U.S. patent application number 16/118379 was filed with the patent office on 2020-03-05 for method of making a porous nitrogen-doped carbon electrode from biomass.
The applicant listed for this patent is KING SAUD UNIVERSITY. Invention is credited to TANSIR AHAMAD, ABDULLAH M. AL-ENIZI, SAAD M. ALSHEHRI, MU. NAUSHAD.
Application Number | 20200075268 16/118379 |
Document ID | / |
Family ID | 69640191 |
Filed Date | 2020-03-05 |
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United States Patent
Application |
20200075268 |
Kind Code |
A1 |
AHAMAD; TANSIR ; et
al. |
March 5, 2020 |
METHOD OF MAKING A POROUS NITROGEN-DOPED CARBON ELECTRODE FROM
BIOMASS
Abstract
The method of making a porous nitrogen-doped carbon electrode
from biomass is a chemical activation-based method of making a
porous graphite carbon electrode for supercapacitors and the like.
Date palm pollen grains are used as a precursor biomass carbon
source for producing the porous graphite carbon. A volume of date
palm (Phoenix dactylifera L.) pollen grains is mixed into an
aqueous solution of potassium hydroxide to produce a precursor
carbon solution. The precursor carbon solution is dried to produce
precursor carbon, and the precursor carbon is heated in an inert
atmosphere to produce porous nitrogen-doped graphite carbon. The
porous nitrogen-doped graphite carbon is washed, dried and mixed
with a polyvinylidene difluoride binder, carbon black, and a
solvent to form a slurry. The slurry is then coated on nickel foam
to form a porous nitrogen-doped carbon electrode. The porous
nitrogen-doped carbon electrode is dried, weighted and pressed into
a sheet electrode.
Inventors: |
AHAMAD; TANSIR; (RIYADH,
SA) ; NAUSHAD; MU.; (RIYADH, SA) ; AL-ENIZI;
ABDULLAH M.; (RIYADH, SA) ; ALSHEHRI; SAAD M.;
(RIYADH, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KING SAUD UNIVERSITY |
Riyadh |
|
SA |
|
|
Family ID: |
69640191 |
Appl. No.: |
16/118379 |
Filed: |
August 30, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 11/26 20130101;
H01G 11/24 20130101; H01G 11/44 20130101; H01G 11/86 20130101; H01G
11/34 20130101 |
International
Class: |
H01G 11/86 20060101
H01G011/86; H01G 11/34 20060101 H01G011/34; H01G 11/44 20060101
H01G011/44 |
Claims
1. A method of making a porous nitrogen-doped carbon electrode from
date palm (Phoenix dactylifera L.) pollen grains, comprising the
steps of: stirring a volume of date palm (Phoenix dactylifera L.)
pollen grains into an aqueous solution of potassium hydroxide (KOH)
for one hour to produce a precursor carbon solution; drying the
precursor carbon solution for a period of six hours at a
temperature of 80.degree. C. to produce precursor carbon; heating
the precursor carbon at a temperature of 800.degree. C. for two
hours under an argon atmosphere to produce porous nitrogen-doped
graphite carbon; washing the porous nitrogen-doped graphite carbon
in an aqueous solution of HCl, deionized water, and ethanol; drying
the porous nitrogen-doped graphite carbon for 24 hours at a
temperature of 80.degree. C.; mixing the porous nitrogen-doped
graphite carbon with a polyvinylidene difluoride (PVDF) binder and
carbon black in an isopropanol solvent to form a slurry; and
coating nickel foam with the slurry to form a porous nitrogen-doped
carbon electrode and dried at a temperature of 100.degree. C.,
wherein the dried nitrogen-doped carbon electrode has a porous,
cage-type structure wherein the pore volume is at least 0.8
cm.sup.3/g, having a Brunauer-Emmett-Teller (BET) surface area
within about 86-87 m.sup.2/g, a wall thickness of at least about
30.8-80.0 nm and a mean pore diameter in the range of about 50 to
about 450 nm.
2-4. (canceled)
5. The method of making a porous nitrogen-doped carbon electrode as
recited in claim 1, wherein the step of heating the precursor
carbon in inert atmosphere comprises heating the precursor carbon
at a rate of 5.degree. C./min.
6-9. (canceled)
10. The method of making a porous nitrogen-doped carbon electrode
as recited in claim 1, further comprising the step of pressing the
porous nitrogen-doped carbon electrode into a sheet electrode.
11. The method of making a porous nitrogen-doped carbon electrode
as recited in claim 10, wherein the step of pressing the porous
nitrogen-doped carbon electrode into the sheet electrode comprises
pressing the porous nitrogen-doped carbon electrode at a pressure
of 10 MPa.
