WO2005028716A1

WO2005028716A1 - Method and system for monitoring fluids of an electrochemical cell stack

Info

Publication number: WO2005028716A1
Application number: PCT/CA2004/001729
Authority: WO
Inventors: Jianming Ye; Ali Rusta-Sallehy; Ricardo Bazzarella
Original assignee: Hydrogenics Corp
Current assignee: Hydrogenics Corp
Priority date: 2003-09-22
Filing date: 2004-09-22
Publication date: 2005-03-31
Anticipated expiration: 2006-03-22

Abstract

A system for monitoring a fluid of an electrochemical cell stack is described. The monitoring system includes a plate, a first conduit in the plate for transporting the fluid, a second conduit in the plate, in fluid communication with the first conduit; and a fluid sensor, a portion of which is disposed in the second conduit for monitoring the fluid of the electrochemical cell stack.

Description

Method and System for Monitoring Fluids of An Electrochemical Cell Stack

FIELD OF INVENTION The present invention relates to electrochemical cell stacks, and more specifically relates to monitoring fluids of electrochemical cell stacks.

BACKGROUND OF THE INVENTION Electrochemical cell stacks include fuel cell stacks, which are used as a source of power, and electrolytic cell stacks (or electrolyzers), which are used as a source of hydrogen.

Fuel cells are attractive as a clean, efficient and environmentally friendly source of power produced by bringing a fuel (typically hydrogen gas) and an oxidant (typically air or oxygen gas) into contact with two suitable electrodes and an electrolyte. The fuel is introduced at a first electrode where it reacts electrochemically in the presence of the electrolyte to produce electrons and cations. The electrons are circulated from the first electrode to a second electrode via an electrical circuit. Cations pass through the electrolyte to the second electrode.

Simultaneously, the oxidant is introduced to the second electrode where the oxidant reacts electrochemically in presence of the electrolyte and catalyst, producing anions and consuming the electrons circulated through the electrical circuit; the cations are consumed at the second electrode. The anions formed at the second electrode or cathode react with the cations to form a reaction product. The first electrode or anode may alternatively be referred to as a fuel or oxidizing electrode, and the second electrode may alternatively be referred to as an oxidant or reducing electrode.

The half-cell reactions at the two electrodes are, respectively, as follows: H₂ → 2H+ + 2e- O 2005/028716

1/2O₂ + 2H+ + 2e- → H₂0 The external electrical circuit withdraws electrical current and thus receives electrical power from the fuel cell. The overall fuel cell reaction produces electrical energy as shown by the sum of the separate half-cell reactions written above. Water and heat are typical by-products of the reaction.

Conceptually, electrolyzers are fuel cells run in reverse, and share many of the same components as fuel cell stacks. A current is supplied to the electrolyzer for hydrolysis, generating oxygen from its anode and hydrogen from its cathode. Similar to a fuel cell, a typical solid polymer water electrolyzer (SPWE) or proton exchange membrane (PEM) electrolyzer includes an anode, a cathode and a proton exchange membrane disposed between the two electrodes. Water is introduced to, for example, the anode of the electrolyzer, which is connected to the positive pole of a suitable direct current voltage. Oxygen is produced at the anode according to the reaction H₂0 → 1/2O₂ + 2H+ + 2e-

The protons then migrate from the anode to the cathode through the membrane. On the cathode, which is connected to the negative pole of the direct current voltage, the protons conducted through the membrane are reduced to hydrogen following 2H+ + 2e- → H₂.

In practice, fuel cells and electrolyzers are not operated as a single cell. Rather, cells are connected in series, stacked one on top of the other, or placed side by side, to form a cell stack. As used herein, the term "cell stack" includes the special case where just one cell is present, although typically a plurality of cells are stacked together to form a cell stack.

In a fuel cell stack, the fuel and oxidant are directed through manifolds to the electrodes, while cooling is provided either by the reactants or by a cooling fluid or coolant. Also within the stack are current collectors, cell-to-cell seals and insulation, with required piping and instrumentation provided externally of the cell stack. A cell stack includes two end plates that sandwich components of the cell stack. End plates provide integrity to the cell stack by acting as an anchor for rods or bolts that are used to compress together various components of the cell stack resting between the end plates. Moreover, end plates contain connection ports to which are attached fuel, oxidant and coolant ducts or hoses. These process fluids flow through the connection ports into and out of the cells stack.

