Metal-organic frameworks (MOFs) as fuels for advanced applications

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Metal-organic frameworks (MOFs) as fuels for advanced applications: evaluating and modifying the combustion energy of popular MOFs Hatem M. Titi, Mihails Arhangelskis, Athanassios D. Katsenis, Cristina Mottillo, Ghada Ayoub, Jean-Louis Do, Athena M Fidelli, Robin D. Rogers, and Tomislav Friscic Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b01488 • Publication Date (Web): 03 Jun 2019 Downloaded from http://pubs.acs.org on June 4, 2019

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Chemistry of Materials

Metal-organic frameworks (MOFs) as fuels for advanced applications: evaluating and modifying the combustion energy of popular MOFs Hatem M. Titi,a Mihails Arhangelskis,a Athanassios D. Katsenis,a Cristina Mottillo,a,b Ghada Ayoub,a Jean-Louis Do,a,c Athena M. Fidelli,a Robin D. Rogers*d,e and Tomislav Friščić*,a a) Department of Chemistry, McGill University, 801 Sherbrooke St. W. H3A 0B8 Montreal, Canada; b) ACSYNAM, Inc. Montreal, H1P 1W1, Canada; c) Department of Chemistry & Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada; d) 525 Solutions, Inc., PO Box 2206, Tuscaloosa, AL 35403, USA; e) College of Arts & Sciences, The University of Alabama, Tuscaloosa, AL 35487, USA. ABSTRACT: Systematic investigation of combustion energies for popular metal-organic framework (MOF) materials reveals energy content comparable to conventional energetic materials, that can be further modified and fine-tuned through control of framework topology or isostructural ligand replacement to yield energy densities comparable to conventional energetic materials such as TNT and hydrazine-, diesel- or kerosene-based fuels.

Introduction Metal-organic frameworks (MOFs) have emerged over the past two decades as readily designable microporous materials that can be functionalized for a wide range of applications, from catalysis and selective gas separation, to different types of conduction or light harvesting.1-11 Recently, MOF formation was reported as a route to generate new energetic materials, by using energetic molecules as ligands.12-19 Our group20 has demonstrated a MOF-based strategy for generating new hypergolic solid fuels, i.e. fuels that ignite simultaneously upon contact with an external oxidizer.21 Such hypergolic MOFs, being developed as advanced, safer alternatives to toxic hydrazine fuels in aerospace industries (e.g. for in-orbit propulsion),22,23 are based on using suitably functionalized imidazolate ligands as linkers in the synthesis of zeolitic imidazolate frameworks (ZIFs).20,24,25 Importantly, while hypergolic MOFs exhibit ultrashort ignition delays, they do not involve explosive, heat- or impact-sensitive components. Instead, the energetic effect upon ignition results solely from aerobic combustion of the framework.18 Similarly, the Matzger group has shown how a conventional MOF can be rendered explosive via inclusion of explosive guests, also taking advantage of the framework material as a fuel for explosive combustion.26 While the described materials open new uses for MOFs as cleaner fuels or safer explosives, these advanced applications will depend on the still poorly explored thermochemical properties of conventional MOFs,27-29 notably energy density (Ev, in MJ/dm3 or kJ/cm3) and specific energy (Eg, in MJ/kg or kJ/g). In order to evaluate the potential of conventional MOF designs for use in advanced fuel systems, we have now used combustion calorimetry to measure experimental specific energies, and determine energy densities and combustion enthalpies (cH) for representative examples of the most

popular classes of MOFs (Figure 1). The herein presented systematic study on conventional MOFs that are either commercially available or readily synthesized in the laboratory reveals that Eg for several carboxylate-based MOFs is close to that of the energetic compounds like trinitrotoluene (TNT) and hydrazine,30 whereas the specific energies of ZIFs can be significantly higher.29 Importantly, we show how Eg and Ev of ZIFs can be readily modified through control of MOF topology and/or engineered by chemical functionalization of the linker, leading to materials with specific energies higher than hydrazine fuels and approaching at least 60-65% of hydrocarbon fuels (Table 1), as well as tunable energy densities comparable to or exceeding those of hydrazine- or gasoline-based fuels.31-33 Results and Discussion The HKUST-1,34 MIL-53(Al)35 and ZIF-836 MOFs were purchased from Sigma-Aldrich, with a sample of ZIF-8 also obtained from ACSYNAM. The UiO-6637 and UiO-66-NH238 frameworks, as well as a series of ZIFs39-42 based on 2substituted imidazolate ligands were synthesized via reported procedures (Figure 1, also see SI Sections S1,S2).43,44 All materials were washed with methanol, evacuated and stored in argon before use. Identity and purity of all explored MOFs were validated by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) in air. Brunauer-Emmet-Teller (BET) and Langmuir surface areas for all materials were established by nitrogen sorption measurements, yielding values consistent with literature reports (see SI Sections S3-S6, also Table 1). All combustion experiments were carried on a 6200 Isoperibol Calorimeter using ca. 0.5 gram of the MOF. The herein reported Eg value for each MOF is an average of three measurements, and the corresponding Ev was calculated from it by taking into account the density and molecular weight calculated from the reported structural

