U.S. patent application number 11/752897 was filed with the patent office on 2007-10-04 for method for catalytic surface protection.
This patent application is currently assigned to MIDWEST RESEARCH INSTITUTE. Invention is credited to Se-Hee Lee, Ping Liu, J. Roland Pitts, C. Edwin Tracy.
Application Number | 20070231466 11/752897 |
Document ID | / |
Family ID | 37766252 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070231466 |
Kind Code |
A1 |
Liu; Ping ; et al. |
October 4, 2007 |
Method for Catalytic Surface Protection
Abstract
A method for protecting catalytic metal-based sensor for sensing
the presence of hydrogen in an environment comprising, depositing a
protective layer on said sensor, said protective layer being
permeable to hydrogen.
Inventors: |
Liu; Ping; (Irvine, CA)
; Pitts; J. Roland; (Lakewood, CO) ; Lee;
Se-Hee; (Lakewood, CO) ; Tracy; C. Edwin;
(Golden, CO) |
Correspondence
Address: |
PAUL J WHITE, SENIOR COUNSEL;NATIONAL RENEWABLE ENERGY LABORATORY (NREL)
1617 COLE BOULEVARD
GOLDEN
CO
80401-3393
US
|
Assignee: |
MIDWEST RESEARCH INSTITUTE
425 Volker Boulevard
Kansas City
MO
64110
|
Family ID: |
37766252 |
Appl. No.: |
11/752897 |
Filed: |
May 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11161874 |
Aug 19, 2005 |
7233034 |
|
|
11752897 |
May 23, 2007 |
|
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Current U.S.
Class: |
427/58 |
Current CPC
Class: |
H01M 2004/8684 20130101;
H01M 4/96 20130101; G01N 33/005 20130101; H01M 4/92 20130101; G01N
31/22 20130101; H01M 4/8657 20130101; Y10T 436/22 20150115; H01M
4/8867 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
427/058 |
International
Class: |
B05D 5/12 20060101
B05D005/12 |
Goverment Interests
CONTRACTUAL ORIGIN
[0002] The United States Government has rights in this invention
under Contract No. DEA36-99GO10337 between the U.S. Department of
Energy and the National Renewable Energy Laboratory, a Division of
Midwest Research Institute.
Claims
1. A method for protecting a catalytic metal-based sensor for
sensing the presence of hydrogen in an environment comprising
depositing a protective layer on said sensor, said protective layer
being permeable to hydrogen.
2. The method as defined by claim 1, wherein said protective layer
is deposited at room temperature.
3. The method as defined by claim 1, wherein said protective
material is a carbon material.
4. The method as defined by claim 3, wherein said carbon material
is amorphous.
5. The method as defined by claim 1, wherein said protective layer
is deposited using a vapor deposition process.
6. The method as defined by claim 5, wherein said deposition
process is plasma enhanced chemical vapor deposition process.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S. patent
application Ser. No. 11/161,874, filed on Aug. 19, 2005.
TECHNICAL FIELD
[0003] A hydrogen permeable protective coating for a surface,
preferably a catalytic metal-based surface, wherein the
dissociation of hydrogen into atomic hydrogen is preserved, namely,
the catalytic activity is allowed to proceed without contamination.
One such embodiment includes a protective coating for a catalytic
metal-based surface (e.g., a sensor or other detecting device for
sensing the presence of a hydrogen gas. More particularly, a
protective coating for a catalytic metal-based hydrogen sensor
having a hydrogen, catalyst palladium (Pd) layer, (however, the
layer may also comprise or be composed of platinum group metals and
their alloys, e.g., palladium copper alloys and palladium silver
alloys.) Another embodiment includes applications to the catalytic
activity of platinum group metal surfaces involving hydrogen
dissociation for fuel cell anodes.
