Flow field configurations for electrochemical cells

Abstract

The following disclosure relates to electrochemical or electrolysis cells and components thereof, specifically to improved flow field configurations and geometries for electrochemical cells. In one example, the flow field may include a plurality of channels configured to transfer fluid to or receive fluid from an adjacent layer of the electrochemical cell and a plurality of lands configured to abut the adjacent layer of the electrochemical cell, each of the plurality of lands separating two adjacent channels of the plurality of channels, wherein a width of each of the plurality of lands is larger than a width of each of the plurality of channels.

Description

FLOW FIELD CONFIGURATIONS FOR ELECTROCHEMICAL CELLS

[0001] The present patent document claims the benefit of United States Provisional Patent Application No. 63 / 636,215, filed April 19, 2024, which is hereby incorporated by reference in its entirety.FIELD

[0002] The following disclosure relates to electrochemical or electrolysis cells and components thereof. More specifically, the following disclosure relates to flow field configurations and flow field geometries for improving transport of electrons, fluids, and heat within electrochemical cells.BACKGROUND

[0003] Hydrogen has been considered as an ideal energy carrier to store renewable energy. Proton exchange membrane water electrolysis (PEMWE) as a means for hydrogen production offers high product purity, fast load response times, small footprints, high efficiencies, and limited maintenance efforts. It is regarded as a promising technology, especially when coupled with renewable energy sources.

[0004] An electrolysis cell or system uses electrical energy to drive a chemical reaction. For example, water is split to form hydrogen and oxygen. The products may be used as energy sources for later use. In recent years, improvements in operational efficiency have made electrolyzer systems competitive market solutions for energy storage, generation, and / or transport. For example, the cost of generation may be below $6 per kilogram of hydrogen in some cases. Increases in efficiency and / or improvements in operation will continue to drive the installation of electrolyzer systems.

[0005] Flow fields, porous transport layers (PTLs), and gas diffusion layers (GDLs) play important roles in fluid transport and electrochemical cell performance. A PTL, positioned between an anode catalyst layer and an anode flow field of the electrochemical cell, may assist in transporting water and oxygen on the anode side and in transporting electrons away from the anode catalyst layer. A GDL, positioned between a cathode catalyst layer and a cathode flow field of the electrochemical cell, may assist in transporting hydrogen on the cathode side of the cell and in transporting electrons towards the cathode catalyst layer.

[0006] There remains a desire for improved performance properties within electrochemical cells, including improved transport of electrons, heat, and fluids within the cell.SUMMARY

[0007] In one embodiment, a flow field for an electrochemical cell is provided. The flow field includes a plurality of channels configured to transfer fluid to or receive fluid from an adjacent layer of the electrochemical cell; and a plurality of lands configured to abut the adjacent layer of the electrochemical cell, each land of the plurality of lands separating two adjacent channels of the plurality of channels. Each channel includes a first side wall, a second side wall, and a back wall, wherein the back wall extends between the first side wall and the second side wall, wherein the first side wall extends between the back wall and a first adjacent land, and wherein the second side wall extends between the back wall and a second adjacent land. A width of each land of the plurality of lands is larger than a width of each channel of the plurality of channels. The width of each land refers to a distance between one end of the respective land at a side wall of a first channel and an opposite second end of the respective land at a side wall of a second adjacent channel, and the width of each channel refers to a largest distance between the first side wall and the second side wall of the respective channel at an opening of the respective channel.In another embodiment, an electrochemical cell including a flow field, a membrane, and a porous layer positioned between the flow field and the membrane. Within the cell, the flow field may include a plurality of channels configured to transfer fluid to or receive fluid from the porous layer of the electrochemical cell and a plurality of lands configured to abut the porous layer of the electrochemical cell, each land of the plurality of lands separating two adjacent channels of the plurality of channels. In the flow field, each channel includes a first side wall, a second side wall, and a back wall, wherein the back wall extends between the first side wall and the second side wall, wherein the first side wall extends between the back wall and a first adjacent land, and wherein the second side wall extends between the back wall and a second adjacent land. A width of each land of the plurality of lands is larger than a width of each channel of the plurality of channels. The width of each land refers to a distance between one end of the respective land at a side wall of a first channel and anopposite second end of the respective land at a side wall of a second adjacent channel, and the width of each channel refers to a largest distance between the first side wall and the second side wall of the respective channel at an opening of the respective channel.

[0008] In yet another embodiment, an electrochemical system including a plurality of electrochemical cells stacked on top of one another is provided. Each electrochemical cell within the plurality of electrochemical cells includes a flow field and an additional flow field, as defined herein.

[0009] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Exemplary embodiments are described herein with reference to the following drawings.

[0011] Figure 1 depicts an example of an electrolytic cell.

[0012] Figure 2 depicts an additional example of an electrolytic cell.

[0013] Figures 3A, 3B, and 3C depict cross-sectional views of an example of an electrochemical cell with a limited number of flow channels of flow fields depicted for clarity.

[0014] Figures 4A and 4B depict a side view and a top view, respectively, of portions of such an electrode flow field having a limited number of flow channels and lands depicted for clarity.

[0015] Figure 4C illustrates an interdigitated flow field in accordance with one example of the present disclosure.

[0016] Figure 5 illustrates a partial side view of a flow field in accordance with one example of the present disclosure.

[0017] Figure 6 illustrates graph showing the effect of channel and land with on performance of an electrochemical cell.

[0018] Figure 7 illustrates a graph showing the effect of a ratio of land width divided by channel width on the current density in an electrochemical cell.

[0019] Figure 8 illustrates a graph showing voltage distribution at an interface between a catalyst layer and a porous layer for channels having various widths.

[0020] Figure 9 illustrates a graph showing a spatial distribution of scaled current density at a catalyst layer for flow fields including various different ratios of land width over channel width.

[0021] Figure 10 illustrates a graph showing a spatial distribution of power density for flow fields including various different ratios of land width over channel width.

[0022] Figure 11 illustrates a mechanical model showing the effects of land width, channel width, and a ratio of land width over channel width on displacement of catalyst coated membrane.

[0023] Figure 12 illustrates a graph illustrating a mass fraction of water at the middle of a land for both anode side flow fields and cathode side flow fields having varying land widths and fixed channel widths.

[0024] Figure 13 illustrates a diagram showing various relationships between anode side and cathode side flow fields.DETAILED DESCRIPTION

[0025] The following disclosure provides flow field configurations and geometries for improved transport of electrons, fluids, and heat within an electrochemical cell. Specifically, described herein are flow field configurations including various geometric or structural properties / configurations, for example, land width, channel width, channel depth, number of channels, channel length, and the like configured to improve transport of electrons, fluids, and heat within an electrochemical cell. According to the present disclosure, channel width, land width, channel depth, and a number of channels in an electrolyzer flow plate may be optimized for a given active area span and length,

[0026] Additionally, described herein are flow field configurations including various relationships or ratios between structural properties of the flow field configured to improve one or more operational properties of the electrochemical cell or stack.