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Figure 1. a) Organic ligands used in the herein explored MOFs and b) structures of herein studied MOFs, with hydrogen atoms omitted for clarity. Atoms of Zn/CoII, CuII, Al, Zr, N, O and C are shown in purple, green, pink, cyan, blue, red and grey, respectively.

data and chemical composition, respectively. Combustion enthalpy (cH) was calculated from Eg by considering the change in number of moles of gas in the combustion reaction (see SI) to form metal oxides ZnO (for explored zinc-based ZIFs), Co3O4 (for ZIF-67), CuO (for HKUST-1), Al2O3 (for MIL-53(Al)) and ZrO2 (for UiO-66 and UiO-66NH2) (see SI). Results of combustion calorimetry and selected structural information for all herein studied MOFs are shown in Table 1, and the corresponding plot of Eg and Ev is shown in Figure 2. For carboxylate MOFs, the data reveals high Eg values, nearing 15 kJ/g for zirconium-based UiO-frameworks and MIL-53(Al), while Ev values range from 14 kJ/cm3 to 17 kJ/cm3. Whereas these Eg values are close to that reported for the energetic compound TNT, the Ev values are significantly lower than for most popular fuels or energetic compounds, consistent with the microporous nature of the explored MOFs (Table 1). The measured Eg and Ev are the lowest for copper(II)-based HKUST-1, which can tentatively be related to a difference in linker structure and oxidation state of the metal, compared to other herein explored carboxylate MOFs. Specifically, HKUST-1 is based on 1,3,5benzenetricarboxylate linkers (Figure 1), exhibiting three metal-ligand connection sites per molecule, unlike terephthalate linkers in aluminum-based MIL-53(Al) and zirconium-based UiO-systems (Figure 1), which exhibit only two metal-ligand connection sites. At the same time, the oxidation state of the Cu2+ metal ion in HKUST-1 is lower compared to Al3+ and Zr4+ ions in MIL-53- and UiO-MOFs, respectively. These parameters dictate a 1:1.5 stoichiometric ratio of organic linkers to metal ions in the

formula unit of HKUST-1, which is lower than the 1:1 ratio found in the formula units of MIL-53(Al) and UiO-MOFs (Table 1). As the linker represents combustion fuel, the lower ligand-to-metal ratio in HKUST-1 is expected to lead to a lower Hc. Overall, Hc for carboxylate MOFs increases in the order HKUST-1 < MIL-53(Al) < UiO-66  UiO-66-NH2, a trend which might also be related to stabilities of the resulting oxides. Significantly larger Eg, Ev and Hc are observed for ZIFs. Using an in-house synthesized sample, we have reported20 that the popular sodalite (SOD) topology framework ZIF-8, based on zinc nodes and 2-methylimidazolate (MeIm-, Figure 1) linkers, exhibits Hc of ca. 4,800 kJ/mol. This Hc value translates to Eg and Ev of ca. 21 kJ/g and 20 kJ/cm3, which exceeds the values for TNT and hydrazine.20 These observations are here confirmed using ZIF-8 samples obtained from two commercial sources, Sigma-Aldrich and ACSYNAM (Table 1). The Eg, Ev and Hc are further slightly increased (by ca. 5%) in ZIF-67, a SOD-framework isostructural to ZIF-8, but based on cobalt(II) nodes. This small increase in cH might be associated to additional oxidation of metal nodes to form Co3O4,46 which does not take place in case of zinc frameworks. Although small, this difference in cH between ZIF-8 and ZIF-67 illustrates change in choice of metal node as a potential means to control combustion energy content of a MOF. A different route to modify fuel properties of a ZIF is revealed by comparing ZIF-8 to its non-porous diamondoid (dia) topology polymorph. Whereas the Hc values for the two polymorphs are expected to be very similar due to their identical chemical composition, the higher density of close-