12-20. (canceled)
Description
BACKGROUND
1. Field
[0001] The disclosure of the present patent application relates to
porous carbon electrodes, and particularly to a method of making a
porous nitrogen-doped carbon electrode from biomass for
supercapacitors and the like utilizing date palm (Phoenix
dactylifera L.) pollen grains as the carbon source.
[0002] 2. Description of the Related Art
[0003] A supercapacitor (also referred to as an electric
double-layer capacitor) is a high-capacity capacitor with
capacitance values much higher than other capacitors, but with
lower voltage limits, that bridge the gap between electrolytic
capacitors and rechargeable batteries. Supercapacitors typically
store 10 to 100 times more energy per unit volume or mass than
electrolytic capacitors, can accept and deliver charge much faster
than batteries, and tolerate many more charge and discharge cycles
than rechargeable batteries. Unlike ordinary capacitors,
supercapacitors do not use a conventional solid dielectric. Rather,
they use electrostatic double-layer capacitance and electrochemical
pseudo-capacitance, both of which contribute to the total
capacitance of the capacitor.
[0004] Electrostatic double-layer capacitors typically use carbon
electrodes with much higher electrostatic double-layer capacitance
than electrochemical pseudocapacitance, achieving separation of
charge in a Helmholtz double layer at the interface between the
surface of a conductive electrode and an electrolyte. The
separation of charge is on the order of 0.3-0.8 nm, which is much
smaller than that in a conventional capacitor. This extremely thin
double-layer distance in a supercapacitor is made possible by the
extremely large surface area of activated carbon electrodes. As is
well known, activated carbon is a form of carbon processed to have
small, low-volume pores that increase the surface area available
for adsorption or chemical reactions. Due to its high degree of
microporosity, just one gram of activated carbon has a surface area
in excess of 3,000 m.sup.2.
[0005] Solid activated carbon, also sometimes referred to as
consolidated amorphous carbon (CAC), is the most commonly used
electrode material for supercapacitors. It is produced from
activated carbon powder pressed into the desired shape, forming a
block with a wide distribution of pore sizes. An electrode with a
surface area of about 1000 m.sup.2/g results in a typical
double-layer capacitance of about 10 .mu.F/cm.sup.2 and a specific
capacitance of 100 F/g. One of the most common sources for powdered
activated carbon used in supercapacitors is coconut shells.
Although coconut shells produce activated carbon with more
micropores than that made from wood charcoal, the relative
availability of coconuts in non-tropical regions makes coconut
shells an expensive carbon precursor source. Additionally, the
conversion process of coconut shells to activated carbon of
sufficient purity for supercapacitor manufacture can be both
expensive, time consuming and complex.
[0006] Further, it has been demonstrated that the incorporation of
heteroatoms, such as sulfur, boron, nitrogen and oxygen, into the
carbon lattice can significantly enhance mechanical,
semiconducting, field emission, and electrical properties of carbon
materials. For example, nitrogen doping is presently considered to
be the most promising method for enhancing surface polarity,
electric conductivity and electron-donor tendency of the activated
carbon. To prepare these materials, one common approach involves
the use of nitrogen-containing original precursors, such as ionic
liquids, for pyrolysis. Another approach is to post-treat carbon
with N-containing dopants, such as ammonia, amine or urea. Given
the attractiveness of biomass an original precursor, in addition to
factors such as cost, environmental friendliness and availability,
nitrogen content of the biomass is also a consideration. In
addition to finding a biomass carbon precursor that is readily
available in large quantities in numerous places throughout the
world, it would be desirable to provide a biomass precursor which
is also nitrogen-rich. Thus, a method of making a porous
nitrogen-doped carbon electrode from biomass solving the
aforementioned problems is desired.
SUMMARY
[0007] The method of making a porous nitrogen-doped carbon
electrode from biomass is a chemical activation-based method of
making a porous graphite carbon electrode for supercapacitors and
the like. Date palm pollen grains are used as a precursor biomass
carbon source for producing the porous graphite carbon. A volume of
date palm (Phoenix dactylifera L.) pollen grains is mixed into an
aqueous solution of potassium hydroxide (KOH) to produce a
precursor carbon solution. Date palm pollen grains are naturally
rich in protein, which is used as a nitrogen source, as well as
carbohydrates and sporopollenin, which are both sources of carbon.
The precursor carbon solution is dried to produce precursor carbon,
and the precursor carbon is heated in an inert argon atmosphere to
produce porous nitrogen-doped graphite carbon. The porous
nitrogen-doped graphite carbon is washed, dried and mixed with a
polyvinylidene difluoride binder, carbon black, and an isopropanol
solvent to form a slurry. The slurry is then coated on nickel foam
to form a porous nitrogen-doped carbon electrode. The porous
nitrogen-doped carbon electrode is dried, weighted and pressed into
a sheet electrode.
