U.S. patent application number 17/158558 was filed with the patent office on 2021-05-20 for compositions and methods of making metal-organic frameworks with redox-active centers.
The applicant listed for this patent is King Abdullah University of Science and Technology. Invention is credited to Bilal AHMED, Husam N. ALSHAREEF, Mohamed EDDAOUDI, Arijit MALLICK, Osama SHEKHAH.
Application Number | 20210151262 17/158558 |
Document ID | / |
Family ID | 1000005360859 |
Filed Date | 2021-05-20 |
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United States Patent
Application |
20210151262 |
Kind Code |
A1 |
MALLICK; Arijit ; et
al. |
May 20, 2021 |
COMPOSITIONS AND METHODS OF MAKING METAL-ORGANIC FRAMEWORKS WITH
REDOX-ACTIVE CENTERS
Abstract
Embodiments of the present disclosure describe an electrode
material comprising a metal ion cluster and an organic linker with
a redox-active center associated with the metal ion cluster
sufficient to form a metal-organic framework. Embodiments of the
present disclosure further describe a method of forming an
electrode material comprising contacting a metal ion cluster with
an organic linker including a redox-active center sufficient to
form a metal-organic framework. Embodiments of the present
disclosure also describe a metal-organic framework composition
comprising a metal ion cluster and an organic linker with a
redox-active center associated with the metal ion cluster.
Inventors: |
MALLICK; Arijit; (Thuwal,
SA) ; AHMED; Bilal; (Thuwal, SA) ; SHEKHAH;
Osama; (Thuwal, SA) ; ALSHAREEF; Husam N.;
(Thuwal, SA) ; EDDAOUDI; Mohamed; (Thuwal,
SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
King Abdullah University of Science and Technology |
Thuwal |
|
SA |
|
|
Family ID: |
1000005360859 |
Appl. No.: |
17/158558 |
Filed: |
January 26, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16471812 |
Jun 20, 2019 |
10903019 |
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PCT/IB2017/058522 |
Dec 29, 2017 |
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17158558 |
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62440573 |
Dec 30, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 11/86 20130101;
C07F 7/003 20130101; C07D 471/06 20130101; H01G 11/30 20130101 |
International
Class: |
H01G 11/30 20060101
H01G011/30; C07D 471/06 20060101 C07D471/06; C07F 7/00 20060101
C07F007/00; H01G 11/86 20060101 H01G011/86 |
Claims
1-20. (canceled)
21. An electrode material comprising: a plurality of metal ion
clusters, and a plurality of organic linkers including redox-active
centers, wherein the plurality of organic linkers associate with
the plurality of metal ion clusters to form a metal-organic
framework.
22. The electrode material of claim 21, wherein the plurality of
metal ion clusters include at least one of Fe, Ce, V, Zr, Hf, La,
Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Tb, and Y.
23. The electrode material of claim 21, wherein the plurality of
metal ion clusters include at least one of Fe, V, and Ce.
24. The electrode material of claim 21, wherein the plurality of
metal ion clusters include hexanuclear metal ion clusters.
25. The electrode material of claim 21, wherein the plurality of
metal ion clusters are characterized by the formula
[M.sub.6O.sub.4(OH).sub.4].sup.8+, where M is a metal.
26. The electrode material of claim 21, wherein the plurality of
organic linkers include
N,N'-bis(terphenyl-4,4''-dicarboxylate).
27. The electrode material of claim 21, wherein the redox-active
centers includes at least one of naphthalenediimide, anthraquinone,
benzoquinone, perlinedianhydride, and an organic nitroxide
radical.
28. The electrode material of claim 21, wherein the plurality of
organic linkers include N,N'-bis(terphenyl-4,4''-dicarboxylate) and
anthraquinone.
29. The electrode material of claim 21, wherein the plurality of
organic linkers include N,N'-bis(terphenyl-4,4''-dicarboxylate) and
benzoquinone.
30. The electrode material of claim 21, wherein the plurality of
organic linkers include N,N'-bis(terphenyl-4,4''-dicarboxylate) and
perlinedianhydride.
31. The electrode material of claim 21, wherein the plurality of
organic linkers include N,N'-bis(terphenyl-4,4''-dicarboxylate) and
an organic nitroxide radical.
32. The electrode material of claim 21, wherein the metal-organic
framework further includes a plurality of organic pillars
associated with the plurality of metal ion clusters.
33. The electrode material of claim 32, wherein the plurality of
organic pillars include a dicarboxylate.
34. The electrode material of claim 32, wherein the plurality of
organic pillars include a biphenyl dicarboxylate (BPD).
35. The electrode material of claim 32, wherein the plurality of
organic pillars include at least one of
4,4'-biphenyl-dicarboxylate;
3,3-dihydroxybiphenyl-4,4-dicarboxylate; and
3,3-dithiobiphenyl-4,4-dicarboxylate.
36. The electrode material of claim 32, wherein the plurality of
organic pillars include 2,2-bipyridine-4,4-dicarboxylate.
37. The electrode material of claim 21, wherein the metal-organic
framework has a scu topology.
38. An electrode comprising: an electrode material according to
claim 21.
39. A supercapacitor electrode comprising: an electrode material
according to claim 21.
40. The supercapacitor electrode of claim 39, wherein the electrode
material further includes a plurality of organic pillars associated
with the plurality of metal ion clusters.
Description
BACKGROUND
[0001] Energy storage nowadays is considered a key element in most
renewable energy systems. Existing technologies, such as wind
turbines and solar photovoltaics are intermittent by nature. Thus,
energy storage technologies (e.g., batteries and supercapacitors
(SC)) have the potential to mitigate this intermittency problem of
renewable energy sources, through storing the generated energy for
later use upon demand Supercapacitors are becoming important
storage technology due to their charge storage mechanism, which
does not involve irreversible chemical reactions. Stable porous
materials are considered attractive electrode materials for
capacitive energy storage applications, since they provide high
surface areas, and their open structures can enhance rapid ion
transport. These features can increase capacitance and rate
performance of the supercapacitors.
[0002] Supercapacitors exemplify an importance class of energy
storage devices largely due to their high power density.
Supercapacitors are useful for heavy electrical vehicles that need
to burst electrical power for rapid acceleration (e.g., electric
vehicles, high-speed bullet trains, elevators in high-rise
buildings, weight-lifting cranes, hill-climbing cars, etc.).
Generally, battery power has been utilized to accelerate vehicles,
for example, but supercapacitors provide an efficient release of
power that is much quicker than batteries. In addition, as compared
to batteries, supercapacitors require no maintenance, offer high
cycle-life, require only a simple charging circuit, experience no
"memory effect," and operate under safer conditions. Commercial
supercapacitors use porous carbon and graphene, electrodes which
operate at a very high charge/discharge rate, and have a long cycle
life. However, emerging applications demand even higher
capacitances. In contrast, pseudocapacitive materials with
redox-active metal centers have higher capacitance, but shorter
cycle life.
[0003] As a result, there is a need to develop electrodes that
combine both redox and electric double layer capacitances with long
cycle life.