[0027] For example, the improved flow field configurations disclosed herein may advantageously improve electron transport within the ce I l / stack, therein providingimproved current spreading / distribution, improved catalyst utilization in channel areas, and less ohmic losses.

[0028] Additionally, the improved flow field configurations disclosed herein may advantageously provide better mechanical support for the membrane, therein providing less pillowing of membrane into the channels, improved durability and degradations, and elimination of stretching of the catalyst layer and hence discontinuity in lateral current leading to improved catalyst utilization.

[0029] Further, the improved flow field configurations disclosed herein may advantageously provide efficient reactant supply, product, and electroosmotic drag water removal, therein avoiding water starvation under lands, avoiding excessive gas accumulation under lands, and facilitating a lower stoic ratio.

[0030] Further, the improved flow field configurations disclosed herein may advantageously avoid local hot spots within the adjacent layer under the lands of the flow field via a balancing of heat rejection via conduction through the land areas and via convection through water flow in the channels.

[0031] In other words, the flow field configurations provided herein may advantageously improve electrochemical efficiency, power, performance, and durability of an electrochemical cell. For example, by improving efficiency of the electrochemical cell through an improved flow field configuration, this may advantageously allow for an increase in an amount of reactant water supplied to the membrane / catalyst layer of the cell, therein allowing the cell to operate at higher power levels without a mass transfer limitation occurring. Additionally, improving efficiency of the removal of gaseous products from the cell may advantageously create a more uniform gas-liquid saturation profile throughout the porous layer of the cell. Further, a more uniform gas-liquid saturation profile may advantageously provide a more uniform temperature distribution across the cell.Electrochemical Cells

[0032] Figure 1A depicts an example of an electrochemical system including an electrochemical stack having a plurality of electrochemical cells. In certain examples, the electrochemical stack may contain 50-1000 cells, 50-100 cells, 500-700 cells, or more than 1000 cells. Any number of cells may make up a stack. The electrochemical cells within theelectrochemical stack may be configured to operate with 200 mV or less of pure resistive loss when operating at a high current density (e.g., at least 3 Amps / cm2, at least 4 Amps / cm2, at least 5 Amps / cm2, at least 6 Amps / cm2, at least 7 Amps / cm2, at least 8 Amps / cm2, at least 9 Amps / cm2, at least 10 Amps / cm2, at least 11 Amps / cm2, at least 12 Amps / cm2, at least 13 Amps / cm2, at least 14 Amps / cm2, at least 15 Amps / cm2, at least 16 Amps / cm2, at least 17 Amps / cm2, at least 18 Amps / cm2, at least 19 Amps / cm2, at least 20 Amps / cm2, at least 25 Amps / cm2, at least 30 Amps / cm2, in a range of 1-30 Amps / cm2, in a range of 3-20 Amps / cm2, in a range of 3-15 Amps / cm2, in a range of 3-10 Amps / cm2, or in a range of 10-20 Amps / cm2). In additional examples, the amount of water (e.g., deionized (DI) water) transferred to or circulated through each cell of the stack may be less than 5 mL / Amp / cell / min, less than 1 mL / Amp / cell / min, less than 0.5 mL / Amp / cell / min, less than 0.1 mL / Amp / cell / min, less than 0.05 mL / Amp / cell / min. In other examples, the amount of water transferred to or circulated through each cell of the stack may be in a range of 0.05- 0.1 mL / Amp / cell / min, 0.05-0.25 mL / Amp / cell / min, 0.05-0.5 mL / Amp / cell / min, 0.05-1 mL / Amp / cell / min, 0.05-5 mL / Amp / cell / min, 0.1-1 mL / Amp / cell / min, 0.1-5 mL / Amp / cell / min, 0.25-1 mL / Amp / cell / min, in a range of 0.25-5 mL / Amp / cell / min, or in a range of 0.5-1 mL / Amp / cell / min.

[0033] As illustrated in the system of Figure 1A, water (H2O) may be supplied to the anodic inlet of an electrolytic cell stack 12. In some embodiments, only the anodic inlet of the cell stack 12 may receive water. In these embodiments, the cathode side of the cell stack 12 may not receive water (e.g., a dry cathode side may be used). In another embodiment, a cathode inlet may also receive water, wherein the water may be supplied to the cathode inlet to cool the cell stack 12 during electrolysis.

[0034] The water supplied to the anodic inlet flows to an anodic inlet manifold that distributes the water to the anode side of the plurality of cells contained with the cell stack 12. In embodiments where water is supplied to the cathode inlet, water supplied to the cathode inlet flows to a cathodic inlet manifold that distributes the water to the cathode side of the plurality of cells in the cell stack 12. In certain examples, the amount of water (e.g., deionized (DI) water) transferred to or circulated through each cell of the stack may be less than 5 mL / Amp / cell / min, less than 1 mL / Amp / cell / min, less than 0.5 mL / Amp / cell / min,less than 0.1 mL / Amp / cell / min, less than 0.05 mL / Amp / cell / min. In other examples, the amount of water transferred to or circulated through each cell of the stack may be in a range of 0.05-0.1 mL / Amp / cell / min, 0.05-0.25 mL / Amp / cell / min, 0.05-0.5 mL / Amp / cell / min, 0.05-1 mL / Amp / cell / min, 0.05-5 mL / Amp / cell / min, 0.1-1 mL / Amp / cell / min, 0.1-5 mL / Amp / cell / min, 0.25-1 mL / Amp / cell / min, in a range of 0.25-5 mL / Amp / cell / min, or in a range of 0.5-1 mL / Amp / cell / min.

[0035] During electrolysis, oxygen (O2) is produced at the anode side of the electrolytic cells and hydrogen (H2) is produced at the cathode side of the electrolytic cells. Specifically, a water splitting electrolysis reaction is configured to take place within each individual cell in the cell stack 12. Each cell includes one interface (the anode side of the cell) configured to run an oxygen evolution reaction (OER) and another interface (the cathode side of the cell) configured to run a hydrogen evolution reaction (HER) (such as depicted in Figure IB).

[0036] During electrolysis, some of the water supplied to the anode side of an electrolytic cell may not be converted into oxygen. Accordingly, a two-phase flow of oxygen and unreacted water is outlet from each of the anode sides of the cells into an anodic outlet manifold 13. The two-phase flow of oxygen and unreacted water flows from out of the cell stack 12 through the anodic outlet manifold 13. This stream within the anodic outlet manifold 13 may be configured to be transferred to a gas detection and conditioning system, such as described in greater detail below, for analysis of the composition within the stream. Specifically, this anodic stream may be analyzed to identify if any undesirable hydrogen gas has leaked (i.e., cross-leaked) across the membranes from the cathode sides of the cells to the anode sides of the cells within the cell stack.

