FIELD OF THE INVENTION
The present invention relates to proton exchange membrane fuel cells (PEMFC)
and high temperature polymer electrolyte membrane fuel cells (HTPEMFC) which
convert chemical energy directly into electrical energy. More particularly, the
present invention relates to an improved device for enhancing performance of
PEMFC and HTPEMFC through internal gas pre-heating.
BACKGROUND OF THE INVENTION
Fuel cell is an electrochemical device that converts chemical energy directly into
electrical energy. One type of such fuel cell is proton exchange membrane fuel
cell (PEMFC). It consists of two electrodes anode, cathode and a polymer
electrolyte membrane (PEM), often called a proton exchange membrane that
permits only protons to pass between an anode and a cathode electrodes of the
fuel cell. At the anode, hydrogen (fuel) is reacted to produce protons (H+) that
pass through the PEM. The electrons produced by this reaction travel through
circuitry that is external to the fuel cell to form an electrical current. At the
cathode, oxygen is reduced and reacts with the protons to form water. The
anodic and cathodic reactions are described by the following equations
Anode
Cathode
In general, fuel cell power output is increased by increasing the cell operating
temperature (limited by the electrolyte used in the fuel cell), fuel and air flow to
the fuel cell in proportion to the stoichiometric ratios dictated by the equations
listed above. Thus, a controller of the fuel cell system may monitor the output

power of the stack and based on the monitored output power, estimate the fuel
and air flows required to satisfy the power demand. In this manner, the
controller regulates the required hydrogen flow, and in response to the controller
detecting a change in the output power, the controller estimates new flow rates
of fuel and air and controls them accordingly. In addition to this, critical
parameters like cell operating temperature would be maintained at constant
value irrespective of the external load changes to the fuel cell stack.
Conventional PEM fuel cell (low temperature PEMFC) operates at a relatively low
temperature, between 60 °C and 80° C. This enables the fuel cell to reach its
operating temperature quickly. Despite, the advantage of quick startup, low
temperature PEMFC requires hydration in the electrolyte membrane (PEM) for
ionic (H+) conduction, therefore requires an addition external or internal
subsystems for maintaining the required humidity levels in the fed reactant
gases. In addition to this, water formation on cathode side may lead to flooding
on the cathode side which is undesirable and limits the electrical load applied to
the stack.
In practice, cooling load required for maintaining such low temperature of stack
draws more energy than to maintain a high temperature for the same electrical
output. Apart from containing a Fuel Cell stack, a conventional PEMFC power pack
would also contain the following sub-systems for i) Air supply; ii) Fuel supply; iii)
humidification iv) stack cooling v) power conditioning & vi) controls. In addition to
this, low temperature PEM fuel cells require pure hydrogen, in terms of CO
content (CO<10 ppm) present in the reactant feed gas. Considering the afore
said facts and to meet the requirements of fuel cell operating conditions,
subsystems like humidification, cooling and air supply subsystems are
indispensable in addition to the PEM fuel cell stack.

In case of High Temperature PEM Fuel Cells (HT PEMFC), whose operating
temperature is above 120°C, humidification subsystem can be discarded because
Poly Benz Imidazole (PBI) and Pyridine based polymer electrolytes retain ionic
conductivities even in the absence of membrane hydration. As the typical operating
temperature of an HT PEMFC is between 150°C to 210°C, these power packs can
be used in for Combined Heat & Power (CHP) mode in which high grade heat is
made available to the end user. Moreover, the relatively higher temperatures of
operation of the HT PEMFC, not only enhances the electrochemical kinetics of Pt
catalyst, it also improves catalyst's tolerance to CO poisoning. It may be noted that
as compared to the CO tolerance of upto 10 ppm in the case of conventional
PEMFCs, the HT PEMFCs can tolerate upto 3 % of CO (30000 ppm) in the fuel
(Hydrogen) stream, making it possible to integrate the HT PEMFCs with
commercially available compressed natural gas (CNG), Methanol, ethanol, Liquefied
petroleum as (LPG) and Diesel reformers etc.
High temperature proton electrolyte exchange membrane (HTPEM) fuel cells are
widely used because of its operating temperature range (150°C to 210°C), which
contributes improved CO tolerances up to 3% in hydrogen feed gas. Moreover,
this temperature range provides i) easy thermal management, ii) eliminates zero
water management problems iii) allows use of humid free feed reactant gases and
iv) Simplifies overall system operability. Apart from the advantages as stated
hereinabove, the HTPEM fuel cells, are relatively cheaper because of having less
number of subsystems. Further, HTPEM cells are easily integratable with the
commercial reformers and more efficient when used in CHP applications.
Performance of HTPEM fuel cell is influenced by the ionic conductivity of the
membrane; prior art high temperature membranes for HTPEM fuel cell applications