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Chemistry of Materials based fuels monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH)(Table 1).31-33

packed dia-Zn(MeIm)2 leads to a significant increase in Ev, to ca. 33 kJ/cm3. This energy density is close to values for conventional hydrocarbon fuels such as gasoline or kerosene, and exceeds values for hypergolic hydrazine-

Table 1. Unit formula, relative molecular weight of unit formula (Mr), decomposition temperature (Td), calculated density (ρc), surface areas, Cambridge structural database (CSD) codes, specific energy (Eg), energy density (Ev) and combustion enthalpy (Hc) of herein explored MOFs, compared to those of selected fuels and energetic materials.

MOF

Unit formula

Mr

c

Td[a] (C)

(g/cm3)

surface area (m2/g) BET

Langmuir

CSD code

Eg[b] (kJ/g)

Ev (kJ/cm3)

Hc (kJ/mol)

SOD-Zn(MeIm)2 (ZIF-8) [c],36

C8H10N4Zn

227.9

498

0.925

1350

1760

VELVOY

20.9(1)

19.4(1)

-4769(19)

SOD-Zn(MeIm)2 (ZIF-8) [d],36

C8H10N4Zn

227.9

656

0.925

1350

1780

VELVOY

21.6(8)

20.0(7)

-4919(175)

dia-Zn(MeIm)239

C8H10N4Zn

227.9

498

1.579

-

-

OFERUN0 1

20.76(3)

32.7(1)

-4722(10)

SOD-Co(MeIm)2 (ZIF-67)40

C8H10N4Co

221.1

397

0.903

1510

1990

GITTOT01

22.9(5)

20.7(5)

-5068(119)

RHO-Zn(EtIm)236

C10H14N4Zn

255.6

471

0.814

1210

1620

MECWOH

24.0(3)

19.5(3)

-6132(81)

ANA-Zn(EtIm)237

C10H14N4Zn

255.6

461

1.091

610

700

MECWIB

24.3(1)

26.5(1)

-6218(28)

qtz-Zn(EtIm)241

C10H14N4Zn

255.6

492

1.590

-

-

EHETER

23.5(2)

37.2(3)

-5988(55)

ANA-Zn(PrIm)242

C12H18N4Zn

283.7

484

1.221

440

520

GUPFAZ

25.8(3)

31.4(3)

-7307(78)

ANA-Zn(BuIm)2

C14H22N4Zn

311.8

566

1.295

70

100

this work

28.0(5)

36.3(6)

-8726(152)

HKUST-1[c],34

C6H2CuO4

201.6

350

0.879

1340

1780

FIQCEN

11.5(1)

10.1(1)

-2324(10)

14.1(2)

14.4(1)

-2937(29)

MIL-53(Al)[c],35

C8H5AlO5

208.1

618

1.019

950

1270

SABVUN0 1

UiO-6637

C8H4.67O5.33Zr

277.4

584

1.246

870

1149

RUBTAK

13.3(1)

16.6(2)

-3691(45)

UiO-66-NH238

C8H5.67NO5.33 Zr

292.4

449

1.295

960

1275

SURKAT

12.26(1)

15.87(2)

-3584(13)

TNT30

C7H5N3O6

227.1

5

1.655

-

-

ZZZMUC0 1

15.0

24.8

-3399

diesel29

-

-

-

0.83

-

-

-

45.4

38.6

-

gasoline29

-

0.71

-

-

-

46.4

34.2

-

gasohol E8529,[e]

-

-

-

-

-

-

-

33.1

25.6

-

kerosene29

-

-

-

0.81

-

-

-

43.8

35.1

-

19.5[f]

-622

2834

hydrazine33

N2H4

32.0

-

1.00

-

-

-

19.4[f]

MMH33

CH6N2

46.1

-

0.87

-

-

-

28.3[f]

24.7[f]

-1304

UDMH33

C2H8N2

60.1

-

0.79

-

-

-

32.9[f]

25.9[f]

-1979

magnesium48

Mg

24.3

-

1.74

-

-

-

24.0

43.0

-

aluminum48

Al

27.0

-

2.70

-

-

-

31.0

83.8

-

boron49,50

B

10.8

-

2.37

-

-

-

58.5

135.8

-

[a] Measured by DSC in air, at a heating rate of 10 oC/min; [b] measured by combustion calorimetry; [c] obtained from Sigma-Aldrich; [d] obtained from ACSYNAM, Inc.; [e] 85:15 mixture of ethanol and petrol; [f] calculated from Hc values from reference 33.