[0037] Additionally, in some embodiments, water may be supplied to the cathode side of the cell stack as a coolant. Accordingly, a two-phase flow of hydrogen and water is outlet from each of the cathode sides of the cells to a cathodic outlet manifold 14. The two-phase flow of hydrogen and water flows out of the cell stack 12 through the cathodic outlet manifold 14. Similarly, this particular stream within the cathodic outlet manifold 14 may be configured to be transferred to a gas detection and conditioning system (separate from the anodic gas detection and conditioning system) for analysis of the composition within the stream. Specifically, this cathodic stream may be analyzed to identify if any undesirableoxygen gas has leaked (i.e., cross-leaked) across the membranes from the anode sides of the cells to the cathode sides of the cells within the cell stack.

[0038] Figure IB depicts an example of an electrochemical or electrolytic cell for hydrogen gas and oxygen gas production through the splitting of water. The electrochemical cell within Figure IB may be one of the plurality of cells within the electrochemical stack in Figure 1A. The electrolytic cell includes a cathode, an anode, and a membrane positioned between the cathode and anode. The membrane may be a proton exchange membrane (PEM) that may have a catalyst coating on one or both surfaces of the PEM. In other examples, the membrane may be positioned within an electrochemical cell having a catalyst coating on an adjacent supporting layer within the cell (e.g., a gas diffusion layer or porous transport layer near or abutting the membrane).

[0039] Proton Exchange Membrane (PEM) electrolysis involves the use of a solid electrolyte or ion exchange membrane. Within the water splitting electrolysis reaction, one interface runs an oxygen evolution reaction (OER) while the other interface runs a hydrogen evolution reaction (HER). For example, the anode reaction is H2O->2H++>2O2+2e and the cathode reaction is 2H++2e->H2.

[0040] Figure 2 depicts an additional example of an electrochemical or electrolytic cell. Specifically, Figure 2 depicts a portion of an electrochemical cell 200 having a cathode flow field 202, an anode flow field 204, and a membrane 206 positioned between the cathode flow field 202 and the anode flow field 204.

[0041] In certain examples, the membrane 206 may be a catalyst coated membrane (CCM) having a cathode catalyst layer 205 and / or an anode catalyst layer 207 positioned on respective surfaces of the membrane 206. As used throughout this disclosure, the term "membrane" may refer to a catalyst coated membrane (CCM) having such catalyst layers. The overall thickness (i.e., for all layers of the membrane combined including the catalyst coatings, if present) may be less than 1000 microns, less than 500 microns, less than 100 microns, less than 50 microns, less than 10 microns, less than 5 microns, less than 2 microns, less than 1 micron, in a range of 1-1000 microns, in a range of 2-500 microns, in a range of 5-100 microns, or in a range of 10-50 microns.

[0042] In certain examples, additional layers may be present within the electrochemical cell 200. For example, one or more additional layers 208 may be positioned between the cathode flow field 202 and membrane 206. In certain examples, this may include a gas diffusion layer (GDL) 208 may be positioned between the cathode flow field 202 and membrane 206. This may be advantageous in providing a hydrogen diffusion barrier adjacent to the cathode on one side of the multi-layered membrane to mitigate hydrogen crossover to the anode side. In other words, the GDL is responsible for the transport of gaseous hydrogen to the cathode side flow field. For a wet cathode PEM operation, liquid water transport across the GDL is needed for heat removal in addition to heat removal from the anode side.

[0043] In certain examples, the GDL is made from a carbon paper or woven carbon fabrics. The GDL is configured to allow the flow of hydrogen gas to pass through it. The thickness of the GDL may be within a range of 100-1000 microns, for example. As used herein, a "thickness" by which is film is characterized refers to the distance, or median measured distance, between the top and bottom faces of a film in a direction perpendicular to the plane of the film layer. As used herein, the top and bottom faces of a film refer to the sides of the film extending in a parallel direction of the plane of the film having the largest surface area.

[0044] Similarly, one or more additional layers 210 may be present in the electrochemical cell between the membrane 206 and the anode 204. In certain examples, this may include a porous transport layer (PTL) positioned between the membrane 206 (e.g., the anode catalyst layer 207 of the catalyst coated membrane 206) and the anode flow field 204.

[0045] In certain examples, the PTL is made from a titanium (Ti) mesh / felt. As used herein, a Ti mesh / felt may refer to a structure created from microporous Ti fibers. The Ti felt structure may be sintered together by fusing some of the fibers together. Ti felt may be made by a special laying process and a special ultra-high temperature vacuum sintering process. The Ti felt may have an excellent three-dimensional network, porous structure, high porosity, large surface area, uniform pore size distribution, special pressure, and corrosion resistance, and may be rolled and processed.

[0046] Similar to the GDL, the PTL is configured to allow the transportation of the reactant water to the anode catalyst layers, remove produced oxygen gas, and provide good electrical conductivity for effective electron conduction. In other words, liquid water flowing in the anode flow field is configured to permeate through the PTL to reach the CCM.Further, gaseous byproduct oxygen is configured to be removed from the PTL to the flow fields. In such an arrangement, liquid water functions as both reactant and coolant on the anode side of the cell.

[0047] The thickness of the PTL may be within a range of 100-1000 microns, for example. The thickness may affect the mass transport within the cell as well as the durability / deformability and electrical / thermal conductivity of the PTL. In other words, a thinner PTLs compared to thicker PTLs (e.g., 1 mm) may provide better mass transport. However, when the PTL is too thin (e.g., less than 100 microns), the PTL may suffer from poor two phase flow effects as well. PTLs are less prone to deformation compared to GDLs. Thickness of PTLs may also affect lateral electron conduction resistance along the lands in between channels.

[0048] In some examples, an anode catalyst coating layer may be positioned between the anode 204 and the PTL.

[0049] The cathode 202 and anode 204 of the cell may individually include a flow field plate composed of metal, carbon, or a composite material having a set of channels machined, stamped, or etched into the plate to allow fluids to flow inward toward the membrane or out of the cell. In certain examples, the flow field plate may be formed using a computer numerical control (CNC) manufacturing process to cut the plate and form the grooves or openings (e.g., flow channels) in one or both surfaces of the plate material. A CNC flow plate may be advantageous in providing a higher degree of precision and accuracy in the location, width, and depth of each flow channel within the plate, for example.

[0050] Figures 3A, 3B, and 3C depict examples of an electrochemical or electrolytic cell with flow fields. In these particular examples, the electrochemical cell includes a cathode flow field 302, cathode flow channels 303, an anode flow field 304, anode flow channels 305, and a membrane 306 positioned between the cathode and the anode. Additionally, the electrochemical cell 300 includes a gas diffusion layer 308 positioned between the catalystcoated membrane 306 and the cathode flow channels 303. Further, a porous transport layer 310 is positioned between the catalyst coated membrane 306 and the anode flow channels 305.

[0051] In the particular example depicted in Figures 3A and 3B, the cathode and anode flow fields are arranged to provide a cross-fluid flow. In such a cross-fluid arrangement, the fluid flow through the cathode flow channels is arranged perpendicular to the fluid flow through the anode flow channels. Specifically, Figure 3A depicts the cross-sectional view of the electrochemical cell with the cathode flow channels displayed, while Figure 3B depicts the cross-sectional view of the electrochemical cell rotated 90 degrees to display the anode flow channels.

