Cosmos - - Cosmos Science Club -

One kilo­gram of hy­dro­gen yields 120 mega­joules – that’s nearly three times as much energy as the same mass of petrol. By vol­ume, though, petrol wins: a litre of petrol can pro­vide 32 mega­joules while a litre of liq­uid hy­dro­gen yields just eight mega­joules. Stor­ing huge vol­umes of hy­dro­gen for fuel cells isn’t so much a prob­lem for sta­tion­ary power gen­er­a­tors or even large ve­hi­cles. But for stan­dard cars, where space is at a pre­mium, cart­ing around a gi­ant tank of hy­dro­gen is sim­ply not an op­tion.

How hy­dro­gen is stored, too, is im­por­tant from a safety per­spec­tive. Com­pressed hy­dro­gen gas can be ex­plo­sive in a car ac­ci­dent. So re­searchers are find­ing ways to store hy­dro­gen at high den­sity – to yield the most power per tank – but not high pres­sure, so it’s safer to cart around.

Promis­ing can­di­dates come in the form of metal­licor­ganic frame­works, or MOFS. MOFS are ma­te­ri­als that look a bit like molec­u­lar scaf­folds, with metal atoms joined up with or­ganic mol­e­cules.

Gaps in the crys­tal pat­tern can snare other mol­e­cules, such as car­bon diox­ide, oil or hy­dro­gen.

With lim­it­less num­ber of com­bi­na­tions of me­tals and or­ganic mol­e­cules, MOFS can be cus­tomised to do just about any­thing – from cap­tur­ing car­bon diox­ide from coal-fired power plant emis­sions to clean­ing oil from wa­ter – and, of course, stor­ing hy­dro­gen.

When hy­dro­gen mol­e­cules are trapped by some MOFS, they seem to calm down. An ideal MOF packs loads of hy­dro­gen mol­e­cules in – boost­ing den­sity – while stop­ping them from jig­gling around too much, which eases pres­sure.

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