End plates must be strong enough to bear the forces required to compress components of the cell stack and to secure fuel, oxidant and coolant ducts or hoses to the respective ports of the end plate. For this reason, end plates are thicker than most of the other components of the cell stack. Combined with the many cells stacked on top of one another, the size of the cell stack is not insignificant. Increasing the effective volume of the cell stack even further is the myriad of sensors used to monitor the process fluids.

In particular, in an electrochemical cell system, the condition of process fluids is monitored to ensure that the electrochemical cell stack operates properly. Typical parameters that are measured include pressure, temperature and flow rate of the process fluid at various points. Sensors are usually provided adjacent to the inlet and outlet of an electrochemical cell stack to monitor the condition of the process fluids flowing through the stack and/or the performance of the stack. This requires that multiple sensors be disposed in the flow paths of the process fluids. These sensors are conventionally provided along pipelines of the process fluids, which takes up space and makes the system bulky and complicated. This also leads to difficulties in repair and maintenance. Thus, any innovation that could help reduce the effective size of a cell stack would increase the performance and range of application of such stacks, and would therefore be most welcome in the field of electrochemical cell stacks.

SUMMARY OF THE INVENTION To address the aforementioned difficulties associated with large cell stacks, sensors are inserted into conduits in plates of the cell stack to monitor fluids, instead of inserting them externally in the hoses delivering or removing fluids to and from the stack. >

In particular, described herein is a plate, such as an end plate, and a system for monitoring a fluid of an electrochemical cell stack. The monitoring system includes a plate, a first conduit in the plate for transporting the fluid, and a second conduit in the plate, in fluid communication with the first conduit. A portion of a fluid sensor is disposed in the second conduit for monitoring the fluid of the electrochemical cell stack.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which show preferred embodiments of the present invention and in which:

Figure 1 illustrates an exploded perspective view of a fuel cell unit located within a fuel cell stack; Figure 2 illustrates a monitoring system for monitoring a fluid of an electrochemical cell stack in accordance with the present invention; Figure 3 illustrates a monitoring system for monitoring a fluid of an electrochemical cell stack in accordance with the present invention; Figure 4 illustrates an exploded perspective view of an electrolytic cell located within a fuel cell stack; Figure 5 illustrates a perspective view of an electrochemical cell stack having an end plate in accordance with the present invention; Figure 6 illustrates a first perspective view of an inner face of the end plate in accordance with the present invention; Figure 7 illustrates a second perspective view of the inner face of the end plate in accordance with the present invention; Figure 8 illustrates a third perspective view of an outer face of the end plate in accordance with the present invention; Figure 9 illustrates a front elevational view of the end plate in accordance with the present invention; Figure 10 illustrates a top view of the end plate in accordance with the present invention; Figure 11 illustrates a first side view of the end plate in accordance with the present invention; Figure 12 illustrates a second side view of the end plate in accordance with the present invention; Figure 13 illustrates a back elevational view of the end plate in accordance with the present invention; Figure 14 illustrates a partial view of the end plate in accordance with the present invention, along direction F in Figure 9; Figure 15 illustrates a partial view of the end plate in accordance with the present invention, along direction H in Figure 9; Figure 16 illustrates a sectional view of the end plate in accordance with the present invention, taken along line A-A in Figure 9; Figure 17 illustrates a sectional view of the end plate in accordance with the present invention, taken along line B-B in Figure 9; Figure 18 illustrates a sectional view of the end plate in accordance with the present invention, taken along line C-C in Figure 9; Figure 19 illustrates a sectional view of the end plate in accordance with the present invention, taken along line D-D in Figure 13; and Figure 20 illustrates a sectional view of the end plate in accordance with the present invention, taken along line E-E in Figure 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows an exploded perspective view of a fuel cell unit 100.

The fuel cell unit 100 includes an anode flow field plate 120 and a cathode flow field plate 130 that sandwich a membrane electrode assembly (MEA). Various sizes are possible for the plates 120 and 130. In one embodiment, the short edge of the flow field plates 120, 130 is about 12 cm. Each plate 120 and 130 has an inlet region, an outlet region, and open-faced channels (not shown). The channels fluidly connect the inlet region to the outlet region, and provide a way for distributing the reactant gases to the outer surfaces of the MEA 124. The MEA 124 comprises a solid electrolyte (i.e. a proton exchange membrane or PEM) 125 disposed between an anode catalyst layer (not shown) and a cathode catalyst layer (not shown). A first gas diffusion layer (GDL) 122 is disposed between the anode catalyst layer and the anode flow field plate 120, and a second GDL 126 is disposed between the cathode catalyst layer and the cathode flow field plate 130. The GDLs 122, 126 facilitate the diffusion of the reactant gas, either the fuel or oxidant, to the catalyst surfaces of the MEA 124. Furthermore, the GDLs enhance the electrical conductivity between each of the anode and cathode flow field plates 120, 130 and the membrane 125.