SUMMARY
[0004] In general, embodiments of the present disclosure describe a
metal-organic framework composition, electrode materials, and
methods of forming a metal-organic framework and electrode
material.
[0005] Accordingly, embodiments of the present disclosure describe
an electrode material comprising a metal ion cluster and an organic
linker with a redox-active center associated with the metal ion
cluster sufficient to form a metal-organic framework.
[0006] Embodiments of the present disclosure further describe a
method of forming an electrode material comprising contacting a
metal ion cluster with an organic linker including a redox-active
center sufficient to form a metal-organic framework.
[0007] Another embodiment of the present disclosure is a
metal-organic framework composition comprising a metal ion cluster
and an organic linker with a redox-active center associated with
the metal ion cluster.
[0008] The details of one or more examples are set forth in the
description below. Other features, objects, and advantages will be
apparent from the description and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0009] This written disclosure describes illustrative embodiments
that are non-limiting and non-exhaustive. In the drawings, which
are not necessarily drawn to scale, like numerals describe
substantially similar components throughout the several views. Like
numerals having different letter suffixes represent different
instances of substantially similar components. The drawings
illustrate generally, by way of example, but not by way of
limitation, various embodiments discussed in the present
document.
[0010] Reference is made to illustrative embodiments that are
depicted in the figures, in which:
[0011] FIG. 1 is a schematic diagram of a metal-organic framework
with a redox-active center, according to one or more embodiments of
the present disclosure.
[0012] FIG. 2 is a flowchart of a method of forming an electrode
material, according to one or more embodiments of the present
disclosure.
[0013] FIGS. 3A-3B illustrate (a) a schematic representation of the
synthetic route for Zr-BTD-NDI-MOF showing different topologies
that can be obtained and (b) the active core in the NDI linker with
the two electron redox process, according to one or more
embodiments of the present disclosure.
[0014] FIG. 4 is a graphical view of .sup.1H NMR spectra for the
linker showing characteristic peaks, according to one or more
embodiments of the present disclosure.
[0015] FIG. 5 is a graphical view of .sup.13C NMR spectra for the
linker showing characteristic peaks, according to one or more
embodiments of the present disclosure.
[0016] FIG. 6 is a graphical view of mass spectra for the linker
showing the exact molecular weight as calculated from the formula,
according to one or more embodiments of the present disclosure.
[0017] FIG. 7 is a schematic diagram illustrating the structure of
Zr-BTD-NDI-MOF depicted in a thermal ellipsoid model with 50%
probability, according to one or more embodiments of the present
disclosure.
[0018] FIGS. 8A-8B are schematic diagrams illustrating (a) the
crystal structure of Zr-BTD-NDI-MOF along the a-axis, and (b) the
hexanuclear Zr-cluster with 8 carboxylate form the linker,
according to one or more embodiments of the present disclosure.
[0019] FIGS. 9A-9F relate to Zr-NDI-BPy-MOF symmetric devices and
illustrate (a) a graphical view of CV curves measured at different
scan rates; (b) a graphical view of GCD curves measured at
different current densities; (c) a graphical view of cyclic
stability performed at 2 A g.sup.-1 up to 10,000 cycle; (d) a
graphical view of a PXRD pattern comparison before and after the
electrochemical measurement; and (e,f) SEM images of the electrode
before (e) and after (f) the electrochemical measurement, according
to one or more embodiments of the present disclosure.
[0020] FIG. 10 is a graphical view of a time dependent PXRD pattern
for Zr-BTD-NDI-MOF showing the peak shift with removal of the
trapped solvent, according to one or more embodiments of the
present disclosure.
[0021] FIG. 11 is a graphical view of a temperature dependent PXRD
pattern for Zr-BTD-NDI-MOF showing the thermal stability up to
400.degree. C., according to one or more embodiments of the present
disclosure.
[0022] FIG. 12 is a graphical view of TGA plots of the synthesized
MOFs showing their thermal stability, according to one or more
embodiments of the present disclosure.
[0023] FIGS. 13A-13D relate to MOF electrodes for supercapacitors
in 1 M H.sub.2SO.sub.4 and illustrate (a) graphical views of CV
curves collected at 50 mV s.sup.1, (b) graphical views of GCD
profiles at 1 A g.sup.-1, (c) graphical views of capacitance as a
function of scan rate (mV s.sup.-1), and (d) graphical views of
stability tests performed at 5 A g.sup.-1, according to one or more
embodiments of the present disclosure.
[0024] FIG. 14 is a graphical view of 1H NMR spectra for the pillar
installed MOFs (for .sup.1H NMR analysis of Zr-BTD-NDI-BP and
Zr-BTD-NDI-BPy-MOF, the samples (around 5 mg) were digested by 12 M
HCl aqueous solution and dried in a 100.degree. C. oven; the solid
was dissolved in about 0.5 mL d.sup.6-DMSO), according to one or
more embodiments of the present disclosure.
[0025] FIGS. 15A-15B are Ar adsorption isotherms for (a) Zr-BTD-NDI
and pore size distribution plot in inset and (b) Zr-BTD-NDI-BP and
Zr-BTD-NDI-BPy, with graphical views of pore size distribution
provided in the insets, according to one or more embodiments of the
present disclosure.
[0026] FIG. 16 is a schematic diagram of the structure of the
Zr-BTD-NDI-MOF and the insertion of two organic pillars, according
to one or more embodiments of the present disclosure.
[0027] FIG. 17 is a graphical view showing a comparison of FT-IR
spectra of the linker and Zr-BTD-NDI-MOF, according to one or more
embodiments of the present disclosure.
[0028] FIG. 18 is a graphical view showing a comparison of the PXRD
pattern of bulk Zr-BTD-NDI-BP-MOF and Zr-BTD-NDI-BPy-MOF crystal
with their simulated pattern, according to one or more embodiments
of the present disclosure.
[0029] FIG. 19 is a graphical view showing a comparison of PXRD
pattern of experimental with simulated for Zr-BTD-NDI-MOF,
according to one or more embodiments of the present disclosure.
[0030] FIGS. 20A-20F are graphical views of (a,c,e) CV curves and
(b,d,f) CD curves recorded at different scan rates and current
densities, respectively, for (a,b) Zr-BTD-NDI-MOF, (c,d)
Zr-BTD-NDI-BP-MOF, and (e,f) Zr-BTD-NDI-BPy-MOF in three-electrode
measurements using 1 M H.sub.2SO.sub.4 as electrolyte, according to
one or more embodiments of the present disclosure.
[0031] FIG. 21 is a graphical view of the current density versus
potential for determination of the potential window of the
Zr-BTD-NDI-BPy-MOF, according to one or more embodiments of the
present disclosure.
[0032] FIGS. 22A-22C illustrate low- (top panel) and
high-magnification (bottom panel) SEM images of (a) carbon cloth
(CC) electrode, (b) Zr-BTD-NDI-BPy-MOF on CC electrode, and (c) MOF
electrode after cycling, according to one or more embodiments of
the present disclosure.
[0033] FIGS. 23A-23B are graphical views of (a) Cell capacitance of
the Zr-BTD-NDI-BPy-MOF symmetric devices and (b) Ragone plots
showing the energy density of power density, according to one or
more embodiments of the present disclosure.
