U.S. patent application number 14/328635 was filed with the patent office on 2015-04-09 for electrodes containing iridium nanoparticles for the electrolytic production of oxygen from water.
The applicant listed for this patent is Toyota Motor Engineering & Manufacturing North America, Inc.. Invention is credited to Kenneth J. McDonald, Michael Paul Rowe.
Application Number | 20150096887 14/328635 |
Document ID | / |
Family ID | 57112516 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150096887 |
Kind Code |
A1 |
McDonald; Kenneth J. ; et
al. |
April 9, 2015 |
ELECTRODES CONTAINING IRIDIUM NANOPARTICLES FOR THE ELECTROLYTIC
PRODUCTION OF OXYGEN FROM WATER
Abstract
Electrodes employing as active material iridium nanoparticles
synthesized by a novel route are provided. The nanoparticle
synthesis is facile and reproducible, and provides iridium
nanoparticles of very small dimension and high purity for a wide
range of metals. The electrodes utilizing these nanoparticles have
excellent efficiency catalyzing the electrolytic production of
oxygen from water.
Inventors: |
McDonald; Kenneth J.; (Oak
Forest, IL) ; Rowe; Michael Paul; (Pinckney,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toyota Motor Engineering & Manufacturing North America,
Inc. |
Erlanger |
KY |
US |
|
|
Family ID: |
57112516 |
Appl. No.: |
14/328635 |
Filed: |
July 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14046120 |
Oct 4, 2013 |
|
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14328635 |
|
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14219836 |
Mar 19, 2014 |
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14046120 |
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Current U.S.
Class: |
204/292 ; 75/343;
75/354 |
Current CPC
Class: |
Y02E 60/50 20130101;
B22F 9/24 20130101; B22F 9/04 20130101; C25B 1/04 20130101; H01M
4/88 20130101; B22F 2009/043 20130101; H01M 4/0404 20130101; B22F
1/0018 20130101; B22F 2301/25 20130101; Y02E 60/10 20130101; B22F
9/20 20130101; C25B 11/0473 20130101; B22F 2304/054 20130101; H01M
4/139 20130101; B22F 2999/00 20130101; Y02E 60/36 20130101; B22F
2999/00 20130101; B22F 2301/25 20130101; B22F 2999/00 20130101;
B22F 2304/054 20130101 |
Class at
Publication: |
204/292 ; 75/343;
75/354 |
International
Class: |
C25D 17/10 20060101
C25D017/10; C22B 3/00 20060101 C22B003/00; B22F 9/24 20060101
B22F009/24 |
Claims
1. An electrode comprising iridium nanoparticles, the iridium
nanoparticles synthesized by a method comprising: adding surfactant
to a reagent complex according to Formula I, Ir.sup.0X.sub.y I,
wherein Ir.sup.0 is zero-valent iridium, X is a hydride, and y is
an integral or fractional value greater than zero.
2. The electrode of claim 1 wherein the reagent complex is obtained
by a process that includes a step of: ball milling a mixture that
includes a hydride and a preparation composed of iridium.
3. The electrode of claim 1 wherein the hydride is lithium
borohydride.
4. The electrode of claim 1 wherein the iridium nanoparticles have
an average maximum dimension less than 100 nm.
5. The electrode of claim 1 wherein the iridium nanoparticles have
an average maximum dimension less than 10 nm.
6. The electrode of claim 1 wherein the iridium nanoparticles have
an average maximum dimension less than 5 nm.
7. The electrode of claim 1 which catalyzes the half-cell reaction:
2H.sub.2OO.sub.2+4H.sup.++4e.sup.-.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application
Ser. Nos. 14/046,081 and 14/046,120, filed 4 Oct. 2013, and a
continuation-in-part of application Ser. No. 14/219,836, filed 19
Mar. 2014, the specifications of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates in general to iridium
nanoparticles synthesized by a novel route and their use as
catalysts of electrochemical water splitting.
BACKGROUND
[0003] Electrochemical oxidation/reduction of water, or "water
splitting"--conversion of H.sub.2O to H.sub.2 and O.sub.2 by
application of electrical potential across electrodes of a
cell--can in theory be a useful approach to produce hydrogen and
oxygen fuels. As a practical matter, such an approach is severely
limited by the fact that energy input generally exceeds the energy
obtainable from the produced fuels. Electrode materials which
increase the quantity of product at a given voltage can potentially
overcome this challenge.