are PBI and Pyridine based membranes doped with Phosphoric acid, whose ionic
conductivity varies from 0.08 S-cm to 0.12 S-cm. It is essential to operate the
HTPEM fuel cell/ stack above 100°C to avoid the formation of liquid water, due to
which acid content of the membrane is leached out which leads to degradation
of ionic conductivity. Therefore, it is essential to start the HTPEM fuel cell above
100°C, in order to meet the requirement of startup temperature. HTPEM fuel cell
is heated above 100°C by various methods i) external preheating of the reactants
before they are fed into the anode and cathode inlets of the fuel cell stack ii)
continuous circulation of the hot fluid through the stack cooling passages until
the stack reaches a specified startup temperature iii) circulation of the fuel
burner exhaust gases through the stack coolant passages and iv) circulation of
catalytic combustor exhaust gases through the stack inlets of either cathode,
anode and coolant channels depends on the fuel used in catalytic combustor. In
case of catalytic combustion process, fuel (hydrogen/methanol/natural gas etc) is
mixed with oxygen in the form air at specified ratio before they are fed into
catalytic oxidation chamber, where fuel and oxygen reacts in presence of catalyst
and gives heat, the exhaust hot gases are in fluid communication with the
appropriate stack inlets.
As described hereinabove, HTPEM fuel cells are required to be operated at above
120°C (startup temperature). In practice, a control system ensures that the
electrical load is ON once the fuel cell temperature reaches its startup
temperature. Stack startup temperature can be achieved using either of the
methods as mentioned above. Stack temperature increases soon after the stack
external electrical load is ON, due to exothermic reaction of water formation on
cathode side. Once the stack is subjected to an external electrical load, a
continuous rise in stack temperature takes place. In order to obtain optimal stack

performance, stack temperature is controlled at specified value between 160°C
and 210°C depending on the electrolyte used in the fuel cell. Typically, the stack
temperature is controlled either using radiator fans by which ambient air is
circulated through the cooling channels or by continuous circulation of high
boiling temperature liquid through the cooling channels. In case of liquid
circulation method, stack hot exit coolant fluid is cooled further with the
assistance of external radiators provided or the heat is recovered for various
applications.
It is known that performance of any fuel combustion process depends on the
temperature of fuel and oxidants fed into the combustion chamber. In order to
meet the requirement of specified temperatures of fuel and oxidant (air),
preheating systems are used. Performance of either PEM/HTPEM fuel cell further
depends on inlet temperatures of the reactants. Therefore, the reactants are
heated either with externally or internal heat source to a specified temperature
to obtain better fuel cell performance. In case of external heating process, an
external heat exchanger is used, wherein the reactants, they are typically heated
by utilizing the available stack heat carried away by the coolant or by the heat
released from a catalytic combustor placed after the fuel cell stack to ensure
clean emissions. Accordingly, the hydrogen exited by unconverted anode, and air
exited by cathode side are fed into the catalytic combustion chamber followed by
mixing where they react each other and produces heat. In case of internal
reactants preheating process, the reactants are heated within the stack assembly
without using any external heat exchanger. In this regard, significant numbers of
patents have been filed on utilization of heat generated during the operation
HTPEM fuel cells, in particular the stack heat is used for preheating liquid fuel
before it is fed into fuel processor for hydrogen generation.