DETAILED DESCRIPTION
[0034] The invention of the present disclosure relates to electrode
materials. In particular, the invention of the present disclosure
relates to electrode materials including organic linkers with
redox-active centers that associate with metal ion clusters
sufficient to form a metal-organic framework (MOF). This is the
first time a stable and rigid metal-organic framework has been
fabricated with a redox-active center for enhancing faradaic energy
storage. The redox-active centers of the organic linkers permit the
storage of electrical energy via pseudocapacitance (e.g.,
metal-oxide and/or electrochemical pseudocapacitance), as well as
modification and tuning of the performance characteristics of the
electrode material. The high surface area and uniform pore
distribution of the metal-organic frameworks enhances the storage
of electrical energy via double-layer capacitance (e.g.,
electrostatic double-layer capacitance). In this way, the electrode
materials exhibit the high performance characteristics necessary
for a variety of applications, including electrochemical capacitors
(e.g., supercapacitors).
[0035] The electrode materials of the present disclosure include
metal-organic frameworks. Metal-organic frameworks are modular
crystalline porous materials composed of both organic (e.g.,
organic linkers and/or ligands) and inorganic components (e.g.,
metal ions and/or metal ion clusters) arranged in a periodic
networked structure. A feature of metal-organic frameworks of the
present disclosure is that the organic and inorganic components may
be tuned to target and design metal-organic frameworks with high
capacitance and long life cycle behavior. The metal-organic
frameworks of the present disclosure have been tuned to integrate
different functionalities (e.g., redox centers) in their structure
by using strategically designed organic linkers that have the
targeted center for supercapacitor applications. Metal-organic
frameworks also exhibit one or more of high and/or uniform
porosity, high surface area, and chemical stability. In many
embodiments, the metal-organic framework is utilized as an
electrode material for supercapacitors. In other embodiments, the
metal-organic framework may be utilized as an electrode separator
and/or in lithium-ion batteries. These embodiments, however, are
not limiting and the metal-organic framework of the present
disclosure may be utilized in any application known to a person of
skill in the art.
[0036] The metal-organic frameworks of the present disclosure may
be integrated in supercapacitors (e.g., as electrode materials).
Supercapacitors generally require high performing electrode
materials and outperform other types of capacitors, including
electrolytic capacitors and batteries, with respect to energy
density (e.g., amount of energy stored per unit volume or more),
rate performance (e.g., rate of accepting and delivering charge),
and life cycle (e.g., number of charge and discharge cycles before
failure). While most capacitors include a solid dielectric between
two electrodes, supercapacitors do not utilize a solid dielectric.
Rather, supercapacitors include an electrolyte and a separator
(e.g., ion-permeable membrane) between two electrodes. When a
voltage is applied, a monolayer of solvent molecules at the
electrode-electrolyte interface forms that functions as a thin
molecular dielectric.
[0037] FIG. 1 is a schematic diagram of a metal-organic framework
with a redox-active center, according to one or more embodiments of
the present disclosure. Metal-organic frameworks, such as the one
shown in FIG. 1, may be utilized as electrode materials in
supercapacitors, for example. Embodiments of the present disclosure
describe an electrode material that includes a metal ion cluster
and an organic linker with a redox-active center that associates
with the metal ion cluster sufficient to form a metal-organic
framework.
[0038] The metal ion cluster may include a polynuclear inorganic
building block. In some embodiments, the metal ion cluster may be
characterized by the formula [M.sub.6O.sub.4(OH).sub.4].sup.12+,
where M includes one or more of an alkali metal, rare-earth metal,
transition metal, lanthanide, and/or post-transition metal. Alkali
metals may include one or more of lithium, sodium, potassium,
rubidium, caesium, and francium. Rare-earth metals may include one
or more of cerium, dysprosium, erbium, europium, gadolinium,
holmium, lanthanum, lutetium, neodymium, praseodymium, promethium,
samarium, scandium, terbium, thulium, ytterbium, and yttrium.
Transition metals may include one or more of scandium, titanium,
vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc,
yttrium, zirconium, niobium, molybdenum, technetium, ruthenium,
rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten,
rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium,
dubnium, seaborgium, bohrium, hassium, meitnerium, darmstadtium,
roentgenium, and copernicium. Lanthanides may include one or more
of lanthanum, cerium, praseodymium, neodymium, promethium,
samarium, europium, gadolinium, terbium, dysprosium, holmium,
erbium, thulium, ytterbium, and lutetium. Post-transitiona metals
may include one or more of aluminum, gallium indium, tin, thallium,
lead, bismuth, nihonium, flerovium, moscovium, and livermorium.
[0039] The organic linker may include a ligand with a redox-active
center. In many embodiments, the organic linker is
N,N'-bis(terphenyl-4,4''-dicarboxylic acid) naphthalenediimide,
wherein N,N'-bis(terphenyl-4,4''-dicarboxylic acid) is the ligand
and naphthalenediimide (NDI) is the redox-active core. In other
embodiments, the organic linker may include one or more of
anthraquinone, benzoquinone, perylinedianhydride, and organic
nitroxide radicals.
[0040] The metal ion cluster and organic linker with a redox-active
center associate to form a metal-organic framework. The
metal-organic framework may include a scu topology. The
metal-organic frameworks may exhibit high stability towards
moisture, low pH media, and electrolyte medium (e.g., including
acidic conditions), leading to a long cycle life relative to
conventional materials. In some embodiments, the metal ion clusters
provide high chemical stability and increase the life cycle of the
capacitor. The redox-active centers of the organic linkers permit
the storage of electrical energy via pseudocapacitance (e.g.,
metal-oxide and/or electrochemical pseudocapacitance), as well as
modification and tuning of the performance characteristics of the
electrode material (e.g., associated redox capabilities). The open
and/or periodic structure, high surface area, and uniform pore
distribution of the metal-organic frameworks increase the storage
of energy via double-layer capacitance (e.g., electrostatic
double-layer capacitance) and facilitate rapid ion transport
without blocking the accessible pore system/surface area. The
resulting metal-organic framework is an electrode material with
high capacitive performance.
[0041] The metal-organic framework may exhibit a high porosity, a
high surface area, and/or uniform pore distribution. In many
embodiments, the surface area of the metal-organic framework is
equal to or greater than about 1,000 cm.sup.2/g. Whereas
conventional carbon-based electrodes (e.g., activated carbon
electrodes) suffer from low capacitance (e.g., about 10%
capacitance) due to irregular porosity distribution, the
metal-organic frameworks exhibit a uniform or nearly uniform pore
distribution. Conventional electrodes also suffer from inaccessible
micropores due to electrolyte blocking, resulting in a formation of
double layers on the surface only (about 2 nm depth), as opposed to
the entire pore system. Metal-organic frameworks, on the other
hand, are highly porous and exhibit uniformly accessible
porosity.
