Simple filter may inspire smaller fuel cells

energy

Fuel cells designed for use in laptops and cellphones could be a step closer with simple devices that extract waste gas and vapour.
The device, developed by Chinese researchers, extracts by-products that normally impair the efficiency of "direct methanol" fuel cells (DMFCs), without requiring extra power.
Electronics firms including Samsung and Toshiba are interested in using this type of fuel cell to power portable devices, since the conversion of methanol is potentially more efficient on this scale than using either hydrogen or standard batteries (see Batteries not included).
In one half of a DMFC, fuel is oxidised by a catalyst, forming carbon dioxide, protons and electrons. The protons and electrons take different routes to the opposite side of the cell where they recombine to make water. On the way round, the electrons provide electrical power. This diagram explains the process in more detail.
Waste removal
However, waste CO2, along with water and methanol vapour, normally collect inside the cell, diluting the fuel concentration and reducing the power output. Pumps can remove these by-products, but require space and power, reducing overall efficiency.
Researchers at National Tsing Hua University, Taiwan, have now developed a waste removal system that works without power, which could mean smaller DMFCs with more space for fuel.
The new device acts like a filter, collecting gas and vapour in a few simple steps. Firstly, around a hundred 50-micron-wide holes, each coated with water-repelling Teflon, allow CO2 to escape into the surrounding air.
At the same time methanol and water vapour condense on the surface around the holes. The condensed liquid then flows 5 millimetres towards a reservoir for collection. A surface treated to repel water strongly at the start, and less so towards the collection point, pushes the liquid into the collection chamber. It can then be disposed of or recycled by extracting the methanol.
Short lifespan
Trials on working cells are underway, and tests suggest the system could draw off gas and vapour at 10 times the rate needed for a micro fuel cell.
"This is targeted at a real need," says Paul Christensen, a fuel cell researcher at Newcastle University in the UK. "Scooting the water away without power is a clever idea."
But Christensen warns that other improvements will be needed before the technology is ready for cellphones or laptops. For example, the lifetime of fuel cells is currently limited because the material used to make the electrolyte erodes rapidly. Despite promises from various companies, slow progress in commercialisation "shows the challenges we face", says Christensen.
Journal reference: Journal of Micromechanics and Microengineering DOI: 10.1088/0960-1317