Water filter abstract
Silica may form as a degradation product in an electrochemical
fuel cell system and may be found within the water management subsystem
thereof. The silica may polymerize and/or react to form insoluble
metal silicates which may lead to reduced lifetime or performance
of individual components within the fuel cell system. These problems
can be eliminated or reduced by adding a silica absorber such as
aluminum, either as alumina granulate or an aluminum plate to the
water management subsystem, for example in, upstream and/or downstream
of the water filter. In addition, the silica absorber may be in,
upstream and/or downstream of the water tank.
Water filter claims
1. An electrochemical fuel cell system comprising an electrochemical
fuel cell stack and a water management subsystem, the water management
subsystem comprising a water tank, a water filter, a silica absorber
and a pump all fluidly connected.
2. The electrochemical fuel cell system of claim 1 wherein the
silica absorber is in the water filter.
3. The electrochemical fuel cell system of claim 1 wherein the
silica absorber is in the water tank.
4. The electrochemical fuel cell system of claim 1 wherein the
silica absorber is upstream of the water filter.
5. The electrochemical fuel cell system of claim 1 wherein the
silica absorber comprises aluminum oxide.
6. The electrochemical fuel cell system of claim 5 wherein the
silica absorber is granulate.
7. The electrochemical fuel cell system of claim 5 wherein the
silica has a specific surface area of 100 to 240 m.sup.2/g.
8. The electrochemical fuel cell system of claim 5 wherein the
silica absorber further comprises activated carbon.
9. The electrochemical fuel cell system of claim 8 wherein the
activated carbon is downstream of the aluminum oxide.
10. The electrochemical fuel cell system of claim 8 wherein the
activated carbon and the aluminum oxide are mixed.
11. The electrochemical fuel cell system of claim 1 wherein the
water filter comprises a single cartridge comprising both the silica
absorber and an ion-exchanger resin.
12. The electrochemical fuel cell system of claim 1 wherein the
water management subsystem comprises deionized water.
13. The electrochemical fuel cell system of claim 1 further comprising
a reactant humidification subsystem and wherein the water management
subsystem supplies water to the reactant humidification subsystem.
14. The electrochemical fuel cell system of claim 13 wherein reactant
humidification subsystem humidifies the oxidant stream.
15. The electrochemical fuel cell system of claim 13 wherein reactant
humidification subsystem humidifies the fuel stream.
16. The electrochemical fuel cell system of claim 1 further comprising
a fuel processing subsystem and wherein the water management subsystem
supplies water to the fuel processing subsystem.
17. The electrochemical fuel cell system of claim 1 wherein the
water management subsystem supplies water to the electrochemical
fuel cell stack for cooling the electrochemical fuel cell stack.
Water filter description
BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to water filters for electrochemical
fuel cells and more particularly for water filters in a water management
subsystem for an electrochemical fuel cell system.
 2. Description of the Related Art
 Electrochemical fuel cells convert reactants, namely fuel
and oxidant fluid streams, to generate electric power and reaction
products. Electrochemical fuel cells employ an electrolyte disposed
between two electrodes, namely a cathode and an anode. The electrodes
each comprise an electrocatalyst disposed at the interface between
the electrolyte and the electrodes to induce the desired electrochemical
reactions. The location of the electrocatalyst generally defines
the electrochemically active area.