US patent No. 20050014040 to Ian W. Kaye utilized the heat generated in the
stack for preheating the reformer liquid fuel (methanol/ Ethanol/ Ethanol) in
efficient way in view of increasing the fuel cell system efficiency. In this case,
liquid fuel is preheated in a heat exchanger by utilizing the hot air which is being
heated in the fuel cell stack housing. The exhaust air from the heat exchanger is
finally fed into the fuel burner for maintaining the catalytic reformer
temperature. In this case air required for burner is passed over the appended
heat transfer plate, on the other hand, cathode air is fed with separate air blower
through a separate air line.
US patent No. 20060099467 to Richard H. Cutright et al. developed an
integrated high temperature PEM fuel cell system. An overall fuel cell system
comprises, a High temperature fuel cell stack for generating electricity, air supply
system for supplying the oxidant to cathode, auto thermal reformer system for
supplying hydrogen rich gas to anode side, cooling system for maintaining the
temperature of subsystem and control system for ensuring the specific operating
conditions of the individual subsystems. In their invention, the cathode side
receives ambient air directly through the blower and reacts on cathode side of
PEM fuel cell. The exhaust of cathode side air is in communication with the auto
thermal reformer, where partial amount of exhaust cathode air is fed into the
reformer inlet section. The exhaust of reformer, hydrogen rich gas is in fluid
communication with the anode inlet of HTPEM fuel cell stack. The exhaust of
stack anode, hydrogen lean gas is fed to the oxidizer along with the partial
amount of cathode side exit gas where the unconverted hydrogen is oxidized in
the catalytic converter (oxidizer) and then the exhaust of oxidizer is vented to
atmosphere. In their invention, the exhaust hot air from the HTPEM fuel cell
stack is directly fed into the oxidizer and auto thermal reformer by which they
have improved the system overall efficiency.

US patent 20020160239, PEM fuel cell system is integrated with a fuel processor
and an exhaust gas oxidizer to ensure clean emissions. In their study HTPEM fuel
cell is used with an operating temperature of 120-200° C. Cathode exhaust of
fuel cell is used to provide steam and oxygen to a reformer to convert a
hydrocarbon fuel to hydrogen, wherein the hydrogen is provided to a fuel cell. In
addition to this partial amount of cathode exhaust is fed into the oxidizer along
with anode side exhaust gases to result in clean emissions.
US patent 20056,899,062 fuel cell stack is cooled by ambient air using a blower,
exhaust hot air from the blower is directly fed into the cathode inlet as a result
cathode side hot feed supply is achieved. US patent 20060099467, fuel cell stack
having a cathode inlet to receive a flow of ambient air and a cathode outlet to
provide a cathode exhaust flow; and a fuel processing reactor having an inlet
and an outlet, the inlet and outlet being in fluid communication with a catalyst
suitable for converting a hydrocarbon into a gas containing hydrogen and carbon
monoxide, the outlet being in fluid communication with an anode chamber of
the fuel cell and the outlet of the reactor being in fluid communication with the
cathode outlet for combustion of exhaust gases.
US patent 20107666539B2, by Jennifer E Branley et al. In their invention,
unconverted or exhaust gases of burner are passed over heat transfer appendages
which are thermally in contact with the stack bipolar plates finally the burner
exhaust gasses passes through catalytic combustor which is intact with the stack
externally, the outlet gases of the catalytic combustor are thermally in contact with
stack using a heat pipe. In which the appendages are thermal bridging pieces
between a thermal catalytic combustion and bipolar plates. In more details, part of
the appendages is coated with a thermal catalyst by which the temperature of the

circulating gas will be increased further to heat the stack. In all their invention, heat
is recovered efficiently external to the stack. In addition to this, cathode exhaust is
used for preheating the methanol fuel which fed into reformer for generation of
hydrogen.
US patents 20050271915, 201000062293 teach internal alcohol fuel cells using
different electrolytes such as CsH2PO3, PBI and pyridine whose operating
temperature varied from 180 °C to 240 °C depends on the electrolyte being used
the cell. In all their developments, methanol and water mixture of required ratio is
used as the reactant feed at anode side and air is used as the cathode side
reactant. In their developments, conventional and modified electrodes were used
on cathode and anode sides respectively. The cathode side electrode is a carbon
supported Pt ink coated one, on the other hand, the anode electrode comprises
two catalyst layers, carbon supported Pt layer followed reformed catalyst layer. The
alcohol-water mixture is being fed at anode side electrode where it reacts first with
reformed catalyst, the reaction as follows
CH3OH + H2O H2 + CO2(Endothermic reaction)
During the process, generated hydrogen is being transferred across the reformed
catalyst to the carbon supported Pt layer electrode layer where it reacts and
gives protons (H+) and electrons. The protons moves from anode to cathode
through an electrolyte where it reacts with oxygen present in the air. The
reactions are follows
Anode
Cathode