[0004] Iridium metal and/or oxide have been used as an electrode
active material for the electrolytic production of oxygen gas from
water. The efficiency of such an electrode can be improved through
the use of nanoparticulate iridium. Nanoparticulate iridium of high
quality is difficult and expensive to obtain in production scale
quantity.
SUMMARY
[0005] Electrodes and iridium nanoparticles synthesized by a novel
route are provided.
[0006] In an embodiment, an electrode comprising iridium
nanoparticles is disclosed, wherein the iridium nanoparticles are
synthesized by a method comprising adding surfactant to a reagent
complex according to Formula I:
Ir.sup.0Xy I,
wherein Ir.sup.0 is zero-valent iridium, X is a hydride, and y is
an integral or fractional value greater than zero. The electrode
which contains iridium nanoparticles synthesized by this method has
excellent ability to electrolytically produce oxygen from
water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Various aspects and advantages of the invention will become
apparent and more readily appreciated from the following
description of the embodiments taken in conjunction with the
accompanying drawings, of which:
[0008] FIG. 1 is first cycle voltammograms of electrochemical cells
having iridium-containing electrodes where the iridium is either
directly from a commercial source or is nanoparticulate iridium
synthesized by a disclosed method;
[0009] FIG. 2 is second cycle voltammograms of the electrochemical
cells of FIG. 1; and
[0010] FIG. 3 is tenth cycle voltammograms of the electrochemical
cells of FIG. 1.
DETAILED DESCRIPTION
[0011] The present disclosure describes iridium nanoparticles
suitable for use as active material in an electrode of an
electrochemical cell. The disclosure also describes the electrodes
which include such nanoparticles. The iridium nanoparticles are
synthesized by a mechanochemical method which is facile, easily
scalable to industrial needs, and produces pure iridium
nanoparticles free of contaminants to the low nanometer(nm)
scale.
[0012] The iridium nanoparticles and electrodes of the present
disclosure can be useful in the electrochemical production of
oxygen gas from water.
[0013] A reagent complex for the synthesis of metallic iridium
nanoparticles is described by Formula I:
Ir.sup.0X.sub.y I,
wherein Ir.sup.0 is zero-valent iridium metal and X is a hydride.
The subscript y can be any positive fractional or integral value.
In some cases, y can be a value from 1 to 4, inclusive. In some
cases, y can be a value from 1 to 2, inclusive. In some cases, y
will be approximately 2.
[0014] The hydride employed in Formula I can be a solid metal
hydride (e.g. NaH, or IrH.sub.2), metalloid hydride (e.g.
BH.sub.3), complex metal hydride (e.g. LiAlH.sub.4), or salt
metalloid hydride also referred to as a salt hydride (e.g.
LiBH.sub.4). In some examples the hydride will be LiBH.sub.4,
yielding a reagent complex having the formula IrLiBH.sub.4. In some
specific examples, the reagent complex will have the formula
Ir(LiBH.sub.4).sub.2. It is to be appreciated that the term hydride
as used herein can also encompass a corresponding deuteride or
tritide.
[0015] The reagent complex can be a complex of individual molecular
entities, such as a single metal atom in oxidation state zero in
complex with one or more hydride molecules. Alternatively the
complex described by Formula I can exist as a molecular cluster,
such as a cluster of metal atoms in oxidation state zero
interspersed with hydride molecules, or a cluster of metal atoms in
oxidation state zero, the cluster surface-coated with hydride
molecules or the salt hydride interspersed throughout the
cluster.
[0016] One process by which a reagent complex according to Formula
I can be obtained includes a step of ball-milling a mixture which
includes both a hydride and a preparation composed of iridium. The
preparation composed of iridium can be derived from any source of
metallic iridium, but will typically be a source of metallic
iridium that contains zero-valent iridium at greater than 50%
purity and at a high surface-area-to-mass ratio. For example, a
suitable preparation composed of iridium would be an iridium powder
comparable to commercial grade iridium powder.
