U.S. patent application number 11/028765 was filed with the patent office on 2005-07-07 for electrode structure.
Invention is credited to Cooper, Susan Joy, Hoogers, Gregor.
Application Number | 20050147867 11/028765 |
Document ID | / |
Family ID | 10843817 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050147867 |
Kind Code |
A1 |
Cooper, Susan Joy ; et
al. |
July 7, 2005 |
Electrode structure
Abstract
A poison tolerant anode structure for use in fuel cells, in
particular suitable for use on proton exchange membrane fuel cells,
comprising a first catalytic component Pt--Y where Y is a bronze
forming element, and optionally a third metal X alloyed with the
platinum, and a second catalytic component Pt-M where M, metal, is
alloyed with the platinum. An anode, a catalysed membrane, a
membrane electrode assembly and a fuel cell comprising the
electrode structure, are disclosed.
Inventors: |
Cooper, Susan Joy; (Reading,
GB) ; Hoogers, Gregor; (Birkenfeld, DE) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
10843817 |
Appl. No.: |
11/028765 |
Filed: |
January 4, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11028765 |
Jan 4, 2005 |
|
|
|
09857759 |
Sep 10, 2001 |
|
|
|
6855452 |
|
|
|
|
09857759 |
Sep 10, 2001 |
|
|
|
PCT/GB99/04081 |
Dec 9, 1999 |
|
|
|
Current U.S.
Class: |
429/480 ;
429/483; 429/524; 429/534 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01M 4/921 20130101; H01M 8/1004 20130101; H01M 2300/0082
20130101 |
Class at
Publication: |
429/040 ;
429/044; 429/030 |
International
Class: |
H01M 004/90; H01M
004/92; H01M 008/10; H01M 004/94 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 1998 |
GB |
9826940.0 |
Claims
What is claimed:
1. An electrode structure comprising a first catalytic component
and a second catalytic component, wherein: (a) said first catalytic
component comprises one or more electrocatalyst(s) comprising a
formula Pt--Y, wherein Y is Mo, W or an oxide of Mo or W; and (b)
said second catalytic component comprises one or more
electrocatalyst(s) comprising a formula Pt-M, where M is a metal
alloyed with the platinum and is one or more metals selected from
the group consisting of Ru, Rh, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr,
Hf and Sn; and wherein the first and second catalytic components
are formulated into one mixed layer and are in ionic contact with
each other.
2. An electrode structure according to claim 1, wherein M is
selected from Ru or Rh.
3. An electrode structure according to claim 1, wherein the first
catalytic component is selected from the group consisting of:
Pt/Mo, Pt/Mo/Co, Pt/W/Co, Pt/Ru/WO.sub.3 and Pt/Ti/W; and the
second catalytic component is Pt/Ru.
4. An electrode comprising an electrode structure according to
claim 1 wherein the electrocatalyst materials are present on one
side of a gas diffusion material.
5. A catalysed membrane comprising an electrode structure according
to claim 1 wherein the electrocatalyst materials are present on one
side of a polymer electrolyte membrane material.
6. An MEA comprising an electrode structure according to claim
1.
7. A fuel cell comprising an electrode structure, comprising a
first catalytic component and a second catalytic component,
characterised in that the first catalytic component comprises one
or more electrocatalyst(s) comprising a formula Pt--Y where Y is
Mo, W, or an oxide of Mo or W, and the second catalytic component
comprises one or more electrocatalyst(s) comprising a formula Pt-M,
where M is a metal alloyed with the platinum and is one or more
metals selected from the group consisting of Ru, Rh, Ti, Cr, Mn,
Fe, Co, Ni, Cu, Ga, Zr, Hf and Sn, and wherein the first and second
catalytic components are formulated into one mixed layer and are in
ionic contact with each other.
8. An electrode structure according to claim 1 wherein said first
catalytic component comprises a third metal component X which is
alloyed with the platinum and which is one or more metals selected
from the group consisting of Ru, Rh, Ti, Cr, Mn, Fe, Co, Ni, Cu,
Ga, Zr, Hf and Sn.
9. An electrode structure according to claim 8 wherein X is
selected from the group consisting of Ru, Mn, Co, Ni, and Rh.
10. A fuel cell according to claim 8 wherein said first catalytic
component comprises a third metal component X which is alloyed with
the platinum and which is one or more metals selected from the
group consisting of Ru, Rh, Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Hf
and Sn.
11. The electrode structure according to claim 1 wherein Y is Mo
and M is Ru.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/857,759, filed Sep. 10, 2001 (which is
incorporated by reference herein, in its entirety), which is the
U.S. national phase application of International Application No.
PCT/GB99/04081, filed Dec. 9, 1999, and claims priority of British
Application No. 9826940.0, filed Dec. 9, 1998.
[0002] The invention relates to an improved electrode structure and
specifically to a poison-tolerant anode structure for fuel cells,
suitable for use in particular in proton exchange membrane fuel
cells. The invention further relates to an anode, a catalysed
membrane, a membrane electrode assembly and a fuel cell comprising
an electrode structure.
[0003] Electrochemical cells invariably comprise at their
fundamental level a solid or liquid electrolyte and two electrodes,
the anode and cathode, at which the desired electrochemical
reactions take place. A fuel cell is an energy conversion device
that efficiently converts the stored energy of its fuel into
electrical energy by combining hydrogen, stored as a gas, or
methanol, stored as a liquid or gas, with oxygen to generate
electrical power. The hydrogen or methanol is oxidised at the anode
and oxygen reduced at the cathode. In these cells gaseous reactants
and/or products have to be diffused into and/or out of the cell
electrode structures. The electrodes therefore are specifically
designed to be porous to gas diffusion in order to optimise the
contact between the reactants and the reaction sites in the
electrode to maximise the reaction rate. An electrolyte is required
which is in contact with both electrodes and which may be alkaline
or acidic, liquid or solid. In a solid polymer fuel cell (SPFC),
also known as a proton-exchange membrane fuel cell (PEMFC), the
electrolyte is a solid proton-conducting polymer membrane, commonly
based on perfluorosulphonic acid materials. These electrolytes must
be maintained in a hydrated form during operation in order to
prevent loss of ionic conduction through the electrolyte; this
limits the operating temperature of the PEMFC to between 70.degree.