 Polymer electrolyte membrane (PEM) fuel cells generally
employ a membrane electrode assembly (MEA) consisting of an ion-exchange
membrane disposed between two electrode layers comprising porous,
electrically conductive sheet material as fluid diffusion layers,
such as carbon fiber paper or carbon cloth. In a typical MEA, the
electrode layers provide structural support to the ion-exchange
membrane, which is typically thin and flexible. The membrane is
ion conductive (typically proton conductive), and also acts as a
barrier for isolating the reactant streams from each other. Another
function of the membrane is to act as an electrical insulator between
the two electrode layers. The electrodes should be electrically
insulated from each other to prevent short-circuiting. A typical
commercial PEM is a sulfonated perfluorocarbon membrane sold by
E.I. Du Pont de Nemours and Company under the trade designation
 The MEA contains an electrocatalyst, typically comprising
finely comminuted platinum particles disposed in a layer at each
membrane/electrode layer interface, to induce the desired electrochemical
reaction. The electrodes are electrically coupled to provide a path
for conducting electrons between the electrodes through an external
 In a fuel cell stack, the MEA is typically interposed between
two separator plates that are substantially impermeable to the reactant
fluid streams. The plates act as current collectors and provide
support for the electrodes. To control the distribution of the reactant
fluid streams to the electrochemically active area, the surfaces
of the plates that face the MEA may have open-faced channels formed
therein. Such channels define a flow field area that generally corresponds
to the adjacent electrochemically active area. Such separator plates,
which have reactant channels formed therein are commonly known as
flow field plates. In a fuel cell stack a plurality of fuel cells
are connected together, typically in series, to increase the overall
output power of the assembly. In such an arrangement, one side of
a given plate may serve as an anode plate for one cell and the other
side of the plate may serve as the cathode plate for the adjacent
cell. In this arrangement, the plates may be referred to as bipolar
 The fuel fluid stream that is supplied to the anode typically
comprises hydrogen. For example, the fuel fluid stream may be a
gas such as substantially pure hydrogen or a reformate stream containing
hydrogen. Alternatively, a liquid fuel stream such as aqueous methanol
may be used. The oxidant fluid stream, which is supplied to the
cathode, typically comprises oxygen, such as substantially pure
oxygen, or a dilute oxygen stream such as air. In a fuel cell stack,
the reactant streams are typically supplied and exhausted by respective
supply and exhaust manifolds. Manifold ports are provided to fluidly
connect the manifolds to the flow field area and electrodes. Manifolds
and corresponding ports may also be provided for circulating a coolant
fluid through interior passages within the stack to absorb heat
generated by the exothermic fuel cell reactions.
 In conventional solid polymer fuel cell stacks, cooling
of the fuel cells is typically accomplished by providing cooling
layers disposed between adjacent pairs of stacked fuel cells. Often
the cooling layer is similar in design to a reactant flow field
plate wherein a coolant, typically water, is fed from an inlet manifold
and directed across the cooling plate in channels to an outlet manifold.
This type of fuel cell stack typically requires three plates between
each adjacent MEA, namely an anode plate, a cathode plate and a
cooling plate. The coolant channels thus superpose the active area
of the fuel cell. In operation, heat generated in the fuel cells
is drawn away from each fuel cell by the coolant through the thickness
of the plates perpendicular to the plane of the fuel cell assemblies.
Heat is then transferred to and carried away by a circulating coolant.
Cooling with an additional coolant layer can be called "interstitial"
 It is desirable to seal reactant fluid stream passages to
prevent leaks or inter-mixing of the fuel and oxidant fluid streams.
U.S. Pat. No. 6057054 incorporated herein by reference in its
entirety, discloses a sealant material impregnating into the peripheral
region of the MEA and extending laterally beyond the edges of the
electrode layers and membrane (i.e. the sealant material envelopes
the membrane edge).
 For a PEM fuel cell to be used commercially in either stationary
or transportation applications, a sufficient lifetime is necessary.
For example, 5000 hour operations may be routinely required. In
practice, there are significant difficulties in consistently obtaining
sufficient lifetimes as many of the degradation mechanisms and effects
remains unknown. Accordingly, there remains a need in the art to
understand degradation of fuel cell components and to develop design
improvements to mitigate or eliminate such degradation. The present
invention fulfills this need and provides further related advantages.
BRIEF SUMMARY OF THE INVENTION
 A possible degradation product in fuel cell systems is silica
that can be found in soluble or insoluble forms within the water
management subsystem of an electrochemical fuel cell system and
may react with metal particulates or metal surfaces to form metal
silicates. In particular, silica scale may be found within the humidification
subsystem of the fuel cell system. Such degradation products building
up and collecting on fuel cell components may lead to reduced performance
and/or reduced lifetime of the fuel cell components or the system
as a whole. The water management subsystem may supply deionized
water to one or all of the humidification subsystem for humidifying
the oxidant stream, the fuel stream or both; the fuel processing
subsystem; or the electrochemical fuel cell stack for cooling purposes.