[0017] The ball-milling step can be performed with any type of ball
mill, such as a planetary ball mill, and with any type of
ball-milling media, such as stainless steel beads. It will
typically be preferable to perform the ball-milling step in an
inert environment, such as in a glove box under vacuum or under
argon.
[0018] The reagent complex described above and by Formula I can be
used in a method for synthesizing iridium nanoparticles. The method
for synthesizing iridium nanoparticles includes the step of adding
surfactant to a reagent complex according to Formula I, the reagent
complex being in all particulars as described above. In some
examples of the method for synthesizing iridium nanoparticles, the
reagent complex can be in suspended contact with a solvent or
solvent system. Suitable solvents in which the reagent complex can
be suspended during addition of surfactant will typically be
solvents in which the suspended reagent complex is stable for at
least an hour. In some examples, such suitable solvents can include
ethereal solvents or aprotic solvents. In some particular examples,
such a suitable solvent will be THF. In some instances, it may be
preferred to perform the method for synthesizing iridium
nanoparticles in an inert environment, such as in a glove-box under
vacuum or argon.
[0019] In some variations of the method for synthesizing iridium
nanoparticles, the surfactant can be in suspended or solvated
contact with a solvent or solvent system. In different variations
wherein the reagent complex is in suspended contact with a solvent
or solvent system and the surfactant is suspended or dissolved in a
solvent or solvent system, the reagent complex can be in suspended
contact with a solvent or solvent system of the same or different
composition as compared to the solvent or solvent system in which
the surfactant is dissolved or suspended.
[0020] In some variations of the method for synthesizing iridium
nanoparticles, the reagent complex can be combined with surfactant
in the absence of solvent. In some such cases a solvent or solvent
system can be added subsequent to such combination. In other
aspects, surfactant which is not suspended or dissolved in a
solvent or solvent system can be added to a reagent complex which
itself is in suspended contact with a solvent or solvent system. In
yet other aspects, surfactant which is suspended or dissolved in a
solvent or solvent system can be added to a reagent complex which
is not in suspended contact with a solvent or solvent system.
[0021] The surfactant utilized in the method for synthesizing
iridium nanoparticles can be any known in the art. Usable
surfactants can include nonionic, cationic, anionic, amphoteric,
zwitterionic, and polymeric surfactants and combinations thereof.
Such surfactants typically have a lipophilic moiety that is
hydrocarbon based, organosilane based, or fluorocarbon based.
Without implying limitation, examples of types of surfactants which
can be suitable include alkyl sulfates and sulfonates, petroleum
and lignin sulfonates, phosphate esters, sulfosuccinate esters,
carboxylates, alcohols, ethoxylated alcohols and alkylphenols,
fatty acid esters, ethoxylated acids, alkanolamides, ethoxylated
amines, amine oxides, alkyl amines, nitriles, quaternary ammonium
salts, carboxybetaines, sulfobetaines, or polymeric
surfactants.
[0022] In some instances the surfactant employed in the method for
synthesizing iridium nanoparticles will be one capable of
oxidizing, protonating, or otherwise covalently modifying the
hydride incorporated in the reagent complex. In some variations the
surfactant can be a carboxylate, nitrile, or amine. In some
examples the surfactant can be octylamine.
[0023] Also disclosed is an electrode suitable for use in an
electrochemical cell. The electrode includes as active material
iridium nanoparticles. The iridium nanoparticles included in the
electrode have an average maximum dimension less than 100 nm. In
some instances, the iridium nanoparticles included in the electrode
have an average maximum dimension of 10 nm or less. In some
instances, the iridium nanoparticles included in the electrode have
an average maximum dimension of 5 nm or less. The iridium
nanoparticles included in the electrode are, in some variations,
generally of uniform size. The iridium nanoparticles included in
the electrode can be obtained by the process for synthesizing
iridium nanoparticles, as disclosed above.
[0024] In some instances, an electrode of the present disclosure
can, when deployed in an appropriately configured electrochemical
cell, catalyze the half-cell reaction:
2H.sub.2OO.sub.2+4H.sup.++4e.sup.-.
