Progress and problems in hydrogen storage methods

A technique of hydrogen storage has to meet the DOE criterion for the volumetric and gravimetric density of the stored hydrogen and the reversibility criterion for the charging/discharging processes. There are basically five candidate methods that have attracted the common interest: compression, liquefaction, physisorption, metallic hydrides, and complex hydrides. An overview was given for the storage methods available today with respect to the progress made recently and problems still there.