C. and 120.degree. C., depending on the operating pressure. The
PEMFC does, however, provide much higher power density output than
the other fuel cell types, and can operate efficiently at much
lower temperatures. Because of this, it is envisaged that the PEMFC
will find use in vehicular power generation and small-scale
residential power generation applications. In particular, vehicle
zero-emission regulations have been passed in areas of the United
States that are likely to restrict the use of the combustion engine
in the future. Pre-commercial PEMFC-powered buses and prototype
PEMFC-powered vehicles are now being demonstrated for these
applications.
[0004] Due to the relatively low operating temperatures of these
systems, the oxidation and reduction reactions require the use of
catalysts in order to proceed at useful rates.
[0005] Catalysts, which promote the rates of electrochemical
reactions, such as oxygen reduction and hydrogen oxidation in a
fuel cell, are often referred to as electrocatalysts.
[0006] Precious metals, in particular platinum, have been found to
be the most efficient and stable electrocatalysts for all
low-temperature fuel cells operating below 300.degree. C. The
platinum electrocatalyst is provided as very small particles
(.about.20-50 .ANG.) of high surface area, which are often, but not
always, distributed on and supported by larger macroscopic
conducting carbon particles to provide a desired catalyst loading.
Conducting carbons are the preferred materials to support the
catalyst.
[0007] In the PEMFC the combined laminate unit formed from the
membrane and the two electrodes is known as a membrane electrode
assembly (MEA). The MEA will typically comprise several layers, but
can in general be considered, at its basic level, to have five
layers, which are defined principally by their function. On either
side of the membrane an anode and cathode electrocatalyst is
incorporated to increase the rates of the desired electrode
reactions. In contact with the electrocatalyst containing layers,
on the opposite face to that in contact with the membrane, are the
anode and cathode gas diffusion substrate layers. The anode gas
diffusion substrate is designed to be porous and to allow the
reactant hydrogen or methanol to enter from the face of the
substrate exposed to the reactant fuel supply, and then to diffuse
through the thickness of the substrate to the layer which contains
the electrocatalyst, usually platinum metal based, to maximise the
electrochemical oxidation of hydrogen or methanol. The anode
electrocatalyst layer is also designed to comprise some level of
the proton conducting electrolyte in contact with the same
electrocatalyst reaction sites. With acidic electrolyte types the
product of the anode reaction are protons and these can then be
efficiently transported from the anode reaction sites through the
electrolyte to the cathode layers. The cathode is also designed to
be porous and to allow oxygen or air to enter the substrate and
diffuse through to the electrocatalyst layer reaction sites. The
cathode electrocatalyst combines the protons with oxygen to produce
water. Product water then has to diffuse out of the cathode
structure. The structure of the cathode has to be designed such
that it enables the efficient removal of the product water. If
water builds up in the cathode, it becomes more difficult for the
reactant oxygen to diffuse to the reaction sites, and thus the
performance of the fuel cell decreases. In the case of methanol
fuelled PEMFCs, additional water is present due to the water
contained in the methanol, which can be transported through the
membrane from the anode to the cathode side. The increased quantity
of water at the cathode requires removal. However, it is also the
case with proton exchange membrane electrolytes, that if too much
water is removed from the cathode structure, the membrane can dry
out and the performance of the fuel cell also decreases.
[0008] The complete MEA can be constructed by several methods. The
electrocatalyst layers can be bonded to one surface of the gas
diffusion substrates to form what is known as a gas diffusion
electrode, which can be either an anode or a cathode. The MEA is
then formed by combining two gas diffusion electrodes with the
solid proton-conducting membrane. Alternatively, the MEA may be
formed from two porous gas diffusion substrates and a solid
proton-conducting polymer membrane which has been catalysed on both
sides; or indeed the MEA may be formed from one gas diffusion
electrode and one gas diffusion substrate and a solid
proton-conducting polymer catalysed on the side facing the gas
diffusion substrate.
[0009] Electrodes, catalysed membranes or MEA's are employed in
many different electrochemical devices in addition to fuel cells,
including metal-air batteries, electrochemical gas sensors, and
electrochemical reactors for the electrosynthesis of useful
chemical compounds.
[0010] In most practical fuel cell systems, the hydrogen fuel is
produced by converting a hydrocarbon-based fuel (such as methane)
or an oxygenated hydrocarbon fuel (such as methanol) to hydrogen in
a process known as reforming. This fuel, referred to as reformate,
contains (in addition to hydrogen) high levels of carbon dioxide
(CO.sub.2), of around 25%, and small amounts of impurities such as
carbon monoxide (CO), typically at levels of around 1%. For fuel
cells operating at temperatures below 200.degree. C., and
especially for the PEMFC operating at temperatures around
100.degree. C., it is well known that CO, even at levels of 1-10
ppm, is a severe poison for the platinum electrocatalysts present
in the electrodes. This leads to a significant reduction in fuel
cell performance, ie the cell voltage at a given current density is
reduced. This deleterious effect is more pronounced in PEMFCs
operating at lower temperatures. In addition, it has been found
that the CO.sub.2 present in the fuel stream can also cause a loss
of performance. This performance decay is usually small compared to
the effect of CO.
[0011] Various methods have been employed to alleviate anode CO
poisoning. For example, reformer technology has been redesigned to
include an additional catalytic reactor, known as a preferential or
selective oxidation reactor. This involves the injection of air or
oxygen into the hydrogen-containing reactant gas stream, prior to
it passing over the selective oxidation catalyst, to oxidise the CO
to CO.sub.2. This can reduce the levels of CO from 1-2% down to
below 100 ppm. However, even at these levels, the anode
electrocatalyst in the PEMFC is still poisoned.
[0012] It has also been found that poisoning of the electrocatalyst
by CO at levels of 1-100 ppm can be reduced by the use of an oxygen
or air bleed directly into the anode gas stream just before it
enters the anode chamber of the fuel cell itself. This is described
by Gottesfeld and Pafford in J. Electrochem. Soc., 135, 2651 et seq
(1988). This technique is believed to have the effect of oxidising
the residual CO in the fuel to CO.sub.2, the reaction being
catalysed by electrocatalyst sites present in the anode:
CO+1/2O.sub.2.fwdarw.CO.sub.2
[0013] This technique provides fuel cell performance that is much
closer to the performance observed when no CO is present in the
fuel stream. However, the air bleed technique does not usually
improve the deleterious effects of CO.sub.2 on performance and
there are concerns over the long-term sustainability of the cell
performance when this approach is employed. This is particularly
the case if high levels of air bleed, equivalent to 4% and above of
the total reformate fuel volume, are required.
