U.S. patent application number 12/229076 was filed with the patent office on 2009-09-24 for device and method for recovering catalyst for fuel cell.
This patent application is currently assigned to Hyundai Motor Company. Invention is credited to Byung Ki Ahn, Kook Il Han, Sae Hoon Kim.
Application Number | 20090235651 12/229076 |
Document ID | / |
Family ID | 41087536 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090235651 |
Kind Code |
A1 |
Kim; Sae Hoon ; et
al. |
September 24, 2009 |
Device and method for recovering catalyst for fuel cell
Abstract
The present invention provides a device and method for
recovering a catalyst for a fuel cell, in which a carbon nanotube
filter is provided in an air circulation loop of the fuel cell to
recover catalyst particles washed away from a catalyst layer of an
air electrode during operation of the fuel cell.
Inventors: |
Kim; Sae Hoon; (Gyeonggi-do,
KR) ; Ahn; Byung Ki; (Gyeonggi-do, KR) ; Han;
Kook Il; (Seoul, KR) |
Correspondence
Address: |
EDWARDS ANGELL PALMER & DODGE LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Assignee: |
Hyundai Motor Company
Seoul
KR
|
Family ID: |
41087536 |
Appl. No.: |
12/229076 |
Filed: |
August 19, 2008 |
Current U.S.
Class: |
60/295 |
Current CPC
Class: |
H01M 4/92 20130101; H01M
8/04089 20130101; H01M 8/0687 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
60/295 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2008 |
KR |
10-2008-0024666 |
Claims
1. A device for recovering a catalyst for a fuel cell, the device
comprising at least one filter means provided at a predetermined
position or positions in an air circulation loop of a fuel cell
stack to recover catalyst particles washed away from a catalyst
layer of an air electrode of the fuel cell stack.
2. The device of claim 1, wherein the catalyst contains
platinum.
3. The device of claim 1, wherein the filter means is a carbon
nanotube filter.
4. The device of claim 1, wherein the filter means is provided on
either or both an air supply line for supplying air to the air
electrode of the fuel cell stack and an air discharge line through
which reaction air is discharged from the air electrode.
5. The device of claim 4, wherein the catalyst contains
platinum.
6. The device of claim 4, wherein the filter means is a carbon
nanotube filter.
7. A method for recovering a catalyst for a fuel cell, the method
comprising: passing air discharged from an air electrode of a fuel
cell stack through a carbon nanotube filter; performing, at the
carbon nanotube filter, a spontaneous reduction of catalyst ions
and, at the same time, adsorbing reduced catalyst nanoparticles to
carbon nanotubes to be recovered; introducing the air passing
through the carbon nanotube filter and containing a small amount of
catalyst ions into a humidifier; and mixing, at the humidifier, the
small amount of catalyst ions with water and supplying the mixture
to the fuel cell stack together with fresh air.
8. The device of claim 4, wherein the catalyst comprises platinum.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims under 35 U.S.C. .sctn.119(a) the
benefit of Korean Patent Application No. 10-2008-0024666 filed Mar.
18, 2008, the entire contents of which are incorporated herein by
reference.
BACKGROUND
[0002] (a) Technical Field
[0003] The present invention relates to a device for recovering a
catalyst for a fuel cell. More particularly, the present invention
relates to a device and method for recovering a catalyst for a fuel
cell, in which a carbon nanotube filter is provided in an air
circulation loop of the fuel cell to recover platinum catalyst
particles washed away from a catalyst layer of an air electrode
during operation of the fuel cell.
[0004] (b) Background Art
[0005] Generally, a fuel cell is a device that generates electrical
energy through an electrochemical reaction between hydrogen
(H.sub.2) and oxygen (O.sub.2) and includes a membrane electrode
assembly (MEA). The MEA includes a fuel electrode (anode) as an
electrode catalyst layer to which hydrogen is supplied, and an air
electrode (cathode) as an electrode catalyst layer to which air is
supplied, with an electrolyte membrane, where hydrogen ions
(H.sup.+) are transmitted, interposed therebetween. The MEA further
includes a gas diffusion layer (GDL) disposed on the outside of the
anode and the cathode, respectively.