[0042] The electrode material may store electrical energy via one
or more of double-layer capacitance and pseudocapacitance. In many
embodiments, the electrode material stores electrical energy via
double-layer capacitance and pseudocapacitance. The storage of
electrical energy via double-layer capacitance may be based on
electrostatic forces and not on charge transfer between electrode
and electrolyte. In particular, double-layer capacitance may
include the formation of a monolayer of solvent molecules at the
electrode-electrolyte interface between two electrical layers. One
of the layers may be formed in a lattice structure of the electrode
(e.g., metal-organic framework) and the other layer of solvated
ions with opposite polarity may form in the electrolyte. The
monolayer of solvent molecules may adsorb to the surface of the
electrode and functions as a thin molecular dielectric by
separating charge at the interface between the electrode and the
electrolyte. Pseudocapacitance, on the other hand, is the storage
of electrical energy via faradaic redox reactions, intercalation,
and/or adsorption. In an electrochemical capacitor, an electron
charge-transfer occurs when a de-solvated ion comes out of the
electrolyte, pervades the double-layer, and adsorbs on a surface of
the electrode. In many embodiments, the electrode material exhibits
a high areal supercapacitor performance that may be about a 15-fold
increase over conventional materials (e.g., activated carbon). In
embodiments where the materials are post-functionalized with an
organic pillar, the areal supercapacitor performance may be about a
19-fold increase over conventional materials.
[0043] The electrode material may further include an organic
pillar. For example, the electrode material may be further tuned
via post-functionalization with an organic pillar. The organic
pillar may further increase a rigidity and surface area of the
electrode material and/or metal-organic framework. The electrode
material may be tuned with an organic pillar without affecting
redox activity (e.g., maintaining the same redox activity) of the
redox-active center of the organic linker. In many embodiments, the
organic pillar includes biphenyl-dicarboxylic acid. In other
embodiments, the organic pillar includes one or more of pillar
linkers, such as one or more of 2,2-bipyridine-4,4-dicarboxylic
acid, and 3,3-dihydroxybipheyl-4,4-dicarboxylic acid.
[0044] FIG. 2 is a flowchart of a method of forming an electrode
material, according to one or more embodiments of the present
disclosure. Any of the embodiments described in the present
disclosure may be utilized with respect to this embodiment.
[0045] At step 201, a metal ion may be contacted with an organic
linker including a redox-active center. Any of the metal ions/metal
ion clusters, organic linkers, and/or redox-active centers
discussed above may be utilized with respect to step 201. In many
embodiments, a metal ion cluster may be contacted with an organic
linker including a redox-active center sufficient to form a
metal-organic framework. As used herein, "contacting" refers to the
act of touching, making contact, or of bringing to immediate or
close proximity, including at the cellular or molecular level, for
example, to bring about a physiological reaction, a chemical
reaction, or a physical change, e.g., in a solution, in a reaction
mixture, in vitro, or in vivo. Accordingly, treating, tumbling,
vibrating, shaking, mixing, and applying are forms of contacting to
bring two or more components together.
[0046] At step 202, the metal-organic framework may be modified
with an organic pillar. Any of the organic pillars discussed above
may be utilized with respect to step 202. In many embodiments, the
metal-organic framework is modified via post-functionalization with
an organic pillar. As used herein, "modifying" refers to adjusting,
introducing, installing, contacting, providing, altering, adding,
treating, and any other similar terms understood by a person of
skill in the art. Post-functionalization generally refers to
chemical treatment of a fabricated metal-organic framework, with
the structure remaining intact. By modifying the metal-organic
framework in this way, the surface area and rigidity of the
metal-organic framework may be tuned (e.g., increased and/or
enhanced). Step 202 is optional.
[0047] Alternatively, in other embodiments, metal-organic
frameworks may be fabricated by utilizing pristine metal-organic
frameworks to store electrical energy on internal surfaces through
electrochemical double-layer capacitance or redox reactions of a
metal center may be exploited to store energy. In other
embodiments, metal-organic frameworks may be fabricated by
decomposing/destroying metal-organic frameworks to afford metal or
metal-oxides and to store energy faradaically via charge transfer
between electrolyte and electrolyte. In other embodiments,
metal-organic frameworks may be fabricated by pyrolyzing
metal-organic frameworks to give microporous carbons and enhance
capacitance by increasing conductivity. These methods may be used
alone or in any combination to fabricate metal-organic
frameworks.
[0048] The following Examples are intended to illustrate the above
invention and should not be construed as to narrow its scope. One
skilled in the art will readily recognize that the Examiners
suggest many other ways in which the invention could be practiced.
It should be understand that numerous variations and modifications
may be made while remaining within the scope of the invention.
Example 1
Zr-NDI-MOF and Zr-NDI-BPD-MOF
[0049] Supercapacitors are attractive power sources, compared with
batteries. Supercapacitors require no maintenance, offer a high
cycle-life, require only a simple charging circuit, experience no
"memory effect," and are generally much safer. Physical energy
storage--as opposed to chemical energy storage--is a key reason for
their safe operation and extraordinarily high cycle-life.
Supercapacitors' high energy density has fueled a growing interest
in supercapacitors in the electronics industry. Stable and porous
materials are attractive for capacitive energy storage because they
provide high surface areas for increased double-layer capacitance,
open structures for rapid ion transport, and redox-active centers
that enable faradaic (pseudocapacitive) energy storage. Porous
carbon and graphene are commercially used supercapacitors, which
operate at a very high charge/discharge rate with a long life
cycle. However, carbon- and graphene-based supercapacitors have low
capacitance. In contrast, metal-oxide pseudocapacitors exhibit high
capacitance, but redox reactions lead to low life cycle.
[0050] The following Example describes, for the first time, the
synthesis of a pre-designed Zr-based-MOF having a redox active
organic linker and the use of it as a supercapacitor electrode. A
naphthalenediimide (NDI) core has deliberately been incorporated as
the redox center in the organic linker, which exhibited a two-step
redox process. The combination of the high porosity of the designed
Zr-NDI-MOF with the redox centers, contributed double-layer and
pseudo-capacitance, respectively, led to enhancing the capacitance
performance of this new MOF. The possibility also to
post-synthetically modify the Zr-NDI-MOFs using organic pillars led
to an enhancement in the surface area and increased the capacitance
performance of this MOF by a factor of at least two.
Materials and Methods
[0051] All reagents were obtained from commercial sources and used
without further purification, unless otherwise noted. Powder X-ray
diffraction (PXRD) measurements were carried out at room
temperature on a PANalyticalX'Pert PRO diffractometer 45 kV, 40 mA
for Cu K.alpha. (.lamda.=1.5418 .ANG.), with a scan speed of
1.0.degree. min.sup.-1 and a step size of 0.02.degree. in 2.theta..
