U.S. patent application number 14/842077 was filed with the patent office on 2016-03-24 for voltage efficiency of alkaline water electrolysis by using a mixed metal oxide cathode catalyst.
This patent application is currently assigned to PHILLIPS 66 COMPANY. The applicant listed for this patent is PHILLIPS 66 COMPANY. Invention is credited to Madhu Anand, Mahaprasad Kar, Neal McDaniel, Scott McGee.
Application Number | 20160083857 14/842077 |
Document ID | / |
Family ID | 55525213 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160083857 |
Kind Code |
A1 |
Kar; Mahaprasad ; et
al. |
March 24, 2016 |
VOLTAGE EFFICIENCY OF ALKALINE WATER ELECTROLYSIS BY USING A MIXED
METAL OXIDE CATHODE CATALYST
Abstract
A mixed metal oxide electrode for alkaline water electrolysis.
The mixed metal oxide comprises Ir, Ru, and a non-noble metal
selected from periods 4, 5 and 6 of the periodic table such as W,
Ce, Ni, V and Co.
Inventors: |
Kar; Mahaprasad; (Ponca
City, OK) ; Anand; Madhu; (Bartlesville, OK) ;
McGee; Scott; (Ponca City, OK) ; McDaniel; Neal;
(Ochelata, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHILLIPS 66 COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
PHILLIPS 66 COMPANY
Houston
TX
|
Family ID: |
55525213 |
Appl. No.: |
14/842077 |
Filed: |
September 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62051982 |
Sep 18, 2014 |
|
|
|
Current U.S.
Class: |
204/291 |
Current CPC
Class: |
C25B 11/0426
20130101 |
International
Class: |
C25B 11/04 20060101
C25B011/04 |
Claims
1. An electrode for alkaline water electrolysis comprising: a mixed
metal oxide comprising of: Ir, Ru, and a non-noble metal selected
from the group consisting of: elements selected from periods 4, 5
and 6 of the periodic table.
2. The electrode of claim 1, wherein the non-noble metal is
selected from the group consisting of W, Ce, Ni, V and Co.
3. The electrode of claim 1, wherein the electrode is a cathode
electrode.
4. The electrode of claim 1, wherein Ir and Ru are at equimolar
ratios of each other.
5. The electrode of claim 1, wherein hydroxide ions are produced by
the electrode during the alkaline water electrolysis.
6. The electrode of claim 1, wherein the non-noble metal is Co.
7. The electrode of claim 1, wherein the mixed metal oxide consists
essentially of: Ir, Ru, and a non-noble metal selected from the
group consisting essentially of: elements selected from periods 4,
5 and 6 of the periodic table.
8. The electrode of claim 1, wherein the molar ratio of
Ir:Ru:non-noble metal is 0.25:0.25:0.50.
9. An cathode electrode for generating hydroxide ions for an
alkaline water electrolysis comprising: a mixed metal oxide
consisting essentially of Ir, Ru and Co in a molar ratio of
0.25:0.25:0.50.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application which
claims the benefit of and priority to U.S. Provisional Application
Ser. No. 62/051,982 filed Sep. 18, 2014, entitled "Improving the
Voltage Efficiency of Alkaline Water Electrolysis by Using a Mixed
Metal Oxide Cathode Catalyst," which is hereby incorporated by
reference in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
FIELD OF THE INVENTION
[0003] This invention relates to a mixed metal oxide cathode
catalyst for use in alkaline water electrolysis.
BACKGROUND OF THE INVENTION
[0004] The electrolyzer is a device that generates hydrogen and
oxygen from water through the application of electricity and
consists of a series of porous graphite plates through which water
flows while low voltage direct current is applied. Electrolyzers
split the water into hydrogen and oxygen gases by the passage of
electricity, normally by breaking down compounds into elements or
simpler products. An electrolyzer has to fulfil requirements such
as high efficiency, low cost, large range of operation etc.
Physically a practical electrolyzer stack will consist of several
cells linked in series. Electrolysis cells are characterized by
their electrolyte type. There are two types of low temperature
electrolysis: alkaline electrolysis and proton exchange membrane
(PEM) electrolysis.
