. The announcement marks PolyFuel’s first public disclosure of its significant and growing expertise in fuel cell technology outside the membrane.

“PolyFuel’s breakthrough is important for portable electronics – particularly laptop computers,” said Henry Voss, vice president of engineering for PolyFuel and holder of 27 fuel cell patents. “It is the first time, to my knowledge, that anyone has demonstrated a Direct Methanol Fuel Cell stack with this high a power density.” In layman’s terms, explained Voss, this means that long-running fuel cell power supplies of a size and weight attractive to consumers, and that physically integrate with a laptop in the same fashion as today’s Lithium ion batteries, are technically within reach.

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Fuel cells can be thought of as “refillable” batteries. But unlike a battery, which when exhausted must be recharged or discarded, fuel cells will run continuously, as long as there is fuel available. As conceived by most consumer electronics manufacturers, many of whom have aggressive fuel cell development programs, the consumer would simply “pop in” a replacement cartridge of methanol fuel when necessary. Spare, lightweight, plastic cartridges – made readily available in convenience stores – could be carried in ones pocket or purse. Eight to ten hours of laptop runtime per cartridge is a common industry goal.

The fuel cell “stack” is a precisely-engineered, dense “sandwich” of repeated thin layers of fuel cell membranes, electrodes, and bipolar plates. The membrane is the heart of the fuel cell, and the various layers of the sandwich are designed to deliver fuel and air to as much membrane surface area as possible, while diffusing away moisture and CO2 byproducts.

Certain layers additionally provide a current path to carry off electrons produced at the membrane’s surface. This current is used to power the portable device. PolyFuel’s 56 Watt stack has a volume of just over 111 cubic centimeters (see photo).

Caption: Power density is a measure of the size of a fuel cell stack relative to its power. The higher the power density, the smaller the fuel cell stack can be for a given power level. This stack, developed to a particular customer specification, measures 8.8 by 4.5 by 2.8 cm and produces 56 watts at peak power. To the best of PolyFuel’s knowledge, the stack delivers the highest power density of any portable DMFC stack ever made – over 500 watts/liter.

PolyFuel has been quietly but aggressively designing fuel cell stacks and other fuel cell system components over the years to best understand the properties that need to be engineered into its membranes. In addition, it has increasingly shared its growing expertise with its customers to assist them in optimizing their fuel cell development efforts, particularly around PolyFuel’s popular hydrocarbon membranes. Although the company believes that the new stack is the highest-performing direct methanol fuel cell stack ever developed, its purpose remains to provide developers of fuel cells or fuel cell components with tangible examples of how a consumer-acceptable fuel cell design can be accomplished, particularly with PolyFuel’s hydrocarbon membranes.

A pent-up demand for long-running, portable power supplies has been developing in the last few years as portable electronics devices increasingly gain additional functionality – particularly motion video – and consumers are essentially “eating up” emerging, power-hungry applications. Improvements in lithium-ion batteries – the benchmark for portable power sources – are slow and measured, about 8% per year in terms of energy density, and are being pushed to their limits, as evidenced in part by the many recent Li-ion battery safety recalls.

By contrast, with PolyFuel’s latest results, the power density of direct methanol fuel cell stacks can now be shown to be increasing at a much faster rate – more in line with the rising power demand of portable devices.

However, industry observers have often commented that until the amount of power produced by a portable fuel cell power pack can meet or exceed that produced by a lithium ion battery pack of the same size, fuel cell adoption would be limited to those consumers – such as traveling executives – for whom “unlimited” run times might justify some inconvenience in terms of size. Now, with PolyFuel’s