Variable Temperature Powder X-ray Diffraction (VT-PXRD)
measurements were collected on a PANalyticalX'Pert Pro MPD X-ray
diffractometer equipped with an Anton-Parr CHC+ variable
temperature stage. Measurements were collected at 45 kV, 40 mA for
Cu K.alpha. (.lamda.=1.5418 .ANG.) with a scan speed of 1.0.degree.
min.sup.-1 and a step size of 0.02.degree. in 2.theta.. Samples
were placed under vacuum during analysis and the sample was held at
the designated temperatures for at least 15 minutes between each
scan. High resolution dynamic thermogravimetric analysis (TGA) were
performed under a continuous N.sub.2 flow and recorded on a TA
Instruments hi-res TGA Q500 thermogravimetric analyzer with a
heating rate of 1.degree. C. per minute. Fourier-transform Infrared
(FT-IR) spectra (4000-600 cm.sup.-1) were recorded on a Thermo
Scientific Nicolet 6700 apparatus. Low pressure gas adsorption
studies of the MOFs were conducted on a fully automated micropore
gas analyzer Autosorb-IC (Quantachrome Instruments) at relative
pressures up to 1 atm. The temperature was controlled using a
cryocooler system (cryogen-free) capable of temperature control
from 20 to 320 K.
[0052] Synthesis of Ligands and Metal Organic Frameworks (MOFs).
Scheme 1 is a reaction scheme for the synthesis of ligands from
starting materials:
##STR00001##
[0053] Preparation of anilene-3,5-dibenzoicacid: CH.sub.3CN (40 ml)
was placed in a 250 ml round-bottom flask sealed with septum, the
flask was evacuated/backfilled with argon 3.times., then solvent
was bubbled with argon for 1.5 h. 1,3-Dibromo-anilene (1.83 g; 10
mmol), 4-carboxyphenylboronic acid (3.66 g; 22 mmol), 5%
Pd(PPh.sub.3).sub.2Cl.sub.2 (0.4 g) and 40 mL aqueous potassium
carbonate (5.3 g; 80 mmol) solution were then added, the flask was
evacuated/backfilled with argon 3.times. and heated at 100.degree.
C. for 48 h with vigorous stirring. It was cooled to room
temperature and the mixture was diluted with water (200 ml),
filtered through paper, filter cake was washed thoroughly with
water, the filtrate acidified to pH=1 with 2 N HCl and the
precipitate was filtered, washed with water, followed by hexane,
dried briefly on air, then at high vacuum at 50.degree. C.
overnight to give 3.11 g (79%) of white powder in sufficient
purity. The NMR data match the reported values.
[0054] Preparation of N,N'-bis(terphenyl-4,4''-dicarboxylic acid)
naphthalenediimide (H4BTD-NDI): 1,4,5,8-tetracarboxydianhydride
(0.268 g, 1.0 mmol) was taken into a 250 mL round bottomed flask
and suspended in 25 mL acetic acid. The mixture was stirred for 10
min. To this solution, anilene-3,5-dibenzoicacid (0.698 g, 2.2
mmol) was added and the solution allowed reflux for 12 h. The
reaction was allowed to cool to room temperature and water (90 ml)
was added to precipitate the product. The product was collected by
filtration, washed with ethanol, and dried in vacuum to yield 2.4 g
of off-white solid (isolated yield=2.4 g, 77%). The compound was
recrystallized from DMF as an off-yellow materials (isolated
yield=2.1 g, 67%).
[0055] Synthesis of the Zr-BTD-NDI-MOF: 15 mg ZrCl.sub.4 (0.064
mmol) was taken into a 20 mL glass scintillation vial containing
NDI-linker (6.0 mg, 0.006 mmol) and 3 mL DMF. To this 400 mg F-BzA
and 0.3 mL formic acid were added. This reaction mixture was
sonicated for 5 min, placed into a preheated oven at 120.degree. C.
for 48 hours, and cooled to room temperature yielding light yellow
needle shaped crystals. Single crystals of the MOFs were collected
and washed with DMF. The crystals were stored in the same solvent
for further application and characterizations.
[0056] Synthesis of the Zr-BTD-NDI-BP-MOF & Zr-BTD-NDI-BPy-MOF:
Compounds 2 and 3 were synthesized by the linker installation of
Zr-BTD-NDI-MOF with BP (4,4'-biphenyldicarboxylate) and BPy
(2,2'-bipyridine-4,4'-dicarboxylate), respectively, through an acid
and base reaction. Scheme 1 shows the chemical equation of linker
installation process. Generally, Zr-BTD-NDI-MOF (100 mg) were
treated with the solution of linear linkers in DMF (0.03 M, 40 mL)
at 85.degree. C. for 24 h. The materials were collected by
filtration and washed with fresh DMF 3 times (yield: 96%).
[0057] Single crystal XRD and crystal structure of
Zr-BTD-NDI-MOF._SCXRD data of 1 were collected using Bruker X8
PROSPECTOR APEX2 CCD diffractometer using Cu K.alpha.
(.lamda.=1.54178 .ANG.) radiation. Indexing was performed using
APEX2 (Difference Vectors method). Data integration and reduction
were performed using SaintPlus 8.34A. Absorption correction was
performed by multi-scan method implemented in SADABS. Space group
was determined using XPREP implemented in APEX2. Structure was
solved using Direct Methods (SHELXS-2013) and refined using
SHELXL-2014 (full-matrix least-squares on F2) contained WinGX.
Crystal data and refinement conditions are shown in Table 51. A
full list of restraints and constraints is contained within the CIF
file. A set of DFIX, SADI, FLAT and RIGU was applied on organic
ligand to make its geometry and thermal parameters reasonable. All
attempts to refine peaks of residual electron density as solvent
molecules were unsuccessful. The data were corrected for
delocalized electron density using of the SQUEEZE procedure as
implemented in PLATON. The total solvent-accessible void volume of
13337 .ANG. with a total electron count of 5406 was found in the
unit cell.
TABLE-US-00001 TABLE 1 Crystal data and structure refinement
conditions for Zr-BTD-NDI-MOF Empirical formula
C.sub.108H.sub.68N.sub.4O.sub.40Zr.sub.6 Formula weight 2608.98
Crystal system, space group Orthorhombic, Cmmm Unit cell dimensions
a = 20.7974(9) .ANG., b = 34.320(1) .ANG., c = 24.2844(9) .ANG.
Volume 17333(1) .ANG..sup.3 Z, calculated density 2, 0.500 Mg
m.sup.-3 F(000) 2608 Temperature (K) 100.0(1) Radiation type,
.quadrature. Cu K.quadrature..quadrature..quadrature.1.54178 .ANG.