[0008] These and other features of the present invention will
become readily apparent upon further review of the following
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a graph showing Fourier transform-infrared (FTIR)
results for porous nitrogen-doped graphite carbon prepared by the
present method of making a porous nitrogen-doped carbon electrode
from biomass.
[0010] FIG. 2 is a graph showing Raman spectra of the porous
nitrogen-doped graphite carbon prepared by the present method of
making a porous nitrogen-doped carbon electrode from biomass.
[0011] FIG. 3 shows X-ray diffraction (XRD) results of the porous
nitrogen-doped graphite carbon prepared by the present method of
making a porous nitrogen-doped carbon electrode from biomass.
[0012] FIG. 4 is a scanning electron microscope (SEM) image of the
porous nitrogen-doped graphite carbon prepared by the present
method of making a porous nitrogen-doped carbon electrode from
biomass.
[0013] FIG. 5 shows cyclic voltammetry (CV) curves for a porous
nitrogen-doped carbon electrode prepared by the present method of
making a porous nitrogen-doped carbon electrode from biomass for
different scan rates.
[0014] FIG. 6 is a plot showing specific capacitance of the porous
nitrogen-doped carbon electrode prepared by the present method of
making a porous nitrogen-doped carbon electrode from biomass as a
function of scan rate.
[0015] Similar reference characters denote corresponding features
consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The method of making a porous nitrogen-doped carbon
electrode from biomass is a chemical activation-based method of
making a porous graphite carbon electrode for supercapacitors and
the like. Date palm pollen grains are used as a precursor biomass
carbon source for producing the porous graphite carbon. A volume of
date palm (Phoenix dactylifera L.) pollen grains is stirred into a
0.5 M aqueous solution of potassium hydroxide (KOH) to produce a
precursor carbon solution. Date palm pollen grains are rich in
protein, which is used as a nitrogen source, as well as
carbohydrates and sporopollenin, which are both sources of carbon.
The stirring to mix the pollen grains into the KOH solution occurs
for approximately one hour. The precursor carbon solution is dried
at about 80.degree. C. for about six hours to produce precursor
carbon. The precursor carbon is heated in an inert argon atmosphere
to produce porous nitrogen-doped graphite carbon. The heating of
the precursor carbon occurs at a temperature of about 800.degree.
C. for about two hours, and may take place in a tube furnace with a
heating rate of about 5.degree. C./min.
[0017] The porous nitrogen-doped graphite carbon is then cooled to
room temperature, followed by washing in 1.0 M HCl solution,
deionized water and ethanol (several times), followed by drying at
a temperature of about 80.degree. C. for about 24 hours. The porous
nitrogen-doped graphite carbon is then mixed with carbon black and
a polyvinylidene difluoride (PVDF) binder in a mass ratio of 8:1:1.
This mixture is then solvated in isopropanol solvent to form a
slurry. The slurry is coated on nickel foam and dried overnight at
a temperature of about 100.degree. C. to form a porous
nitrogen-doped carbon electrode. The porous nitrogen-doped carbon
electrode is then weighted and pressed at a pressure of about 10
MPa into a sheet electrode having a thickness of about 300.+-.2
.mu.m.
[0018] In order to test the porous nitrogen-doped carbon electrode
prepared by the method described above, porous nitrogen-doped
carbon electrodes were made with the active materials on each
electrode having a total mass of about 5.0 mg. A conventional
three-electrode electrochemical test cell was used with a 6.0 M
aqueous solution of KOH used as the electrolyte. In the test cell,
an Ag/AgCl electrode was used as the reference electrode, and a Pt
wire was used as the counter electrode. As will be described in
detail below, cyclic voltammetry (CV) and cycle-life stability
galvanostatic charge/discharge (GCD) were performed using an
electrochemistry workstation (model CHI660D, manufactured by
Chenhua Co. Ltd. of Shanghai, China).
[0019] Further, the practical electrochemical performance of the
porous nitrogen-doped carbon electrode was assessed by assembling a
symmetric supercapacitor using qualitative filter paper (grade 4),
manufactured by Whatman.RTM. Paper Ltd. Co. of the United Kingdom,
used as a separator, along with two porous nitrogen-doped carbon
electrodes (each with the same mass of active materials of 5.0 mg)
in a 6.0 M KOH aqueous solution. The areal capacitance, CA, of the
electrodes was determined by the galvanostatic charge/discharge
(GCD) curves as CA=(I.times..DELTA.t)/(A.times..DELTA.V), where CA
is measured in F/cm.sup.2, I (measured in A) is constant current,
.DELTA.t (s) is discharge time of the GCD test, A is area
(cm.sup.2), and .DELTA.V (V) is the voltage change excepting IR
drop.