[0005] Generally, the efficiencies of proton exchange membranes are
higher than alkaline electrolyzers due to the presence of a
membrane. The half reaction taking place on the anode side of a PEM
electrolyzer is commonly referred to as the Oxygen Evolution
Reaction (OER). Here the liquid water reactant is supplied to
catalyst where the supplied water is oxidized to oxygen, protons
and electrons. The half reaction taking place on the cathode side
of a PEM electrolyzer is commonly referred to as the Hydrogen
Evolution Reaction (HER). Here the supplied electrons and the
protons that have conducted through the membrane are combined to
create gaseous hydrogen. The reactions at the electrodes are as
follows: [0006] Anode reaction:
H.sub.2O.fwdarw.1/2O.sub.2+2H.sup.++2e.sup.- [0007] Cathode
reaction: 2H.sup.++2e.sup.-.fwdarw.H.sub.2 [0008] Overall cell
reaction: H.sub.2O.fwdarw.H.sub.2+1/2O.sub.2
[0009] In contrast alkaline water electrolysis is a type of
electrolyzer that is characterized by having two electrodes
operating in a liquid alkaline electrolyte without a membrane.
Although alkaline water electrolysis is a more mature technology
than proton exchange membranes electrolysis it is plagued by the
need of high electrical consumption costs. Common types of
electrolyte used include KOH and NaOH. The reactions at the
electrodes are as follows: [0010] Anode reaction:
2HO.sup.-.fwdarw.1/2O.sub.2+H.sub.2O)+2e.sup.- [0011] Cathode
reaction: 2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2HO.sup.- [0012]
Overall cell reaction: H.sub.2O.fwdarw.H.sub.2+1/2O.sub.2
[0013] As shown above the reactions at the electrodes are
completely different between alkaline water electrolysis and proton
exchange membrane electrolysis. To elaborate on this fact the
hydroxide ions produced in the cathode reaction of the alkaline
water electrolysis cannot be produced at the cathode reaction of
the proton exchange membrane. Therefore electrode materials
described in patent applications geared towards proton exchange
membranes, such as 2003/0057088, cannot be used as alkaline water
electrolysis electrodes.
[0014] There exists a need to improve upon alkaline electrolysis
process for hydrogen production by improving the electrode catalyst
activity and lowering the electrical consumption cost.
BRIEF SUMMARY OF THE DISCLOSURE
[0015] A mixed metal oxide electrode for alkaline water
electrolysis. The mixed metal oxide comprises Ir, Ru, and a
non-noble metal selected from periods 4, 5 and 6 such as W, Ce, Ni,
V and Co.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] A more complete understanding of the present invention and
benefits thereof may be acquired by referring to the follow
description taken in conjunction with the accompanying drawings in
which:
[0017] FIG. 1 depicts a scanning electron micrograph of IrO.sub.2
catalysts synthesized using the aqueous hydrolysis method.
[0018] FIG. 2 depicts a scanning electron micrograph and
corresponding energy dispersive x-ray spectrogram for
Ir.sub.0.33Ru.sub.0.33Co.sub.0.33O.sub.2 catalysts.
[0019] FIG. 3 depicts the voltage efficiencies of cobalt-based
cathode catalysts.
[0020] FIG. 4 depicts the voltage efficiencies of different mixed
metal oxide cathode catalysts.
DETAILED DESCRIPTION
[0021] Turning now to the detailed description of the preferred
arrangement or arrangements of the present invention, it should be
understood that the inventive features and concepts may be
manifested in other arrangements and that the scope of the
invention is not limited to the embodiments described or
illustrated. The scope of the invention is intended only to be
limited by the scope of the claims that follow.
[0022] The term "electrolysis" describes the process of passing
electricity through water to liberate its elemental parents,
hydrogen and oxygen gas. A basic water electrolysis unit consists
of two electrodes (an anode and a cathode), a power supply, and an
aqueous electrolyte solution. A direct current (DC) is applied by
the power supply across the two electrodes, causing electrons to
flow from the negative terminal of the DC source to the cathode at
which the electrons are consumed by hydrogen ions (cations) to from
hydrogen. Maintaining charge balance, hydroxide ions transfer
through the electrolyte solution to the anode, where they give up
electrons to form oxygen. These electrons are then captured at the
positive terminal of the DC source, completing the circuit.
Overall, water is being reduced to dihydrogen at the cathode and
oxidized to dioxygen at the anode.
[0023] The present embodiment is directed towards a mixed metal
oxide electrode for alkaline water electrolysis. The mixed metal
oxide comprises Ir, Ru, and a non-noble metal selected from periods
4, 5 and 6 such as W, Ce, Ni, V and Co.