 To remove silica from the fuel cell system, a silica absorber
may be present. More particularly, an electrochemical fuel cell
system may comprise an electrochemical fuel cell stack and a water
management subsystem which comprises a water tank, a water filter,
a silica absorber and a pump all fluidly connected.
 In an embodiment, the silica absorber is within a separate
compartment of the water filter. Alternatively, the silica absorber
may be in a separate cartridge and either upstream, downstream or
both from the water filter. The silica absorber may comprise, for
example, aluminum. In particular, the silica absorber may be aluminum
oxide (also known as alumina). In a more specific embodiment, the
silica absorber may be alumina granulate with a specific surface
area of 100 to 240 m.sup.2/g. The silica absorber may also comprise
activated carbon. If a combination of alumina and activated carbon
is used, then the particles can be mixed within a single compartment
or isolated in separate compartments of the same or different cartridge.
 Similarly, the silica absorber may be in the water tank,
for example as an aluminum plate located within the water tank.
Alternatively or in addition, a silica absorber may be upstream,
downstream or both of the water tank.
 These and other aspects of the invention will be evident
upon reference to the attached figures and following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a schematic of a fuel cell system.
 FIG. 2 is a schematic of a water management subsystem for
a fuel cell system.
 FIG. 3 is a scanning electron microscope image of an oxidant
humidifier after operation in a fuel cell.
 FIG. 4 is a cross-sectional illustrative view of a water
filter of the present invention.
 FIG. 5 is a scanning electron microscope image of a typical
water filter after operation in a fuel cell system.
 FIG. 6 is a scanning electron microscope image of a water
filter of the present invention after operation in a fuel cell system.
 FIG. 7 is a scanning electron microscope image of alumina
granulate particles from a water filter of the present invention
after operation in a fuel cell system.
 FIG. 8 is a scanning electron microscope image of activated
carbon particles from a water filter of the present invention after
operation in a fuel cell system.
 In the above figures, similar references are used in different
figures to refer to similar elements.
DETAILED DESCRIPTION OF THE INVENTION
 A hydrocarbon fueled proton exchange membrane fuel cell
electric power generation system is the subject of commonly-owned
U.S. Pat. Nos. 5360679 and 6316134 which are hereby incorporated
by reference in their entirety. FIG. 1 is a schematic of the fuel
cell system 1 as described in the '679 patent. In particular, the
elements of fuel cell system 1 comprise:  an electric power
generation subsystem 10 for producing electricity, heat, and water
from a hydrogen-containing fuel stream and an oxidant stream; 
a fuel processing subsystem 20 for producing a hydrogen-rich fuel
for the electric power generation subsystem 10;  an oxidant
subsystem 30 for delivering pressurized oxidant to the electric
power generation subsystem 10;  a water management subsystem
40 for recovering the water produced in the electric power generation
subsystem 10 and optionally for cooling the electric power generation
subsystem 10;  a power conversion subsystem 50 for converting
the electricity produced into utility grade electricity; and 
a control subsystem 60 for monitoring and controlling the supply
of fuel and oxidant streams to the electric power generation subsystem.
 FIG. 2 shows a schematic of water management subsystem 40
in more detail. Specifically, water management subsystem 40 comprises
a water tank 42 water filter 44 and pump 46. Water management subsystem
40 recovers water by collecting excess water from the streams in
other subsystems (for example from electric power generation subsystem
10 fuel processing subsystem 20 oxidant subsystem 30 anode exhaust
70 and cathode exhaust 80) and returning the recovered water to
water tank 42. Water separators and water traps may be used to recover
water from the relevant subsystems as required. Other water filters
(not shown) may also be used in addition to or instead of water
filter 44 prior to introduction of water into water tank 42.
 Pump 46 can then pump recovered water from water tank 42
through water filter 44 to provide a purified water stream to the
following subsystems:  electric power generation subsystem
10 for cooling the fuel cell stack as shown by arrows 12 and 14;
 the fuel processing subsystem 20 (see arrow 22) for use in
the hydrocarbon reforming process and for humidifying the fuel stream
fed to the fuel cell stack (see arrow 24); and  the oxidant
subsystem 30 (see arrow 32) for humidifying the oxidant stream fed
to the fuel cell stack (see arrow 34).