[0014] However, the preferred technique for alleviating fuel cell
performance reduction due to anode CO poisoning is to employ an
anode electrocatalyst that is itself more poison-tolerant, but
which still functions as a hydrogen oxidation catalyst in the
present of CO. As described by, for example, Niedrach et al in
Electrochem. Technol., 5, 318, (1967), the use of a bimetallic
anode electrocatalyst comprising platinum/ruthenium, rather than
the more conventionally-used mono-metallic platinum-only
electrocatalyst, shows a reduction in the poisoning effect of the
CO at typical PEMFC operating temperatures. However, again, it was
not possible fully to attain the performance observed on pure
hydrogen, ie in the absence of CO in the fuel stream, by using this
approach in isolation.
[0015] There have been a number of attempts to improve the
performance of anode electrocatalysts operating in the presence of
hydrogen fuels containing CO. These have taken the approach of
modifying existing state-of-the-art catalysts, such as combining
platinum/ruthenium with other components. In 1995, Chen et al (J.
Electrochem. Soc., 142, (10)) discussed the need to develop
CO-tolerant catalysts and studied the oxidation of impure H.sub.2
on Teflon.RTM.-bonded carbon-supported platinum/ruthenium/tungsten
oxide electrodes. The use of tungsten oxide (WO.sub.3) as a
promoter of improved activity of platinum catalysts towards impure
H.sub.2 was not new. As far back as 1965, it was known that
tungsten oxides were effective in promoting the electro-oxidation
of CO on platinum-containing electrodes in acid-electrolyte fuel
cells (Niedrach and Weinstock, Electrochem. Technol., 3, 270-5
(1965)). A more recent example of a catalyst having improved CO
tolerance is given in European patent specification no. EPA 838
872.
[0016] EPA 838 872 relates to a ternary catalyst comprising Pt-M-Y,
wherein Pt-M is an alloy of platinum and one or more metals
selected from the transition metal elements or from Groups IIIA or
IVA of the Periodic Table in "Handbook of Chemistry and Physics"
64th Edition, CRC Press, and Y is a bronze forming element or an
oxide thereof, characterised in that the Pt-M alloy is in intimate
contact with Y, and provided that M is not Ru if Y is WO.sub.3.
[0017] However, such electrocatalysts aimed at improving CO
tolerance apparently do not also have the effect of improving
performance when CO.sub.2 is present in the reformate fuel. Hence,
for example, in the case of certain materials described in EPA 838
872, improved CO tolerance is observed, but at the same time the
presence of CO.sub.2 in the reformate stream causes larger
performance losses than those observed with state-of-the-art alloys
of platinum and ruthenium. This behaviour is most likely due to the
CO tolerance mechanism for the catalysts described in EPA 838 872
differing from that observed with Pt/Ru alloys.
[0018] We have now surprisingly found that significant improvement
in both CO and CO.sub.2 tolerance can be achieved by providing an
electrode structure in which the state-of-the-art Pt/Ru-type
electrocatalyst is functionally linked with a further
electrocatalyst. This has never before been achieved.
[0019] An anode structure of the present invention when used in a
PEMFC shows improved tolerance to both CO and CO.sub.2 poisons
whilst maintaining high activity for the desired electrochemical
reaction, and is therefore of use in fuel cells which use an impure
feed. The anode structure may be of benefit in both phosphoric acid
and solid polymer fuel cells. Specifically, it shows tolerance to
both CO and CO.sub.2 poisons in reformate fuel. The anode structure
may also be of benefit in these fuel cells when the fuel is
methanol.
[0020] Accordingly, the present invention provides an electrode
structure, comprising a first catalytic component and a second
catalytic component, characterised in that the first catalytic
component comprises one or more electrocatalyst(s) of formula Pt--Y
where Y is a bronze forming element, and optionally a third metal
component X which is alloyed with the platinum, and the second
catalytic component which comprises one or more electrocatalyst(s)
of formula Pt-M where M is a metal alloyed with the platinum.
[0021] The term "functionally linked" in the context of the present
invention means that both materials are in ionic contact with each
other. This may be achieved by adding an ion conducting material to
each of the catalysts when they are formulated into the electrode
structure of the invention. In the case of an anode structure for a
PEMFC, the ion conducting material is a proton conducting material,
which can be the same as that employed as the polymeric electrolyte
membrane of the MEA.
[0022] The Pt-M or Pt--X alloy is preferably more than a mere
physical mixture of Pt with metal(s), since the platinum and
metal(s) are preferably heat-treated to promote a measurable
interaction between the platinum and metal(s) to change the
intrinsic properties of the platinum metal. Heat-treatment causes a
significant number of atoms of the metal(s) to be incorporated into
the atomic crystal lattice, or unit cell, of the platinum particle.
This process usually distorts the dimensions of the platinum unit
cell, since the atoms of the metal(s) will generally be of a
different size from those of the platinum, and this can usually be
measured by techniques such as X-ray diffraction. The
characteristic dimensions of the platinum unit cell, referred to by
crystallographers as the lattice parameter, can be shown to have
altered due to the fact that two or more metals, with different
atomic sizes, have been incorporated into a single, homogeneous
metal alloy particle at the atomic level.
[0023] Preferably, the one or more metals(s) X or M, when present,
is or are selected from the groups IVB, VB, VIIB, VIIB, VIII, IB,
IIB, IIIA or IVA of the Periodic Table in "Handbook of Chemistry
and Physics" 64th Edition, CRC Press; for example, X metals can be
from the group Ru, Rh, Ti, Cr, Mn, Fe, Co, Ni, Cu, V, Ga, Zr, Hf
and Sn; especially Ru, Mn, Ti, Co, Ni and Rh and M metals can be
from the same group especially Ru and Rh.
[0024] Component Y may either be alloyed with the Pt--X alloy (the
resulting alloy being as defined hereinbefore) or may be unalloyed
but in physical contact with the alloy. Component Y may be a
bronze-forming element or an oxide thereof. A `bronze` material is
defined by Wold and Dwight in Solid State Chemistry--Synthesis,
Structure, and Properties of Selected Oxides and Sulfides, Chapman
& Hall as " . . . an oxide with intense colour (or black),
having a metallic lustre and showing either semi-conducting or
metallic behaviour. A principle characteristic of bronzes is their
range of composition, which results in the transition metal
exhibiting a variable formal valence." Suitable bronzes include
non-stoichiometric alloys of the transition metal with
hydrogen.