A first current collector plate 116 abuts against the rear face of the anode flow field plate 120, where the term "rear" indicates the side facing away from the MEA 124. Likewise, the term "front" refers to the side facing the MEA. A second current collector plate 118 abuts against the rear face of the cathode flow field plate 130. Each of the first and second current collector plates 116 and 118 respectively has a tab 146 and 148 protruding from the side of the fuel cell stack. A first insulator plate and second insulator plates 112, 114 are located immediately adjacent the first and second current collector plates 116, 118, respectively. First and second end plates 102, 104 are located immediately adjacent the first and second insulator plates 112, 114, respectively. Pressure may be applied on the end plates 102, 104 to press the unit 100 together. Moreover, sealing means are usually provided between each pair of adjacent plates. Preferably, a plurality of tie rods 131 may also be provided. The tie rods 131 are screwed into threaded bores in the anode endplate 102, and pass through corresponding plain bores in the cathode endplate 104. Fastening means, such as nuts, bolts, washers and the like are provided for clamping together the fuel cell unit 100. The end plate 104 is provided with a plurality of connection ports for the supply of various fluids. Specifically, the second endplate 104 has first and a second air connection ports 106, 107, first and second coolant connection ports 108, 109, and first and second hydrogen connection ports 110, 111. The MEA 124, the anode and cathode flow field plates 120, 130, the first and second current collector plates 116, 118, the first and second insulator plates 112, 114, and the first and/or second end plates 102, 104 have three inlets near one end and three outlets near the opposite end, which are in alignment to form fluid ducts for air as an oxidant, a coolant, and hydrogen as a fuel. Also, it is not essential that all the outlets be located at one end, i.e., pairs of flows could be counter current as opposed to flowing in the same direction. The inlet and outlet regions of each plate are also referred to as manifold areas. Although not shown, it will be understood that the various ports 106 - 111 are fluidly connected to ducts that extend along the length of the fuel cell unit 100.

In the fuel cell stack shown in Figure 1 , the fuel cell stack runs in "closed-end" mode, which means process fluids and coolant are supplied to and discharged from same end of the fuel cell stack. It should be understood that in other versions, the fuel cell may run in "flow-through" mode where process fluids and coolant enter the fuel cell stack from one end and leave the stack from the opposite end. This requires the first end plate 102 be provided with corresponding connection ports for process fluids. It should also be understood that in practice it is useful to stack the several plates 130, 120 and MEAs 124 to form a fuel cell stack to produce a greater current output. Cell stacks may have more than one hundred MEAs 124.

Although it is often beneficial to stack many cells in a stack to increase the voltage output, there is a price to be paid in the overall size and weight of the cell stack when stacking many cells. Aggravating the shortcomings that arise from copious stacking and thick end plates is the myriad of sensors connected to pipelines for the process fluids and coolant, which sensors increase the effective volume of the stack. To address this shortcoming, and to facilitate maintenance and repair, a new architecture for the fluid sensors is provided that significantly reduces the effective volume of the cell stack.

Figure 2 shows a monitoring system 10 for monitoring a fluid of an electrochemical cell stack, in other words, a process fluid (fuel or oxidant) or coolant. The monitoring system 10 includes a plate 12, which could be one of a flow field plate, a current collector plate, an insulator plate and an end plate. For concreteness, the plate 12 shown is an end plate for a fuel cell stack. The monitoring system 10 also includes a first conduit 14 in the plate 12 for transporting the fluid. In the embodiment shown, the first conduit 14 takes the form of a through hole extending from the inner face 16 of the plate 12 to a port 18 on the outer face 20 of the plate 12. The term "outer face" indicates a side perpendicular to the stacking direction that is closest to the outside of the cell stack. The term "inner face" indicates a side perpendicular to the stacking direction that is furthest from the outside of the cell stack. A port fitting 22 is connected to the port 18. A second conduit 24 in the plate 12 is in fluid communication with the first conduit 14, the second conduit 24 extending from a side face 26 of the plate 12 to the first conduit 14. The monitoring system 10 further includes a fluid sensor 28, a portion

