Impact of Preparation and Handling on the Hydrogen Storage Properties of Zn₄O(1,4-benzenedicarboxylate)₃ (MOF-5)

TLDR

MOF‑5 (Zn₄O(BDC)₃) degrades gradually in humid air, forming a nonporous solid. The authors aimed to develop improved synthesis and handling procedures for MOF‑5 to enhance its gas adsorption capacities. They implemented these procedures, resulting in significant increases in N₂ and H₂ adsorption capacities. The optimized MOF‑5 shows a maximum N₂ uptake of 44.5 mmol g⁻¹ and BET surface area of 3,800 m² g⁻¹, H₂ adsorption rising from 5.0 % to 7.1 % excess wt % at 77 K/40 bar and reaching 11.5 % wt % (77 g L⁻¹) at 170 bar, representing the highest gravimetric and volumetric cryogenic H₂ storage reported, with no capacity loss over 24 cycles and a 2‑min loading time at 45 bar.

Abstract

The prototypical metal-organic framework Zn4O(BDC)3 (MOF-5, BDC2- = 1,4-benzenedicarboxylate) decomposes gradually in humid air to form a nonporous solid. Recognizing this, improved procedures for its synthesis and handling were developed, leading to significant increases in N2 and H2 gas adsorption capacities. Nitrogen adsorption isotherms measured at 77 K reveal an enhanced maximum N2 uptake of 44.5 mmol/g and a BET surface area of 3800 m2/g, compared to the 35.8 mmol/g and 3100 m2/g obtained for a sample prepared using previous methods. High-pressure H2 adsorption isotherms show improvements from 5.0 to 7.1 excess wt % at 77 K and 40 bar. The total H2 uptake was further observed to climb to 11.5 wt % at 170 bar, corresponding to a volumetric storage density of 77 g/L. Thus, the air-free compound exhibits the highest gravimetric and volumetric H2 uptake capacities yet demonstrated for a cryogenic hydrogen storage material. Moreover, no loss of capacity was apparent during 24 complete adsorption−desorption cycles, while kinetics measurements showed a loading time of 2 min with application of just 45 bar of pressure.