Figure 2. Comparison of energy density (Ev) and specific energy (Eg) for herein explored MOFs, calculated from experimentally measured ΔcH values.

kerosene-based jet fuel (35.1 kJ/cm3),31,32 with a microporous surface area of 440 m2/g (Table 1). In order to effect a further increase in energy density, we used 2-butylimidazole (HBuIm) as the ligand. To the best of our knowledge, the Zn(BuIm)2 framework has so far not been reported. Mechanochemical synthesis provided a material that, based on PXRD analysis (see SI), was isostructural to ANA-topology Zn(EtIm)2 and Zn(PrIm)2 frameworks (Table 2). The composition Zn(BuIm)2 for the new material was confirmed by TGA in air (see SI), and the crystal structure was elucidated by structure solution from PXRD data. Rietveld refinement in the cubic space group Ia3d (Figure 3a) with the unit cell parameter a=26.765(2) Å revealed a structure analogous to ANA-Zn(EtIm)2. The neighboring hydrocarbon chains in the ANA-Zn(BuIm)2 form voids along the (111)-direction that are accessible to a spherical probe of 3.0 Å diameter and amount to ca. 4% (ca. 800 Å3) of unit cell volume (see SI, Section S8), indicating that the MOF should not exhibit a high surface area. This was confirmed by nitrogen sorption analysis at 77 K, which revealed a BET surface area of only 70 m2/g (Figure 3b).

The significant effect of polymorphism on energy density is also evident from comparing the three topologically distinct varieties of the zinc 2-ethylimidazolate Zn(EtIm)2 framework, with zeolite rho (RHO), analcime (ANA) and quartz (qtz) topologies. The Hc values for all three polymorphs are comparable, as expected, and are around 66.2 kJ/mol. Similarly, the corresponding Eg values are mutually similar, and are around 24 kJ/g. However, due to density increasing in the order RHO < ANA < qtz, the corresponding Ev differs greatly between the materials and ranges from 19.5 kJ/cm3 for the low-density RHOZn(EtIm)2 to a high value of 37.5 kJ/cm3 for non-porous qtzZn(EtIm)2. The Ev for qtz-Zn(EtIm)2 exceeds the values for gasoline (34.2 kJ/cm3), kerosene-based jet fuel (35.1 kJ/cm3), and is on par with diesel (38.6 kJ/cm3, Table 1).31 The comparison of combustion energy for polymorphs of Zn(MeIm)2 and Zn(EtIm)2 clearly demonstrates control over framework topology and polymorphism as potential tools to increase or decrease the energy density of a ZIF. The comparison of Hc reveals a higher value for Zn(EtIm)2 compared to Zn(MeIm)2 systems. This difference, readily explained by the presence of an additional CH2 fuel group in the Zn(EtIm)2 framework (see SI Section S7 for the analysis of combustion energy with respect to content of C, H, N, O and metal), illustrates a potential strategy to manipulate the combustion energy properties of ZIFs by introducing additional hydrocarbon groups. Switching from a 2-ethylsubstituted linker in RHO-, ANA- or qtz-Zn(EtIm)2 frameworks to an analogous but more fuel-rich 2propylimidazolate linker, yields the previously reported ANA-topology Zn(PrIm)2 framework, which is isostructural to ANA-Zn(EtIm)2. The measured Hc for ANA-Zn(PrIm)2 was found to be around -7,300 kJ/mol, which is ca. 1,100 kJ/mol more exothermic than its 2-ethyl-substituted homologue, providing a MOF that combines a high energy density (31 kJ/g) close to that of gasoline (34.2 kJ/cm3) or

Figure 3. (a) The final Rietveld fit and an illustration of the crystal structure of ANA-Zn(BuIm)2 along the crystallographic (100) direction,with hydrogen atoms omitted for clarity. (b) Nitrogen sorption isotherms at 77 K for ANA-Zn(BuIm)2, corresponding to a BET surface area of 70 m2/g. Adsorption and desorption are shown by blue and red circles, respectively.