[0006] Accordingly, electrical energy is generated by an
electrochemical reaction occurring when hydrogen as a fuel or a
mixed gas containing a large amount of hydrogen is supplied to one
of the electrode catalyst layers (anode, fuel electrode, or
hydrogen electrode), and oxygen or air containing oxygen is
supplied to the other electrode catalyst layer (cathode, air
electrode, or oxygen electrode).
[0007] That is, the hydrogen supplied to the fuel electrode is
dissociated into hydrogen ions (H.sup.+) and electrons (e.sup.-).
The dissociated hydrogen ions move to the air electrode through the
electrolyte membrane and, at the air electrode, the hydrogen ions
(H.sup.+) transferred from the fuel electrode combine with the
electrons (e.sup.-) transferred through an external conducting wire
and oxygen supplied to the air electrode to produce water and heat
at the same time, thus generating electrical energy.
[0008] A fuel cell system based on the above-described principle of
electricity generation includes a fuel cell stack for generating
electrical energy, a fuel supply system (hydrogen tank, hydrogen
recirculation line, etc.) for supplying fuel (hydrogen) to the fuel
cell stack, an air supply system (air supplier, membrane
humidifier, etc.) for providing oxygen in the air, which is an
oxidizer required for the electrochemical reaction, to the fuel
cell stack, and a thermal management system (coolant pump,
radiator, etc.) for removing the reaction heat of the fuel cell
stack to the outside of the system and controlling the operation
temperature of the fuel cell stack.
[0009] In particular, the air supply system includes an air blower
for introducing fresh air from outside, an air supply line
connected between an outlet of the air blower and an inlet of the
air electrode of the fuel cell stack, a humidifier provided on the
air supply line to humidify the fresh air (dry air), and an air
discharge line through which the air after the reaction is
discharged from the air electrode of the fuel cell stack to the
humidifier.
[0010] Accordingly, the fresh air (dry air) introduced into the air
supply system by the air blower is humidified by the humidifier,
and then the humidified air is supplied to the air electrode of the
fuel cell stack through the air supply line.
[0011] As a result, the oxygen supplied to the air electrode
combines with the hydrogen ions (H.sup.+) transferred from the fuel
electrode and the electrons (e.sup.-) transferred through an
external conducting wire to produce water and heat at the same
time, thus generating electrical energy.
[0012] However, there is a problem in that catalyst particles
(e.g., particles containing platinum (Pt)) may be washed away from
the air electrode, i.e., the electrode catalyst layer, during a
long-term operation of the fuel cell stack.
[0013] That is, carbon corrosion occurs during the operation of the
fuel cell stack and, especially, the catalyst is washed away from
the catalyst layer of the air electrode during the long-term
operation of the fuel cell stack.
[0014] FIG. 1 are microphotographs of a fresh MEA containing
platinum as a catalyst and the MEA after being used for about 1500
hours. The fresh MEA shows no catalyst loss. In contrast, the used
MEA shows a catalyst loss; that is the thickness of the electrode
catalyst layer is reduced due to the catalyst loss from the
catalyst layer of the air electrode after the long-term operation
of the fuel cell stack.
[0015] Since the platinum of the catalyst layer of the air
electrode is washed away in the form of ions, the platinum is
drained away to the outside and thus cannot be recovered. As a
result, it is not possible to recycle the platinum after mass
production of the fuel cell vehicle.
[0016] The reason that the catalyst is washed away during the
operation of the fuel cell will be described in detail below.
[0017] When the start-up and shut-down of the fuel cell are
repeated for a long time, a carbon carrier in the catalyst layer of
the air electrode, as shown in the dotted line box of FIG. 2, is
oxidized and, at the same time, the platinum (Pt) is oxidized in
the form of PtO.sub.X. At this time, since there are plentiful
humidification water and product water in the corresponding air
electrode as a result of the reaction, the platinum (Pt) may be
eluted in an aqueous solution.
[0018] Like this, when the platinum of the electrode catalyst layer
is washed away due to the repetition of the start-up and shut-down
for a long time, the MEA itself is damaged, and accordingly the
cell voltage is continuously lowered as shown in the graph of FIG.
3, thus deteriorating the performance of the fuel cell.
[0019] The above information disclosed in this Background section
is only for enhancement of understanding of the background of the
invention and therefore it may contain information that does not
form the prior art that is already known in this country to a
person of ordinary skill in the art.
SUMMARY OF THE DISCLOSURE
[0020] Accordingly, the present invention has been made in an
effort to solve the above-described drawbacks.