 In other embodiments, each subsystem may be supplied by
an independent water management subsystem instead of having one
central water management system provide water to the various subsystems.
In yet other embodiments, hydrogen gas is supplied directly without
the use of a fuel processing subsystem. In which case, the water
management subsystem may provide a purified water stream for humidifying
the hydrogen gas fuel prior to being fed to the fuel cell stack.
In yet further embodiments, a separate cooling subsystem is used
to supply a coolant other than water (for example polyethylene glycol)
to the fuel cell stack, in which case the water management subsystem
is independent of the cooling of the fuel cell stack. In any event,
most, if not all fuel cell systems will contain a water management
subsystem for at least one of the functions of cooling, fuel processing
 Degradation pathways present in the fuel cell system can
result in contaminants that reduce the lifetime of the various components.
FIG. 3 is a scanning electron microscope image of an oxidant humidifier
after continued operation of a fuel cell system. Particles can be
clearly seen on the surface of the humidifier. The smallest particles
observed were 7 to 17 .mu.m though many of the particles were hundreds
of microns long. In particular, these particles formed downstream
of a 40 .mu.m particulate filter. Thus it is insufficient to simply
rely on a particulate filter to eliminate contamination of the humidifier.
Without being bound by theory, these particles may have formed by
the growth of polymeric silica on the aluminum surfaces of the humidifier
to form aluminosilicates. Particle formation would also be expected
on other components of the fuel cell system and would not be specific
to the humidifier.
 Silica is a polymer with the basic repeating unit of SiO.sub.2.
There are both polymeric and monomeric forms of silica and can be
represented as: Of the monomeric forms of silica, formula 1 H.sub.2SiO.sub.3
is also known as mono-silicic acid and formula (2) H.sub.4SiO.sub.4
is also known as ortho-silicic acid.
 Silica can be a difficult family of compounds to remove
from water and can be present in three forms: dissolved, colloidal
or suspended, or a combination thereof. Silica will not necessarily
stay in one form in solution and may convert to another form by
polymerization depending on the water conditions (temperature, pH,
total alkalinity and metals concentration). Monomeric silica tends
to be soluble whereas polymeric silica may be colloidal and granular
silica may be suspended.
 In addition silica can form insoluble metal silicates with
some trace metals in solution or on metal surfaces. Basic "ortho"
silicates are of the form M.sub.2SiO.sub.4 where M can be a divalent
metal such as Mg.sup.2+ or Fe.sup.2+. Aluminum silicates are also
very common though their structure is more complex. Further, metal
silicates tend to be chemically stable, particularly within the
temperature and pH conditions typically found within a fuel cell
 Without being bound by theory, silica and silicates may
be observed as a result of degradation of silicone used in other
components within the fuel cell system, for example from silicone
 Silica may be removed from the water management subsystem
by employing a silica absorber. For the purposes of this application,
a silica absorber comprises a metal that removes silica from an
aqueous solution thereof. Without being bound by theory, the mechanism
by which the silica absorber removes the silica may be either chemically
(for example, through the formation of metal silicates) or by physical
mechanisms (for example, through adsorption on materials with high
specific surfaces). Representative examples of silica absorbers
include magnesium, iron and aluminum, their metal oxides and combinations
thereof. In a more specific embodiment, the silica absorber comprises
aluminum oxide (also known and referred to herein as alumina).
 FIG. 4 is a schematic of a modified filter 44 comprising
an ion exchange resin 90 activated carbon 92 and alumina granulate
94. The different compartments for ion exchange resin 90 activated
carbon 92 and alumina granulate 94 are partitioned through the use
of partition filters 96. Filter 44 further comprises intake filter
95 and exit filter 98 at the water inlet and water outlet respectively.