Combustion measurement for ANA-Zn(BuIm)2 revealed an Eg of 28.0 kJ/g (Hc value of ca. -8,700 kJ/mol) that is around 60-65% of the value reported for gasoline and related fuels, and a high Ev of 36.3 kJ/cm3, which exceeds hypergolic rocket fuels MMH and UDMH, and is in the range of popular hydrocarbon fuels (Table 1).31 These values are below those of some actual (aluminum) or proposed


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Chemistry of Materials (boron) high-energy solid fuels,48-50 but already close to those of magnesium fuel (Table 1, Figure 4, also see SI Section S9).

Figure 4. Comparison of Eg and Ev for herein studied MOFs to those of typical gasoline, hydrazine (MMH and UDMH) and magnesium fuel.29,48,49 Values for carboxylate MOFs are in green, ZIFs in red.

Figure 5. Dependence of Ev on framework density (in tetrahedral nodes per unit volume, T/nm3) for selected ZIFs. As ANA-Zn(EtIm)2, ANA-Zn(PrIm)2 and ANAZn(PrIm)2 frameworks are isostructural, increasing the length of the 2-hydrocarbon chain substituent on the linker effectively increases the energy released in the combustion with almost no impact on the overall structure or network density (i.e. the number of tetrahedral centers per unit volume, T/nm3, Figure 5) of the material. Specifically, the Ev

for isostructural, topologically-identical ANA-Zn(EtIm)2, Zn(PrIm)2 and -Zn(BuIm)2 consistently increases by 4.9 kJ/cm3 per CH2 unit. To the best of our knowledge, such ability to engineer Ev without introducing any significant change in structure of the material is unique to MOFs and has so far not been reported in the design of fuel materials. Furthermore, the network density of ANA-Zn(EtIm)2 (2.57 T/nm3) is very close to that of ZIF-8 (2.45 T/nm3). Consequently, the herein explored ANA-topology ZIFs and ZIF-8 reveal the ability to fine-tune the energy density of a MOF across almost 20 kJ/cm3, with little or no change in network density and with retention of microporosity even at relatively high Eg (440 m2/g for ANA-Zn(PrIm)2). Conclusions In summary, we presented the first systematic investigation of combustion energies, including energy density, specific energy and combustion enthalpy for a range of conventional and mostly commercially available MOFs. In contrast to traditional microporous materials such as zeolites, MOFs can be considered as potential fuels which, upon combustion, are able to generate energy comparable to popular hydrocarbon fuels. This is particularly true for ZIFs based on nitrogen-containing heterocycles, exhibiting a high specific energy, approaching >60-65% that of gasoline. Importantly, we show that the energy density of MOFs can be tuned to approach or even exceed those of kerosene, diesel, magnesium or hydrazine rocket fuels. Whereas the specific energies and energy densities of herein investigated MOFs are smaller than for high combustion energy solids such as boron,49,50 the specific energy values are close to those of magnesium and aluminium fuels, with energy density in some cases exceeding that of magnesium. Our study shows that the modular design and the ability to direct framework topology of ZIFs offer a means to control energy content in a way that is not accessible to conventional fuels. Switching between different ZIF topologies enables tuning of energy density without changes to the chemical composition, as illustrated by qtz-, ANA- and RHO-topology frameworks of zinc 2ethylimidazolate. Conversely, modular design of ZIFs enables the introduction of increasingly fuel-rich substituents and tuning of combustion energy without changing the overall structure of the material, as illustrated by the isostructural series of ANA-topology zinc 2-ethyl-, 2propyl- and 2-n-butyl-substituted ZIFs. Overall, these results provide a so far missing overview of combustion energy properties of conventional MOFs, and demonstrate that different classes of frameworks, particularly ZIFs, can exhibit high, as well as tunable energy density and specific energy. We believe that these results, in combination with intermediate-to-high microporosity and high thermal stability in general,23,46 indicate ZIFs as suitable, highly promising materials for the development of advanced tunable fuels and hypergols. Experimental section More details on experimental procedures and calculations are provided in the Supplementary Information (Sections S1, S2). Despite high energy contents, the herein explored



