A polymer riddled with tiny pores could lead to a novel hydrogen fuel tank, say chemists in the US.

Frantisek Svec of the Lawrence Berkeley National Laboratory and colleagues at the University of California, Berkeley, made the highly porous materials from polyaniline. Svec used hypercrosslinking to give a mesh-like material with a strong affinity for hydrogen, and a high surface area.

'Using hydrogen as a CO₂-free fuel is a nice idea,' said Svec. But storing the gas is complicated as the gas is 'very difficult to compress or liquefy. One alternative is to store it in materials with a very high surface area.'

The Berkeley team made the new material by adding small molecular crosslinkers to polyaniline that had been swelled in solvent. These short, rigid crosslinks hold the polymer chains apart even when the solvent is removed, leaving a material full of nanometre-scale pores. The resulting mesh had a surface area eight times higher than the best previous porous polyaniline, and a high affinity for hydrogen.

'The key advance with this work is the new approach to make porous polymers,' said Andrew Cooper, who studies hydrogen storage polymers at the University of Liverpool, UK. The materials are still far from practical hydrogen stores, Cooper added: 'With what you'd have to change in structure to achieve room temperature hydrogen storage, it's arguable whether you could still call it the same material.'

Svec agreed there is still a lot of work ahead. 'We need polyanilines with a much higher surface area - we need small pores, and a lot of them,' he said. The Berkeley team is currently trying different crosslinkers, and different reaction conditions, to increase the material's proportion of 1-2 nm pores.

James Mitchell Crow