U.S. patent application number 15/041930 was filed with the patent office on 2017-08-17 for process to make iron based electrocatalyst, an anode material, an electrochemical system and a process for water conversion, catalysis and fuel generation.
The applicant listed for this patent is Khurram Saleem Joya. Invention is credited to Khurram Saleem Joya.
Application Number | 20170233885 15/041930 |
Document ID | / |
Family ID | 59561337 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170233885 |
Kind Code |
A1 |
Joya; Khurram Saleem |
August 17, 2017 |
PROCESS TO MAKE IRON BASED ELECTROCATALYST, AN ANODE MATERIAL, AN
ELECTROCHEMICAL SYSTEM AND A PROCESS FOR WATER CONVERSION,
CATALYSIS AND FUEL GENERATION
Abstract
This invention provides a simple approach for the
straightforward and direct preparation of iron-oxide based
electrocatalytic materials film (FeO.sub.x--Ci) on a simple Fe
substrate by controlled surface-anodization and/or self-deposition
in simple and low-cost carbonate buffer. The FeO.sub.x--Ci based
electrocatalysts may advantageously be employed as electrode and as
anode material in water oxidation, water conversion systems and
fuel generation assemblies. The FeO.sub.x--Ci exhibits remarkably
low over potential (.eta..apprxeq.360) for anodic oxygen evolution
relative to other Fe-oxide based catalysts, and show very high
activity and stability for long-term water electrolysis
operation.
Inventors: |
Joya; Khurram Saleem;
(Lahore, PK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Joya; Khurram Saleem |
Lahore |
|
PK |
|
|
Family ID: |
59561337 |
Appl. No.: |
15/041930 |
Filed: |
February 11, 2016 |
Current U.S.
Class: |
205/217 |
Current CPC
Class: |
C25B 1/04 20130101; C25D
11/34 20130101; Y02E 60/366 20130101; C25B 11/0452 20130101 |
International
Class: |
C25D 11/34 20060101
C25D011/34; C25B 11/04 20060101 C25B011/04; C25B 1/04 20060101
C25B001/04 |
Claims
1. A method of making a catalytic comprising: providing an anode
and a cathode in an electrochemical cell; cleaning the electrodes
with acid wash and water; immersing the electrodes in an aqueous
bicarbonate/carbonate buffer system at a pH ranging from 8.5 to 13;
and, applying constant current or constant potential to the
electrodes suitable to electrochemically produce surface anodizing
leading to deposit of iron oxide on the surface of the anode.
2. The method of claim 1, wherein, the anode is made of iron metal,
an iron alloy or an iron-derived material.
3. The method of claim 1, wherein the anode is coated with
nanoparticles.
4. The method of claim 1, wherein the applied voltage is higher
than 1.40 volts.
5. The method of claim 1, wherein the voltage is applied from 0.1
minutes to 24 hours or more.
6. The method of claim 1, wherein the applied current is above 0.1
milliampere per square meter of the surface of anode.
7. The method of claim 1, wherein the size of deposited particles
ranges between 25 and 250 nm.
8. The method of claim 1, wherein the thickness deposited iron
oxide on the anode is 5 to 250 nm.
9. The method of claim 1, wherein the electrolytic solution is free
of transition metal ions.
10. A method of converting water into oxygen and releasing hydrogen
comprising: providing the anode of claim 1 and a cathode in an
electrochemical cell; applying a suitable voltage to split water
molecules into electrons and protons to make hydrogen as fuel,
energy carrier, chemical feedstock, or non-fossil fuel when
combined with carbon dioxide.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention describes a process for forming and
electro-assembling of metal oxide electrocatalytic material, a
process to prepare an anode material, an electrochemical cell, and
a process to convert water by electrochemical technology into
oxygen and protons, via controlled surface-anodization and/or
self-deposition of a simple iron surface and/or iron-derived
substrates and alloys.
[0002] Water, using renewable electricity and/or solar energy, can
be converted into oxygen and protons via processes referred to as
catalytic water oxidation or water splitting in an electrochemical
system or via photo-electrochemical (PEC) methods. This is a
promising technology and a feasible process for the direct
conversion of light energy into renewable fuels and cheap energy
carriers using simple water. The beauty of water splititng is the
release of four electrons and four protons per O.sub.2 trunover,
that can be used either to make hydrogen as clean and high energy
density fuel or in combination of CO.sub.2 to direclty reduce it,
and to convert it into useul nonfossil feuls and chemical energy
carriers (FIG. 1). This scheme looks promissing and provides a
route to renewable and alternative energy carriers obtain from
abundant water and enormous sun light.