materials are highly thermally stable and would not ignite even upon exposure to a blowtorch. Combustion calorimetry The combustion calorimetry measurements were carried out on a 6200 Isoperibol Calorimeter (Parr Instrument Company, Moline, IL), which is a microprocessor controlled, isoperibol oxygen bomb calorimeter. The combustion calorimeter was calibrated by benzoic acid. All measurements were carried out on a scale of 0.5 g of the sample and repeated three times. Thermal analysis Simultaneous thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were conducted on a TGA/DSC 1 (Mettler-Toledo, Columbus, Ohio, USA), with samples (2 mg to 10 mg) placed in open 70 L volume alumina crucibles. All measurements were done in a dynamic atmosphere of air (25 mL/min), in the range heated up to 800 °C at a constant rate of 10 °C/min. The experimental results are shown in Supplementary Information, Section S4. Sample activation All samples were washed with methanol (30 mL) and centrifuged for 20 minutes at 4500 rpm, and the supernatant separated. This process was repeated two times to assure the absence of any residual starting materials in the samples. The MOF samples were placed in vacuum oven at 80 C - 120 C overnight and kept under argon. The nitrogen isotherms of the activated MOFs were measured on TriStar 3000, and the experiments were conducted at 77 K of liquid nitrogen container. The experimental results are shown in Supplementary Information, Section S3. Powder X-ray diffraction (PXRD) Powder X-ray diffraction data were collected on a Bruker D2 Phaser diffractometer equipped with a LYNXEYE linear position sensitive detector (Bruker AXS, Madison, WI, USA), using Ni-filtered CuKα radiation. The structures of MOF materials were verified by Pawley fitting of the experimental data to previously published structure, and the results are shown in Supplementary Information, Section S5.The PXRD pattern of ANA-Zn(BuIm)2 was collected on a Bruker D8 Advance diffractometer equipped with a LYNXEYE-XE linear position sensitive detector, using Ni-filtered CuKα radiation. Rietveld refinement of the structure ANAZn(BuIm)2 (Table S1) was performed using the software TOPAS Academic v. 6 (Coelho Software). The ANAZn(BuIm)2 structure was refined in the cubic Ia-3d space group. Diffraction peak shapes were described by a pseudoVoigt function, while the background was modelled with a Chebyshev polynomial function. The linker geometry was defined by a rigid body, which was given rotational and translational degrees of freedom, subject to the space group symmetry constraints. In addition, flexible torsion angles were used to refine the conformation of the butyl substituent. Fourier-transform infrared attenuated total reflectance spectroscopy (FTIR-ATR)

Spectra were recorded using a Bruker Alpha FT-IR (Bruker Optics Ltd., Milton, ON, Canada) decorated by diamond crystal in the range of 4000-450 cm-1 and with resolution of 4 cm-1. The experimental results are shown in Supplementary Information, Section S6.

ASSOCIATED CONTENT Supporting Information. Further details of experimental procedures and calculations, as well as PXRD, FTIR/ATR and TGA/DSC data. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data for ANAZn(BuIm)2 structure in CIF format was deposited with the Cambridge Crystallographic Data Centre, deposition code CCDC 1906483.

AUTHOR INFORMATION Corresponding Authors * Assoc. Prof. Tomislav Friščić, Department of Chemistry, McGill University, 801 Sherbrooke St. W. H3A 0B8 Montreal, Canada. E-mail: [email protected] * Prof. Robin D. Rogers, 525 Solutions, Inc. P.O. Box 2206, Tuscaloosa, AL 35403, USA. E-mail: [email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Funding Sources NSERC Discovery Grant (RGPIN-2017-06467) NSERC E. W. R. Steacie Fellowship (SMFSU 507347-17) NSERC Strategic Grant (STPGP 521582-18) Canada Research Excellence Chair program (grant 240634) AFOSR (FA9550-14-1-0306).

Notes

CM and TF are co-founders, and RDR is the scientific advisory board member of ACSYNAM, Inc., which has provided one of the materials for the study.

ACKNOWLEDGMENT We thank Dr. A. Djuric, McGill University, for help in acquiring BET data. We acknowledge funding from the NSERC Discovery Grant (RGPIN-2017-06467), NSERC E. W. R. Steacie Fellowship (SMFSU 507347-17), NSERC Strategic Grant (STPGP 52158218), Canada Research Excellence Chair program (grant 240634) and AFOSR (FA9550-14-1-0306).

ABBREVIATIONS HMeIm, 2-methylimidazole; MeIm-, 2-methylimidazolate; HEtIm, 2-ethylimidazole; EtIm-, 2-ethylimidazolate; HPrIm, 2propylimidazole; PrIm-, 2-propylimidazolate; HBuIm, 2butylimidazole; H3BDC, 1,3,5-benzenetricarboxylic (trimesic) acid; H2BDC, 1,4-benzenedicarboxylic (terephthalic) acid; H2BDC-NH2, 2-amino-1,4-benzenedicarboxylic (2aminoterephthalic) acid.

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Metal-organic frameworks (MOFs) as fuels for advanced applications

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