[0025] The component Y is suitably selected from one or more of the
Group IVB to VIB elements and rhenium or an oxide thereof, for
example Ti, V, Nb, Ta, Mo, W, Re, or an oxide thereof; suitably Ti,
V, Ta, Mo, W, or an oxide thereof; preferably Mo or W, or an oxide
thereof.
[0026] Preferably, the second catalytic component is one wherein
the Pt-M is Pt (alone) or an alloy (as defined) of Pt/Ru.
[0027] The term "electrode structure" in the context of the present
invention means the specific compositional aspects of those parts
of the electrochemical cell at which the electrochemical reactions
take place. It does not specifically refer to any particular
physical embodiment of the invention. The physical embodiments of
the invention can take several forms. The electrocatalyst materials
can be applied to one side of a gas diffusion substrate material to
produce an electrode, which can be either an anode or cathode,
comprising the electrode structure of the invention. Thus in a
further aspect, the present invention provides an electrode
comprising an electrode structure of the present invention wherein
the electrocatalyst materials are present on one side of a gas
diffusion substrate material.
[0028] Alternatively the electrocatalyst materials can be applied
to one side of the polymer electrolyte membrane material to produce
a catalysed membrane, comprising the electrode structure of the
invention.
[0029] Thus in a further aspect the present invention provides a
catalysed membrane comprising an electrode structure according to
the present invention wherein the electrocatalyst materials are
present on one side of the polymer electrolyte membrane
material.
[0030] An MEA for use in, for example, a PEMFC, as herein described
is a five layer unit, comprising a polymer electrolyte membrane in
the centre, with an electrocatalyst containing layer either side of
the membrane and a gas diffusion substrate layer in contact with
the electrocatalyst containing layers on the opposite face of the
layer to that in contact with the membrane. An MEA comprising the
electrode structure of the invention, can be formed from electrodes
as defined above, by bonding two electrodes, at least one of which
comprises the electrode structure of the invention, either side of
a polymer electrolyte membrane. Alternatively the MEA may be formed
from the catalysed membrane by applying gas diffusion substrate
materials either side of a catalysed membrane, in which at least
one catalysed side of the membrane comprises the electrode
structure of the invention.
[0031] Thus in a further aspect, the present invention provides an
MEA comprising an electrode structure according to the present
invention.
[0032] In the above aspects of the present invention namely when
formed into electrodes, catalysed membranes or an MEA from either
of these two components, the two catalyst materials can be
formulated into two separate layers which are applied to one side
of either the gas diffusion substrate material or to the polymer
electrolyte membrane, but in which they are still functionally
linked. It is also possible that the two catalyst materials may be
mixed together and formed into one layer containing both catalysts
and applied to one side of either the gas diffusion substrate
material or the polymer electrolyte membrane.
[0033] An electrode comprising the electrode structure of the
invention may be formed wherein each catalyst is formulated into a
separate layer in which a first layer comprising the first catalyst
material, as herein defined, is in contact with one side of the gas
diffusion substrate material, and a second layer comprising the
second catalyst material is in contact with the opposite face of
the first catalyst layer to that in contact with the gas diffusion
substrate. Alternatively a catalysed membrane comprising the
electrode structure of the invention may be formed wherein each
catalyst is formulated into a separate layer in which a first layer
comprising the second catalyst material, as herein defined, is in
contact with one side of the polymer electrolyte membrane material,
and the second layer comprising the first catalyst material is in
contact with the opposite face of the second catalyst layer to that
in contact with the polymer electrolyte membrane.
[0034] In a further aspect, the present invention provides a fuel
cell comprising an electrode structure, comprising a first
catalytic component and a second catalytic component, characterised
in that the first catalytic component comprises one or more
electrocatalyst(s) of formula Pt--Y where Y is a bronze forming
element, and optionally a third metal component X which is alloyed
with the platinum, and the second catalytic component which
comprises one or more electrocatalyst(s) of formula Pt-M, where M
is a metal alloyed with platinum.
[0035] In a final aspect, the present invention provides the use of
an electrode structure according to the present invention in a fuel
cell.
[0036] The invention will now be described further with reference
to the following Examples and drawings in which:
[0037] FIG. 1: shows fuel cell performance data of cell voltage vs
time for operation of two PtRu (thick line and line with
.circle-solid.), PtRuW (line with .box-solid.), PtTiW (line with X)
and PtCoMo (line with .tangle-solidup.) catalysts in a gas stream
containing 100 ppm CO in hydrogen. The anode platinum loadings are
respectively 0.37, 0.25, 0.29, 0.45 and 0.29 mg Pt/cm.sup.2.
[0038] FIG. 2: shows fuel cell performance data of cell voltage vs
time for operation of the two PtRu (thick line and line with
.circle-solid.), PtRuW (line with .box-solid.), PtTiW (line with X)
and PtCoMo (line with .tangle-solidup.) catalysts in a gas stream
containing 25% CO.sub.2 and 75% hydrogen. The anode platinum
loadings are the same as in FIG. 1.
[0039] FIG. 3 presents single cell performance data for electrode
bilayers according to the invention operating in 25% CO.sub.2 and
75% hydrogen. The bilayers comprise of catalyst layers of PtTiW
(line with X), PtRuW (line with .box-solid.), PtCoMo (line with
.tangle-solidup.) and PtCoW (dashed line) containing 0.16, 0.12,
0.26 and 0.27 mg Pt cm.sup.-2 and layers of PtRu catalyst at
loadings of 0.13, 0.25, 0.14 and 0.24 mg Pt cm.sup.-2,
respectively. FIG. 3 also shows the comparative example PtRu (thick
line) which is also presented in FIG. 1.
[0040] FIG. 4 shows that, at the same time, the performance of the
bilayer electrodes of the invention in hydrogen containing 100 ppm
CO is significantly improved over the comparative PtRu sample
performance decay, while the total platinum loading in both layers
is very similar in all cases.