[0052] In alternative examples, the flow fields may have a co-flow configuration or a counter-flow configuration. Figure 3C depicts an alternative example, wherein the channels and lands of the anode flow field are parallel with the channels and lands of the cathode flow field. With the parallel arrangement, in a co-flow configuration, the flow of fluid through the anode flow field channels is in the same direction as the flow of fluid through the cathode flow field channels. Alternatively, a counter-flow configuration may be present with the parallel arrangement of the anode and cathode flow fields, wherein the flow of fluid through the anode flow field channels is in an opposite direction as the flow of fluid through the cathode flow field channels.

[0053] The orientation or configuration of fluid flow between the anode flow field and cathode flow field may be advantageous in adjusting or controlling the pressure distribution or temperature distribution within the electrochemical cell.

[0054] Regarding these anode and cathode flow fields depicted in Figures 3A and 3B, such flow fields may be configured to have paths of channels and land. The channels are configured for directing the flow of water and gas, while the lands are configured to contact an adjacent layer of the electrochemical cell (e.g., the GDL or PTL) providing electrical contact. Figures 3A and 3B depict examples of cells having three cathode flow channels and three anode flow channels, respectively. The number of flow channels are depicted for simplicity of a design, and in potential commercial use, may include many more flowchannels. As such, the disclosure is not limited to such configurations as depicted in Figures 3A and 3B.

[0055] Figures 4A and 4B depict a side view and a top view, respectively, of such an electrode flow field having a plurality of channels and lands positioned between inlet and outlet manifolds (or plenums). In this particular example, the flow field includes 3 parallel channels and 4 lands, wherein each channel is positioned between adjacent lands. In this example, the plenums are depicted in a rectangular configuration for illustration purposes only. For example, the flow field does not necessarily require parallel channels and lands extending the length of the flow field between the inlet and outlet manifolds. In certain examples, the channels and lands may have a parallel arrangement within a section less than the entire length of the channel / land between the inlet and outlet manifold. Further, in certain examples, while not depicted in Figures 4A and 4B, the channels may be positioned closer together or farther apart from each other as they approach the inlet or outlet manifold, for fluid flow improvement to / from the manifold. In other words, in practice, the manifold or plenum configuration would be in a different shape for improved fluid flow characteristics (see, e.g., Figure 5). Therefore, as described herein, the arrangement or configuration between channels and lands (such as depicted in Figure 5, for example), may refer to a segment or cross-section through the flow field channel (e.g., in the center of the flow field, equidistant from the inlet and outlet manifolds).

[0056] Figure 4C depicts an electrode flow field according to another example of the present disclosure. Specifically, Figure 4C illustrates a flow field including a plurality of interdigitated, dead-end channels that are fluidically connected with the adjacent porous transport layer or gas diffusion layer.

[0057] As depicted in FIG. 4C, the flow field (on the anode and / or cathode side of the cell) has an inlet for water to flow into the flow field from an outside source and a plurality of dead end channels only connected to the inlet. In this configuration water is configured to flow into each of the inlet channels and subsequently into the adjacent porous layer of the cell (e.g., PTL or GDL). Specifically, in this configuration, the dead end of the inlet channel may advantageously force water flowing in inlet channel to flow into the adjacent porous layer (e.g., PTL or GDL).

[0058] Additionally, as depicted in FIG. 4C, the flow field (on the anode and / or cathode side of the cell) has an outlet and a plurality of dead end channels only connected to the outlet. The plurality of dead end channels only connected to the outlet may be configured to receive and transport water and any hydrogen gas (cathode) or oxygen gas (anode) produced in the water splitting reaction at the membrane from the adjacent porous layer (e.g., PTL or GDL). Further, as depicted in FIG. 5, a land may be disposed between each pair of adjacent or alternating inlet and outlet channels.Geometric Optimization of Channel Flow Fields

[0059] Provided herein are flow field configurations for improved transport of electrons, fluids, and heat in electrochemical cells. As noted above, the flow fields (e.g., anode flow field and cathode flow field) perform various functions in an electrochemical cell.Specifically, the flow fields facilitate electron transport, fluid transport, and heat transport within the electrochemical cells. Accordingly, structural or geometric properties of flow fields must be designed in consideration of their impact on a flow field's ability to transport each of electrons, fluids, and heat. Further, performance (e.g., efficiency, production) of an electrochemical cell is heavily dependent on a balanced and steady supply of liquid reactant and electric current (e.g., electrons) being provided to a reaction site (e.g., a catalyst coated membrane). Structural or geometric properties of an electrode flow field (e.g., anode flow field, cathode flow field) significantly change transport phenomena in electrochemical cells, including transport of electrons, heat, and fluids, thereby having a direct impact on cell performance, durability, and degradation and the fluid and thermal efficiencies of the cell.

[0060] Specifically, provided herein are flow field configurations including specific geometric or structural properties including channel width, land width, channel depth, parallel channel length, and number of channels configured to improve transportation of electrons, fluids, and heat within an electrochemical cell. Additionally, provided herein are flow field configurations including specific relationships or ratios between various geometrical or structural properties of a flow field configured to improve transportation of electrons, fluids, and heat in electrochemical cells.

[0061] The geometric or structural properties and / or relationships between the various geometric or structural properties of a flow field provided herein may be applied to both open ended channels, such as those described above with respect to FIGS. 3A-4B.

[0062] The flow field configurations described herein may optimize various interplaying transport phenomena to increase electrochemical efficiency, increase power, increase performance, and improve durability of an electrochemical cell by increasing attainable current density and minimizing parasitic losses while also maintaining minimal pressure drop requirements.

[0063] As noted above, by improving efficiency of the electrochemical cell, this may advantageously allow for an increase in an amount of reactant water supplied to the membrane / catalyst layer of the cell, therein allowing the cell to operate at higher power levels without a mass transfer limitation occurring. Additionally, improving efficiency of the removal of gaseous products from the cell may advantageously create a more uniform gasliquid saturation profile throughout the porous layer of the cell. Further, a more uniform gas-liquid saturation profile may advantageously provide a more uniform temperature distribution across the cell.