[0003] Many millions of years ago, nature has devised an efficient
system to convert water and CO.sub.2 into energy storable
substances using sun light. In natural photosynthesis, the
catalytic oxidation of water in photosystem II (PS-II) is
facilitated by the presence of MnCaO based water oxidation
material/complex that splits water with high efficiency and at a
tremendous rate. Scientists are trying hard to mimic this
state-of-the-art material in labs using both material-science and
molecular approaches to be obtained from cheap sources and
earth-abundant elements.
[0004] Ru-oxide and Ir-oxide are established and benchmarking
materials for electrochemical water splitting. But they are too
expensive to be employed on large scale application. Recently,
catalytic materials based on oxides of the abundant first row
transition metals such as Ni, Co, Mn and Cu have been emerged as
substitute of the noble metals based electrocatalysts.
[0005] These transition metal-oxide electrocatalysts were developed
by conducting substrates from metal ions solutions under
electrochemical conditions. The presence of metal ions is a
prerequisite for their activity and long-term water electrolysis
performance and metal ions may possibly interact to contaminate and
poison the cathode for the reduction reaction. In order to avoid
the metal ions interaction, membranes or separators are usually
employed, which make the system more complex and introduce
resistance and diffusion limitations. Thus, new materials and
methods are required to develop high activity water oxidation
electrocatalysts. At the same time, there is a need to develop
easily accessible and robust water oxidation catalytic systems
operating at low overpotential with high rate turnover for anodic
oxygen evolution and performing with high stability for long-term
application.
[0006] Applicant discovered a simple method for the formation of
nanoscale metals-based and metal-oxides based electrocatalysts to
be advantageously employed as electrode and as anode materials in
water oxidation, water conversion systems and fuel generation
assemblies.
BRIEF SUMMARY OF THE INVENTION
[0007] Iron is interesting metal and it is the most abundant
element among transition metals in the earth's crust. Iron is also
the main component of many biological systems and enzymes for
oxygen activation. Iron-oxide (Fe.sub.2O.sub.3) is a very good
candidate for photocatalytic water oxidation, however iron or
iron-oxide based materials have been scarcely explored for anodic
oxygen evolution reactions.
[0008] It is difficult to prepare iron-oxide layer via
electrodeposition as it requires Fe.sup.II/Fe.sup.III ions which
easily precipitates out from water under near-neutral conditions
and Iron-oxide is not stable in low pH solutions.
[0009] The present invention is a process for the direct
preparation, electrodeposition and surface-assembling of iron-based
and/or iron-oxide based electrocatalysts and/or anode materials by
surface-anodization and/or self-deposition of an amorphous iron
and/or iron-derived substrates and alloys in simple but not
limiting to bicarbonate/carbonate (HCO.sub.3.sup.-/CO.sub.3.sup.2-)
buffer system.
[0010] Next, the present invention comprising the steps of: (1)
surface cleaning of simple amorphous iron and/or iron-derived
substrates and alloys with neat water, following cleaning with
dilute acid and washing with water, and (2) immersing the clean
amorphous iron and/or iron-derived substrates and alloys as an
anode in an aqueous bicarbonate/carbonate
(HCO.sub.3.sup.-/CO.sub.3.sup.2-) buffer system at a pH in the
range from 8.5 to 13.5, and (3) applying a current over the anode
and cathode suitable for electrolytically surface-anodizng and/or
self-depositing the iron-based and/or iron-oxide based
electrocatalysts and/or anode materials, and (4) using the thus
obtained surface-assembled electrocatalytic material in a suitable
electrolyte systems of water electrolysis and its conversion into
fuel.
[0011] Further, the present invention relates to the use of the
iron-derived material as an electrolysis catalyst applicable to a
wide range of pH and variety of electrolyte systems.
[0012] Further again, the present invention relates to an
iron-based and/or iron-oxide based catalytic electrode material
having moderate water electrolysis overpotential (.eta.) from 300
to 500 mV.
[0013] Further again, the present invention relates to an
iron-based and/or iron-oxide based catalytic electrode material
having very high activity and stability for long-term water
electrolysis systems.
[0014] Further again, the present invention relates to simple and
direct formation of an iron-based and/or iron-oxide based catalytic
material thus avoiding the difficulties during electrodeposition
from metal ions in the neutral and above neutral pH system that
cause the precipitation and reduce catalytic formation and
electro-activity.