[0041] FIG. 5 shows the single cell performances of two MEA's, one
an electrode bilayer according to the invention, and the other a
single catalyst layer, operating on gas mixtures of CO and CO.sub.2
in hydrogen, which has been used to simulate reformate gas
compositions. The MEA's have been tested on two different gas
mixtures; 40 ppm CO and 25% CO.sub.2 in hydrogen (closed symbols),
and 100 ppm CO and 25% CO.sub.2 in hydrogen (open symbols). The
bilayer comprises of a catalyst layer of PtCoMo at loadings of 0.15
mg Pt/cm.sup.2 and a layer of a PtRu catalyst at a loading of 0.31
mg Pt/cm.sup.2 (lines with squares). The single layer electrode
comprised of the same PtRu catalyst at a loading of 0.29 mg
Pt/cm.sup.2 (lines with circles).
COMPARATIVE EXAMPLE 1
[0042] A catalyst containing platinum and ruthenium at 41.80 wt %
Pt and 20.78 wt % Ru supported on Cabot Vulcan XC72R carbon, was
prepared using a process comprising the deposition of Pt onto the
conductive carbon black substrate by the hydrolysis of an aqueous
solution of chloroplatinic acid and ruthenium trichloride by a
solution of sodium hydrogen carbonate in the presence of the carbon
black, as disclosed in EP 450 849. The catalyst was reduced using
aqueous formaldehyde solution, filtered, washed free of soluble
chloride salts and dried at 100.degree. C. X-ray diffraction
analysis of the resulting catalyst showed a single cubic phase with
a lattice parameter of 3.87X, indicating significant alloying of
the Ru with the Pt. From this catalyst, a catalyst ink was prepared
and a fuel cell anode was printed onto pre-teflonated Toray TPG90
paper. Inks and electrodes are prepared as detailed in Example 2 of
European patent specification no. EPA 731 520. The platinum loading
of this electrode was 037 mgPt/cm.sup.2.
COMPARATIVE EXAMPLE 2
[0043] A catalyst containing platinum and ruthenium at 19.2 wt % Pt
and 93 wt % Ru supported on Cabot Vulcan XC72R carbon, was prepared
using the process as described in Comparative Example 1 and as
disclosed in EP 450 849. X-ray diffraction analysis of the
resulting catalyst showed a single cubic phase with a lattice
parameter of 3.88X, indicating significant alloying of the Ru with
the Pt. An Electrode was prepared in the same way as described in
Comparative Example 1. The platinum loading of this electrode was
0.25 mgPt/cm.sup.2.
COMPARATIVE EXAMPLE 3
[0044] A catalyst containing platinum, ruthenium and tungsten at
16.65 wt % Pt, 832 wt % Ru and 10.77 wt % W was prepared. A PtRu
catalyst (75 g), as described in Comparative Example 2, was
slurried in 1 litre of demineralised water for one hour. A 1 wt %
solution of sodium tungstate in demineralised water was prepared
containing 1.98 g tungsten. This solution was converted to tungstic
acid by passing it through an exchange column, comprising Dowex
50-X8 ion-exchange resin, and fed directly into the slurry. The
resultant catalyst was stirred overnight and then filtered, dried
at 105.degree. C. in air and fired at 500.degree. C. in a gas
mixture containing 6% CO in CO.sub.2. X-ray diffraction analysis of
the resulting catalyst showed a single cubic phase with a lattice
parameter of 3.87X, indicting significant alloying of the Ru with
the Pt, together with the presence of crystalline WO.sub.3. An
electrode containing this catalyst was prepared in the same way as
described in Comparative Example 1. The platinum loading of this
electrode was 0.29 mgPt/cm.sup.2.
COMPARATIVE EXAMPLE 4
[0045] A catalyst containing Pt, Ti and W at 34.41 wt % Pt, 2.02 wt
% Ti and 10.63 wt % W was prepared. To a stirred suspension of
Cabot Vulcan XC72R carbon (16 g) in a 6 litre solution of potassium
hydrogen carbonate (25 g) under reflux, was added a 2 wt % solution
of chloroplatinic acid (containing 8 g Pt). The resulting slurry
was filtered, and washed with demineralised water until no chloride
was detectable in the washings. The catalyst was dried at
100.degree. C. in air. The catalyst was re-slurried in a litre
solution of potassium hydrogen carbonate (2.5 g) and heated till
under reflux. A 2 wt % solution of titanium trichloride (containing
0.45 g Ti) and urea (3.39 g) was added dropwise. The ratio of
alkali to metal salts for both steps was such as to ensure complete
hydrolysis and precipitation of the metal hydrous oxides/hydroxides
onto the carbon.
[0046] The slurry was filtered, and washed with demineralised water
until no chloride was detectable in the washings. The wet cake was
then dispersed in a litre of demineralised water. To this slurry
was added dropwise a 1 wt % solution of tungsten (232 g) in water.
This was prepared by the dissolution of tungsten powder in hydrogen
peroxide solution, followed by decomposition of the excess peroxide
by platinum black. The combined slurry was then evaporated to
dryness. The resulting catalyst was then heated at 650.degree. C.
in flowing 5% hydrogen in nitrogen for 1 hour. X-ray diffraction
analysis of the resulting catalyst showed a single cubic phase with
a lattice parameter of 393X, which indicated little alloying of the
components. An electrode containing this catalyst was prepared in
the same way as described in Comparative Example 1. The platinum
loading of this electrode was 0.45 mgPt/cm.sup.2.
COMPARATIVE EXAMPLE 5
[0047] A catalyst containing Pt, Co and Mo at 21.0 wt % Pt 0.2 wt %
Co and 1.0 wt % Mo was prepared. To a stirred suspension of Cabot
Vulcan XC72R carbon (945 g) in a 6 litre solution of sodium
hydrogen carbonate (67.4 g) under reflux, was added first a 2 wt %
solution of chloroplatinic acid (containing 24.2 g Pt), followed by
a 2 wt % solution of cobalt dichloride (containing 1.7 g Co). The
amount of sodium hydrogen carbonate was calculated to be sufficient
to just precipitate both Pt and Co as their hydrous
oxides/hydroxides. The resulting catalyst was filtered, washed with
demineralised H.sub.2O until chloride free and dried at 100.degree.