BACKGROUND
[0004] Hydrogen gas is clean, non-polluting fuel and chemical
reagent, which is currently used in many industries. With the
demand for hydrogen growing every year and the fact the hydrogen is
explosive at only a four (4%) percent concentration in air, the
ability to detect hydrogen gas leaks economically and with inherent
safety is desirable and could facilitate commercial acceptance of
hydrogen fuel in various applications. For example, hydrogen-fueled
passenger vehicles will require hydrogen leak detectors to signal
the activation of safety devices such as shutoff valves,
ventilating fans, and alarms. In fact, such detectors will be
required in several key locations within a vehicle--namely,
wherever a leak could pose a safety hazard. Therefore, it is
critically important to carefully measure, monitor, and strictly
control hydrogen wherever and whenever it is used.
[0005] The real and perceived hazards of hydrogen fuel use, its
production, and storage require extensive safety precautions.
Local, state and federal codes must be put in place before any
serious movement can be made towards a hydrogen based energy
future. Currently, commercial hydrogen detectors are not practical
for widespread use, particularly in transportation industry
applications, because commercial detectors are too bulky,
expensive, and dangerous.
[0006] There exist several hydrogen sensors having a palladium
layer that is particularly attractive for transportation industry
applications. These hydrogen sensors are termed Hydrogen Field
Effect Transistors (HFET), thick film (e.g., incorporating a
palladium alloy paste), thin film, and fiber optic. The HFET
construction uses a thin film of Pd as the metal contact
controlling the device. The presence of hydrogen results in the
migration of atomic hydrogen to the interface between the metal
film and the insulator, which results in change in the output of
the device that is scaled to the hydrogen concentration. The thick
film device uses a thick film Pd alloy paste to form a
four-resistor network (i.e., a Wheatstone bridge) on a ceramic
substrate. The configuration is such that two opposed resistors
result in a change in resistivity of the thick film material and a
shift in the balance point of the bridge, which can be scaled to
the hydrogen concentration. The thin film device is equivalent in
design to the thick film, with only much thinner films (typically
vacuum deposited) used as the resistors.
[0007] The fiber optic hydrogen sensor is a gasochromic-type (i.e.,
one that changes color when activated by hydrogen) sensor and is
available in a variety of configurations with coatings, typically
either palladium or platinum, at the end of an optical fiber that
sense the presence of hydrogen in air. When the coating reacts with
hydrogen, the optical properties of the coating are changed. Light
from a central electro-optic control unit is projected down the
optical fiber where the light is either reflected from the sensor
coating back to a central optical detector, or is transmitted to
another fiber leading to the central optical detector. A change in
the reflected or transmitted intensity indicates the presence of
hydrogen. While the fiber optic detector offers inherent safety by
removing the application of electrical power and by reducing
signal-processing problems by minimizing electromagnetic
interference, critical detector performance requirements (i.e., for
all four configurations described above) include high selectivity,
response speed, and durability as well as potential for low-cost
fabrication. The optical senor is not necessarily limited to a
fiber optic delivery system but may be included on any optical
element.
[0008] Unfortunately, all of the conventional catalytic metal-based
hydrogen sensors have the potential for degradation in their
performance over time due to mechanisms that are inherent in their
construction, a result of their cyclic interaction with hydrogen,
or contamination from impurities in the environments in which they
will be used, While various attempts have been made to protect the
palladium or platinum catalytic surfaces, these attempts have not
significantly improved sensor performance. Therefore, a need exists
to limit degradation thereby allowing hydrogen sensors to operate
over extended periods of time in the presence of contaminants.
[0009] Another application is in the proton electrolyte membrane
(PEM) fuel cell. This fuel cell is an electrochemical device that
produces electricity from a combined chemical reaction and
electrical charge transport. The device uses a simple chemical
process to combine hydrogen and oxygen into water, producing an
electric current in the process. At the anode, hydrogen molecules
are dissociated by a metallic catalyst (usually platinum) into
hydrogen atoms, which eventually gives up electrons to form
hydrogen ions. The electrons travel through an external circuit to
produce usable electric energy while the hydrogen ions are
transported internally to the cathode where they both combine with
oxygen to form water. The platinum catalyst of the fuel cell anode
is subject to degradation by contaminants similar to that of
catalytic metal-based hydrogen sensor. Application of a protective
coating to the surface of the anode of the platinum catalyst to
prevent fouling and maintain the catalytic activity of hydrogen
dissociation is advantageous to fuel cell performance.
