Solid-state hydrogen storage technology has the advantages of high hydrogen storage density, low working pressure and good safety, and is an important development direction of hydrogen storage and transportation in the future. Among them, metal-organic framework (MOF) is one of the key materials in solid hydrogen storage technology because of its outstanding advantages such as high energy efficiency, fast response to hydrogen adsorption and desorption, and easy control. However, at present, MOF-type hydrogen storage materials still have some problems, such as lack of strong adsorption sites, low volumetric hydrogen storage density, unclear hydrogen adsorption and desorption mechanism, and high material cost, which limit their promotion and application in hydrogen energy. Besides, green and mild scale-up production of high quality, high stability, and low-cost MOF materials remain still a bottleneck problem for their adsorptive hydrogen storage applications. To address these challenges, we report the synthesis of zirconium/hafnium-based MOF materials in green (no organic solvent), mild (low temperature, atmospheric pressure) and mass synthesis using the strategy of aqueous metal cluster-ligand exchange. Compared to traditional electric heating, microwave modulation could significantly accelerate the crystallization processes and thus reduce the overall reaction time to a few minutes, which is more beneficial for the large-scale production of MOFs. As such, microwave-assisted modulated hydrothermal (MW-MHT) synthesis has led to a space time yield (STY) up to 3000 kg/m3/day for both UiO-66 and MOF-808 materials. After modulation, the BET surface area of MOF-808 (Zr) can reach ~2400 m2/g, which is 20% higher than that synthesized by traditional solvothermal method. The gravimetric hydrogen storage density is 4.5 wt.% at 77 K and 100 bar, and the volumetric hydrogen storage density can reach 42 g/L (based on crystal density). This study thus provides theoretical basis and technical support for further research and development of more efficient MOF hydrogen storage materials and hydrogen storage and transportation technology.
