Aluminium doping composite metal-organic framework by alane nanoconfinement: Impact on the room temperature hydrogen uptake

Abstract

Metal-organic frameworks (MOFs) have been studied immensely in the past several years in the area of hydrogen storage. Various strategies of modifications in MOFs have been performed to enhance the hydrogen storage capacity both at room and cryogenic temperatures. In the present study a hybrid composite MOF was synthesised by adding activated carbon (AC) NORIT-RB3 in situ during the synthesis of MIL-101. Alane (AlH3) was synthesised and nanoconfined inside the pores of the composite MOF by solution impregnation method. Aluminium doped composite MOF was prepared by controlled thermal treatment of the alane nanoconfined composite MOF. Three different concentrations of aluminium doped composite MOF was synthesised by changing the initial alane concentration used for impregnation. The nonlocal density functional theory (NLDFT) method was used to calculate the pore size distribution (PSD) curves of the samples. Hydrogen adsorption-desorption studies were performed at 298 K up to 100 bar in all the samples. The results showed that the room temperature hydrogen uptake capacity of MIL-101 can be considerably enhanced by the combined modification of MIL-101 using activated carbon and aluminium doping. To our knowledge we present the first experimental doping of MOF materials by aluminium capable to multiply the room temperature hydrogen uptake capacity of the material by 3.5 times. Moreover, activated carbon NORIT-RB3 is not costly compared to other carbon materials such as carbon nanotubes and thus the modification strategy is comparatively cheaper. This combined modification by activated carbon incorporation and alane impregnation for aluminium doping in MOFs provides new insight for the development of materials for hydrogen storage application at ambient temperature.