In both the cases, the reformed catalyst coated over the anode side electrode
layer where reformation of methanol takes place to give hydrogen rich gas and
oxidation of hydrogen take place to give protons simultaneously at anode side.
This is most thermal efficient method by which hydrogen is being generated from
the inlet liquid fuel, thermal energy required for internal reformation is absorbed
from cathode side exothermic water formation reaction. Despite the advantages
of less system complexity having an internal reformer adjacent to anode side,
degradation of the anode electrode performance is relatively high when
compared with the hydrogen supplied from an isolated reformer this may be due
to the result of excess ohmic losses.
In the internal reformed HTPEM fuel cells, methanol is directly fed into anode inlet,
where simultaneous methanol reformation to give hydrogen and oxidation of
hydrogen takes place on the anode side electrode itself. Moreover, inlet
temperature of the reactants play a significant role in improving the performance
of conventional PEM/ HTPEM/ internal reformed HTPEM fuel cell. In case of
conventional PEM, the reactant gases of hydrogen and air are fed into the fuel
cell anode cathode inlets respectively followed by humidification. In such cases,
water vapour carried by the reactants may condense between the lines of
humidifier and stack inlet which is undesirable for a conventional PEM fuel cell.
On the other hand, inlet reactants temperature for HTPEM or internal reformed
PEM fuel cells has to be maintained above 120°C to avoid the acid leaching in the
electrolyte at the local sites of the membrane. Many of the inventors used a
process of external heating to achieve the prerequisite reactants temperature.
A prior art PEM fuel cell (single) comprises three basic components such as
electrolyte, anode and cathode. Electrolyte is used for ionic conduction between
two electrodes (anodes and cathode). Oxidation of hydrogen takes place at

anode over catalyst to give protons and electrons; the electrons are transferred
to the external circuit through electrical conduction medium and protons are
conducted to another side (cathode) through ionic conducting medium (proton
electrolyte membrane). At cathode, reduction reaction between hydrogen ions,
electrons and oxygen takes place in presence of catalyst to form water, as a
result of the exothermic reaction significant amount of heat would be released.
In case of conventional PEM fuel cells, perflurosulfonic acid based polymer
membrane is used as the electrolyte, carbon supported Pt is used as the
electrocatalyst for anode and cathode electrodes. In practice these electrodes
are prepared by coating the electrocatalyst over the substrate of gas diffusion
layer having property of thermal and electrical conductivity. In order to form a
complete single cell, the membrane is hot pressed between two electrodes to
form a membrane electrode assembly (MEA). Further, the MEA is placed
between two copper plates followed by gas flow field plates on each side of MEA;
finally the whole assembly is tightened between two end plates to form complete
single PEM fuel cell. The fuel cell has a terminal voltage of up to one volt DC. For
purposes of producing much larger voltages, several fuel cells are electrically
connected in series and assembled together between the end plates to form an
arrangement called a fuel cell stack.
OB3ECTES OF THE INVENTION
1. Development of integrated plate which is suitable to integrate within the
existing stack housing assembly on cathode side for preheating the
cathode side inlet feed reactants
2. Development of Integrated plate which is suitable to integrate within the
existing stack housing assembly on anode side for preheating the anode
side inlet feed reactants.

3. Heat recovery from the cathode side exhaust gases using the developed
integrated plates.
4. Heating of HTPEM fuel cell stack to meet the stack startup temperature
using integrated plate with the heat source supplied to the integrated
plate.
It is therefore an object of the invention to propose an improved device for
preheating reactants in PEM/ HTPEM fuel cell stacks. Another object of the
invention is to propose a method of pre-heating reactants in PEM/HTPEM fuel
performance of the fuel stocks.
SUMMARY OF THE INVENTION
According to the invention, an improved device is provided for heating of the
reactant gases such as Hydrogen and Air/ Oxygen within the stack assembly
(internal gas preheating) before they are fed into electrochemical active zone of
anode and cathode sides respectively in low temperature / high temperature
PEM fuel cells. Internal gas preheating involves, a plate provided with a heating
source is placed between the stack insulating plate and current collector plate. In
this case, the gas preheating plate receives the reactant gas through the regular
stack inlet and then the gas is circulated around the heating source where the
gas is being heated then the hot reactant gas exits from the heating plate and
enters into the electrochemical active zones of stack anode and cathode sides
respectively.