C. A portion of the dried catalyst (21.8 g) was reslurried in 15
litres of demineralised H.sub.2O and stirred. To this was added
disodium molybdate dihydrate (1.7 g) and the slurry stirred until
complete dissolution. To the resulting slurry was added a solution
of 1,8-hydroxyquinoline (1.0 g) in 40 cm.sup.3 of ethanol. The
amount of 1,8-hydroxyquinoline added being 2 molar equivalents of
the amount of Mo added. The slurry was heated until under reflux
and the pH adjusted to 4 by the addition of acetic acid. The slurry
was boiled for 60 minutes to remove the ethanol, after which the
slurry was cooled, filtered, washed free of salts and dried at
100.degree. C. The dried catalyst was heat treated under flowing
10% H.sub.2/N.sub.2 for 1 hour at 650.degree. C. to decompose the
1,8-hydroxyquinoline. X-ray diffraction of resulting catalyst
showed a single cubic phase with a lattice parameter of 3.91, which
indicates little alloying of the components. An electrode
containing this catalyst was prepared in the same way as described
in Comparative Example 1. The platinum loading of this electrode
was 0.29 mgPt/cm.sup.2.
COMPARATIVE EXAMPLE 6
[0048] A catalyst containing Pt and Ru at 38.7 wt % Pt and 20.7 wt
% Ru supported on Cabot Vulcan XC72R carbon was prepared as
described in Comparative Example 1. X-ray analysis of the resulting
catalyst showed a single cubic phase with a lattice parameter of
3.90X, indicating significant alloying of the Ru with the Pt. An
electrode containing this catalyst at a platinum loading of 0.29
mgPt/cm.sup.2 was prepared as described in Comparative Example
1.
EXAMPLE 1
(Pt/Mo/Co)/(Pt/Ru)
[0049] A catalyst containing Pt, Mo and Co at 20.30 wt % Pt, 1.44
wt % Co and 0.65 wt % Mo was prepared. To a stirred suspension of
Cabot Vulcan XC72R carbon (30.2 g) in a solution of sodium hydrogen
carbonate (223 g) under reflux, was added a 2 wt % solution of
chloroplatinic acid (containing 8 g Pt) and cobalt dichloride
(containing 0.6 g Co). After refluxing for 2.5 hrs, the resulting
slurry was filtered, and washed with demineralised water until no
chloride was detectable in the washings. The catalyst was dried at
100.degree. C. in air.
[0050] The dried catalyst was then re-dispersed in 1 litre of
demineralised water for one hour at ambient temperature. To this
slurry was added a solution of molybdenum (1.21 g) prepared by
passing a 1 wt % solution of sodium molybdate through an ion
exchange column containing Dowex 50-X8 ion exchange resin to covert
to colloidal molybdic acid. The combined slurry was then evaporated
to dryness. The resulting catalyst was then heated at 695.degree.
C. in flowing 5% hydrogen in nitrogen to ensure reduction and
alloying of the components. X-ray diffraction analysis of the
resulting catalyst showed a single cubic phase with a lattice
parameter of 3.87X, indicating significant alloying of the
components.
[0051] An electrode containing the catalyst at a platinum loading
of 0.26 mgPt/cm.sup.2 was prepared as described in Comparative.
Example 1. On top of this catalyst layer, an additional layer of
PtRu catalyst made according to Comparative Example 1 was applied
using the method described in Comparative Example 1. The additional
Pt loading in this catalyst layer was 0.14 mgPt/cm.sup.2.
EXAMPLE 2
(Pt/W/Co)/(Pt/Ru)
[0052] A catalyst containing Pt, W and Co at 14.7 wt % Pt, 1.0 wt %
Co and 3.8 wt % W was prepared. To a stirred suspension of Cabot
Vulcan XC72R carbon (32 g) in 6 litres of a solution of sodium
hydrogen carbonate (185 g) under reflux, was added a 2 wt %
solution of chloroplatinic acid (containing 5.7 g Pt). The
resulting slurry was heated under reflux for 2 hrs, before being
filtered and washed with demineralised water, until no chloride was
detected in the washings. The catalyst was then dried at
100.degree. C. in air. The dried catalyst was re-dispersed in 6
litres of sodium hydrogen carbonate (1.1 g) solution and heated
till under reflux. To this slurry was added a 2 wt % solution of
cobalt dichloride (containing 0.4 g Co). The slurry was then
filtered and washed with demineralised water until no chloride was
detected in the washings. The wet cake was re-slurried in 1 litre
of demineralised water for 1 hr at ambient temperature. To this was
added was added a solution of tungsten (15 g). The tungsten
solution was prepared by dissolving tungsten powder in hydrogen
peroxide (100 cm.sup.3 of 28 wt % H.sub.2O.sub.2 solution),
followed by decomposition of the excess peroxide by platinum black,
and subsequent dilution to a 1 wt % solution by dimineralised
water. The combined slurry was then evaporated to dryness. The
resulting catalyst was then heated to 900.degree. C. in flowing
nitrogen for 1 hour. X-ray diffraction analysis of the resulting
catalyst showed a single cubic phase with a lattice parameter of
3.90X indicating significant alloying of the components.
[0053] An electrode containing this catalyst at a platinum loading
of 0.27 mgPt/cm.sup.2 was prepared as described in Comparative
Example 1. On top of this catalyst layer, an additional layer of a
catalyst containing Pt and Ru at 37.1 wt % Pt and 17.9 wt % Ru
supported on Cabot Vulcan XC72R carbon was prepared as described in
Comparative Example 1, was applied using the method described in
Comparative Example 1. The additional Pt loading in this catalyst
layer was 0.24 mgPt/cm.sup.2. X-ray analysis of this catalyst
showed a single cubic phase with a lattice parameter of 3.90X,
indicating significant alloying of the Ru with the Pt. An electrode
containing this catalyst at a platinum loading of 0.29
mgPt/cm.sup.2 was prepared as described in Comparative Example
1.
EXAMPLE 3
(Pt/Ru/W)/(Pt/Ru)
[0054] A catalyst containing Pt, Ru and W was prepared as described
in Comparative Example 2. An electrode containing this catalyst at
a platinum loading of 0.12 mgPt/cm.sup.2 was prepared as described
in Comparative Example 1. On top of this catalyst layer, an
additional layer of PtRu catalyst as used in Example 2 was applied
using the method described in Comparative Example 1. The additional
Pt loading in this catalyst layer was 0.25 mgPt/cm.sup.2.