[0020] FIG. 1 shows the Fourier-transform infrared spectroscopy
(FTIR) results for the porous nitrogen-doped graphite carbon, made
as described above, and FIG. 3 shows the X-ray diffraction (XRD)
patterns for the porous nitrogen-doped carbon electrode. The XRD
patterns show a broad peak at about 25.8.degree., corresponding to
the (002) reflection of the turbostratic carbon structure,
suggesting an amorphous structure with a low crystalline fraction.
Another obvious peak is located at about 44.4.degree., which can be
assigned to the (100) diffraction of the graphitic carbon with an
amorphous and disordered structure, revealing a greater interlayer
stacking extent in porous nitrogen-doped graphite carbon that can
effectively enhance the electronic conductivity of the
materials.
[0021] The specific nature of the porous nitrogen-doped graphite
carbon was further characterized by its Raman spectra, as shown in
FIG. 2. As can be seen in FIG. 2, the peak centered at 1329
cm.sup.-1 (D-band) is reflection of the defect and shows disorder
in the samples. Another peak located at 1612 cm.sup.-1 (G-band) can
be assigned to the vibration of all sp.sup.2 hybridized carbon
atoms (both in chains and rings). The chemical environment of
elements of C and N, and the composition of the as-prepared porous
nitrogen-doped graphite carbon, were determined by elemental
analysis characterization. The results revealed that the C, O and N
content in the porous nitrogen-doped graphite carbon are 90.4%,
5.5% and 4.1%, respectively. It should be noted that the ratio of
C:O is very high (20.8:1), suggesting good electron conductivity in
the carbon material.
[0022] Additionally, the porosity of the as-prepared porous
nitrogen-doped graphite carbon was analyzed by N.sub.2
adsorption-desorption measurements. The isotherms showed a pore
volume of at least 0.8 cm.sup.3/g. The macroporous carbon has a
Brunauer-Emmett-Teller (BET) surface area within about 86-87
m.sup.2/g. The morphology of the porous nitrogen-doped graphite
carbon is shown in FIG. 4, where it can be seen that the porous
nitrogen-doped graphite carbon has a porous, cage-type structure.
The macroporous carbon has a size within the range of about 18-20
.mu.m. The macroporous carbon material is in the form of carbon
having a thickness of about 10-10.2 .mu.m. Typically, the
macroporous activated carbon will have a wall thickness of at least
about 30.8-80.0 nm. Additionally, the macroporous activated carbon
possesses a three-dimensional network structure with a mean pore
diameter in the range of about 50 to about 450 nm, which can not
only act an ion-buffering reservoir for electrolyte ion
transportation, but also facilitate electrolyte ions to fast
diffuse into the inner micropores of electrode materials,
especially at high charging rates. It is interesting to note that
an interconnected porous layered structure can also be observed,
which can effectively shorten the electrolyte ion diffusion path
and enhance the structure's stability during a rapid
charge/discharge process.
[0023] As noted above, the electrochemical properties of the porous
nitrogen-doped graphite carbon were analyzed by cyclic voltammetry
(CV) measurements in a three-electrode configuration using 6.0 M
KOH aqueous solution as an electrolyte. As shown FIG. 5, the CV
curves display a nearly symmetrical rectangular shape. The
reversible behavior of the curves was maintained, even at a scan
rate increased to 100 mV/s, suggesting a very high rate of
performance. Further, GCD curves of the porous nitrogen-doped
graphite carbon were obtained over various current densities,
ranging from 0.5 to 50 A/g. The GCD curves presented a
quasi-symmetrical shape, rather than a completely symmetrical
triangle. This may be due to the effect of heteroatom doping (O and
N elements). Particularly, the N-doping (pyrrole and pyridine)
could provide pseudo-capacity to the overall capacitance, thus
causing the GCD curve to deform and deviate from a symmetrical
triangle at low current densities.
[0024] FIG. 6 shows the specific capacitance of the porous
nitrogen-doped graphite carbon electrodes calculated from the CV
curves at various scan rates (5-100 mV/s). It has been demonstrated
that the electrolyte ions on the electrode surface do not have
adequate time to diffuse into the inner pores if the charging
current increases. This is because a large amount of micropores
make electrolyte ion transport difficult, particularly at high
current densities. These results indicate that the micro-scale
porous structure of the porous nitrogen-doped graphite carbon
facilitates electrolyte ions to diffuse into inner active
materials, especially with high active material loading.
[0025] It is to be understood that the method of making a porous
nitrogen-doped carbon electrode from biomass is not limited to the
specific embodiments described above, but encompasses any and all
embodiments within the scope of the generic language of the
following claims enabled by the embodiments described herein, or
otherwise shown in the drawings or described above in terms
sufficient to enable one of ordinary skill in the art to make and
use the claimed subject matter.
* * * * *