[0064] Alternatively, in other examples, an improved flow field configuration as described herein may assist in improving or optimizing fluid flow into the neighboring cell layers, therein allowing for a lower flow rate of reactant water to be supplied to the cell in comparison to conventional electrochemical stacks, while operating at a similar power level. As noted above, through these improved flow field configurations, the amount of water (e.g., deionized (DI) water) transferred to or circulated through each cell of the stack may be less than 5 mL / Amp / cell / min, less than 1 mL / Amp / cell / min, less than 0.5 mL / Amp / cell / min, less than 0.1 mL / Amp / cell / min, less than 0.05 mL / Amp / cell / min. In other examples, the amount of water transferred to or circulated through each cell of the stack may be in a range of 0.05-0.1 mL / Amp / cell / min, 0.05-0.25 mL / Amp / cell / min, 0.05-0.5 mL / Amp / cell / min, 0.05-0.1 mL / Amp / cell / min, 0.05-0.25 mL / Amp / cell / min, 0.05-0.5 mL / Amp / cell / min, 0.05-1 mL / Amp / cell / min, 0.05-5 mL / Amp / cell / min, 0.1-1 mL / Amp / cell / min, 0.1-5 mL / Amp / cell / min, 0.25-1 mL / Amp / cell / min, in a range of 0.25-5 mL / Amp / cell / min, or in a range of 0.5-1 mL / Amp / cell / min.

[0065] Several geometric or structural properties of an electrode flow field (e.g., anode flow field, cathode flow field) are described below with respect to FIG. 5.

[0066] Referring to FIG. 5, a partial side view or cross section of flow field 400 is illustrated in accordance with one example of the present disclosure. As noted above, the partial side view / cross section in FIG. 5 may represent a section of the flow field positioned between the inlet manifold and outlet manifold, such as in the center of the flow field, equidistant from the inlet and outlet manifolds. In other words, the flow field arrangement between channels and lands depicted in FIG. 5 may not necessarily extend the entire length of the flow field between the inlet and outlet manifolds.

[0067] As illustrated in FIG. 5, the flow field 400 includes a plurality of lands 410 and a plurality of channels 420. According to some examples of the present disclosure, each land of the plurality of lands 410 included in the flow field 400 may have a same configuration (e.g., have the same width or size) and each channel of the plurality of channels 420 included in the flow field 400 may have a same or variable configuration (e.g., have the same width, depth, and size). Specifically, according to some examples, each of the lands 410 included in the flow field 400 and each of the channels 420 included in the flow field 400 may have a same configuration, such that, the flow field may uniformly distribute fluid and / or current (e.g., electrons) to or receive fluid and / or current (e.g., electrons) from an adjacent layer (e.g., PTL or GDL).

[0068] Each of the channels 420 included in the flow field 400 may be configured to transfer fluid to and / or receive fluid from an adjacent layer (e.g., PTL or GDL) of an electrochemical cell.

[0069] As illustrated in FIG. 5, each channel 420 may include a first side wall 422, a second side wall 423, and a back wall 424 extending between the first side wall 422 and the second side wall 423. The first side wall 422 may extend between the back wall 424 of the channel 420 and an adjacent land 410 (e.g., on a first side of the channel 420). Further, the second side wall 423 may extend between the back wall 424 of the channel 420 and adjacent land 410 (e.g., on a second side of the channel 420). Additionally, each channel 420 may have a channel width 421 corresponding to a largest distance between the first side wall 422 and the second side wall 423. Each channel 420 may have a depth 450corresponding to a distance between the back wall 424 of the channel 420 and a surface of an adjacent land 410.

[0070] While the example depicted in FIG. 5 includes linear segments abutting each other between the side walls, back walls, and adjacent lands, the disclosure is not limited to such arrangements. In particular, the transition between the land to a side wall may be curved and / or the transition between a side wall and the back wall may be curved.

[0071] Each of the lands 410 included in the flow field 400 may be configured to abut an adjacent layer (e.g., PTL or GDL) of an electrochemical cell. Each of the plurality of lands may be disposed between and separate an adjacent pair of channels 420. Further, each land 410 may have a width corresponding to a distance between an adjacent pair of channels 420 separated by the land 410.

[0072] Further, the flow field 400 may have a pitch corresponding to a sum of the number of lands 411 and the number of channels 421 in the flow field. In certain examples, the anode side pitch (i.e., number of channels and lands within the anode flow field) may be equal to the cathode side pitch (i.e., number of channels and lands within the cathode flow field). Alternatively, the anode side pitch may be greater than the cathode side pitch. In some examples, the ratio between the anode side pitch and cathode side pitch may be in a range of 1:1 to 50:1, in a range of 1:1 to 20:1, in a range of 1:1 to 10:1, in a range of 2:1 to 50:1, in a range of 2:1 to 20:1, in a range of 2:1 to 10:1, in a range of 5:1 to 50:1, in a range of 5:1 to 20:1, or in a range of 5:1 to 10:1.

[0073] In accordance with some examples of the present disclosure as illustrated in FIG. 5, the channels 420 may have a channel slope or curvature G of greater than 90 degrees and less than 110 degrees, greater than 90 degrees and less than 100 degrees, greater than 90 degrees and less than 95 degrees, or 90 degrees. Specifically, in certain examples, a difference between the width of the back wall of each channel and the width of each channel at the opening of the respective channel provides a channel slope or curvature of greater than 90 degrees and less than 100 degrees defines as an angle between the back wall and the respective side wall. In other words, the width at the opening of the channel is greater than the width along the back wall of the channel.

[0074] In other examples, the channels 420 may have no channel slope, i.e., the slope © is 90 degrees, wherein there is no difference between the width of the back wall of each channel and the width of each channel at the opening of the respective channel such that the side walls extend perpendicular from the surface of the back wall toward the opening of the channel, forming a 90 degree angle between the back wall and the side wall.

[0075] In yet other examples, then channels 420 may have an acute angle channel slope or curvature 0 such that the width at the opening of the channel is less than the width along the back wall of the channel, therein creating a dovetail channel configuration. In such an alternative configuration, the difference between the width of the back wall of each channel and the width of each channel at the opening of the respective channel provides a channel slope or curvature of between 70 and 90 degrees, between 80 degrees and 90 degrees, or between 85 degrees and 90 degrees. As noted above, the slope © is defined by the angle between the back wall and the respective side wall.

[0076] As noted above, the flow fields (e.g., anode flow plate, cathode flow plate) facilitate transportation of electrons within an electrochemical cell. Specifically, electrons may move to or from a flow field (e.g., anode side and cathode side) at an interface between the lands included in the flow field and an adjacent porous layer (e.g., PTL or GDL). On the anode side, electrons may travel from the anode flow field into the PTL at an interface between the lands included in the flow field and the PTL. Conversely, on the cathode side, electrons may travel from a GDL into the cathode flow field at an interface between the lands included in the flow field and the GDL. On both the anode and cathode sides, the size or area of an interface between the flow field and the adjacent porous layer may depend on the width of the lands. Accordingly, the ability of the flow field to transfer electrons to or receive electrons from an adjacent layer (e.g., PTL, GDL) is influenced by the width of the lands included in the flow field.

[0077] Additionally, as noted above, the flow fields (e.g., anode flow field and cathode flow field) facilitate transportation of fluids within the electrochemical cell. Specifically, on the anode side, channels in the flow field may provide liquid water as both a reactant and coolant to the PTL. Additionally, on the anode side, the channels in the flow field may receive product oxygen and liquid water as coolant from the porous transport layer. On thecathode side, the channels in the flow fields may receive product hydrogen from the GDL. In some examples, in addition to receiving product hydrogen, the channels may provide to the GDL and receive from the GDL liquid water as a coolant.