Absorption coefficient 1.67 mm.sup.-1 Absorption correction
Multi-scan Max and min transmission 0.125 and 0.041 Crystal size
0.003 .times. 0.03 .times. 0.15 mm Shape, colour Plate, colourless
.theta. range for data collection 4.4-50.4.degree. Limiting indices
-20 .ltoreq. h .ltoreq. 20, -34 .ltoreq. k .ltoreq. 21, -23
.ltoreq./.ltoreq. 24 Reflection collected/unique/22259/4918
(R.sub.int = 0.053)/3701 observed with I > 2s(I) Completeness to
q.sub.max = 50.4.degree. 99.4% Refinement method Full-matrix
least-squares on F.sup.2 Data/restraints/parameters 4918/192/216
Final R indices [I > 2s(I)] R.sub.1 = 0.052, wR.sub.2 = 0.172
Final R indices (all data) R.sub.1 = 0.062, wR.sub.2 = 0.177
Weighting scheme [s.sup.2(Fo.sup.2 + (0.1207P).sup.2].sup.-1*
Goodness-of-fit 1.06 Largest diff. peak and hole 0.49 and -0.59 e
.ANG..sup.-3 *P = (Fo.sup.2 + 2Fo.sup.2)/3
[0058] High-resolution dynamic thermal gravimetric analysis (TGA)
was performed under a continuous N.sub.2 flow (25 mL/min) with a
heating rate of 1.degree. C./min using a hi-res TGA Q500 thermal
gravimetric analyzer. Low-pressure gas sorption measurements were
performed on a fully automated micropore gas analyzer Autosorb-IC
(Quantachrome Instruments) at relative pressures up to 1 atm. The
powder X-ray diffraction patterns and the variable-temperature and
variable-humidity powder X-ray diffraction patterns (VT-PXRD and
VH-PXRD) were collected over the 20 range 4-40.degree. on a
high-resolution PANalytical X'Pert MPDPRO X-ray diffractometer with
Cu K.alpha.1 radiation (.lamda.=1.5406 .ANG., 45 kV/40 mA) equipped
with an Anton-Parr CHC+ variable-temperature stage, with a scan
speed of 1.degree./min and a step size of 0.03.degree. in 2.theta..
The sample was placed under vacuum during analysis and held at the
designated temperatures for at least 20 min between each scan.
Single-crystal X-ray diffraction data were collected using (1) an
X8 Prospector APEX2 CCD diffractometer (Cu K.alpha. .lamda.=1.54178
.ANG.) and (2) a Bruker Apex 2 DUO CCD diffractometer with a
multilayer monochromator (Mo K.alpha. .lamda.=0.71073 .ANG.).
[0059] Electrochemical measurements. The electrochemical
measurements were performed on a Bio-Logic VMP3 potentiostat in
both 3-electrode and 2-electrode configurations using 1 M
H.sub.2SO.sub.4 as electrolyte at room temperature. In 3-electrode
measurements, the MOF material was mixed with carbon black and
polyvinylidene fluoride (PVDF) with a weight ratio of 8:1:1 in
N-methyl pyrrolidone (NMP) to form a homogeneous ink, which was
then drop-casted onto a carbon cloth electrode. After drying in a
vacuum oven overnight, the carbon cloth with active material on it
was then used as the working electrode. A Ag/AgCl electrode and a
Pt wire were used as the reference and counter electrode,
respectively. For 2-electrode measurement, two pieces of the
as-fabricated carbon cloth electrodes with almost the same mass
loading were used as the positive and negative electrodes
respectively with a porous polymer membrane (Celgrad 3501) as the
separator to assemble a coin cell. The capacitance (C, F g.sup.-1)
reported in this work was calculated from CV curves:
C = .intg. i cathodic dV m .upsilon..DELTA. V ##EQU00001##
where i (mA) is the current, .nu. (mV s.sup.-1) is the scan rate, m
(g) is the mass of the active materials on the single electrodes,
and V (V) the potential window. The energy density (E, Wh
kg.sup.-1) and power density (P, W kg.sup.-1) were calculated from
the GCD curves:
E = i .intg. Vdt M .times. 3.6 ##EQU00002## P = E t .times. 3600
##EQU00002.2##
where i (A) is the current, V (V) the cell voltage window, t (s)
the discharge time, and M (g) the mass of the active materials on
both the positive and negative electrodes.
Results and Discussion
[0060] This Example reports the design and synthesis of particular
MOFs, where an organic linker having a redox center was
strategically incorporated into MOFs and a metal node was
judiciously selected to construct a highly porous and stable
framework (FIG. 3). The N,N'-bis(terphenyl-4,4''-dicarboxylic acid)
naphthalenediimide (H.sub.4BTD-NDI) was synthesized and used as the
organic linker (Scheme 1; FIGS. 4-6;), where naphthalenediimide
(NDI) core was the redox-active center, that is known to have two
characteristic electron redox processes (FIG. 3b). On the other
hand, the [Zr.sub.6O.sub.4(OH).sub.8(H.sub.2O).sub.8].sup.8+
cluster was chosen as metal node to provide the right connectivity
to generate the targeted porous structure with a high chemical
stability, which is a key factor for long life cycling stability of
the supercapacitor performance. Moreover, the high surface area was
expected to increase the double-layer capacitance, and the open
framework structures was expected to facilitate ion transport (FIG.
3).
[0061] The synthetic conditions for the targeted MOF were optimized
to grow single crystals, which was achieved by the reaction of
zirconium chloride (ZrCl.sub.4) and H.sub.4BTD-NDI-linker with
excess formic acid and benzoic acid, as reaction modulators, at
120.degree. C., that led to the formation of needle shape
Zr-BTD-NDI-MOF single crystals. The single crystal X-ray
diffraction studies revealed that the targeted Zr-BTD-NDI-MOF
crystallized in the orthorhombic Cmmm space group with a formula
unit of (BTD-NDI.sub.2Zr.sub.6O.sub.4(OH).sub.4) and cell
parameters of a=20.80; b=34.32; c=24.28 .alpha.=.beta.=.gamma.=90
(Table 1). The Zr-BTD-NDI-MOF possessed a neutral framework with
octahedral [Zr.sub.6O.sub.4(OH).sub.8(H.sub.2O).sub.8].sup.8+
clusters, bridged by eight BTD-NDI ligands, while leaving four
pairs of terminal H.sub.2O groups at equatorial plane appropriate
for further modification (FIG. 3 and FIGS. 7-8). The crystal
lattice possessed three types of pores: smaller ones (atom-to-atom
separation 14.84.times.5.06 .ANG.) along the b-axis (b-pores),
(13.37.times.14.84 .ANG.) along the a-axis (a-pores), and larger
ones (11.36.times.26.69 .ANG.) along the c-axis (c-pores). The NDI
cores were arranged parallel to the c-pores, which favored the
interaction with the incoming guest moieties The topological
analysis of the MOF represented the 8-connected hexanuclear Zr(IV)
molecular building block (MBB), that can be viewed as a cube
secondary building unit (SBU), while the organic ligand can be
rationalized as a 4-connected building unit to give (4,8)-c scu-a
net or can be viewed as 3-c SBUs resulting in a (3,8)-c derived
tty-a net (FIG. 3).
[0062] The phase purity of the Zr-BTD-NDI-MOF was confirmed by
matching the powder X-ray diffraction (PXRD) pattern of the
experimental and simulated pattern obtained from the crystal
structure (FIG. 9d). Interestingly, a phase change was observed
from the PXRD pattern upon activation or solvent exchange of the
sample (FIG. 10). This phase change was attributed to the
flexibility of the framework upon solvent removal. This was
confirmed from variable temperature PXRD (VT-PXRD) (FIG. 11), which
shows the shift of the PXRD peak at 4.7 to 5.1 degrees. The
permanent porosity of the Zr-BTD-NDI-MOF was confirmed by surface
area analysis from the Ar sorption isotherm measured at 78 K and 1
bar. The Zr-BTD-NDI-MOF showed a surface area around 810
m.sup.2g.sup.-1. However, the framework did not show the optimum
pore volume compared to the calculated pore volume, which was
mainly due to the flexible nature of this framework. The framework
flexibility was also confirmed from the shape of the isotherm,
where, a step was obtained at 0.25 bar relative pressure
(p/p.sub.o) (FIG. 12a).