[0010] The foregoing examples of the related art and limitations
related therewith are intended to be illustrative an not exclusive.
Other limitations of the related art will become apparent to those
of skill in the art upon a reading of the specification and a study
of the drawing.
SUMMARY
[0011] The following embodiments and aspects thereof are described
and illustrated in conjunction with systems, tools and methods that
are meant to be exemplary and illustrative, not limiting scope. In
various embodiments, one or more of the above-described problems
have been reduced or eliminated, while other embodiments are
directed to other improvements.
[0012] An exemplary, preferably amorphous (i.e., a lack of
long-range crystalline order) hydrogen permeable protective coating
for catalytic metal surfaces is disclosed. This exemplary
embodiment has unique and novel application for sensing the
presence of hydrogen gas in an environment. The exemplary coating
material comprises a layer permeable to hydrogen with the layer
being deposited on a surface, for example, a sensor between the
metal catalyst layer and the environment.
[0013] Accordingly, an exemplary protective coating for a surface
comprises a layer permeable to hydrogen, the coating being
deposited on a catalyst layer, wherein the catalytic activity of
the catalyst layer is preserved. In the disclosed exemplary
protective coating for the catalyst layer is a carbon material
which is preferably amorphous; it may be deposited using a vapor
deposition process, preferably a plasma enhanced chemical vapor
deposition process and the protective coating is preferably
deposited at room temperature. The catalyst layer is composed of
platinum group metals, and/or platinum group metals and their
alloys. The exemplary protective coating further includes a
chromogenic layer underlying the catalyst layer; and a substrate
layer underlying the chromogenic layer. However, it will be
apparent to those skilled in the art that the protective layer may
be understood to overlie the catalyst layer. Under these
circumstances the catalyst layer would accordingly overlie the
chromogenic layer; and the chromogenic layer would overlie a
substrate layer.
[0014] Additionally, a sensor for sensing the presence of hydrogen
gas in an environment is disclosed, comprising: a protective layer
permeable to hydrogen; a catalyst layer deposited on said
protective layer; a chromogenic layer deposited on said catalyst
layer; and a substrate layer deposited on said chromogenic lawyer,
wherein the catalytic activity of the catalyst layer is
preserved.
[0015] Further, an exemplary method for protecting catalytic
metal-based sensor for sensing the presence of hydrogen in an
environment is disclosed by depositing a protective layer on the
sensor, wherein protective layer is permeable to hydrogen.
[0016] In addition to the exemplary aspects and embodiments
described above, further aspects and embodiments will become
apparent by reference to the drawings and by study of the following
descriptions.
BRIEF DESCRIPTION OF THE DRAWING
[0017] An exemplary embodiment is illustrated in the referenced
figure of the drawing. It is intended that the embodiment and
figure disclosed herein is to be considered illustrative rather
than limiting.
[0018] FIG. 1 is a sectional view of an exemplary protective
coating for a catalytic metal-based hydrogen sensor.
DETAIL DESCRIPTION
[0019] As illustrated in FIG. 1, an exemplary protective coating
(material or layer), indicated generally as 10, for catalytic metal
(including gasochromic) sensor 12 is used sensing the presence of
hydrogen gas (as indicated by the arrow). While sensor 12 can
detect different types of gas on a surface or in an environment,
including, but not limited to, rooms buildings, chemical process
plants, refineries, etc., the construction and design of senor 12
especially suits the sensing of hydrogen leaks in hydrogen-fueled
vehicles or similar applications. Therefore, in discussing
exemplary protective coating 10 of sensor 12, applicants will
particularly describe sensor 12 in conjunction with transportation
(namely, vehicle) use. It should be noted, however, that any
variety of catalytic metal-based sensors including, but not limited
to, HFET, thick film, thin film, and fiber optic sensors, are
envisioned and contemplated by those skilled in the art.