[0024] Although it is feasible that the mixed metal oxide electrode
could be used for both the cathode and the anode of the alkaline
water electrolysis it is anticipated that the cathode would use the
mixed metal oxide electrode while the anode would use typical
metals associated with alkaline water electrolysis. Typical metals
for alkaline water electrolysis include sole elements and mixtures
of: titanium, nickel or zirconium.
[0025] Catalyst Synthesis
[0026] Salts of the required metals were weighed corresponding to
the desired ratios in the final product. The salts were dissolved
in 25 ml of ultrapure water and stirred at room temperature. 0.2 g
of NaOH was added to the salt, resulting in an increase of the pH
beyond 12. This solution was stirred and heated at a temperature of
80.degree. C. for 1 hour resulting in the formation of hydroxides
or oxides of the corresponding metals. 1 M HNO.sub.3 was added to
the resulting solution in order to reduce the pH below 8 and
oxidize the remaining metal compounds. The precipitate was
collected upon centrifugation at 4000 r.p.m. for 5 minutes in two
cycles, and ethanol/water was added to the collected solids to
prepare a catalyst ink with a solids concentration of 10 mg/ml.
[0027] Table 1 below describes a list of representative chemicals
that can be used for the catalyst synthesis.
TABLE-US-00001 TABLE 1 Chemical Name Chemical Formula Purity (%)
Dihydrogen Hexachloroiridate H.sub.2IrCl.cndot.4H.sub.2O 99.90
Ruthenium Chloride RuCl.sub.3.cndot.xH.sub.2O 99.99 Cobalt Nitrate
Hexahydrate Co(NO.sub.3).sub.2.cndot.6H.sub.2O 99.00 Sodium
Hydroxide NaOH 99.10 Nickel Nitrate Hexahydrate
Ni(NO.sub.3).sub.2.cndot.6H.sub.20 99.00 Cerium Ammonium Nitrate
(NH.sub.4).sub.2Ce(NO.sub.3)6 >98.50 Ammonium Vanadium Oxide
NH.sub.4VO.sub.3 99.93 Sodium Tungsten Oxide Dihydrate
Na.sub.2WO.sub.4.cndot.2H.sub.2O 99.00-101.00 Nitric Acid HNO.sub.3
96.20 Ethanol C.sub.2H.sub.5OH 95.00 Oxalic Acid Dihydrate
C.sub.2O.sub.4H.sub.2.cndot.2H.sub.20 99.98
[0028] Table 2 below describes the atomic percentages of Ir, Ru and
Co intended in the catalysts and the corresponding weights of the
precursors taken to synthesize 0.25 mmols of final product.
TABLE-US-00002 TABLE 2 Sam- Ir Ru Co H.sub.2IrCl.cndot.4H.sub.2O
RuCl.sub.3 Co(NO.sub.3).sub.2.cndot.6H.sub.2O ple (%) (%) (%) (mg)
(mg) (mg) 1 50 50 0 60 26 0 2 44 44 12 52 23 9 3 37.5 37.5 25 45 19
18 4 34 34 33 40 17 24 5 25 25 50 30 13 36 6 12.5 12.5 75 15 6 55 7
0 0 100 0 0 73
[0029] FIG. 1 depicts a scanning electron micrograph of IrO.sub.2
catalysts synthesized using the aqueous hydrolysis method. The
sizes of the nanoparticles are in the range of 10 to 50 nm.
[0030] FIG. 2 depicts a scanning electron micrograph and
corresponding energy dispersive x-ray spectrogram for
Ir.sub.0.33Ru.sub.0.33Co.sub.0.33O.sub.2 catalysts. The spectrogram
confirms the presence of Ir, Ru and Co in the solids in the desired
ratios.
[0031] Electrode Fabrication
[0032] Titanium foils were all used as substrates for catalyst
deposition. All the electrode materials were cut to approximately 1
cm.times.2 cm coupons. The coupons were etched in 10% oxalic acid
at a temperature of 80.degree. C. for 30 minutes. The electrodes
were then cleaned with DI water, 100% ethanol and DI water again
and blown dry using compressed air. The catalyst ink was
ultrasonicated in a bath for 5 minutes to disperse the solids. The
dispersed ink was then deposited on the etched Titanium electrode
drop-wise as a suspension (100-200 microliter) followed by covering
the substrates by placing a watch-glass upside-down on them to
ensure the slow-drying of the solvent. All the electrodes mentioned
here had a catalyst loading of 1 mg/cm.sup.2.
