A STONE’S throw from the birthplace of the atomic bomb in Los Alamos, New Mexico, physicist Bob Hockaday is working on a more benevolent source of energy. He is developing long-life power packs that promise a revolution in portable electronics.
It may take a few years, but Hockaday believes that with his help the common-or-garden battery will begin the slow slide to extinction. Its nemesis? Micro fuel cells. Based on a 160-year-old concept, these compact power plants could soon be keeping your mobile phone, laptop and PDA juiced up for weeks at a time.
“Our ultimate goal is to build mobile phone fuel cells that last for one month before you have to change anything,” says Hockaday, founder of the R&D company Energy Related Devices and one of the pioneers in the field. He hopes his first fuel cells will burst onto the high street within a year. And he is not alone. Electronics giants such as Samsung, Toshiba and Motorola already have accelerated programmes of their own in pursuit of the same dream.
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The reason for all this feverish activity is that the standard power sources used in mobile devices – lithium-ion batteries – have irritating limitations. Anyone with a mobile phone or laptop knows the sinking feeling of running out of juice at the wrong moment, and the annoyance of having to plug the thing into the wall for several hours before it’s up and running again. And the problem can only get worse as devices incorporate ever more power-hungry features.
Liquid energy
Micro fuel cells look like the best bet to overcome the problem. Like all fuel cells, they work by extracting electrical energy from the reaction of hydrogen with oxygen to form water (Inside Science No. 141, Â鶹´«Ă˝, 16 June 2001). But they don’t use hydrogen as their primary fuel. Hydrogen is cumbersome to store and carry around, which makes it an awkward fuel at the best of times, and totally impractical in a device such as a mobile phone where space is at a premium.
The standard solution to this problem has been to use a liquid fuel such as methanol and extract the hydrogen from it. But there are difficulties with this too. The “reforming” reaction that converts methanol and water into hydrogen and waste carbon dioxide requires a separate, bulky reaction vessel and works best at 250 °C.
In recent years, however, researchers have developed a class of fuel cells called direct methanol fuel cells (DMFCs), which use a platinum catalyst to extract hydrogen from methanol at room temperature and so don’t need a reformer. For this reason, DMFCs are widely regarded as the breakthrough that will make miniaturisation possible.
Earlier this year a Munich-based start-up company, Smart Fuel Cell (SFC), unveiled what it claimed was “the world’s most compact direct methanol fuel cell”. The DMFC is about half the size of a brick and weighs 2 kilograms. In tests it produced an output of 40 watts for 8 hours on a single 175-millilitre ampoule of methanol – enough to power a laptop, printer and mobile phone simultaneously. The company claims it has now produced an equally powerful cell about half the size and weight, which it will test in field trials next year. Jens Mueller, chief technology officer at SFC, believes that when economies of scale come into play, the price of cells will be almost as low as a lithium-ion battery of similar size.
The advantage of using DMFCs instead of lithium-ion batteries is that they liberate mobile devices from frequent and lengthy meetings with the recharger. When your laptop or phone runs out of power, you simply insert a fresh methanol cartridge, and you’re up and running. Fuel cells also avoid some of the other problems with lithium-ion batteries. Their power doesn’t dissipate while the device is switched off, and they don’t lose storage capacity with age. “With fuel cells you have a direct correlation between how much fuel you have left and how many operating hours you’re going to get,” says Hockaday.
Despite these attractive features, however, micro fuel cells still have some way to go if they’re to displace lithium batteries, in cellphones at least. The most immediate problem facing SFC is making sure the people can get hold of the methanol ampoules. What if you get caught without a spare canister and no stockist in sight? It will be a long time before methanol ampoules are as readily available as the trusty AA battery. For now, anyone who adopts SFC’s portable fuel cell will have to order batches by mail order direct from the company. “Distribution is a hurdle we will overcome,” Mueller says.
Smaller and cheaper
But there are other challenges too. One of the most serious is power density – essentially, the output you can get per unit mass or volume. This is hugely important in mobile devices because it determines the overall size and weight of the thing. The higher the power density, the smaller and lighter you can make your device.
“I am not convinced that fuel cells will happen in today’s mobile phones,” says David Hart, head of fuel cell and hydrogen research at the Centre for Energy Policy and Technology at Imperial College, London. “It’s technically difficult to make fuel cells small enough to fit mobile phones that have the same power density as a normal battery.”
The problem isn’t power density per se. A lithium-ion battery produces around 150 watt-hours per kilo, whereas SFC’s fuel cell can manage 160. But the fuel canister contributes to the cell’s volume and mass, which makes it difficult to produce small units that are able to carry enough fuel to beat the endurance of ordinary batteries.