[0078] As noted above, in a PEM water electrolyzer, reactant water, electrons, and reaction products (e.g., gaseous oxygen, gaseous hydrogen) may co-exist in a catalyst layer (e.g., anode catalyst layer and cathode catalyst layer) at a triple phase boundary or reaction site where a reaction (e.g., oxygen evolution reaction, hydrogen evolution reaction) occurs. The flow field configurations provided herein may improve or optimize the transport (e.g., of reactant water and current) to the triple phase boundary. Geometric or structural properties of constituent elements of a flow field, such as, land width, channel width, channel depth, and the like and relationships between the between structural properties of the various constituent elements of the flow field may affect transport phenomena at (e.g., the ability of the electrochemical cells to transport electrons and reactant water to) the triple phase boundary.

[0079] Accordingly, channel width, and thus a flow field's capacity for supplying and receiving fluids from an adjacent porous layer, must be balanced with land width, and thus a flow field's capacity to provide and receive electric current (e.g., electrons) from an adjacent porous layer, when designing a flow field.

[0080] As described herein, an increase in performance (e.g., electrochemical efficiency, power, durability) of an electrochemical cell may be obtained with narrower channels and wider lands. For a fixed flow field width, the number of channels, the channel width, and the land width are dependent on each other. Additionally, channel depth may be determined in consideration of pressure drop requirements, with deeper channels allowing for smaller pressure drops. Channel based flow field designs with narrow and deep channels and wide lands can be manufactured by machining, which can use micro-machining end mills, speedforming, or groove-milling.

[0081] As illustrated in FIG. 5, each land 410 has a land width 411, and each channel has a channel width 421. The width 411 of each land 410 refers to a distance between one end of the respective land at a side wall of a first channel and an opposite second end of the respective land at a side wall of a second adjacent channel. Additionally, the width of eachchannel refers to a largest distance between the first side wall and the second side wall of the respective channel at an opening of the respective channel. In certain examples, the width of each land of the plurality of lands is larger than a width of each channel of the plurality of channels.

[0082] In certain examples, the land width 411 of each land is at least 1.1 times greater than the channel width 421 of each channel. In other examples, the land width 411 of each land is at least 1.5 times greater, at least 2 times greater, at least 3 times greater, at least 4 times greater, at least 5 times greater, at least 6 times greater, at least 7 times greater, at least 8 times greater, at least 9 times greater, at least 10 times greater, at least 20 times greater, at least 50 times greater, at least 100 times greater, at least 200 times greater, at least 500 times greater, or at least 1000 times greater than the channel width 421 of each channel. Alternatively, the flow field 400 may include a ratio of land width 411 over channel width 421 in a range of 2 to 10 (i.e., the land width is 2 to 10 times greater than the channel width). In another example, a flow field 400 may include a ratio of land width 411 over channel width 421 in a range of 4 to 7. In other examples, the flow field 400 may include a ratio of land with 411 over channel width 421 in a range of 4.5 to 6.5, in a range of 4 to 6, in a range of 3.5 to 5.5, or in a range of 4 to 5. In yet other examples, the flow field 400 may include a ratio of land with 411 over channel width 421 in a range of 100 to 1000, in a range of 10 to 1000, or in a range of 10 to 100.

[0083] Further, in certain examples, the depth 450 of the channel may be equal to or greater than the width of the channel. In certain examples, the channel depth 450 of each channel is at least 1.1 times greater, at least 1.5 times greater, at least 2 times greater, at least 3 times greater, at least 4 times greater, at least 5 times greater, at least 6 times greater, at least 7 times greater, at least 8 times greater, at least 9 times greater, or at least 10 times greater than the channel width 421 of the respective channel. Alternatively, the flow field 400 may include a ratio of channel depth 450 over channel width 421 in a range of 1.1 to 10 (i.e., the land width is 1.1 to 10 times greater than the channel width). In another example, a flow field 400 may include a ratio of channel depth 450 over channel width 421 in a range of 1.1 to 5, in a range of 1.1 to 4, in a range of 1.1 to 3, in a range of 1.1 to 2, in a range of 2 to 5, in a range of 2 to 4, or in a range of 2 to 3.

[0084] Referring to FIG. , a graph illustrating the effect of channel and land with on performance of an electrochemical cell is depicted. Specifically, FIG. 6 includes voltage on the vertical axis and current density on the horizontal axis. FIG. 6 illustrates the relationship between voltage and current density for several electrochemical cells having centerline aligned anode and cathode channels with anode and cathode flow fields having varying land and channel widths. As shown in FIG. 6, higher current densities were achieved at the same voltage in the electrochemical cells having a larger land width than channel width.

[0085] Therefore, according to some examples of the present disclosure, as illustrated in FIG. 6, a flow field 400 may include a plurality of lands 410 having a land width 411 for each land in the plurality of lands that is larger than a channel width 421 for each channel of the plurality of channels 420 included in the flow field 400.

[0086] FIG. 7 depicts a graph illustrating the effect of a ratio (n) of land width 411 divided by channel width 421 on the current density in an electrochemical cell. Specifically, FIG. 7 includes current density on the vertical axis and a ratio (n) of land width 411 over channel width 421 on the horizontal axis. FIG. 7 illustrates the relationship between electrochemical performance and the ratio (n) of land width 411 over channel width 421. Specifically, as illustrated in FIG. 7, electrochemical performance increases as the ratio (n) of land width 411 over channel width 421 increases. In some examples, as shown in FIG. 7, there may be significant diminishing returns in the increase of electrochemical performance after a ratio (n) of land width 411 to channel width 421 of 10 (i.e., land width being 10 times the channel width). Further, as illustrated in FIG. 7, there may be diminishing returns in the increase of electrochemical performance after a ratio (n) of land width 411 to channel width 421 in a range of 4 to 6.

[0087] Therefore, according to some examples of the present disclosure, a flow field 400 may include a ratio of land width 411 over channel width 421 in a range of 2 to 10. In another example, a flow field 400 may include a ratio of land width 411 over channel width 421 in a range of 4 to 7. In other examples, the flow field 400 may include a ratio of land with 411 over channel width 421 in a range of 4.5 to 6.5, in a range of 4 to 6, in a range of 3.5 to 5.5, or in a range of 4 to 5. In yet other examples, the flow field 400 may include aratio of land with 411 over channel width 421 in a range of 100 to 1000, in a range of 10 to 1000, or in a range of 10 to 100.

