Powerful ally

Portable electronic equipment is a burgeoning market, but one that is increasingly frustrated by battery life not keeping track with the demands of ever more powerful devices.

Since their conception, micro fuel cells have been heralded by scientists as a renewable, long-lasting and environmentally friendly alternative to lithium ion (Li-Ion) batteries for powering mobile devices. But they have not yet become widespread because they are manufactured from hundreds of tiny parts using different materials, making them complicated to develop and expensive to produce.

Now, researchers are using a readily available material and existing machinery to make cost-effective, single-piece ceramic fuels cells.

Dr Michael Stelter and his colleagues at the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) are making the cells from a ceramic film called LTCC (Low Temperature Co-Fired Ceramic), which comes in rolls of plastic-like tape with the consistency of leather. The cells are machined while the film is ‘green’, or unfired.



Difficult environments

LTCC is commonly used as a substrate to produce a multi-layered printed circuit board. Being ceramic, it can withstand higher temperatures, enabling it to be used in difficult environments such as car engines and for military applications. It is reliable and stable — millions of LTCC components are produced daily for electronic engine control.

‘Because it is so widely used, there are many machines available on the market for working with LTCC, making ceramic fuel cells cost-effective to develop,’ said Stelter.

Fuel cells produce electricity from an external supply of fuel and oxygen, which can be replenished. In hydrogen cells, a catalyst at the anode separates the electrons from the protons and allows the protons to pass through a membrane to the cathode. The electrons take a longer route round a circuit, generating a current. The protons and electrons combine with oxygen at the cathodes to produce water.

‘The tools that create geometrically structured machined channels and buried tubes can also conduct liquid and gas in micro fuel cells,’ said Stelter. ‘We use stamping, punching, embossing and laser structuring techniques.’

Individual layers are machined and up to five layers are stacked up. The cells are then laminated like circuit boards while still in the flexible green state, and then fired. The fuel cells are currently hand-assembled, but using the same machines as used in automated mass production.

The power produced by the ceramic micro fuel cells is directly comparable with traditional ones as the method for power production is unchanged. The four-cell unit shown produces 500 milliwatts for a 6cm x 6cm, 6mm-deep block using hydrogen as a fuel.

Stelter and his colleagues are now carrying out functional testing on the cells, which includes fine-tuning the fuel-flow geometry. This involves experimenting with changing the shape of the fuel channels attached to the electro-chemical layer. Durability testing will then follow.



Time to market

According to Stelter, the time to market for ceramic fuel cells depends on the level of integration the customer wants. ‘We could have a product in two years based on today’s state-of-the-art hydrogen technology,’ he said. ‘If, instead, we went for direct methanol fuel, it would take five years or so. We don’t have all the system components such as a micro pump yet.’

The next step is to demonstrate industry applications for ceramic fuel cells. The cell can produce a power range of 30-50 microwatts up to 3W, the upper limit restricted only by production price. For lower wattages, Stelter says it is better to use alternative micro technologies such as structured silicon.

He believes ceramic fuels cells will not be a direct replacement for batteries in all portable electronic equipment. ‘There is not much hope for cell phones — for up to 5W, you can’t beat Li-Ion,’ he said.

One immediate application will be as a power source for portable electronics where there is no mains plug to power a device or recharge a battery.

‘There are lots of applications which need a long running time,’ said Stelter. ‘A ceramic fuel cell could act as a portable power supply, or recharge equipment. It could act as a range extender or charger for a phone or an iPod, or be used in industrial applications where it is not viable to put an electric socket.



Surveillance cameras

‘Another application would be to power devices that require an uninterrupted power source, especially those in difficult-to-access places, such as surveillance cameras.’

Stelter and his team are now working on how to integrate micro actuators, such as micro pumps and micro valves, with the cells. LLTC components are already used in pressure sensors, including industrial sensors such as those used in chemical process control and food processing. Another IKTS department is working on piezoelectric components.

‘We want to see a motherboard integrating electronics, gas power and micro actuators into a micro-integrated fuel cell system,’ said Stelter. ‘It could do everything in a single, flat device. It would be cheaper and more reliable for a fuel cell to carry its own electronics on the stack.’

He sees the integrated systems being used in portable wireless applications and personal medical devices, such as continuous blood pressure monitors.