[0033] The dried films were then placed in a ceramic boat and
heated in a tube furnace in an inert argon atmosphere at a
temperature of 500.degree. C. for 1 hour. Each electrode was then
sealed with a `5-minute Epoxy` by covering 80% of the back side of
the substrate and half the area on the front side, leaving
approximately 1 cm.sup.2 of exposed catalyst area on the front. The
epoxy was then left to set at room temperature for 15 minutes.
[0034] Electrode Testing
[0035] The deposited mixed metal oxide-based electrode was used as
the cathode in the electrolysis of water to produce hydrogen and
oxygen. The electrolysis of water was carried out in a 50 mL beaker
by electrically connecting the anode (SS foil) to the cathode via
the potentiostat. The anode was connected to the positive terminal
and the cathode to the negative terminal of the power source, and
an inter-electrode spacing of 0.5 cm was used. The anode, cathode
and a 30% w/w KOH electrolyte were placed in a 50 mL beaker having
means for heating and agitating (magnetic stirring) the solution.
The temperature of the beaker was maintained at 80.degree. C. by
heating on a heater-plate. Constant currents of 100 mA, 200 mA, 300
mA, 400 mA, 500 mA and 600 mA were used for measuring the voltage
efficiencies. The corresponding cell voltages were recorded by the
computer.
[0036] FIG. 3 depicts the voltage efficiencies for the different
cathode (hydrogen generation electrode) materials using 316
stainless steel as the anode material. Tests run in a beaker with
30% KOH, 5 mm electrode spacing at 80.degree. C. The green curve
shows the efficiency of commercially available Ni--Fe cathodes.
In-house developed IrRuCo oxides demonstrated a higher efficiency
than the commercially developed electrodes as shown in FIG. 3, with
Ir.sub.0.25Ru.sub.0.25Co.sub.0.5O.sub.2 showing the best efficiency
of 86%.
[0037] FIG. 4 depicts the voltage efficiencies of catalysts based
on other non-noble metals such as W, Ce, Ni and V, all of which
demonstrated higher efficiencies than typical commercial
cathodes.
[0038] Table 3 below depicts the voltage efficiency of various
cathode catalysts with a SS anode Tests were performed in a beaker
in 30% KOH at 80.degree. C. and 300 mA/cm.sup.2 with 5 mm electrode
spacing.
TABLE-US-00003 Cathode Efficiency Baseline 70.0
Ir.sub.0.33Ru.sub.0.22V.sub.0.33O.sub.2 77.0
Ir.sub.0.38Ru.sub.0.38V.sub.0.25O.sub.2 74.4 Commercial NiFe
electrode 77.5 Ir.sub.0.33Ru.sub.0.22W.sub.0.33O.sub.2 79.1
Ir.sub.0.33Ru.sub.0.33Ce.sub.0.33O.sub.2 79.3
Ir.sub.0.33Ru.sub.0.33Co.sub.0.33O.sub.2 79.6
Ir.sub.0.5Ru.sub.0.5O.sub.2 81.5
Ir.sub.0.44Ru.sub.0.44Ni.sub.0.12O.sub.2 83.1
Ir.sub.0.5Co.sub.0.5O.sub.2 83.7
Ir.sub.0.25Ru.sub.0.25Co.sub.0.5O.sub.2 85.6
[0039] In closing, it should be noted that the discussion of any
reference is not an admission that it is prior art to the present
invention, especially any reference that may have a publication
date after the priority date of this application. At the same time,
each and every claim below is hereby incorporated into this
detailed description or specification as an additional embodiment
of the present invention.
[0040] Although the systems and processes described herein have
been described in detail, it should be understood that various
changes, substitutions, and alterations can be made without
departing from the spirit and scope of the invention as defined by
the following claims. Those skilled in the art may be able to study
the preferred embodiments and identify other ways to practice the
invention that are not exactly as described herein. It is the
intent of the inventors that variations and equivalents of the
invention are within the scope of the claims while the description,
abstract and drawings are not to be used to limit the scope of the
invention. The invention is specifically intended to be as broad as
the claims below and their equivalents.
* * * * *