EXAMPLE 4
(Pt/Ti/W)/(Pt/Ru)
[0055] A catalyst containing Pt, Ti and W was prepared as described
in Comparative Example 4. An electrode containing this catalyst at
a platinum loading of 0.16 mgPt/cm.sup.2 was prepared as described
in Comparative Example 1. On top of this catalyst layer, an
additional layer of PtRu catalyst made according to Comparative
Example 2 was applied using the method described in Comparative
Example 1. The additional Pt loading in this catalyst layer was
0.13 mgPt/cm.sup.2.
EXAMPLE 5
(PtMoCo)/(PtRu)
[0056] A catalyst containing Pt, Co and Mo was prepared as
described in Comparative Example 5. An electrode containing this
catalyst at a platinum loading of 0.15 mgPt/cm.sup.-2 was prepared
as described in Comparative Example 1. On top of this catalyst
layer, an additional layer of PtRu catalyst made according to
Comparative Example 6 was applied using the method described in
Comparative Example 1. The addition loading in this catalyst layer
was 0.31 mgPtcm.sup.-2.
1 TABLE 1 Assay Characterisation Data/ XRD Characterisation Example
wt % of total catalyst weight Atomic Crystallite Pt lattice Number
Catalyst Pt 2.sup.nd Metal 3.sup.rd Metal Ratio Size/nm parameter/X
Comp. 1 PtRu 41.80 20.78 51:49 2.6 3.87 Comp. 2 PtRu 19.2 9.3 --
52:48 1.9 3.88 Comp. 3 PtRuW 16.65 8.32 10.77 38:36:26 4.6 3.87
Comp. 4 PtTiW 34.41 2.02 10.63 64:15:21 5.6 3.93 Comp. 5 PtCoMo
21.9 0.2 1.0 89:03:08 4.5 3.91 Comp. 6 PtRu 38.7 20.7 49:51 2.7
3.90 1 PtCoMo 20.30 1.44 0.65 77:18:05 4.2 3.87 PtRu 41.80 20.78
51:49 2.6 3.87 2 PtCoW 14.7 1.0 3.76 67:15:18 3.1 3.90 PtRu 19.2
9.3 52:48 1.9 3.88 3 PtRuW 16.65 8.32 10.77 38:36:26 4.6 3.87 PtRu
37.06 17.89 52:48 3.2 3.90 4 PtTiW 34.41 2.02 10.63 64:15:21 5.6
3.93 PtRu 19.2 9.3 52:48 1.9 3.88 5 PtCoMo 21.9 0.2 1.0 89:03:08
4.5 3.91 PtRu 38.7 20.7 49:51 2.7 3.90
EXAMPLE 6
Preparation of MEAs
[0057] The electrode structures of the invention were first
produced as anodes and then bonded to membranes to form MEAs. as
described in Example 2 of EP 731 520. The MEA was fabricated by
hot-pressing the anode and a pure platinum catalyst cathode (with a
platinum loading of 0.6 mg Pt/cm.sup.2) against each face of a
solid proton-conducting electrolyte membrane. The membrane used was
the perfluorinated membrane Nafion.RTM. 115 (from Du Pont de
Nemours). MEAs of 65 cm.sup.2 area were formed by hot-pressing at
pressures of 100 psi (1 psi=6.89.times.10.sup.3 N/m.sup.2) over the
MEA, at temperatures exceeding the glass transition temperature of
the membrane, as is commonly practised in the art. MEAs of 240
cm.sup.2 area were formed by hot pressing at pressures of 400 psi
over the MEA.
EXAMPLE 7
Performance Evaluation
[0058] The MEAs were evaluated in a PEMFC single cell. The single
cell consists of graphite plates into which flowfields are machined
to distribute the reactant gases, humidification water and heating
and cooling water and to remove products. The MEA was located
between the appropriate flowfield plates. The cell is compressed,
typically to a gauge pressure of 70 psig above the reactant gas
pressure.
[0059] The "fuel cell performance" was assessed by measuring the
voltage at a fixed current density of 500 mA cm.sup.2. The fuel
cell operated under conditions representative of those employed in
practical PEM fuel cells. These conditions were typically a
reactant gas inlet temperature of 80.degree. C., a pressure of both
hydrogen and air reactants of 3 atmospheres. For 6.45 cm.sup.2
MEAs, the reactant gas streams were kept constant at 0.1 SLPM
(standard litres at 1 bar and 0.degree. C. per minute); 0.125 SLPM
for 25% CO.sub.2 and 75% hydrogen; and 0.4 SLPM for oxygen. For 240
cm.sup.2 MEAs, the fuel to air gas stoichiometry was 1.5/2. For the
single cell reformate tolerance experiments, the anode gas stream
was changed at time t=0 from pure hydrogen to gas streams composed
of 100 ppm CO in hydrogen, 25% CO.sub.2 in hydrogen, 40 ppm CO and
25% CO.sub.2 in hydrogen or 100 ppm CO and 25% CO.sub.2 in
hydrogen. The fuel cell performance using the binary gas mixtures
was performed using the 6.45 Cm.sup.2 MEAs, while testing using the
ternary gas mixtures was performed using the 240 cm.sup.2 MEAs. At
constant current density of 0.5 Acm.sup.-2, the cell potential was
then monitored with time in order to assess the CO and the CO.sub.2
tolerance of different catalysts under practical conditions. Table
2 summarises the CO, CO.sub.2 and CO/CO.sub.2 tolerances of the
catalysts described in the Examples in the form of voltage losses
(in mV) on the different poisoning gas streams, when compared to
operation on pure hydrogen. The lower the voltage loss, the more
resistant the catalyst or catalyst combination is towards being
poisoned on that particular gas stream.
[0060] FIG. 1 shows fuel cell performance data of cell voltage vs
time for operation of two PtRu, PtRuW, PtTiW and PtCoMo catalysts
in a gas stream containing 100 ppm CO in hydrogen. The anode
platinum loadings are respectively 0.37, 0.25, 0.29, 045 and 0.29
mg Pt/cm.sup.2. FIG. 1 shows that the single cell voltages for all
five MEAs decay from their value at t=0 min when the cell is
operated with pure hydrogen. FIG. 1 shows that the performance
curves of the two MEAs containing PtRu anode catalysts, one
labelled "standard" PtRu and the other labelled "advanced" PtRu.