[0063] Electrochemical measurements were carried out on the
Zr-BTD-NDI-MOF using a three-electrode configuration in 1 M
H.sub.2SO.sub.4 supporting electrolyte. The working electrode was
prepared by drop-casting a homogeneous ink of MOF, carbon black,
and polyvinylidene fluoride (PVDF) binder (8:1:1 in weight ratio)
onto a carbon cloth (CC) electrode (the typical mass loading was
around 1.5-2 mg cm.sup.-2). A Ag/AgCl electrode and a Pt wire were
used as the reference and counter electrode, respectively. FIG. 13a
shows the CV curve (type 1) collected at a scan rate of 50 mV
s.sup.-1. Due to the high surface area of the Zr-BTD-NDI-MOF, it
was expected to show electrochemical double layer capacitance
(EDLC) due to the adsorption of ions during electrochemical
process. Moreover, the NDI moieties within the Zr-BTD-NDI-MOF
underwent reversible redox processes, which exhibited a
well-defined electrochemical response. Indeed, the CV curve
exhibited a quasi-rectangular shape with distinct redox peaks,
indicative of typical hybrid capacitive behavior. Specifically, two
anodic peaks located at about 0.4 and 0.6 V vs Ag/AgCl (FIG. 15a)
were observed, corresponding to the two-step redox reaction as
expected for the NDI core (see inset of FIG. 3). The nonlinear
galvanostatic charge-discharge (GCD) profile further suggested the
faradaic process (FIG. 13b). Overall, the combination of EDLC and
pseudo-capacitive behavior was observed. The capacitance was
calculated from the CV curves and the Zr-BTD-NDI-MOF electrode
delivered a high capacitance of 16.8 F g.sup.-1 at a scan rate of
10 mV s.sup.-1. An interesting feature of the Zr-BTD-NDI-MOF was
the flexible behavior, which was driven by the removal/uptake of
solvent. The flexibility of the Zr-BTD-NDI-MOF may affect
performance as a supercapacitor, since it can lower the surface
area. Careful inspection of the crystal structure showed that each
Zr-cluster contained eight carboxylates from eight linkers and
these carboxylates were rigid along the b- and c-axis and elastic
along the a-axis. As a result, the framework became flexible along
the a-axis and upon removal of solvent a partial rupture of the
framework occurred. Also each Zr-cluster contained eight water
molecules, among them, four water molecules faced the a-axis and
the other four water molecule faced along the c-axis (FIG. 16). The
open sites offered the opportunity to install another linker
through the a-axis by replacing the water molecules. Thus the
flexible framework of the Zr-BTD-NDI-MOF can be transformed into a
more rigid framework via this linker installation (FIG. 16).
[0064] The post-synthetic linker installation was carried out using
4,4-biphenyldicarboxylic acid (BP). The reason behind the selection
of BP was that the distance between the two opposite water
molecules along the c-axis was about 12.36 .ANG., which fit
perfectly with the length of the BP (11.1 .ANG.). The
post-synthetic linker installation was performed by immersing the
solvent exchanged crystals of the Zr-BTD-NDI-MOFs into the DMF
solution of BP at 85.degree. C. for one day. The amount of linker
installed in the framework was estimated via nuclear magnetic
resonance (NMR) spectra of the digested MOF in HCl (FIG. 6). It was
observed that the installed linkers occupied about 85% of the
available binding sites. The post-installation of the linkers was
also confirmed by other techniques like (thermal gravimetrical
analysis (TGA), Infrared spectroscopy (IR), PXRD, elemental
analysis, and surface area analysis (FIGS. 12, 15, 17).
[0065] The obtained Zr-NDI-BP-MOF was fully characterized with PXRD
(FIG. 18), which confirmed the presence of the expected structure
and that the structure maintained its crystallinity. The simulated
PXRD pattern of the linker installed MOFs (Zr-BTD-NDI-BP-MOF) was
obtained from the optimized structure using materials studio
software. The experimental PXRD pattern for the linker installed
MOFs were in good agreement with the simulated pattern (FIG. 18).
In addition, the Ar sorption showed an enhancement in the surface
area, which became 1920 m.sup.2/g after installation (FIG. 15b).
The increase in surface area was obtained due to the maintained
pore opening by the installed linkers. The Ar isotherm also showed
no more steps at higher partial pressure, which confirmed the
microporous framework structure (FIG. 15b) and rigidity of the new
MOF. Such a large increase in surface area was expected to further
boost the supercapacitor performance. Indeed, the CV area of the
Zr-BTD-NDI-BP-MOF (type 2 in FIG. 13a) significantly increased as
compared to that of Zr-BTD-NDI-MOF. Note that for both MOFs, the CV
curves showed similar shapes and redox peaks (FIG. 20). These
results suggested that the capacitance can be greatly enhanced by
simply installing the BP linker. The GCD curve again confirmed such
enhancement (FIG. 13b). The capacitance of the Zr-BTD-NDI-BP-MOF
was calculated to be 32.8 F g.sup.-1 (FIG. 13c), two times that of
Zr-BTD-NDI-MOF, which was in good agreement with the enhancement of
the surface area. These encouraging results led to efforts to
improve the performance of this MOF by replacing the BP pillar with
a more nitrogen rich pillar, i.e.,
2,2'-bipyridine-4,4'-dicarboxylic acid (BPy). The installation of
the BPy pillar was performed using the same procedure for the BP
pillar and was fully characterized using the same techniques, which
confirmed the formation of the targeted structure and the
enhancement in the porosity (1820 m.sup.2g.sup.-1) in comparison to
the pristine Zr-BTD-NDI-MOF. The CV curve of this new rigid
Zr-BTD-NDI-BPy-MOF (type 3 in FIG. 13a, also see FIG. 15) exhibited
a shape similar to Zr-BTD-NDI-BP-MOF (type 2) and Zr-BTD-NDI-MOF
(type 1). The CV area did not show significant increase compared to
that of Zr-BTD-NDI-BP-MOF. However, the potential window was found
to be able to extend to 1.0 V (FIG. 21), which indicated the oxygen
evolution reaction on Zr-BTD-NDI-BPy-MOF was restricted to some
degree. Such widened potential window was preferred as it can
improve the energy and power density of the devices. The pronounced
potential plateaus observed in the GCD profile (FIG. 13b) were
related to the faradaic reactions of the NDI core, which was in
agreement with the CV measurements. The capacitance was further
estimated from CV curves and the Zr-BTD-NDI-BPy-MOF delivered a
capacitance of 30.7 F g.sup.-1 at 10 mV s.sup.-1 (FIG. 13c),
slightly lower than that of Zr-BTD-NDI-BP-MOF, but significantly
higher than that of pristine Zr-BTD-NDI-MOF (16.8 F g.sup.-1 at 10
mV s.sup.-1). These results further confirmed the efficacy of the
strategy of using BPy to greatly boost the electrochemical
performance. All 3 types of MOF materials were highly stable during
measurements in 1 M H.sub.2SO.sub.4 (FIG. 13d). The performance did
not show significant decay for at least 5000 cycles even under a
relatively high current density (5 A g.sup.-1).