30 of which is disposed in the second conduit 24. The fluid sensor 28 can include one of a pressure transmitter for measuring the pressure and a flow meter for measuring the flow of the fluid. The fluid sensor 28 can also include one of a thermocouple and a temperature switch. The thermocouple senses temperature at a given point and sends out electrical signals representing the sensed temperature to a remote device, whereas temperature switches sense temperature and switch between on/off positions based on the sensed temperature. In operation, a fluid of the fuel cell stack, such as hydrogen fuel, can be transported from the port fitting 22 on the outer face 20 of the end plate 12, through the port 18, and to the inner face 16 via the first conduit 14. From there, the fluid can be transported to the inside of the cell stack. As the hydrogen flows through the first conduit 14, the fluid sensor 28 can measure any one of a number of properties of the fluid, such as temperature, pressure and flow. By disposing the portion 30 of the fluid sensor 28 within the plate 12, the effective volume of the cell stack is reduced, thereby increasing the range of possible applications. Figure 3 shows a monitoring system 50 for monitoring a fluid of an electrochemical cell stack. The monitoring system 50 includes a plate 52, which could be one of a flow field plate, a current collector plate, an insulator plate and an end plate. For concreteness, the plate 52 shown is an end plate for a fuel cell stack. The monitoring system 50 also includes a first L-shaped conduit 54 in the plate 52 for transporting the fluid. The first conduit 54 extends from the inner face 56 of the plate 52 to a port 58 on the end face 60 of the plate 52. A port fitting 62 is connected to the port 58. Second, third and fourth conduits 64, 66, 68 in the plate 52 are in fluid communication with the first conduit 54. The second, third and fourth conduits 64, 66, 68 extend from a side face 70 of the plate 52 to the first conduit 54.

The monitoring system 50 further includes three fluid sensors 72,74,76 corresponding to the three conduits 64, 66, 68. Portions 78, 80, 82 of each of the three sensors 72, 74, 76 are disposed in the second, third and fourth conduits 64, 66, 68, respectively. The fluid sensors 72, 74, 76 can measure various properties of the fluid. For example, the fluid sensor 72 may include a thermocouple for measuring the temperature of the fluid, the fluid sensor 74 may include a pressure transmitter for measuring the pressure of the fluid, and the fluid sensor 76 may include a flow meter for measuring the flow of the fluid.

In operation, an oxidant of the fuel cell stack, such as oxygen gas, can be transported from the port fitting 62 on the end face 60 of the end plate 52, through the port 58, and to the inner face 56 via the first conduit 54. From there, the fluid can be transported to the inside of the cell stack. As the oxygen flows through the first conduit 54, the fluid sensors 72, 74, 76 can measure any one of a number of properties of the fluid. In addition to fuel cell stacks, the principles of the present invention can be applied to electrolytic cell stacks. Figure 4 shows an exploded perspective view of an electrolytic cell 500. It is to be understood that while a single electrolytic cell unit is detailed below, in known manner the electrolyzer cell stack will usually comprise a plurality of electrolyzer cell units stacked together.

Each electrolyzer cell of the electrolyzer cell 500 comprises an anode flow field plate 520, a cathode flow field plate 530, and a membrane electrode assembly (MEA) 524 disposed between the anode and cathode flow field plates 520, 530. Each flow field plate has an inlet region, an outlet region, and open-faced channels to fluidly connect the inlet to the outlet, and provide a way for distributing the product gases. The MEA 524 comprises a solid electrolyte (i.e. a proton exchange membrane) 525 disposed between an anode catalyst layer (not shown) and a cathode catalyst layer (not shown). A first gas diffusion layer (GDL) 522 is disposed between the anode catalyst layer and the anode flow field plate 520, and a second GDL 526 is disposed between the cathode catalyst layer and the cathode flow field plate 530. The GDLs 522, 526 facilitate the diffusion of the product gases, from the catalyst surfaces of the MEA 524 to the flow fields of the flow field plates. Furthermore, the GDLs enhance the electrical conductivity between each of the anode and cathode flow field plates 520, 530 and the membrane 525. Metal screens, meshes, carbon based GDL's, stainless steel based GDL's can also be used for this purpose.