According to the present invention, fuel cell reactant gases are pre-heated to a
required temperature before they are fed into the electrochemical active sides of
fuel stack anode and cathode respectively. The proposed step of reactants
preheating can be adapted for conventional, HTPEM and internal reformed
HTPEM fuel cells. Preheating plate is configured such that it can easily be
accommodated within the conventional stack assembly sequence without the
need of change in the regular inlets and outlets of cathode and anode
respectively. Typically a PEM/HTPEM fuel cell assembly follows the sequence of
top pressure plate, insulation plate, copper plate (anode), anode half-bipolar
plate membrane electrode assembly (MEA), bipolar plate, MEA, bipolar plate,
repetitive sequence of MEA followed by bipolar plate, cathode half-bipolar plate,
copper plate (cathode), insulation plate and bottom pressure. All the afore said
components are tied together for a required torque applied over the top and
bottom pressure plates using tie rods to form a PEM cell stack. Complete
schematic of conventional PEM fuel cell stack is shown in Fig.l.
According to the invention, integrated reactants preheating of PEM/ HTPEM fuel
cell/ stack which consists of two metal plates in addition to the conventional
stack assembly components, is made possible. These are anode side reactant
preheating plate which is placed between the insulation plate and anode side
copper plate. On the other hand, cathode side reactant preheating plate is
placed in between the cathode copper plate and insulation plate. These
preheating plates are provided with an electrical heating source, and for
circulating the hot fluid by which the plate is initially heated to a required
temperature is done by the electrical source. Typically the reactants are fed to
the regular stack inlet and the inlet of preheating plate is directly in fluid
communication with the regular stack inlet. The received reactant gas is

distributed all over the heated plate and the gas is being heated while the gas is
flowing between the hot fins of the preheating plate. Finally the reactant gas
leaves through gas preheating plate exit and enters into the regular reactant
manifold line of anode or cathode side.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1. Conventional PEM fuel cell stack assembly
Figure 1.4A. Top view and bottom view of half bipolar plate
Figure 2. PEM fuel cell stack assembly with integrated reactant preheating plates
Figure 3. Gas preheating plate without gas flow grooves
Figure 4A. Complete schematic of anode side gas preheating plate
Figure 4B Flow path streamlines of anode side reactant gas
Figure 5A. Complete schematic of cathode side gas preheating plate
Figure 5B Flow path streamlines of cathode side reactant gas
Figure 6 Process flow chart of reactants preheating in PEM fuel cell stack
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A prior art PEM fuel cell stack is shown in Fig.l, the stack comprises two end
plates (1A, IB) between which the balance components of the PEM fuel stack are
tightened using tie rods (7). The components of PEMFC stack includes insulating
plates (2A, 2B) to protect against thermal and electrical losses, copper plates
(3A, 3B) for collecting the electrons generated at the electrocatalyst sites of the
membrane electrode assemblies (5) through half bipolar plates of anode (4A)
and cathode (4B) respectively. An half bipolar plate (4A or 4B) having a flow
pattern on each side as shown in Fig. 1.4A. The first half (4A) is for routing the
reactant gas (1) and the second half (4B) to allow the coolant circulation whose
pattern (2) is shown. Two such half bipolar plates (4A, 4B) are laminated

together to form a bipolar plate (6) which has a gas flow channels on each side
of the plate, a first side is used for anode side gas distribution including
cathode side gas distribution. The bipolar plate is designed such that one side of
the gas distribution pattern is for receiving the hydrogen from a bulk hydrogen
manifold (11A) and routing to a bulk exit hydrogen manifold (11B) represented
with down and up arrows respectively. In a stack, the hydrogen gas manifolds
(11A, 11B) are directly in fluid communication with their stack inlet (8A) and
outlet (8B) respectively. In case of cathode, the second side of the bipolar plate
(6) has the gas distribution pattern for receiving the oxygen or air from a bulk
inlet manifold (12A) and routing to a bulk exit (12B) represented with up and
down arrows respectively. In a stack, the air manifolds (12A, 12B) are directly in
fluid communication with their stack inlet (9A) and outlet (9B) respectively. In
between these gaseous flow distribution plates, a coolant circulation channels
pattern (2) is used for circulation of coolant medium to cool the stack, (see Fig.
1.4A).
A PEM fuel cell stack as shown in Fig.l has the hydrogen inlet (8A) through
which hydrogen or reformed hydrogen is fed into the fuel cell stack, thereafter,
the reactant gas travels from one end to an opposite dead end (10) through the
common manifold (HA) represented with down arrows from which anode side of
each MEA of the stack receives hydrogen through an anode gas distribution plate
(6A) one such being shown in Fig. 1. The exits of each anode side of the
respective MEA's are connected to an anode exit manifold (11B) represented
with up arrows (diagonal to the inlet manifold 11A) which is in fluid
communication with stack anode exit (8B). In general, one such reactant gas
travel path (1) over a gas distribution plate received from inlet gas manifold to
outlet gas manifold is shown in Fig.l.4A. In similar manner, cathode side
reactant plates of each MEA's of stack receives oxygen/ air through the air inlet

