Abstract
Storage is still limiting the implementation of hydrogen as an energy carrier to integrate the intermittent operation of renewable energy sources. Among different solutions to the currently used compressed or liquified hydrogen systems, physical adsorption at cryogenic temperature in porous materials is an attractive alternative due to its fast and reversible operation and the resulting reduction in storage pressure. The feasibility of cryoadsorption for hydrogen storage depends mainly on the performance of the used materials for the specific application, where metal-organic frameworks or MOFs are remarkable candidates. In this work, gravimetric and volumetric hydrogen uptakes at 77 K and up to 100 bar of commercially available MOFs were measured since these materials are made from relatively cheap and accessible building blocks. These materials also show relatively high porous properties and are currently near to large-scale production. The measuring device was calibrated at different room temperatures to calculate an average correction factor and standard deviation so that the correction deviation is included in the measurement error for better comparability with different measurements. The influence of measurement conditions was also studied, concluding that the available adsorbing area of material and the occupied volume of the sample are the most critical factors for a reproducible measurement, apart from the samples’ preparation before measurement. Finally, the actual volumetric storage density of the used powders was calculated by directly measuring their volume in the analysis cell, comparing that value with the maximum volumetric uptake considering the measured density of crystals. From this selection of commercial MOFs, the materials HKUST-1, PCN-250(Fe), MOF-177, and MOF-5 show true potential to fulfill a volumetric requirement of 40 g·L−1 on a material basis for hydrogen storage systems without further packing of the powders.
Highlights
Storage is still a limiting factor in implementing the large-scale use of hydrogen as an energy carrier to assist the world in the transition to using 100% green energy [1].Despite the acceptance and use of compressed gas and the liquified state for hydrogen storage and transportation, more energetically efficient and operationally safe solutions will be requested
Among the different suggested mechanisms as alternative solutions for hydrogen storage, physical adsorption or physisorption can be advantageous because of its almost complete reversibility, fast adsorption/desorption kinetics, relatively high storage density [3,4], and lower pressure or higher temperature than those involved during compression or liquefaction of hydrogen, respectively, for a similar storage density [1,5]
Compared to covalent-organic frameworks (COF), there are more examples of metal-organic frameworks (MOF) structures exhibiting tridimensionally connected microporous structures, which is an advantageous feature for hydrogen adsorption
Summary
Storage is still a limiting factor in implementing the large-scale use of hydrogen as an energy carrier to assist the world in the transition to using 100% green energy [1]. The gravimetric hydrogen uptake of MOFs has been increased by developing materials with larger surface areas, generally obtaining new structures with larger cavities or higher void fraction by, for example, employing expanded organic linkers with a given topology [15,16]. This approach reduces the density of the resulting crystals, negatively affecting the volumetric storage capacity [17], which is a more relevant parameter for a stationary hydrogen storage application. OQOCAA, BOHJOZ, OFERUN, SUGSEU, MIBQAR, CIGXIA, OQOCAA,LUDLED, LUDLED,RUBTAK, RUBTAK,WIZMAV02, WIZMAV02, XOXTOW, respectively, from top-left to down-right (hydrogen atoms were omitted for clarity)
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