Peter Pfeifer picked a piece of porous carbon

While studying the internal structure of activated carbon, a team of US and European researchers has discovered a material containing a fractal network of “carbon nanopores”, which they reckon could make for a viable storage medium for methane gas in fuel cell technology for cars.

Currently, methane is stored in heavy-walled steel cylinders under extreme pressure which is not the ideal situation for a family car, the nanoporous carbon could allow methane to be stored much more safely simply by adsorbing the fuel into a block of the material and releasing it as needed by the fuel cell.

Physicist Peter Pfeifer of the University of Missouri-Columbia reckons the new material could make methane the fuel of choice for future vehicles, be it for methane-based fuel cells, for conversion into hydrogen for hydrogen-based fuel cells, or for internal combustion engines using methane instead of gasoline.

Peter Pfeifer

Pfeifer and his colleagues at the CNRS lab in France, Alicante University in Spain, University of New Mexico, and the Air Force Research Lab in California, were investigating the common filtration material activated carbon and discovered that a version they synthesised contained a network of uniform channels that penetrated throughout the carbon. Unique though is that the pore system turns out to be fractal, like the bifurcating branches of a tree and so the internal surface area of the pores is very high. Indeed, scattering X-rays from the material gives a “fractal dimension” of almost 3. This implies that the internal nanopores just about fill the inside space, with space! This, suggests Pfeifer, provides for a lot of molecular storage space in a relatively small external volume.

The first porous fractal system could store methane

“Our material offers a number of advantages for methane storage: it’s lightweight, easy to manufacture in large quantities, and relatively inexpensive,” explains Pfeifer, “But most importantly, it would allow the methane to be stored at a safer, significantly lower pressure — about 530 psi – which reduces the risk of an explosion should a methane-powered vehicle be in an accident.”

“By some estimates there is a 10,000-year reserve of methane gas on Earth that could be harnessed for use as fuel.” Pfeifer believes that a commercially viable carbon nanopore storage product could be on the market within five years.

Physical Review Letters