Co-pelletization of a zirconium-based metal-organic framework (UiO-66) with polymer nanofibers for improved useable capacity in hydrogen storage |
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| Authors: | Sonwabo E Bambalaza Henrietta W Langmi Robert Mokaya Nicholas M Musyoka Lindiwe E Khotseng |
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| Affiliation: | 1. HySA Infrastructure Centre of Competence, Centre for Nanostructures and Advanced Materials (CeNAM), Chemicals Cluster, Council for Scientific and Industrial Research (CSIR), Pretoria 0001, South Africa;2. Faculty of Natural Science, University of the Western Cape, Bellville, Cape Town 7535, South Africa;3. Pyrometallurgy Division, Mintek, 200 Malibongwe Drive, Praegville, Randburg, 2194, South Africa;4. Department of Chemistry, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa;5. School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK |
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| Abstract: | We report on a concept of co-pelletization using mechanically robust hydroxylated UiO-66 to develop a metal-organic framework (MOF) monolith that contains 5 wt% electrospun polymer nanofibers, and consists of an architecture with alternating layers of MOF and nanofiber mats. The polymers of choice were the microporous Polymer of Intrinsic Microporosity (PIM-1) and non-porous polyacrylonitrile (PAN). Co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths retain no less than 85% of the porosity obtained in pristine powder and pelletized UiO-66. The composition of the pore size distribution in co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths is significantly different to that of pristine UiO-66 forms, with pristine UiO-66 forms showing 90% of the pore apertures in the micropore region and both UiO-66/nanofiber monoliths showing a composite micro-mesoporous pore size distribution. The co-pelletized UiO-66/nanofiber monoliths obtained improved useable H2 capacities in comparison to pristine UiO-66 forms, under isothermal pressure swing conditions. The UiO-66/PIM-1 monolith constitutes the highest gravimetric (and volumetric) useable capacities at 2.3 wt% (32 g L?1) in comparison to 1.8 wt% (12 g L?1) and 1.9 wt% (29 g L?1) obtainable in pristine UiO-66 powder and UiO-66 pellet, respectively. The co-pelletized UiO-66/PAN monolith, however, shows a significantly reduced surface area by up to 50% less in comparison to pristine UiO-66, but its pore volume only 13% less in comparison to pristine UiO-66. As a result, total gravimetric H2 capacity of the co-pelletized UiO-66/PAN monolith is 50% less in comparison to that of pristine UiO-66, but crucially the useable volumetric H2 capacity is 50% higher for the UiO-66/PAN monolith in comparison to pristine UiO-66 powder. The co-pelletization strategy provides a simple method for generating hierarchical porosity into an initially highly microporous MOF without changing the structure of the MOF through complex chemical modifications. The UiO-66/nanofiber monoliths offer improvements to the typically low H2 useable capacities in highly microporous MOFs, and open new opportunities towards achieving system-level H2 storage targets. |
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| Keywords: | Co-pelletization Hydrogen useable capacity UiO-66 Metal-organic framework Hierarchical porosity |
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