As above, the designations '"front" and "rear" with respect to the anode and cathode flow field plates 520, 530 indicate their orientation with respect to the MEA 524. Thus, the "front" face indicates the side facing towards the MEA 524, while the "rear" face indicates the side facing away from the MEA 524. A first terminal plate 516 abuts against the rear face of the anode flow field plate 520. Similarly, a second terminal plate 518 abuts against the rear face of the cathode flow field plate 530. First and second insulator plates 512, 514 are located immediately adjacent the first and second terminal plates 516, 518, respectively. First and second end plates 502, 504 are located immediately adjacent the first and second insulator plates 512, 514, respectively. Pressure may be applied on the end plates 502, 504 to press the electrolytic cell 500 together. Moreover, sealing means are usually provided between each pair of adjacent plates. Preferably, a plurality of tie rods 531 may also be provided. The tie rods 531 are screwed into threaded bores in the anode endplate 502, and pass through corresponding plain bores in the cathode endplate 504. In known manner, fastening means, such as nuts, bolts, washers and the like are provided for clamping together the electrolyzer cell 50O and the entire electrolyzer cell stack.

Still referring to Figure 4, the endplate 504 is provided with a plurality of connection ports for various fluids. Specifically, the second endplate 504 has a water connection port 506, an oxygen connection port 507, first and second coolant connection ports 508, 509, and first and second hydrogen connection ports 510, 511. As will be understood by those skilled in the art, the MEA 524, the anode and cathode flow field plates 520, 530, the first and second current collector plates 516, 518, the first and second insulator plates 512, 514, and the first and/or second end plates 502, 504 have three inlets near one end and three outlets near the opposite end thereof, which are in alignment to form fluid ducts for water/oxygen, coolant, and hydrogen. Also, it is not essential that all the outlets be located at one end, i.e., pairs of flows could be counter current as opposed to flowing in the same direction . The inlet and outlet regions of each plate are also referred to as manifold areas. Although not shown, it will be understood that the various ports 506 - 511 are fluidly connected to ducts that extend along the length of the electrolyzer cell 500.

In the electrolytic cell stack shown in Figure 4, the electrolyzer cell stack runs in "closed-end" mode, which means process water, coolant and product gases are supplied to and discharged from same end of the electrolyzer cell stack. In other cases, the electrolyzer cell stack may run in "flow-through" mode, which means process fluids and coolant enter the electrolyzer cell stack from one end and leaves the stack from the opposite end thereof. This requires the first end plate 502 be provided with corresponding connection ports for process fluids. Figure 4 only shows an example of electrolytic cell stacks. Actual electrolytic cell stacks may not have coolant flow field. The number of ports for each process fluid may be different. For example there may be only one connection port on each flow field plate for hydrogen. Or there may be multiple ports for each process fluid. Figure 5 shows a different embodiment of an end plate 300 for a different type of electrolytic cell stack 200 according to the present invention. In addition to the end plate 300, the electrolytic cell stack 200 has another end plate 250, between which a plurality of electrolytic cells 210 are secured with tie rods 220. In this example, the electrolytic cell stack 200 operates in a closed-end mode.

The end plate 300 has several connection ports (not shown in Figure 5) to which are secured several fittings, including an anode inlet fitting 232, an anode outlet fitting 252, a first cathode outlet fitting 272 and a second cathode outlet fitting 292. In addition, a vent fitting 202 is attached to the end plate

300. The end plate 300 has several connection ports (not shown in Figure 5) to which are secured several fittings for sensors to monitor the electrochemical cell stack fluids. On one side face 362, a first thermocouple 253, and a first temperature switch 255 are provided. A plug 257 is inserted in one port where another sensor can be attached, if desired. On an inner face 340, a first pressure transmitter 259 is attached to a port (not shown).

On the second side face 364, a second thermocouple 273, and a second temperature switch 275 are provided. A plug 277 is inserted in one port where another sensor can be attached, if desired. On the inner face 340, a second pressure transmitter 279 is attached to a port (not shown).

While the end plate 300 contains various connection ports, in the closed-end mode shown, the other end plate 250 does not contain such ports. Holes (not shown) are provided on both end plates 250 and 300 for clamping the stack 200 with the tie rods 220 that extend throughout the stack 200. It should be understood that connection ports, including connection ports for sensors, could be included in both end plates 250 and 300 in other embodiments, such as stacks employing the flow-through mode described above. Ports for the first thermocouple 253, the first temperature switch 255, the plug 257 and the first pressure transmitter 259 are in fluid communication with the port for the anode outlet fitting 252 via conduits in the end plate 300. These conduits allow portion of these sensors to be inserted therein to monitor the flow of oxygen exiting the fuel cell stack 200 via the anode outlet fitting 252.