[0021] In one aspect, the present invention provides a device for
recovering a catalyst for a fuel cell, the device comprising at
least one filter means provided at a predetermined position or
positions of an air circulation loop of a fuel cell stack to
recover catalyst particles washed away from a catalyst layer of an
air electrode of the fuel cell stack.
[0022] In another aspect, the present invention provides a method
for recovering a catalyst for a fuel cell, the method comprising:
passing air discharged from an air electrode of a fuel cell stack
through a carbon nanotube filter; performing, at the carbon
nanotube filter, a spontaneous reduction of catalyst ions and, at
the same time, adsorbing reduced catalyst nanoparticles to carbon
nanotubes to be recovered; introducing the air passing through the
carbon nanotube filter and containing a small amount of catalyst
ions into a humidifier; and mixing, at the humidifier, the small
amount of catalyst ions with water and supplying the mixture to the
fuel cell stack together with fresh air.
[0023] It is understood that the term "vehicle" or "vehicular" or
other similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like.
[0024] The above and other features and advantages of the present
invention will be apparent from or are set forth in more detail in
the accompanying drawings, which are incorporated in and form a
part of this specification, and the following Detailed Description,
which together serve to explain by way of example the principles of
the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above and other features of the present invention will
now be described in detail with reference to certain exemplary
embodiments thereof illustrated the accompanying drawings which are
given hereinafter by way of illustration only, and thus are not
limitative of the present invention, and wherein:
[0026] FIG. 1 are microphotographs showing that a catalyst layer of
an air electrode is washed away from an MEA after a long-term
operation in comparison with a fresh MEA;
[0027] FIG. 2 is a schematic diagram of a fuel cell stack;
[0028] FIG. 3 is a graph illustrating that a cell voltage is
continuously lowered after a long-term operation of the MEA;
[0029] FIG. 4 is a schematic diagram showing a device for
recovering a catalyst for a fuel cell in accordance with the
present invention; and
[0030] FIG. 5 is a flowchart illustrating a method for recovering a
catalyst for a fuel cell in accordance with the present
invention.
[0031] Reference numerals set forth in the Drawings includes
reference to the following elements as further discussed below:
TABLE-US-00001 10: fuel cell stack 12: air blower 14: air electrode
(cathode) 16: air supply line 18: humidifier 20: air discharge line
22: carbon nanotube filter 24: exhaust line
[0032] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the invention. The specific design features of
the present invention as disclosed herein, including, for example,
specific dimensions, orientations, locations, and shapes will be
determined in part by the particular intended application and use
environment.
DETAILED DESCRIPTION
[0033] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the drawings attached hereinafter, wherein like
reference numerals refer to like elements throughout. The
embodiments are described below so as to explain the present
invention by referring to the figures.
[0034] FIG. 5 is a flowchart illustrating a method for recovering a
catalyst for a fuel cell in accordance with the present invention.
In the illustrated fuel cell, platinum is used as a catalyst. It
should be noted that the method for recovering a catalyst can be
applied to the fuel cell systems containing other catalysts than
platinum.
[0035] An air supply system of a fuel cell includes an air blower
12 for introducing fresh air from outside, an air supply line 16
connected between an outlet of the air blower 12 and an inlet of an
air electrode 14 of a fuel cell stack 10, a humidifier 18 disposed
on the air supply line 16 and humidifying the fresh air (dry air),
and an air discharge line 20 through which the air after the
reaction is discharged from the air electrode 14 of the fuel cell
stack 10 to the humidifier 18.
[0036] Accordingly, the fresh air (dry air) introduced into the air
supply system by the air blower 12 is humidified by the humidifier
18, and then the humidified air is supplied to the air electrode 14
of the fuel cell stack 10 through the air supply line 16.
Subsequently, the air after the reaction at the air electrode 14 of
the fuel cell stack 10 is discharged to the humidifier 18 along the
air discharge line 20 together with product water.
[0037] A filter means, which can recover the platinum catalyst
particles washed away from the catalyst layer of the air electrode
14 of the fuel cell stack 10, is provided at a position in an air
circulation loop of the fuel cell stack 10.
[0038] The filter means is a carbon nanotube filter 22, in which
single-walled carbon nanotubes or multi-walled carbon nanotubes are
filled. The carbon nanotube filter 22 may be provided on either or
both the air supply line 16 and the air discharge line 20.