manifold (12A) represented with up arrows between stack air inlet (9A) and its
respective dead end. Each cathode flow field plate of stack receives air from the
inlet air manifold (12A) which has a direct fluid communication with stack air
inlet (9A), finally the product water and un-reacted gas mixture is routed to the
exit air manifold (12B) through the cathode side gas distribution flow path.
Cathode exit manifold is represented as a line of down arrows in diagonal to the
air inlet manifold (12A). Finally the cathode side exit gas mixture vent through
the stack air or oxygen exit (9B).
Conventional PEM fuel cells operate below 80°C and requires hydration for the
membrane ionic conduction. One such method for maintaining the hydration of
the membrane is by feeding the humidified reactants into the fuel cell stack. In
practice, humidification of the reactants is achieved by external (out side the
stack assembly) methods. In practice, there might be of vapor condensation
between the lines of humidification and reactant inlets of the stack, which may
lead to local condensation of water vapor at the electrocatlyst layer resulting in
adverse effect of drop in cell voltage. In order to overcome this problem,
reactants of either anode side or cathode side gas lines are provided with the
heating arrangement external to the stack. The heating source could be an
electrical or a cathode side exhausts gas.
In principle, the chemistry involved in LTPEM fuel cells and High Temperature
PEM Fuel Cells (HT PEMFC) are same except their operating temperature and
properties of the membrane. HTPEMFC operating temperature is above 120°C,
ionic (H+) conduction of membranes like Poly Benz Imidazole (PBI) and Pyridine
based polymer electrolytes retain their conductivities even in the absence of
membrane hydration. Since these membranes are doped with phosphoric acid for
better ionic conductivity, they become sensitive for the acid leaching in presence of

liquid water. Therefore, the HTPEMFC stack has to be started above 100 °C to
avoid degradation of the membrane ionic conduction. As the typical operating
temperature of an HT PEMFC is between 150 °C to 210 °C, the reactants have to
be heated to a prerequisite temperature preferably above 100 °C. In practice,
HTPEMFC startup temperature is reached by circulating the hot gases through the
cooling channels or by allowing the hot air through cathode inlet. Once the stack is
attained its startup temperature, reactants preferably preheated hydrogen/
reformer hydrogen and air are fed into the anode and cathode inlets of the stack
respectively. Now the electrical load is allowed to turn ON once the stack
temperature reaches the startup temperature. In case of HTPEMFC stack, hot
hydrogen and air have to be fed into stack to obtain better stack perform ance
which is analogues to the conventional air-fuel mixture preheating in combustion
chamber for delivering better performance. In this regard, many of the prior art'
use reformer final outlet hydrogen directly fed at the anode side inlet, on other
hand, hot air from the air cooled stack exhaust is directly used at the cathode inlet
using blower.
Present invention is pertaining with preheating of reactants before they are fed into
the main manifolds where from anode side and cathode side gas distribution plates
receives hydrogen and air respectively. In this case, the reactants are heated within
the fuel cell stack assembly. In contrast to the conventional PEM/ HTPEM fuel cell
as shown in Fig. 1, an integrated PEM/ HTPEM fuel cell stack is shown in Fig. 2 and
comprises two additional plates (15, 16) in addition to the conventional PEM fuel
cell components which are placed adjacent to anode side copper plate (3A) and
cathode side copper plate (3B) respectively. The detailed schematic of a
preheating plate (15,16) is shown in Fig.3 without gas flow grooves. It consists of
common through holes (17,18) for tightening the stack and for routing the
reactants to their respective manifolds. In addition to this, the preheating plate