Likewise, ports for the second thermocouple 273, the second temperature switch 275, the plug 277 and the second pressure transmitter 279 are in fluid communication with the port for the first cathode outlet fitting 272 via conduits in the end plate 300. These conduits allow portion of these fluid sensors to be inserted therein to monitor the flow of hydrogen exiting the fuel cell stack 200 via the first cathode outlet fitting 272.

Figures 6 to 20 show the detailed structure of the end plate 300 in accordance with the present invention. The end plate 300 has an outer face 320 and an inner face 340. In this particular example, the electrolyzer cells 210 are circular in shape and hence the end plate 300 has a semi-circular portion 312 corresponding to the circular electrolyzer cells. The end plate 300 further has a rectangular portion 314, extending laterally with respect to the longitudinal direction of the stack 200, from the semi-circular portion 312. The semi-circular portion 312 has a side face 380. The rectangular portion 314 has an end face 360 and a two side faces 362, 364 that join the side face 380 of the semi-circular portion 312.

The end plate 300 is provided with a plurality of openings on the inner face 340. Specifically, an anode inlet opening 330, an anode outlet opening 350, a first cathode outlet opening 370 and a second cathode outlet opening 390. The openings 330, 350, 370 and 390 are positioned corresponding to the inlets and outlets of the flow field plates of electrolyzer cells. The openings are provided in the form of blind holes or blind slots. An anode inlet port 332 is provided on the side face 380 of the semi-circular portion 312. The anode inlet port 332 extends into the body of the end plate 300 and fluidly communicates with the anode inlet opening 330. The anode inlet port 332 is adapted to receive an anode inlet fitting 232 for connecting to a water source. An anode outlet port 352 is provided on the end face 360 of the rectangular portion 314. The anode outlet port 352 extends into the body of the end plate 300 along an anode outlet conduit 402 and fluidly communicates with the anode outlet opening 350. The anode outlet port 352 is adapted to receive an anode outlet fitting 252 for directing the product oxygen on the anode side of the electrolyzer cells and unreacted excess water out of the electrolyzer cell stack 200.

A first cathode outlet port 372 is provided on the end face 360 of the rectangular portion 314. The first cathode outlet port 372 extends into the body of the end plate 300 along a first cathode outlet conduit 452 and fluidly communicates with the first cathode outlet opening 370. The first cathode outlet port 372 is adapted to receive a first cathode outlet fitting 272 for directing product hydrogen on the cathode side of the electrolyzer cells out of the stack 200. A second cathode outlet port 392 is provided on the side face 380 of the semi-circular portion 312. The second cathode outlet port 392 extends into the body of the end plate 300 and fluidly communicates with the second cathode outlet opening 390. The second cathode outlet port 392 is adapted to receive a second cathode outlet fitting 292. In this particular example, the second cathode outlet opening 390 and the second cathode outlet port 392 are used to purge product hydrogen out of the stack 200. For example, when the electrolyzer cell stack 200 shuts down, for safety reasons, inert gas, e.g. nitrogen, is usually directed to flow through cathode side of the electrolyzer cells to purge residual hydrogen out of the stack. In this case, the first cathode outlet port 372 is closed off while the second cathode outlet port 392 opens, allowing inert gas and hydrogen flow out therethrough. The second cathode outlet port 392 is adapted to receive a second cathode outlet fitting 292 for directing process gases out of the stack 20O.

The inner face 340 of the end plate 300 can be optionally provided with a vent opening 301 in the form of a blind hole. A vent port 302 can be provided on the end face 360. The vent port 302 extends into the body of the end plate 300 and fluidly communicates with the vent opening 301. The vent opening 301 may be in fluid communication with either anode or cathode side of the electrolyzer cells. In case the pressure of gases on either side of the electrolyzer cells increases to a certain level, the gases can be vented through the vent opening 301 and vent port 302. The vent port 302 is adapted to receive a vent fitting 202. A plurality of screw holes 341 can be provided on the inner face 340 of the end plate 300 to accommodate tie rods 220 for clamping the stack 200 together, in a similar manner as described in Figure 4. These holes 341 can also be plain holes or through holes as may be desired. On the outer face 320 of the end plate, a number of mounting holes 311 can be provided for mounting the electrolyzer cell stack 200 to external devices or brackets.