[0066] Encouraged by these promising results, the
Zr-BTD-NDI-BPy-MOF was further investigated by constructing a
symmetrical two-electrode device using two nearly identical
electrodes. The preparation of the Zr-BTD-NDI-BPy-MOF and the
graphite electrodes was performed in the same way as in the
3-electrode measurements, as the positive and negative electrodes,
respectively. The electrolyte used in these measurements was 1 M
H.sub.2SO.sub.4 and based on the three electrode measurements,
these devices were tested in voltage window of 0-1.0 V. FIG. 9a
shows the typical CVs collected at different scan rates, which
exhibited quasi-rectangular mirror-symmetric shape even at high
scan rates (e.g. 200 mV s.sup.-1), indicating highly reversible
charge/discharge response of the device. The triangular symmetric
GCD curves indicated a high columbic efficiency. The cell
capacitance was calculated based on the CV curves and the devices
can deliver a capacitance of 5.7 F g.sup.-1 at 10 mV s.sup.-1. The
scan rate dependence of capacitance is shown in FIG. 21a. This
capacity was achieved in aqueous media with a voltage window of
0.0-1.0 V and the capacitance was higher than most of the reported
values achieved in much more expensive organic electrolytes for MOF
materials (see Table 2, note here areal capacitance was used as to
compare with other MOFs reported in literature). FIG. 9c shows the
cyclic stability of our Zr-BTD-NDI-BPy-MOF in 1 M H.sub.2SO.sub.4
for up to 10,000 cycles. The MOF based devices showed the capacity
retention of 99.9% after 10K cycles, while most of the reported MOF
based supercapacitors retained less than 80% of initial capacitance
after 10K cycles. This was due to the presence of rigid pillars
which gave the structure more stability and hindered the structural
collapse during charge/discharge process. The idea of structural
retention was also supported by the ex-situ XRD and SEM
characterization, where no significant change was observed in the
XRD pattern before and after 10K cycles of charge/discharge process
(FIG. 9d). The SEM images of the electrodes before and after 10K
cycles of charge/discharge process confirmed that the overall
morphology remained the same and was not destroyed during the
electrochemical cycling (FIGS. 9e-9f and FIG. 22).
TABLE-US-00002 TABLE 2 Comparison of the Zr-BTD-NDI-BPy-MOF and
other reported MOFs Areal capacitance Voltage Cycle Capacity
Material (mF cm.sup.-2) Electrolyte window (V) number retention (%)
Zr-BTD-NDI-BPy 6.48 1M H.sub.2SO.sub.4 0.0-1.0 10,000 99.9
nMTV-MOF-5-AE 0.913 1M (C.sub.2H.sub.5).sub.4NBF.sub.4 0.0-2.5
3,000 80 nM7M-MOF-74 1.155 1M (C.sub.2H.sub.5).sub.4NBF.sub.4
0.0-2.5 300 80 nHKUST-1 2.33 1M (C.sub.2H.sub.5).sub.4NBF.sub.4
0.0-2.5 6,000 80 nMOF-177 0.713 1M (C.sub.2H.sub.5).sub.4NBF.sub.4
0.0-2.5 4,000 80 nZIF-8 0.268 1M (C.sub.2H.sub.5).sub.4NBF.sub.4
0.0-2.5 2,500 80 nUiO-66 1.945 1M (C.sub.2H.sub.5).sub.4NBF.sub.4
0.0-2.5 7,000 80 nMOF-867 5.085 1M (C.sub.2H.sub.5).sub.4NBF.sub.4
0.0-2.5 10,000 80 activated carbon 0.783 1M
(C.sub.2H.sub.5).sub.4NBF.sub.4 0.0-2.5 10,000 80 graphene 0.515 1M
(C.sub.2H.sub.5).sub.4NBF.sub.4 0.0-2.5 10,000 80
[0067] The energy density and the power density were further
examined for the Zr-BTD-NDI-BPy-MOF and the result was presented as
the Ragone plot in FIG. 23b. The device delivered an energy density
of 472 mWh kg.sup.-1 at a power density of 250 Wh kg.sup.-1.
[0068] In conclusion, a Zr-BTD-NDI-MOF having an organic linker
with a redox active core was successfully and for the first time
designed and synthesized. A MOF possessing high surface area and
redox core that can provide both electric double layer and pseudo
capacitances, and be used as a supercapacitor electrode, was
deliberately developed. The incorporation of the redox process as
demonstrated was responsible for the pseudo-capacitance (i.e. store
electrical energy via chemical energy) in the MOF. The
Zr-BTD-NDI-MOFs was then post-synthetically modified to
Zr-BTD-NDI-BP-MOF and Zr-BTD-NDI-BPy-MOF, which increased rigidity
to the pristine structure and led to the enhancement in the surface
area and as a result increased their capacitance performance. In
addition, the Zr-BTD-NDI-BPy-MOFs exhibited uniform porosity
distribution, which aided rapid ion transport without blocking the
accessible surface area.
[0069] Other embodiments of the present disclosure are possible.
Although the description above contains much specificity, these
should not be construed as limiting the scope of the disclosure,
but as merely providing illustrations of some of the presently
preferred embodiments of this disclosure. It is also contemplated
that various combinations or sub-combinations of the specific
features and aspects of the embodiments may be made and still fall
within the scope of this disclosure. It should be understood that
various features and aspects of the disclosed embodiments can be
combined with or substituted for one another in order to form
various embodiments. Thus, it is intended that the scope of at
least some of the present disclosure should not be limited by the
particular disclosed embodiments described above.
[0070] Thus the scope of this disclosure should be determined by
the appended claims and their legal equivalents. Therefore, it will
be appreciated that the scope of the present disclosure fully
encompasses other embodiments which may become obvious to those
skilled in the art, and that the scope of the present disclosure is
accordingly to be limited by nothing other than the appended
claims, in which reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated,
but rather "one or more." All structural, chemical, and functional
equivalents to the elements of the above-described preferred
embodiment that are known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the present claims. Moreover, it is not necessary
for a device or method to address each and every problem sought to
be solved by the present disclosure, for it to be encompassed by
the present claims. Furthermore, no element, component, or method
step in the present disclosure is intended to be dedicated to the
public regardless of whether the element, component, or method step
is explicitly recited in the claims.
[0071] The foregoing description of various preferred embodiments
of the disclosure have been presented for purposes of illustration
and description. It is not intended to be exhaustive or to limit
the disclosure to the precise embodiments, and obviously many
modifications and variations are possible in light of the above
teaching. The example embodiments, as described above, were chosen
and described in order to best explain the principles of the
disclosure and its practical application to thereby enable others
skilled in the art to best utilize the disclosure in various
embodiments and with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
disclosure be defined by the claims appended hereto
[0072] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *