Abstract
Porous solids can accommodate and release molecular hydrogen readily, making them attractive for minimizing the energy requirements for hydrogen storage relative to physical storage systems. However, H2 adsorption enthalpies in such materials are generally weak (−3 to −7 kJ/mol), lowering capacities at ambient temperature. Metal-organic frameworks with well-defined structures and synthetic modularity could allow for tuning adsorbent-H2 interactions for ambient-temperature storage. Recently, Cu2.2Zn2.8Cl1.8(btdd)3 (H2btdd = bis(1H-1,2,3-triazolo-[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin; CuI-MFU-4l) was reported to show a large H2 adsorption enthalpy of −32 kJ/mol owing to π-backbonding from CuI to H2, exceeding the optimal binding strength for ambient-temperature storage (−15 to −25 kJ/mol). Toward realizing optimal H2 binding, we sought to modulate the π-backbonding interactions by tuning the pyramidal geometry of the trigonal CuI sites. A series of isostructural frameworks, Cu2.7M2.3X1.3(btdd)3 (M = Mn, Cd; X = Cl, I; CuIM-MFU-4l), was synthesized through postsynthetic modification of the corresponding materials M5X4(btdd)3 (M = Mn, Cd; X = CH3CO2, I). This strategy adjusts the H2 adsorption enthalpy at the CuI sites according to the ionic radius of the central metal ion of the pentanuclear cluster node, leading to −33 kJ/mol for M = ZnII (0.74 Å), −27 kJ/mol for M = MnII (0.83 Å), and −23 kJ/mol for M = CdII (0.95 Å). Thus, CuICd-MFU-4l provides a second, more stable example of optimal H2 binding energy for ambient-temperature storage among reported metal-organic frameworks.
| Original language | English |
|---|---|
| Pages (from-to) | 22759-22776 |
| Number of pages | 18 |
| Journal | Journal of the American Chemical Society |
| Volume | 146 |
| Issue number | 32 |
| DOIs | |
| State | Published - Aug 14 2024 |
Funding
This research was supported by the Hydrogen Materials\u2500Advanced Research Consortium (HyMARC), established as part of the Energy Materials Network under the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy (EERE), Hydrogen and Fuel Cell Technologies Office (HFTO), under Contract No. DE-AC02-05CH11231 with Lawrence Berkeley National Laboratory. Single-crystal X-ray diffraction data were collected at beamlines 12.2.1 of the Advanced Light Source at Lawrence Berkeley National Laboratory, a user facility supported by the U.S. DOE, Office of Science under Contract No. DE-AC02-05CH11231. Nuclear magnetic resonance instruments in this work were supported by the Pines Magnetic Resonance Center\u2019s Core NMR Facility. Powder neutron diffraction and inelastic neutron scattering measurements were performed at the High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS), a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Powder synchrotron X-ray diffraction data were collected on the 17-BM-B at the Advanced Photon Source, a DOE Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank Dr. Henry Z. H. Jiang for helpful discussions with in situ gas-dosing infrared spectroscopy measurements, Dr. Andrey Yakovenko, Dr. Wenqian Xu, and Dr. Benjamin Trump for assistance with powder X-ray diffraction measurements, Dr. Tanya Dax, Dr. Mark Loguillo, Dr. Anibal \u201CTimmy\u201D Ramirez-Cuesta, and the sample environment, health physics, and diffraction teams at the SNS and HFIR for technical assistance, Dr. Hasan Celik, Dr. Raynald Giovine, and the Core NMR Facility of the Pines Magnetic Resonance Center for assistance with NMR measurements, and Dr. Matthew N. Dods and Hyunchul Kwon for helpful discussions. K.M.C. is supported by an Arnold O. Beckman postdoctoral fellowship. R.A.K. gratefully acknowledges support from the U.S. DOE, Office of EERE, HFTO under Contract No. DE-AC36-8GO28308 to the National Renewable Energy Laboratory.