In addition to the openings and ports for process fluids, the end plate 300 of the present invention further comprises a plurality of ports for mounting sensors or other monitoring devices that measures parameters of the process fluids. Specifically, a first anode outlet monitoring port 353, a second anode outlet monitoring port 355 and a third anode outlet monitoring port 357 are provided on side face 362 of the rectangular portion 314. A fourth anode outlet monitoring port 359 is provided on the inner face 340 of the end plate 300. Each of the first, second, third and fourth anode outlet monitoring ports 353, 355, 357, 359 extends into the body of the end plate 300 along respective conduits 404, 406, 408, 410 and fluidly communicates with the anode outlet port 352.

Parameter monitoring devices can be accommodated in these anode outlet monitoring ports for measuring parameters of the process fluids. For example, a first thermocouple 253 can be inserted in the first anode outlet monitoring port 353, a first temperature switch 255 can be inserted in the second anode outlet monitoring port 355 and a first pressure transmitter 259 can be inserted in the fourth anode outlet monitoring port 359. In the example shown in Figure 5, a plug 257 is inserted in the third anode outlet monitoring port 357 to close it off. As may be needed, a flow meter or other devices may be inserted in the third anode outlet monitoring port 357. ^"These monitoring devices measure parameters of product oxygen and water mixture stream.

Similarly, on the cathode side, a first cathode outlet monitoring port 373, a second cathode outlet monitoring port 375 and a third cathode outlet monitoring port 377 are provided on side face 364 of the rectangular portion 314. A fourth cathode outlet monitoring port 379 is provided on the inner face 340 of the end plate 300. Each of the first, second, third and fourth cathode outlet monitoring ports 373, 375, 377, 379 extends into the body of the end plate 300 along respective conduits 454, 456, 458, 460 and fluidly communicates with the cathode outlet port 372. Parameter monitoring devices can be accommodated in these cathode outlet monitoring ports for measuring parameters of the process fluids. For example, a second thermocouple 273 can be inserted in the first cathode outlet monitoring port 373, a second temperature switch 275 can be inserted in the second cathode outlet monitoring port 375 and a second pressure transmitter 279 can be inserted in the fourth cathode outlet monitoring port 379. In the example shown in Figure 5, a plug 277 is inserted in the third cathode outlet monitoring port 377 to close it off. As may be needed, a flow meter or other devices may be inserted in the third cathode outlet monitoring port 377. These monitoring devices measure parameters of product hydrogen stream.

It can be appreciated that the shape of the end plate is not limited to that shown in the accompanying figures. For example, the end plate can be circular, oval and other shapes. Moreover, the shape of connection ports can vary. The number and position of various openings and con ection ports can vary. The monitoring ports can be provided not only to the anode and cathode outlets, but also anode inlet or where coolant is used, coolant inlet and outlet and other points in flow path of a process fluid. It is to be understood that water can also be supplied to the cathode side of the electrolyzer cells. It is also to be understood that the present invention is also applicable to end plates of other electrochemical cells, such as fuel cells. It is anticipated that those having ordinary skills in the art can make various modifications to the embodiments disclosed herein after learning the teaching of the present invention. For example, the number and arrangement of components in the system might be different, different elements might be used to achieve the same specific function. However, these modifications should be considered to fall under the protection scope of the invention as defined in the following claims. In addition, although reference was made to a PEM fuel cell stack of Figure 1 , the principles of the present invention can be applied to other fuel cell types, such as alkaline, molten-carbonate, phosphoric acid and solid oxide cells.

Claims

ClaimsWhat is claimed is:

1. A system for monitoring a fluid of an electrochemical cell stack, the system comprising a plate; a first conduit in the plate for transporting the fluid; a second conduit in the plate, in fluid communication with the first conduit; and a fluid sensor, a portion of which is disposed in the second conduit for monitoring the fluid of the electrochemical cell stack.

2. The system of claim 1 , wherein the electrochemical cell stack is a fuel cell stack.

3. The system of claim 1 , wherein the electrochemical cell stack is an electrolyzer.

4. The system of claim 3, wherein the plate is an end plate having an inner face, an end face and a side face, the first conduit including an outlet opening in the inner face and an outlet port on the end face in fluid communication therewith.