[0015] Further again, the present invention relates to an
iron-based and/or iron-oxide based material catalytically active in
metal-ions free phosphate, borate, carbonate, hydroxide or other
aqueous electrolytes.
[0016] Further, the present invention relates to an iron-based
and/or iron-oxide based electrocatalytic materials with nanosclae
surface morphology with an average particle size in the range of
from 25 nm to 250 nm or more as determined by SEM microscopy.
[0017] Further again, the present invention relates to an
iron-based and/or iron-oxide based materials whereby the surface
nanoparticles have an average thickness of from 10 to 500 nm or
more as determined by SEM microscopy.
[0018] The present invention is an electrochemical cell comprising
an anode comprising the iron and/or iron-oxide nanoparticulate
material according to the invention.
[0019] Further, the present invention relates to a process to
convert water into oxygen, and releasing electrons and protons,
comprising an electrochemical cell according to the invention, and
applying a suitable voltage to the iron-based and/or iron-oxide
derived anode and a cathode, using a power source.
[0020] Further, the present invention relates to a process of water
conversion in an electrochemical cell according to the invention,
using a suitable power source from renewable sources, hydel power,
wind, and from solar energy.
[0021] Further, the present invention relates to a process of
oxidation, catalysis, splitting, oxidation and conversion of water
and for the fuel generation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 depicts a schematic representation of the
electrochemical formation of iron-based and/or iron-oxide derived
electrocatalytic material for water oxidation in-line with a
cathodic hydrogen evolution module.
[0023] FIG. 2 depicts scanning electron microscopy (SEM) images for
starting iron-substrate and for iron-oxide derived electrocatalytic
materials.
[0024] FIG. 3 depicts an enlarged view of the SEM (scanning
electron microscopy) image of iron-oxide based catalytic material,
at 250.times.10.sup.3 magnifications.
[0025] FIG. 4 depicts EDX (energy dispersive X-ray) spectrum of the
electro-generated iron-oxide derived electrocatalytic material.
[0026] FIG. 5 depicts the XPS (X-ray photoelectron spectroscopy)
survey spectrum of electrochemically generated iron-oxide derived
electrocatalytic sample.
[0027] FIG. 6 depicts the XPS (X-ray photoelectron spectroscopy)
spectrum of Fe (2p) and O (1s) in the electrochemically generated
iron-oxide derived electrocatalytic sample.
[0028] FIG. 7 depicts a forward current--potential sweep for oxygen
evolution durong water oxidation catalysis on surface-assembled
iron-oxide derived electrocatalyst in carbonate buffer
(pH.about.11.1), at a scan rate of 25 mV sec.sup.-1.
[0029] FIG. 8 depicts an enlarged view of the CV curve for the
iron-oxide derived electrocatalyst on a concise potential window
under the same conditions as for FIG. 7, at a scan rate of 25 mV
sec.sup.-1.
[0030] FIG. 9 depicts the 1.sup.st and 100.sup.th consecutive
forward potential sweeps for iron-oxide derived electrocatalyst at
a rate of 25 mV sec.sup.-1.
[0031] FIG. 10 depicts a Tafel plot or log i vs overpotential
(.eta.) curve obtained for electrocatalytic oxide derived catalyst
material while oxygen evolution in carbonate buffer.
[0032] FIG. 11 depicts the extended period constant-current water
electrolysis (CCE) on the iron oxide derived electrocatalyst in
carbonate buffer (pH.about.11.1) for current dnesities 15 mA
cm.sup.-2 and 50 mA cm.sup.-2.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The nanoscale iron-based and/or iron-oxide based
electrocatalyst is generated in a metal-ions free solution during
constant-current electrolysis (CCE) at a current density of 5.0 mA
cm.sup.-2 in carbonate buffer (pH.apprxeq.11). The
surface-assembling of iron-oxide (FeO.sub.x--Ci) electrocatalyst on
simple iron substrate can be ascribed to the surface
electrochemical process involving the surface oxidation to from
Fe.sup.n+ type surface species that quickly turned into metal
hydroxide/oxide type composition on Fe surface. These initial
nano-assemblies act as nuclei for the generation and growth of
nano-structured FeO.sub.x--Ci electrocatalyst on simple iron
substrate. (Studies are in progress to explore more insight into
the mechanism of FeO.sub.x--Ci generation on Fe surface in
carbonate buffer). Scanning electron microscope image shows nicely
distributed nano-structures of FeO.sub.x--Ci on the entire surface
of the anodized Fe substrate (FIG. 2a). These nanoscale surface
structures appear to be amalgamation of nanoparticles on the flat
Fe surface (FIG. 2b). The enlarged view of the SEM picture clearly
reveals nano particulates type structures with spongy texture (FIG.