Partition filters 96 and intake filter 95 may be, for example 100
.mu.m filters whereas exit filter 98 may be, for example, a 25 .mu.m
filter. In the embodiment illustrated in FIG. 4 activated carbon
92 and alumina granulate 94 are 15 mm thick. PVDF spacers may be
used (not shown) in making filter 44 and easily obtaining the correct
thickness of layers 92 and 94. Each of the layers 92 and 94 may
represent about 10% of the filter cartridge volume with the remaining
80% (approximately 120 mm) being filled with ion exchange resin
 Ion exchange resin 90 is made up of anion and cation resins,
in approximately equal ratios. The resins remove both anionic and
cationic contaminants. A typical resin is based on the styrene-divinyl
benzene co-polymer though other resins such as acrylic resins are
also used. Typically the resin has a bead structure composed of
an inert skeleton with charged functional groups throughout its
structure. In such a resin, the difference between the anion resin
and the cation resin is the functional group attached to the benzene
 The activated carbon 92 typically has a surface with a relatively
high amount of polar functional groups that can attract contaminants
of a similar polarity. Alumina granulate 94 may be, for example
of the type Saint-Gobain-Norpro (SGN) SA62125. Alumina granulate
SGN SA 62125 in particular has a chemical composition of .gamma.-alumina
with a surface area of 100 to 240 m.sup.2/g and a median pore diameter
of 65 to 120 Angstroms. High surface areas for both the activated
carbon and the alumina granulate is desired in order to increase
the efficiency in which they remove contaminants from the water.
 Water arriving from the water inlet flows through alumina
granulate 94 and activated carbon 92. The large specific surface
area of the two granulate beds 94 and 92 and the surface reaction
between the aluminum ions and the silica causes the silica contaminants
to become absorbed to the surface of the granules. Subsequently,
the water flows through ion exchange resin 90 leading to the removal
of other contaminants and is again filtered at exit filter 98. The
purified water may then be used as needed in the various fuel cell
 Silica can also lead to clogging of filter 44 particularly
from polymeric silica greater than 25 .mu.m in diameter. To illustrate
this and show the improvement of the modified water filter as in
FIG. 4 two fuel cell systems were operated for 16 hours under normal
operating conditions. In fuel cell system A, a conventional water
filter was used without activated carbon 92 nor alumina granulate
94. In comparison, in fuel cell system B, a water filter as in FIG.
4 was used. Scanning electron microscope images were then taken
of exit filter 98. FIG. 5 is the scanning electron microscope image
for the filter used in system A whereas FIG. 6 is the scanning electron
microscope image for the filter used in system B.
 Even with a relatively short operation time of 16 hours,
silica particles can clearly be seen in FIG. 5. In comparison, close
inspection of FIG. 6 shows a significant reduction of silica present
when the modified filter cartridge of the present invention is used.
This would be expected to result in a significantly longer service
life of water filter 44. In addition, absorption of silica at the
water filter would be expected to result in reduced amounts of solubilized
silica in the water thereby leading to reduced formation of metal
silicates on downstream components.
 FIG. 7 is a scanning electron microscope image of the alumina
granulate from the modified filter cartridge in system B. The alumina
granulate shows small surface bound silicon particles. FIG. 8 is
a scanning electron microscope image of the activated carbon granulate
from the same modified filter cartridge. As with the alumina granulate,
the activated carbon also shows significant silica absorption. An
SEM/EDX analysis (not shown) conducted on both the alumina granulate
and the activated carbon showed significant silicon peaks on both
 The composition of the silica absorber can vary significantly
without departing from the scope of the present invention. For example,
only the alumina granulate may be present in the water filter without
the activated carbon. In another embodiment (not shown), the alumina
granulate and the activated carbon are mixed together within a single
compartment and not separated as in FIG. 4.
 In addition, the location of the silica absorber can also
vary significantly. For example, in other embodiments, the silica
absorber is in a separate cartridge from a conventional water filter
and upstream, downstream or both of the water filter. Similarly,
the silica absorber may be upstream, downstream or both of water
 In another embodiment (not shown), replaceable exfoliated
high surface area aluminum plates could be placed in water tank
42. This would allow the silica to plate out as an aluminosilicate
before entering the filtration system. The aluminum plates could
be replaced and washed in caustic or hydrofluoric acid periodically
to regenerate them. However, aluminum fabrics tend to be expensive
and not have as high a surface area as alumina granulate.
 From the foregoing, it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention. Accordingly,
the invention is not limited except as by the appended claims.
 All of the above U.S. patents, U.S. patent application publications,
U.S. patent applications, foreign patents, foreign patent applications
and non-patent publications referred to in this specification and/or
listed in the Application Data Sheet, are incorporated herein by
reference, in their entirety.