(15,16) consists of two semi drilled holes (19) opposite to each other separated
with a solid barrier. In this case these, two holes are inline with the conventional
reactant (air or hydrogen) inlet and its manifold used for receiving and distributing
the concerned reactant to the individual cells of anode or cathode respectively. One
side of the semi drilled hole receives the hydrogen or air from the hydrogen or air
inlet and it is allowed to reach the other side of the semi drilled whole for hydrogen
or air outlet through direct slot (20) provided for direct fluid communication
between top and bottom faces of preheating plate. In addition to this, integrated
preheating plate is provided with through holes (21, 22), few of these holes can be
used for heating the plate by means of inserting an electrical heaters in holes (22)
or to circulate the burner exit gases and the remaining holes would be used for
collecting the heat from the exhaust cathode gases. This can be achieved by
allowing the cathode exit gases through the holes (21) by which the preheating
plate gets heated up by gaining the heat from the cathode exhaust gases, on the
other hand inlet reactant gases are heated up when they flow over the preheating
plate. These preheating plates are in thermal communication with the stack copper
plates of anode and cathode respectively, therefore these plates are useful in
gaining thermal energy from the stack bipolar plates as well transferring the same
to the stack bipolar plates through the copper plates.
In a convention PEMFC stack as shown in Fig. 1, all anode and cathode plates of
stack receives hydrogen and air from their respective inlet gas manifolds (11A,
12A), where inlet manifolds of hydrogen and air are directly in fluid communication
with their inlets of hydrogen (8A) and air (9A), where as in integrated gas
preheating PEMFC stack as shown in Fig. 2, inlet gas manifolds (13A, 14A) are not
directly in fluid communication with their respective gas inlets (8A, 9A). In both the
stacks (Fig. 1, Fig. 2) un-reacted hydrogen and air (contains product water) from

each anode and cathode side plates are routed to their exit gas manifolds (13B,
14B) having a direct fluid communication with their respective gas outlets of
hydrogen (8B) and air (9B).
An integrated gas preheating plate is shown in Fig. 3 is more generic design
without augmentation of any flow pattern designs, gas distribution designs varies
based on the application and purpose for which the plate is used. In case of an
integrated gas preheated PEM fuel cell stack, as mentioned earlier preheating plate
is placed in between the insulation plate and copper plate. For example, a complete
schematic of anode side gas preheating plate is shown in Fig. 4A, consists of
parallel gas distribution patterns (23, 24) represented with a parallel fins on both
the sides of the plate. Typically these fins are heated with the source of heat
provided through the heating source channels (25,26), which can be used for multi
purpose such as to provide electrical heating source using a straight heaters (26) or
to provide hot exhaust gases of burner connecting them to through holes (25).
Preheating plate receives the hydrogen directly from the stack inlet and it is directly
fed to the top side preheating plate manifold through a plate inlet wherein it is
uniformly distributed through the gas flow passages (23) provided on one side,
other side (bottom) of gas flow passages (24) receives the gas through a fluid
communication line (27) positioned in diagonal with a hydrogen inlet (28). In
similar way, gas received from top side through the fluid communication (27) is
again redistributed between the fins of bottom side gas flow passages (24), during
this process the gas is allowed to flow twice over the heated fins, therefore the
reactant gas gains the maximum possible heat from the hot fins. During the
process of gas flow between the hot fins placed on both sides, the gas is being
heated by convective heat transfer. Finally, hot gas with temperature close to plate
temperature exits from a preheating plate outlet (29) into the stack hydrogen inlet

manifold, where from the individual anode side gas distribution plate receives the
hot hydrogen.
Flow of hydrogen over anode side gas preheating plate is shown in Fig. 4B, the
schematic of preheating plate where the top and bottom of the faces are
uncovered. In case of anode side gas preheating plate, the plate consists of one
gas inlet (28), one gas outlet (29) opposite to each other, four gas manifolds (32),
top and bottom side gas flow passages (23, 24) shown with the arrows (30, 31) on
each side which are having a direct fluid communication with the manifolds and
one through slot (20) for fluid communication from onside of manifold to the other
side. Flow of gas over the plate is explained as hydrogen from the stack hydrogen
inlet (8A, Fig. 2) enters at the entrance (1) of the gas preheating plate, flow path
of the gas is given with the arrows as mentioned in the Fig 4B, where the hydrogen
gas received from the inlet (28) flows through the gas passages (23,24) in the
forward direction, the flow of gas is mentioned with the arrows (30). The gas is
being heated once on topside before the bulk gas is guided through the manifold
(32) to the other side of the plate through the slot (20). On the other side (bottom
side), the bulk gas from the manifold is again redistributed through the bottom side
gas flow passages (24), flow path of the gas is in opposite direction with the gas
flow path (30) of top side which is clearly shown with the set of arrows (31)
represents the gas flow path where the gas is again reheated during the traveling
from one end of manifold to the other end. Therefore, the gas gains the maximum
possible heat from hot fins. Finally the hot hydrogen from the plate leaves from the
preheating plate exit (29) and enters into the regular hydrogen manifold; the exit
of gas preheating plate has direct plumbing communication with the hydrogen
manifold, where from the hot hydrogen is supplied to the individual single cells in
the stack.

