The current status of hydrogen storage in metal–organic frameworks†

The rapid consumption of petroleum deposits and the escalating air pollution problems caused by burning fossil fuels have driven the global research community to look for cleaner and renewable energy resources. Albeit not a primary energy source, hydrogen is an ideal energy carrier. It almost triples the gravimetric heat of combustion of gasoline (120 MJ kg 1 vs. 44.5 MJ kg ). More importantly, the energy-releasing procedure of hydrogen oxidation, in either an internal combustion engine or a fuel-cell stack, produces only water as a by-product. Energy spent on transportation accounts for a significant part of total energy consumption. It is estimated that in industrialized countries, one-third of all the energy generated annually is consumed in transportation. For a modern vehicle with a driving range of 400 km per tank of fuel, about 8 kg of hydrogen is needed for a combustion engine-driven automobile and 4 kg for a fuel-cell-driven one. Although these gravimetric requirements are far less demanding than that of gasoline (24 kg), hydrogen is notoriously difficult to compress for on-board storage. Volumetrically, even liquid hydrogen has a much smaller combustion heat than that of gasoline (8960 MJ m 3 vs.