[0020] The sensor 12 has a substrate layer 14, a chromogenic layer
16, and a catalyst layer 18. The catalyst layer 18 underlies
protective coating layer 10; chromogenic layer 16 underlies
catalyst layer 18; and substrate layer 14 underlies chromogenic
layer 16. The catalyst layer 18 is preferably composed or comprised
of palladium, platinum, or their alloys, such that when exposed to
the atmosphere it is reactable to the presence of hydrogen in the
environment. While catalyst layer 18 has been described as being
comprised of palladium, platinum, or their alloys, catalyst layer
18 may be composed of other appropriate materials for example, the
platinum group metals (platinum, palladium, rhodium iridium,
ruthenium, and osmium). Moreover, many of their alloys are
exceptionally good catalysts as will be apparent to those skilled
in the art. Among these, palladium and is alloys work exceptionally
well for applications in hydrogen sensors, because of their ability
to dissociate molecular hydrogen and their very high diffusion
constants for atomic hydrogen, allowing rapid transport through or
to the sensing element and/or material.
[0021] During the sensing operations of sensor 12 in an
environment, the reaction between the hydrogen gas and chromogenic
layer 16 or the catalyst layer 18 changes the chromogenic layer or
the catalyst layer (or both) material's optical properties allowing
sensor 12 to sense the presence of hydrogen. Protection of the
chromogenic layer 16 and catalyst layer 18 from any contaminants.
present in the environment (while simultaneously allowing hydrogen
permeation) is important for the detection of hydrogen gas in the
environment. If the chromogenic layer 16 or the catalyst layer 18
is comprised (e.g., the catalytic hydrogen dissociation sites on
the surface of the catalyst becomes poisoned) by contaminants,
sensor 12 will fail to function properly leading to the possible
failure of hydrogen gas detection in the environment.
[0022] Therefore, protective coating 10 is both a protective (i.e.,
shielding) and hydrogen permeable layer deposited on the catalyst
layer 18 to protect the chromogenic layer 16 and the catalyst layer
18 of sensor 12. Preferably, the protective coating 10 is a
hydrogen permeable carbon coating deposited on the catalyst layer
18 by using any number of vapor deposition processes, however, the
preferred method is a plasma-enhanced chemical vapor deposition
processes, preferable at room temperature. As an example of the
plasma-enhanced chemical vapor deposition process, the radio
frequency (RF) is 150 W, the substrate 14 temperature is thirty
(30.degree.) degrees C; the system pressure is 0.6 torr. Ethylene
is the processing gas and the flow rate is twenty (20) sccm. Once
deposited, the protective carbon coating 10 possess the
characteristics of an amorphous structure, which is permeable to
hydrogen but filters the environment's air prior to any
contaminants reaching the chromogenic layer 16 and catalyst layer
18. Those skilled in the art will appreciate that a wide variety of
system parameters (power, pressure, temperature, etc.) will result
in variety of successful coatings.
[0023] As will be understood by a person skilled in the art, the
protective coating 10 can be deposited or applied to catalyst layer
18 by a variety of techniques at variety of temperatures.
Describing the protective coating 10 as being deposited on the
catalytic layer 18 by a chemical vapor deposition technique at room
temperature is only one of many different deposition techniques and
other techniques will be apparent to those skilled in the art.
[0024] The carbon coating 10 is permeable to hydrogen but can act
effectively as a diffusion barrier to contaminant gas molecules,
such as hydrocarbon, carbon monoxide, and sulfur-bearing gases,
including others. Application of the protective carbon coating 10
to the palladium or platinum catalytic layer 18 of sensor 12
greatly improves the stability and durability of the sensor with a
minimum compromise or degradation in sensor performance. It should
be noted that the carbon coating 10 is also applicable to protect
gas separation devices having platinum group metals or their alloys
as the catalytic and/or functional layer.
[0025] The protective coating 10 extends or increases the lifetime
of sensor 12 in the presence of harmful contaminants and provides
effective protection of palladium- and platinum-based hydrogen
sensors. In fact, the protective coating 10 is also applicable
wherever a platinum group metal or alloy layer is used and is use
is not limited to gasochromic hydrogen sensors.
[0026] While a numbers of exemplary aspects and embodiments have
been discussed above, those of skill in the art will recognize
certain modifications, permutations, additions and sub combinations
thereof. It is therefore intended that the following appended
claims and claims hereafter introduced are interpreted to include
all such modifications, permutations. additions and
sub-combinations as are within their true spirit and scope.
* * * * *