A complete schematic of cathode side gas preheating plate is shown in Fig. 5A and
flow of air streamline over cathode side gas preheating plate is shown in Fig. 5B.
In practice design of anode gas preheating plate and cathode gas preheating plate
are alike, to use the same anode side gas preheating plate as cathode side gas
preheating, the preheating plate inlet (3) is kept inline of stack air inlet, to explain it
more clear, Fig 5A is the result of Fig 4A after rotation of 180° around minor axis,
on the other hand Fig 5B is the result of Fig 4B after rotation of 180° around minor
axis. In principle, heating of air over the cathode side gas preheating plate is
similar to the process of anode side gas preheating plate as discussed above.
Sequential process of reactants preheating is given in Fig. 6

WE CLAIM :
1. An improved device for preheating reactants in PEM/HTPEM fuel cell
stacks, the improvement is characterized by comprising an anode side
reactant preheating plate placed between the insulation plate and the
anode side copper plate; and a cathode side reactant preheating plate
interposed between the cathode copper plate and the insulation plate, the
preheating plates preferably connected to an electrical heating source or
for circulating hot fluid, the plate being initially heated to a pre-
determined temperature, an inlet of the preheating plate disposed directly
in fluid communication with the regular stack inlet receiving reactants, the
received reactant gas distributed all over the heated plate to allow heating
of the reactant gas when flowing between hot fins of the preheating plate,
the reactant gas exiting through the plate exit to ingress the reactant
manifold line of anode or cathode side.
2. The device as claimed in claim 1, wherein inlet of the anode side gas
preheating plate is positioned inline with hydrogen or reformed fuel of
stack inlet.
3. The device as claimed in claim 1, wherein inlet of the cathode side gas
preheating plate is positioned inline with air or oxygen of stack inlet.
4. The device as claimed in claim 1, wherein a fluid communication line is
provided between the preheating plate heat source and cathode exhaust
for heat recovery from the cathode side exhaust gases.

5. A method for enhancing performance of PEMFC and PEM stacks in a
device as claimed in claim 1, through internal gas pre-heating, comprising
the steps of:
- heating the cathode side gas pre-heating plate of the improved device to
a pre-determined temperature through an operably connected heating
source;
- supplying air at the cathode side of the cell/ stack and heating the air
substantially corresponding to plate temperature;
- inputting the hot air to the air manifold of the cathode side for distribution
among all the cathodes of the cells in the stack;
- discharging the un-reacted air and produced water through stack outlet
and recovering the latent heat of the exhaust gases;
- heating the gas pre-heating plates by the heat source, supplying through
gas inlet hydrogen-rich pressurized gas to the anode side pre-heating
plates, and heating the hydrogen gas corresponding to the plate
temperature;
- inputting the heated hydrogen gas to anode side air manifold for
distribution among all the anodes of the cells in the stack;
- discharging the un-reacted gas via the gas outlet; and

- allowing the exhausted hydrogen gas from the anode side to mix with
exhaust air from the cathode side and oxidize in a catalytic combustor.

ABSTRACT

The invention relates to an improved device for preheating reactants in
PEM/HTPEM fuel cell stacks, the improvement is characterized by
comprising an anode side reactant preheating plate placed between the
insulation plate and the anode side copper plate; and a cathode side
reactant preheating plate interposed between the cathode copper plate
and the insulation plate, the preheating plates operably connected to an
electrical heating source for circulating hot fluid the plate being initially
heated to a pre-determined temperature, an inlet of the preheating plate
disposed directly in fluid communication with the regular stack inlet
receiving reactants, the received reactant gas distributed all over the
heated plate to allow heating of the reactant gas when flowing between
hot fins of the preheating plate, the reactant gas exiting through the plate
exit to ingress the reactant manifold line of anode or cathode side.