This represents the range of CO tolerance performance found with
state of the art PtRu catalysts as a function of Pt loading on the
carbon and Pt loading in the catalyst layer. The MEA containing the
advanced PtRu catalyst, shows the lowest drop in performance on
switching between pure hydrogen and 100 ppm CO in hydrogen. This
catalyst has a higher Pt loading on carbon and a higher loading of
catalyst in the electrode compared to the standard PtRu catalyst.
The electrode containing the advanced PtRu catalyst would be
expected to give higher performance due to the higher density of Pt
in the catalyst layer. The performance curves of the MEA's
containing the three ternary catalysts, PtRuW, PtTiW and PtCoMo on
100 ppm CO in hydrogen show them lying between the two PtRu
performance curves, indicating comparable CO tolerance. Considering
that the dispersion of the catalyst particles as shown in Table 1
as Pt crystallite size, are significantly inferior to those
displayed by the two PtRu catalysts, then these catalysts are
intrinsically more CO tolerant than state of the art PtRu
catalysts, in terms of specific activity (ie activity per actual
surface area of Pt present).
[0061] FIG. 2 shows fuel cell performance data of cell voltage vs
time for operation of the two PtRu, PtRuW, PtTiW and PtCoMo
catalysts in a gas stream containing 25% CO.sub.2 and 75% hydrogen.
The anode platinum loadings are the same as in FIG. 1. FIG. 2 shows
that the single cell voltages for al five MEAs decay from their
value at t=0 min when the cell is operated with pure hydrogen. The
performances of the electrodes containing the PtRu catalysts
degrades by 19 and 38 mV respectively, on the introduction of the
gas mixture containing 25% CO.sub.2 and 75% hydrogen. In contrast,
the performance of the electrodes containing the three ternary
catalysts degrade by larger amounts, with the PtCoMo catalyst
losing 211 mV on introduction of the CO.sub.2/H.sub.2 gas mixture.
This shows that although the ternary catalysts have good CO
tolerance, they have inferior CO.sub.2 tolerance to the
`state-of-the-art` PtRu catalysts.
[0062] FIG. 3 presents single cell performance data for electrode
bilayers according to the invention operating in 25% CO.sub.2 and
75% hydrogen. The bilayers comprise of catalyst layers of PtTiW,
PtRuW, PtCoMo and PtCoW containing 0.16, 0.12, 0.26 and 0.27 mg Pt
cm.sup.-2 and layers of PtRu catalyst at loadings of 0.13, 0.25,
0.14 and 0.24 mg Pt cm.sup.-2, respectively. FIG. 3 also shows the
comparative example PtRu which is also presented in FIG. 1. The
bilayer electrodes according to the invention show small decays
when the gas stream is changed at t=0 min from pure hydrogen to 25%
CO.sub.2 and 75% hydrogen. The performance decay of the PtRuW
catalyst when as a bilayer with PtRu shows a significant reduction.
The other electrode samples exhibit a decay around 25 mV, very
close to the comparative PtRu electrode. Therefore, the combination
of Pt ternary catalysts with PtRu catalysts, has overcome the
CO.sub.2 "in-tolerance" of these catalyst seen, when tested as
single catalyst layers.
[0063] FIG. 4 shows that, at the same time, the performance of the
bilayer electrodes of the invention in hydrogen containing 100 ppm
CO is significantly improved over the comparative PtRu sample. When
at t=0 min the gas stream is changed from pure hydrogen to hydrogen
containing 100 ppm CO, all samples exhibit, after some induction
time, a decay of the single cell voltage. This decay is 166 mV for
the comparative PtRu sample. All bilayer samples show lower
performance decay, while the total platinum loading in both layers
is very similar in all cases. The PtCoMo/PtRu bilayer electrode of
the invention shows a performance decay as low as approximately 88
mV. In addition, the PtCoW/PtRu bilayer electrode of the invention
shows a performance decay of 73 mV, although with a higher overall
electrode loading of 051 mg Pt/cm.sup.2.
[0064] FIG. 5 shows the single cell performances of two MEA's, one
an electrode bilayer according to the invention, and the other a
single catalyst layer, operating on gas mixtures of CO and CO.sub.2
in hydrogen, which has been used to simulate reformate gas
compositions. The MEA's have been tested on two different gas
mixtures; 40 ppm CO and 25% CO.sub.2 in hydrogen, and 100 ppm CO
and 25% CO.sub.2 in hydrogen. The bilayer comprises of a catalyst
layer of PtCoMo at loadings of 0.15 mg Pt/cm.sup.2 and a layer of a
PtRu catalyst at a loading of 0.31 mg Pt/cm.sup.2. The single layer
electrode comprised of the same PtRu catalyst at a loading of 0.29
mg Pt/cm.sup.2. FIG. 5 shows that the performance of the bilayer
electrode is superior to the single layer with both the gas
mixtures tested. In particular, the differences between the two
electrodes is increased with the gas mixture with 100 ppm CO.
Clearly, the bilayer electrode according to the invention shows
improved performance when tested in gas streams of CO in hydrogen,
CO.sub.2 in hydrogen and mixtures of CO and CO.sub.2 in hydrogen,
when compared to single layer electrodes of similar Pt loading. In
particular, the combination of two different catalysts within the
bilayer electrode have shown unexpectedly improved performances
based on their performances as single layers.
2 TABLE 2 Voltage Losses on Different Poisoning Gas Streams/mV Pt
loading/ 100 ppm 25% 40 ppm CO/ 100 ppm CO/ Example Catalyst(s) mg
Ptcm.sup.-2 CO/H.sub.2 CO2/H.sub.2 25% CO.sub.2/H.sub.2 25%
CO.sub.2/H.sub.2 Comp. 1 PtRu 0.37 166 19 -- -- Comp. 2 PtRu 0.25
325 38 -- -- Comp. 3 PtRuW 0.29 177 56 -- -- Comp. 4 PtTiW 0.45 195
51 -- -- Comp. 5 PtCoMo 0.29 274 211 -- -- Comp. 6 PtRu 0.29 -- --
114 173 1 PtCoMo/PtRu 0.26/0.14 88 29 -- -- 2 PtCoW/PtRu 0.27/0.24
73 22 -- -- 3 PtRuW/PtRu 0.12/0.25 110 44 -- -- 4 PtTiW/PtRu
0.16/0.13 165 29 -- -- 5 PtCoMo/PtRu 0.15/0.31 -- -- 61 83
* * * * *