[0039] For reference, the carbon nanotube has a graphite structure
consisting of carbon atoms and has electrical conductivity since
p-orbital electrons around the carbon atoms are arranged in the
shape of a plate like free electrons of a metal. On the other hand,
since all bonding electrons are bonded in a diamond structure,
differently from the graphite structure, the carbon nanotube has no
electrical conductivity. As an atomic orbital of the carbon atom
forming the graphite structure, p-orbitals shown in red are
arranged in a line between atoms and form Tr bonding orbitals, thus
having electrical conductivity. In the carbon nanotubes having the
above-described atom and electron arrangements, a nanotube having a
graphite plane is called a single-walled carbon nanotube (SWNT) and
a nanotube having at least two graphite planes is called a
multi-walled carbon nanotube (MWNT).
[0040] The operation of recovering the washed platinum catalyst
particles by the carbon nanotube filter will be described in detail
below.
[0041] The oxygen supplied to the air electrode 14 of the fuel cell
stack 10 combines with the hydrogen ions (H.sup.+) transferred from
the fuel electrode and the electrons (e.sup.-) transferred through
an external conducting wire to produce water and heat at the same
time, thus generating electrical energy.
[0042] During the long-term operation of the fuel cell stack 10,
the platinum (Pt) catalyst is washed away from the air electrode
14, i.e., the electrode catalyst layer, and the Pt catalyst
dissolved in water is mixed with the air discharged from the air
electrode 14 after the reaction.
[0043] Accordingly, when the air including excessive air, water,
and dissolved Pt ions and discharged from the air electrode 14 of
the fuel cell stack 10 is supplied through the air discharge line
20, it passes through the carbon nanotube filter 22 provided on the
air discharge line 20.
[0044] At this time, the Pt ions are reduced to the carbon
nanotubes by a spontaneous reduction in the carbon nanotube filter
22, and thus the reduced Pt nanoparticles are adsorbed to the
carbon nanotubes and recovered.
[0045] That is, the Pt nanoparticles are adsorbed to the surface of
the carbon nanotubes and recovered.
[0046] Subsequently, the exhaust air passing through the carbon
nanotube filter 22 and containing a small amount of Pt ions is
introduced into the humidifier 18 along the air discharge line
20.
[0047] The small amount of Pt ions mixed with water is supplied to
the air electrode 14 of the fuel cell stack 10 together with fresh
air (humidification air) supplied to the inside of the humidifier
18 by the air blower 12.
[0048] In this case, when the exhaust air passing through the
carbon nanotube filter 22 is introduced into the humidifier 18
having the function of a gas-liquid separator along the air
discharge line 20, an excessive amount of air and a portion of
water vapor are discharged to the outside through an exhaust line
24 of the humidifier 18. However, since the Pt ions have a low
vapor pressure, they are mixed with water in the humidifier 18 and
returned to the air electrode 14 of the fuel cell stack 10.
[0049] Thus, since the Pt ions are repeatedly circulated between
the air electrode 14 of the fuel cell stack 10 and the humidifier
18, the Pt ions may be easily adsorbed to the carbon nanotube
filter 22.
[0050] That is, since the elution rate of the Pt during the
operation of the fuel cell stack 10 is not so much high, a small
amount of Pt ions may be continuously detected, and thus the Pt
ions can be recovered by the repetitive circulation between the air
electrode 14 of the fuel cell stack 10 and the humidifier 18.
[0051] As a result, it is possible to readily recover the platinum
particles washed away from the air electrode of the fuel cell stack
using the carbon nanotubes of the carbon nanotube filter. That is,
assuming that the efficiency of the filter is 100%, if the amount
of platinum used at the air electrode is about 56 g and half of the
platinum is washed away after a long-term operation, it is possible
to recover the platinum in an amount of 28 g per unit.
[0052] As described above, according to the present invention, it
is possible to recover and reuse the catalyst in a simple and
cost-effective manner and without the use of a peripheral power
source.
[0053] The invention has been described in detail with reference to
preferred embodiments thereof. However, it will be appreciated by
those skilled in the art that changes may be made in these
embodiments without departing from the principles and spirit of the
invention, the scope of which is defined in the appended claims and
their equivalents.
* * * * *