3). The electro generated nano particulate iron-oxide looks fairly
uniform in size representing their controlled oxidative
electrochemical generation.
[0034] EDX (energy dispersive X-ray) measurements for the elemental
composition show Fe and O in the FeO.sub.x--Ci electrocatalyst
sample (FIG. 4). There is a minor contribution from Na and about 7%
carbon contents are also present in the catalytic deposit.
Previously, we noticed that the electro-induced deposition of
Co--Ci and Ni--Ci based water oxidation catalytic materials in
carbonate/bicarbonate systems incorporated carbon assimilation in
the catalytic deposits that was ascribed to their enhanced
catalytic efficiency. Carbon based materials are thought to support
electron transfer while introducing superior physical properties
such as high surface areas and electronic communication, structural
flexibility and enhanced mechanical strength.
[0035] The surface composition of the nano particulate
FeO.sub.x--Ci is examined by X-ray photoelectron spectroscopy
(XPS). The elemental detection on the XPS survey for electro
generated iron-oxide layer indicates the presence of iron, oxygen
and carbon in the catalytic film (FIG. 5). XPS spectral signatures
for the Fe2p core levels are present in the XPS region from 708 eV
to 738 eV (FIG. 6a) showing the characteristic peaks of Fe(III) in
the deposited layer as the energy separation for high binding
energy Fe 2p3/2 between the main envelope (710.8 eV) and the
satellite peak (719.1 eV) is 8.5 eV. The other lower energy level
Fe 2p1/2 exhibits 724.6 eV as envelop with a satellite peak at 733
eV. The binding energy data for Fe 2p3/2 is consistent with the
presence of only Fe(III) oxidation state, and the presence of
Fe(II) can be excluded as it has 5 eV binding energy difference
between the main envelope and the satellite. Further, the O 1 s
binding energy region on the XPS spectrum clearly shows the
lower-binding-energy peaks at 530.0 eV and 531.4 eV (FIG. 6). This
suggests that there is no presence of amorphous FeOOH based
material in the catalytic layer. The binding-energy peak at 530.0
eV is assigned to the oxygen atoms of oxide ions (in metal oxide)
whereas the 531.4 eV signal is ascribed to the hydroxy groups in
the FeO.sub.x--Ci layer.
[0036] For water oxidation catalysis using FeO.sub.x--Ci
electrocatalyst, voltammetry and long-term water electrolysis
experiments are undertaken in clean carbonate buffer solutions. The
forward sweep voltammetry for the iron-oxide shows onset of the
catalytic current for oxygen evolution at .about.1.59 V vs RHE
(.eta.on=360 mV), following a sharp rise in the current density
(FIG. 7). The current density further grows rapidly reaching 10 mA
cm.sup.-2 and 20 mA cm.sup.-2 at 1.71 V vs RHE (.eta.=470 mV) and
1.74 V vs RHE (.eta.=510 mV), respectively. The 10 mA cm.sup.-2
current density of is an optimal requisite to achieve 10%
efficiency for the solar-to-fuel conversion system. For
FeO.sub.x--Ci electrocatalyst, the oxygen onset potential of
E.sub.on=1.59 V; .eta..sub.on=360 mV (FIG. 8), is much less than
for recently reported Fe-oxide based catalysts showing much higher
E.sub.on (.eta..sub.on>500 mV). The O.sub.2 onset potential for
FeO.sub.x--Ci is also much lower compared to other metal oxides
electro catalysts such as Co--Pi (1.67 V vs. RHE), Ni--Bi (1.71 V
vs. RHE). This makes FeO.sub.x--Ci electrocatalyst a new
electrodeposited Fe-based benchmark material for anodic water
oxidation.
[0037] The repetitive potential sweeps for FeO.sub.x--Ci
electrocatalyst sample reproduce the similar current density
signatures for the 1st and 100th scan suggesting no noticeable
degradation of FeO.sub.x--Ci system and representing remarkable
stability and long-time activity of the new Fe-based electro
catalyst (FIG. 9).