5. The system of claim 4, wherein the second conduit includes an outlet monitoring port in the side face.

6. The system of claim 5, wherein the portion of the fluid sensor is disposed in the outlet monitoring port.

7. The system of claim 6, further comprising a second monitoring port in the side face in fluid communication with the first conduit; a third monitoring port in the side face in fluid communication with the first conduit; a second fluid sensor, a portion of which is disposed in the second monitoring port for monitoring the fluid; and a third fluid sensor, a portion of which is disposed in the third monitoring port for monitoring the fluid.

8. The system of claim 1 , wherein the first conduit and the second conduit coincide.

9. The system of claim 1 , wherein the first and second conduit are distinct.

10. The system of claim 1 , wherein the plate is one of a flow field plate, a current collector plate, an insulator plate and an end plate.

11. The system of claim 1 , wherein the fluid flow sensor is one of a thermocouple, a pressure transmitter, a temperature switch and a flow meter.

12. The system of claim 1 , in combination with an electrochemical cell stack, wherein the electrochemical cell stack is run in closed-end mode.

13. The system of claim 1 , wherein the fluid is one of hydrogen, oxygen and water.

14. An end plate for an electrochemical cell stack, the end plate comprising a first conduit for transporting a fluid; and a second conduit, in fluid communication with the first conduit, wherein the second conduit can receive a portion of a fluid sensor for monitoring the fluid of the electrochemical cell stack.

15. The end plate of claim 14, wherein the first conduit includes an outlet opening in an inner face of the end plate and an outlet port on an end face of the end plate, the outlet opening being in fluid communication with the outlet port.

16. The end plate of claim 15, wherein the second conduit includes an outlet monitoring port in a side face of the end plate.

17. The end plate of claim 16, wherein the portion of the fluid sensor can be disposed in the outlet monitoring port.

18. The end plate of claim 17, further comprising a second monitoring port in the side face in fluid communication with the first conduit; a third monitoring port in the side face in fluid communication with the first conduit, wherein a portion of a second fluid sensor may be inserted in the second monitoring port for monitoring the fluid, and a portion of a third fluid sensor may be inserted in the third monitoring port for monitoring the fluid.

19. The end plate of claim 14, wherein the fluid js one of hydrogen, oxygen and water.

20. The end plate of claim 14, wherein the electrochemical cell stack is an electrolytic cell stack.

21. The end plate of claim 20, wherein the end plate is half-obround having a semicircular portion and a rectangular portion.

22. The end plate of claim 20, wherein the end plate has an inner face that includes an anode inlet opening; an anode outlet opening; a first cathode outlet opening; and a second cathode outlet opening.

23. The end plate of claim 22, wherein the rectangular portion has an end face that includes a first cathode outlet port in fluid communication with the first cathode outlet opening; and an anode outlet port in fluid communication with the anode outlet opening.

24. The end plate of claim 23, wherein the semicircular portion has a side face that includes an anode inlet port in fluid communication with the anode inlet opening; and a second cathode outlet port in fluid communication with the second cathode outlet opening.

25. The end plate of claim 24, wherein the rectangular portion has a side face that includes first, second and third anode outlet monitoring ports in fluid communication with the anode outlet port to monitor a fluid therein.

26. The end plate of claim 25, wherein the rectangular portion has another side face that includes first, second and third cathode outlet monitoring ports in fluid communication with the first cathode outlet port to monitor a fluid therein.

27. An end plate for an electrochemical cell stack, the end plate comprising: an inner face for abutting a stack of electrochemical cells; an outer face, the inner and outer faces being substantially planar and parallel with one another; a side face extending between the inner and outer faces and being at an angle thereto; a first conduit for transporting a fluid and having ports on the inner and outer faces; and a second conduit, in fluid communication with the first conduit, and having a port in the side face.

28. An end plate as claimed in claim 27, wherein the side face is substantially perpendicular to the inner and outer faces, and the second conduit is substantially perpendicular to the first conduit.

29. An end plate as claimed in claim 28, in combination with an electrochemical cell.

30. A method for monitoring a fluid of an electrochemical cell stack, the method comprising providing a plate having a first conduit and a second conduit in fluid communication, the fluid being transported in the first conduit; mounting at least a portion of a fluid sensor in the second conduit; and monitoring the fluid of the electrochemical cell stack with the fluid sensor.