Hydrogen storage materials can be optimised with magnesium, say researchers in Spain.

If hydrogen gas is to have a realistic chance as a green fuel for cars of the future, materials are needed that can not only adsorb and store large amounts of hydrogen, but, crucially, can release it again when required. Gemma Turnes Palomino and colleagues at the University of the Balearic Islands, Palma de Mallorca, Spain, say they have modified porous materials known as zeolites to give them just the right properties to store and release hydrogen effectively.

The ability of a material to release hydrogen gas stored within it depends on the strength of the interaction between the material and the gas, known as the adsorption enthalpy.  If the adsorption enthalpy is too low, stored gas will be released too readily.  If it's too high the gas won't be released at all. The optimum value for this adsorption enthalpy has been reported to be in the region of minus 15 kilojoules per mole.

Zeolites have been shown to have a high capacity for storing hydrogen gas. Their previously reported adsorption enthalpies are around minus 5 to minus 10 kilojoules per mole - lower than the ideal value.

Palomino and colleagues discovered that incorporating magnesium into the structure of zeolites increases the strength of the interaction between the zeolite and hydrogen.  They recorded a hydrogen adsorption enthalpy of minus 17.5 kilojoules per mole - close to optimal. 

Dr Petr Nachtigall, an expert in zeolite chemistry at the Academy of Sciences of the Czech Republic, Prague, welcomed the work. 'This contribution certainly brings very interesting and new findings and it will trigger new interest in metal-exchanged zeolites for hydrogen storage,' said Nachtigall.

Paul O'Sullivan