[0038] Current--over potential (.eta. vs log i) plot of the
FeO.sub.x--Ci electrocatalyst during oxygen generation produces a
Tafel slope of 47 mV dec.sup.-1 (FIG. 10). A Tafel slope of 47 mV
dec.sup.-1 is very impressive and unique for the iron-oxide based
electro catalyst, as other Fe-oxide based electro catalytic systems
show much higher Tafel slopes (Table 1). A small Tafel slope in
important as water oxidation electro catalyst is desired to operate
over a narrow potential window for high performance, and this small
current-voltage window for FeO.sub.x--Ci is attractive for the
integration with photo-responsive materials.
TABLE-US-00001 TABLE 1 Electrochemical and catalytic water
oxidation data for different electrochemically generated Fe-oxides
based electrocatalysts. O.sub.2 onset Eon (vs .eta. at J = 10 mA
Tafel Slope Catalyst/Substrate[a] RHE).sup.[b] cm.sup.-2[c] (mV
dec.sup.-1) Ref FeO.sub.x--Ci/Fe 1.59 V 470 mV 47 This Work
FeOx/ITO 1.67 V ~730 mV 52 16 FeOOH/FT O 1.73 V ~560 mV -- 23
.sup.[a]FeO-based electro catalysts prepared by electrochemical
methods. .sup.[b]Oxygen onset taken from the anodic current at J
>0.1 mA cm.sup.-2. .sup.[c]Overpotential require to achieve a
current density of 10 mA cm.sup.-2.
[0039] For long-term water electrolysis testing and stability
performance of the FeO.sub.x--Ci based electro catalyst, electro
catalytic experiments are conducted in clean metal ions free
carbonate solution. We chose constant-current electrolysis
(chronopotentiometry) experiments while preserving stable current
densities of 15 mA cm.sup.-2 and 50 mA cm.sup.-2 and monitoring the
potential response of the system at the same time. The
FeO.sub.x--Ci electrocatalyst remains remarkably stable during high
activity oxygen evolution at current densities of 15 mA cm.sup.-2.
To achieve 15 mA cm.sup.-2, a very stable steady-state potential of
.about.1.75 V (vs RHE) is preserved for 17 hours of the catalytic
water electrolysis (FIG. 11).
[0040] Meanwhile, a rich stream of oxygen bubble is also coming out
of FeO.sub.x--Ci surface as monitored by online GC. Further, the
current density is switched to a very high magnitude of 50 mA
cm.sup.-2 which is maintained at just .about.2.15 V (vs RHE) in
clean carbonate system (FIG. 11). Remarkably, the monitored
potentials 1.75 V and 2.15 V (vs RHE) to get these high current
densities for oxygen evolution are stable and sustained for long
time. In both instances, there is no noticeable potential change or
catalytic degradation during the water electrolysis test, which is
a direct indication of the stability and superior catalytic
performance of the FeO.sub.x--Ci electrocatalyst during
extended-period water electro oxidation. The chronopotentiometry
data is very impressive for electro catalytic FeO.sub.x--Ci system
representing its remarkable activity and stability in clean
electrolyte solution. For a recently reported FeOx derived
catalytic film (electrodeposited from Fe(II) in acetate solution),
controlled-potential water electrolysis at .about.1.76 V (vs RHE)
in a phosphate buffer (1.35 V; pH=7) to maintain a very small
current density of approximately 0.90 mA cm.sup.-2. During 10 h
water electrolysis, decrease in oxygen evolution current density is
also observed indicating the catalytic degradation of the Fe-oxide
material. This shows that FeO.sub.x--Ci is a new low over potential
and high activity Fe-based water oxidation electrocatalyst.
[0041] A comparative analysis of different Fe-oxide based water
oxidation eletrocatalysts and their electrochemical performance for
oxygen evolution is presented in Table 1. It is evident that
FeO.sub.x--Ci exhibits the lowest onset potential of 1.59 V vs RHE
(.eta.=360 mV) relative to other Fe-based catalysts. FeOOH type
Fe-catalyst exhibits the highest onset over potential, i.e >1.70
V vs RHE. We show that the benchmark current density of 10 mA
cm.sup.-2 is achieved at .eta..apprxeq.470 mV for FeO.sub.x--Ci
sample. Other Fe-oxide based catalysts exhibit much higher over
potentials to reach 10 mA cm.sup.-2. Surface-generated
FeO.sub.x--Ci system also shows the smallest Tafel Slope 47 mV
dec.sup.-1, which is again lowest in the list of Fe-based eletro
catalyst.
* * * * *