[0088] FIG. 8 depicts a graph illustrating voltage distribution at an interface between a catalyst layer (e.g., anode catalyst layer, cathode catalyst layer) and a porous layer (e.g., porous transport layer, gas diffusion layer) for channels 420 having various widths. As noted above, current may be transferred to or from a porous layer (e.g., PTL, GDL) at an interface between the lands 410 included in a flow field and the porous layer. Accordingly, voltage at an interface between the flow field 400 and the porous layer may be greater at an interface between the lands 410 and the porous layer, where current flows to or from the porous layer, than at an interface between the channels 420 and the porous layer. However, it may be beneficial to reduce a variation or difference in voltage across an interface between a catalyst layer (e.g., anode catalyst layer, cathode catalyst layer) and a porous layer (e.g., PTL, GDL) in order to provide a more uniform current density distribution. A more uniform current density may result in a more uniform catalyst utilization (e.g., at locations in the catalyst layer corresponding to the channels and lands), thus increasing the life of the cell.

[0089] Specifically, referring to FIG. 8, a voltage distribution at or across an interface between a PTL and an anode catalyst layer is illustrated. Voltage is included on the vertical axis and position or distance along the interface between the catalyst layer and the porous layer and the location of channels and lands included in the flow field are illustrated on the horizontal axis. FIG. 8 illustrates voltage distributions for channels having multiple different channel widths. As shown in FIG. 8, that voltage distribution is improved, (i.e., that there is smaller difference or variation in voltage across the interface), for flow fields having narrower or smaller channel widths. Specifically, FIG. 8 illustrates that there is a relatively small variation or difference in voltage between a catalyst layer and a porous layer at locations corresponding to the lands 410 and channels 420 included in a flow field in flow fields including channels 420 having a width of 1 mm. Additionally, there is a smallest relative variation or difference in voltage between a catalyst layer and a porous layer at locations corresponding to the lands 410 and channels 420 included in a flow field in flow fields including channels 420 having a width of 0.7 mm.

[0090] Therefore, according to the present disclosure, the flow field 400 may include channels 420 having a width 421 of 1 mm or less, 0.7 mm or less, 0.5 mm or less, 0.3 mm or less, or 0.2 mm or less.

[0091] FIG. 9 depicts a graph illustrating a spatial distribution of scaled current density at a catalyst layer (e.g., anode catalyst layer, cathode catalyst layer) for flow fields including various different ratios of land width 411 over channel width 421. The graph of FIG. 9 includes scaled current density (i.e., current density over maximum current density) on the vertical axis and scaled position (i.e., position over pitch) on the horizontal axis. Accordingly, flow fields including a higher ratio of land width 411 over channel width 421 have a higher scaled current density at the same scaled position. Accordingly, there may be an improved or more uniform current distribution in flow fields including a higher ratio of land width 411 to channel width 421. Specifically, there may be a smaller difference between the maximum current density for a flow field and the current density at a scaled position with respect to a centerline of a channel for flow fields including a larger ratio of land width 411 to channel width 421. As noted above, uniform current density may be advantageous, as a more uniform current density may result in more uniform utilization of the catalyst in the catalyst layer, thus increasing the life of the electrochemical cell.

[0092] FIG. 10 depicts a graph illustrating a spatial distribution of power density (e.g., Watts / Area) for flow fields including various different ratios of land width 411 over channel width 421. The graph of FIG. 10 includes power density on the vertical axis and scaled position (e.g., position over pitch) on the horizontal axis. There may be higher power density (e.g., watts / unit area) at the same scaled position for flow fields having a higher ratio of land width 411 over channels width 421. A higher power density may advantageously result in higher catalyst utilization and thus improve efficiency of the electrochemical cell. Accordingly, flow fields including a higher ratio of land width to channel width may improve efficiency of an electrochemical cell.

[0093] In addition to affecting transport phenomena (e.g., supply of liquid reactant, supply of electric current) at the triple phase boundary, land width 411, channel width 421, and a ratio of land width 411 over channel width 421 may impact mechanical support of the catalyst coated membrane. Thus, land width 411, channel width 421, and a ratio of landwidth 411 over channel width 421 may also affect the durability and degradation of the electrochemical cell as influenced by mechanical forces applied to the catalyst coated membrane.

[0094] Electrochemical cells, and specifically, the membrane included in an electrochemical cell, are exposed to a variety of forces. For example, electrochemical cells are exposed to a clamping force, which squeezes or presses together the various layers included in the cell. In a clamped cell, the membrane may be constrained between an anode flow field and a cathode flow field. The electrochemical cell may be exposed to hydration events, in which the membrane swells as it absorbs water, generating swelling forces. Additionally, the membrane may experience thermal expansion forces as the various layers of the electrochemical cell undergo thermal expansion as a temperature changes during cell operation.

[0095] The ratio of land width 411 over channel width 421 may alter the mechanical forces that directly impact the membrane. In a first example, a ratio of land width 411 over channel width 421 affects pillowing or deformation of the membrane into channels 420 of an adjacent flow field. Specifically, a thickness of the membrane may increase or decrease due to various events during the lifetime of the electrochemical cell. As the membrane expands or swells, it may flow or deform into unconstrained areas, such as the channels 420 of a flow plate 400. Specifically, in some examples, as the membrane swells or expands, both the membrane and a porous layer (e.g., PTL, GDL) disposed between the flow field 400 and the catalyst coated membrane may flow or deform into the channels 420 of the flow field 400.

[0096] As illustrated in FIG. 11, as the membrane flows or deforms into a channel 420 of the flow field 400, it may buckle and form an arch shape. Accordingly, a catalyst layer (e.g., disposed on the surface of the membrane) may be stretched, resulting in a discontinuity in electron transport between catalyst particles in the catalyst layer. Stretching of the catalyst layer may cause non-uniform current density at the catalyst layer resulting in underutilization of the catalyst layer near channel areas and over utilization of the catalyst near the land areas which may cause local hot spots and could serve as failure points for the electrochemical cell.

[0097] According to a second example, the ratio of land width 411 over channel width 421 affects a maximum mechanical stress at unconstrained channel 420 areas caused by tensile and compressive mechanical forces applied to the membrane. The membrane may be prone to deformation at the unconstrained channel areas which may lead to catastrophic failure of the cell and / or reduce the use life of the cell. Specifically, mechanical wear on the membrane may result in leak causing hydrogen gas and oxygen gas to mix, forming an explosive gas mixture which may result in a rapid oxidation event.

[0098] For at least the reasons noted above, mechanical support of the membrane should be considered when selecting geometrical or structural properties of a flow field, and specifically, when determining a ratio of land width 411 to channel width 421 for a flow field. Specifically, minimizing the magnitude of mechanical forces applied to the membrane may improve durability of the electrochemical cell and increase the use life of the cell.

[0099] Referring to FIG. 11, a mechanical model illustrating the effects of land width, channel width, and a ratio of land width over channel width on displacement of membrane is provided. As illustrated in FIG. 11, mechanical deformation and arching or pillowing of the membrane is greater for wider or larger channel widths 421. Accordingly, smaller channel widths 421 may improve performance and durability of an electrochemical cell. Additionally, and described hereinafter in greater detail, asymmetric anode side and cathode side flow fields may reduce mechanical deformation of the membrane, improving performance and durability of the electrochemical cell.