In some such instances, as illustrated below, the disclosed
electrode will catalyze the half-cell reaction with greater
efficiency than does an otherwise identical electrode having
iridium from a different source
[0025] It will be appreciated that the disclosed electrode can,
include additional structural substrates, binding agents, and/or
other active materials. In a non-limiting example, a co-suspension
in THF of iridium nanoparticles synthesized by the disclosed
method, acid-treated carbon black, and fluorinated sulfonic acid
polymer were sonicated and cast on a glassy carbon electrode. For
comparison purposes, an otherwise identical electrode was prepared
in which iridium nanoparticles synthesized by the disclosed method
were replaced with commercially obtained iridium powder.
[0026] Each of the two electrode types, disclosed and comparative,
was deployed in an electrochemical cell opposite a platinum
electrode and with oxygenated sulfuric acid electrolyte. Each of
the cell types was subjected to voltammetric analysis, as shown in
FIGS. 1-3. FIGS. 1, 2, and 3 show first cycle, second cycle, and
tenth cycle voltammetric curves, respectively. In each case, the
solid line represents data for the electrochemical cell having the
disclosed electrode with iridium nanoparticles synthesized by the
disclosed method. The dotted line represents data for the
electrochemical cell having the comparative electrode with
commercially obtained iridium powder.
[0027] Comparison of FIGS. 1-3 indicates that the disclosed
electrode is highly consistent over multiple cycles, generating
similar current density across all voltages in cycle ten as
compared to cycle one. Of significance, each of FIGS. 1-3 shows
that the disclosed electrode has superior electrochemical
performance relative to the comparative electrode. At operative
potentials, the electrode having iridium nanoparticles synthesized
by the disclosed method generates greater current density, and
hence greater quantity of oxygen, than does the electrode having
commercially obtained iridium.
[0028] Various aspects of the present disclosure are further
illustrated with respect to the following Examples. It is to be
understood that these Examples are provided to illustrate specific
embodiments of the present disclosure and should not be construed
as limiting the scope of the present disclosure in or to any
particular aspect.
EXAMPLE 1
Iridium Nanoparticle Synthesis
[0029] To a stainless steel ball mill jar is added 2.0 g of iridium
powder (-325 mesh) and 0.453 g lithium borohydride powder.
Stainless steel balls are added to the jar as well. The mixture is
subjected to 250 rpm for 4 hours, under argon, in a planetary ball
mill. 0.750 g of the resulting Ir(LiBH.sub.4).sub.2 powder is then
added to 10 mL THF, along with 4.110 g octylamine. This mixture is
stirred, under argon, for 4 hours. The nanoparticle product is then
collected and the reaction solution decanted away. The isolated
nanoparticle powder is washed with ethanol, then ethanol/water, and
finally acetone before being dried.
EXAMPLE 2
Iridium Electrode Preparation
[0030] Iridium electrodes were prepared by drop casting a catalyst
ink onto a glassy carbon electrode. The catalyst ink was first
prepared by sonicating a mixture of catalyst, acid-treated carbon
black (CB, Alfa Aesar), Na.sup.+-exchanged Nafion.RTM. solution (5
wt %, Ion Power) with tetrahydofuran (THF, Sigma-Aldrich). After
drop casting, the catalyst film was allowed to dry at room
temperature overnight and the final composition of the film was
expected to be 100, 20, and 20 .mu.g/cm.sup.2 for Iridium
nanoparticles, CB, and Nafion.RTM., respectively.
EXAMPLE 3
Iridium Electrode Testing
[0031] Electrochemistry was used to determine the catalytic ability
of the catalyst. Cyclic voltammetry experiments were performed in
1M H.sub.2SO.sub.4 electrolyte that was saturated with O.sub.2.
Scans were cycles between 1V vs. RHE (reversible hydrogen
electrode) and 1.6 V vs. RHE a total of 10 times at 10 mV/s. The
catalysts-containing working electrode was rotated at 1600 rpm.
Counter electrode used in the cell was a platinum wire separated
from the cell using a glass frit. All potentials were measured
versus a Ag/AgCl electrode but the potentials were converted to RHE
for ease of understanding.
[0032] The foregoing description relates to what are presently
considered to be the most practical embodiments. It is to be
understood, however, that the disclosure is not to be limited to
these embodiments but, on the contrary, is intended to cover
various modifications and equivalent arrangements included within
the spirit and scope of the appended claims, which scope is to be
accorded the broadest interpretation so as to encompass all such
modifications and equivalent structures as is permitted under the
law.
* * * * *