The cost of fuel canisters is another difficulty. Although methanol only costs around 6 pence a litre in bulk, it’s a nasty, corrosive chemical and packaging it won’t come cheap. A 250-millilitre ampoule will set you back around £2. Compared with recharging your phone at the mains, that’s a hefty sum.
DMFCs also need oxygen and produce waste heat and CO2, so they need to be kept well ventilated. The trouble with that, of course, is that mobile phones spend a lot of time stuffed in trouser pockets or bags. “That is an extremely difficult operating environment for a fuel cell,” says Mueller. Hockaday agrees it’s a problem. “Fuel cells have to breathe.”
Another consideration is that the cells tend to work best when oriented in such a way that their liquid fuel flows freely. And they often have moving parts that are vulnerable to the knocks and shocks that a cell phone endures. “It’s like engineering a living thing,” says Hockaday.
If that wasn’t bad enough, Hart believes micro fuel cells will face stiff competition from lithium battery companies. Batteries are improving all the time and manufacturers have a vested interest in squeezing the maximum commercial benefit out of the technology before moving to fuel cells, he says.
Big problems, certainly, but not insurmountable. Hockaday already has some answers. His latest direct methanol fuel cell is the size and shape of a credit card, which he says demonstrates that making fuel cells small enough to fit in your mobile phone is not impossible. He also claims to have cracked the problems of orientation and robustness by eliminating moving parts.
Instead, Hockaday uses an ampoule design in which the methanol diffuses into the cell through a porous surface. The waste water is drawn away from the cell by a capillary effect. “We will depend probably entirely on diffusion for fuel cells in mobile phones,” he explains. “You can hold our fuel cell upside down or drop it and it will not be a problem.”
Hockaday’s first application for the technology is a mobile-phone charger that you can clip on your belt, a sort of recharging holster. “It’s a hybrid approach,” he explains. “You’d still have the lithium battery in your phone, but it would be constantly trickle charged while it’s in the holster.” The prototype in Hockaday’s lab has kept a mobile phone running continuously for six months without being switched off. But although the holster has been ready for over a year, he’s still looking for an industrial partner.
Power-hungry features
While it might be difficult to convince manufacturers of the benefits of mobile phone fuel cells, putting fuel cells in laptops is much more attractive. Laptops are notorious for their short battery life, and the latest models incorporate power-hungry features such as wireless Internet access and brighter displays, which are a serious power drain. Fuel cells could give you up to five times the measly one to two hours of today’s batteries, says Mueller.
SFC is developing a hybrid laptop battery with a fuel cell to keep it topped up. “There are some nice synergies between fuel cells and laptops,” says Mueller. For example, cooling systems are likely to become commonplace in laptops because of the extra heat produced by power-guzzling features. These systems could easily be shared with the fuel cell, which heats up to around 70 °C.
However, Hart says there are non-technical hurdles to overcome. “One real-world test is whether you can carry fuel cells onto a plane, and at the moment no airline will allow ampoules of pure methanol into the cabin,” he says. “If you can’t take it on a plane, no one will be interested.”
Mueller acknowledges that, but says approval is only a matter of time. “We already have official approval [from the International Air Transport Association] to transport our cartridges in the cargo hold, and we are working to allow them in the cabin too,” he says. He points out that methanol is no more flammable than some perfumes you can buy in the in-flight duty-free shop, and that cigarette lighters are not prohibited from the cabin. “So we believe that based on these exemptions we will be able to get approval for our laptop ampoules too.”
These are considerable challenges, but there are plenty of incentives to overcome them – not least third-generation mobile phones. Telecoms companies have gambled huge sums on the success of 3G phones. They have already been rolled out in Japan, but so far have received a cold reception. The main letdown is that users only get 20 to 40 minutes’ operating time before the lithium battery goes dead, as the phones are moving large amounts of data up to 10 times as fast as today’s mobiles via high-frequency signals. “All the major Japanese manufacturers, including NEC, Sony and Toshiba, are developing fuel cells for 3G phones,” says Hart. Micro fuel cells could be just the thing to recharge 3G’s batteries.
Shrink to fit
Perhaps the most futuristic application of fuel cells is in computing. Robert Savinelli, Jesse Wainright and Joe Payer at Case Western Reserve University in Cleveland, Ohio, have developed a fuel cell just 1 centimetre square and a few millimetres thick that could be incorporated directly into a microchip. “We’re developing a procedure that would mean you could create the fuel cell at the same time as you print the electronic circuit,” says Payer. They plan to use microfabrication methods to print the fuel cell components on a ceramic wafer. “The idea is to put power sources on chip so that you have a truly self-contained device,” says Payer.
Their prototype cell can run for 10 hours on a mini-tankful of hydrogen about the same size as the cell itself. If this approach works, it could open up a whole new realm of possibilities, albeit decades in the future. “Ultimately,” says Payer, “they could be used to build the sort of autonomous devices that could be put inside the human body.”