[0100] As noted above, geometric or structural properties, such as land width, channel width, and channel depth, impact a flow fields capacity to supply liquid reactant and electric current to a triple phase boundary or reaction site. Additionally, as noted above, in order to operate efficiently, electrochemical cells require liquid reactant and electric current to be supplied to the catalyst layer in specific proportions. Flow field designs that lead to poor or insufficient liquid reactant supply to the catalyst layer suffer from mass transport overpotential. As current density provided to the catalyst coated membrane increases, so does a magnitude of quantity of mass transport overpotential. Increasing current density also increases cell temperature as additional heat dissipation occurs.

[0101] Accordingly, it is necessary to provide a sufficient flow rate of reactant liquid water to the catalyst layer or reaction site to minimize mass transport losses. Additionally, providing a sufficient flow rate of reactant water to a reaction site reduce the risk of cell failures, for example cell failures do to overheating. Additionally, when an insufficient quantity of reactant water is provided the catalyst layer, gas generated at the reaction sites may accumulate in the adjacent layer (e.g., PTL, GDL). Accordingly, flow field design is critical in achieving sufficient flow of liquid water reactant to the catalyst layer for gas removal and to prevent dehydration of the electrochemical cell. Increasing a flow rate of liquid water reactant provided to the adjacent layer (e.g., PTL, GDL) and catalyst may improve gas liquid exchange (e.g., the removal of gas from the porous layer), but also increases pumping power costs.

[0102] In certain examples, increasing the current density supplied to a catalyst layer while maintaining a fixed flow rate of liquid water reactant to the catalyst layer leads to a significant increase in the quantity or volume of gas within a porous layer as compared to a total quantity or volume of gas and liquid within the porous layer. An increase in gas fraction in the porous layer may occur concurrently with an increase in mass transport overpotential at the catalyst layer.

[0103] A stoic ratio or stoic number is a non-dimensional metric comparing an amount of liquid water supply with respect to an operational current density at a catalyst layer of the cell. An ideal stoic ratio provides that sufficient liquid water is supplied for the electrolysis reaction and that gas is effectively removed from the porous layer (e.g., PTL, GDL). Below a critical stoic ratio, the rate of gas generation may exceed the rate of gas removal, hindering liquid water reactant from reaching the catalyst layer. Even when a small quantity of gas is in the porous layer, if the gas remains stagnant, as opposed to flowing out of the porous layer, hot spots or locations having an elevated temperature may arise. Accordingly, obtaining a critical stoic ratio is crucial to mitigating increasing cell temperatures. Ideal stoic ratio depends in part on the flow field geometry.

[0104] Referring to FIG. 12, a graph illustrating a mass fraction of water at the middle of a land 410 for both anode side flow fields and cathode side flow fields having varying land widths 411 and fixed channel widths 421 is depicted. Specifically, the graph of FIG. 12includes mass fraction of water at the center of a land on the vertical axis and position on the horizontal axis.

[0105] As noted above, it is important to provide a sufficient flow rate of liquid water reactant to a catalyst layer or reaction site in order to minimize mass transport losses, remove gas from the porous layer, and prevent dehydration of the electrochemical cell. In an electrochemical cell, gas may accumulate under land areas (e.g., locations corresponding to an interface between a porous layer and a land abutting the porous layer. Accordingly, a mass fraction of water included in an electrochemical cell may be smallest at location corresponding to the center of a land.

[0106] As shown in FIG. 13, a mass fraction of water at the middle of a land 410 becomes small at a ratio of land width 411 over channel width 421 of about 10. When the mass fraction of water becomes small, less liquid water reactant is supplied to the catalyst layer or reaction reducing a current density at which mass transport overpotential occurs. Additionally, as a mass fraction of water becomes small gas may accumulate under lands, inefficient heat transfer and insufficient liquid reactant under lands may occur. Accordingly, a ratio of land width 411 over channel width 421 in a flow field according to the present disclosure may be less than 10, in order to maintain efficient liquid water reactant supply to the catalyst layer.

[0107] According to some examples of the present disclosure, the geometric or structural properties of the constituent elements of a flow field and / or relationships between constituent elements of a flow field provided herein may be applied to the anode and cathode flow fields individually and separately. Specifically, because the functions or requirements of the anode side flow field and the cathode side flow field may be different, so may flow field designs for the anode and cathode sides. In another example, an anode side flow plate may include a parallel channel flow field and a cathode side flow plate may be a mesh flow field, or vice-versa. According to some examples, the number of channels included in the anode side flow field and the cathode side flow field may be the same or different.

[0108] As noted above, for channel based fields, pitch refers to the sum of a number of lands and a number of channels within a flow field. According to some examples, ifelectrochemical cell components on the cathode side have worse electrical conductivities than their counterparts on the anode side, for example, if a porous carbon based GDL is included on the cathode side and a metal based PTL is included on the anode side, the anode side pitch may be larger than cathode side pitch (e.g., there may be more lands and channels in the anode side flow field than lands and channels in the cathode side flow field). As noted above, the symmetry or lack thereof between an anode side flow field and a cathode side flow field directly impact mechanical support of the catalyst coated membrane. Additionally, the symmetry or lack thereof between an anode side flow field and a cathode side flow field directly impact electron transport, fluid transport, and heat transport within the electrochemical cell.

[0109] FIG. 13 illustrates various relationships between anode side and cathode side flow fields. In some examples, as illustrated in FIG. 13, the anode side channels and cathode side channels may have centerline symmetry. In other examples, a centerline of the anode side channels and a centerline of the cathode side channels may be offset. Further, in some examples, as illustrated in FIG. 13, anode side channels may be opposite cathode side lands and / or cathode side channels may be opposite anode side lands. In addition to geometric design, operating conditions such as flow rate and pressure at the anode and cathode sides may be different.

[0110] Both in plane and through plane distribution and flow of heat are important. Optimal flow and distribution of heat in the cell ensures better performance and reduces the risks of hotspots. A ratio of land width 411 over channel width 421 and channel symmetry / asymmetry on the anode and cathode sides may affect cell temperature by changing the local temperature under lands and channels in the catalyst layer and in the membrane, which may affect the electrochemical performance and durability of the cell.

[0111] The geometric or structural properties of the constituent elements of a flow field and / or relationships between constituent elements of a flow field provided herein may be applied to or manufactured on a flow plate having any size or shape. Specifically, the geometric or structural properties of the constituent elements of a flow field and / or relationships between constituent elements of a flow field provided herein may be included in a circular, square, rectangular, or any other shape flow plate. The flow field configurationsprovided herein may be machined, hydroformed, or etched into a respective flow plate. In some examples, the flow field configurations described herein may be machined into a respective flow plate in order to achieve high aspect ratio channels, narrow and deep channels, and channels having small (e.g., <10 degree) corner curvature.

[0112] According to some examples, a single flow plate may include two flow fields formed therein for adjacent cells in a cell stack. Specifically, each side of two opposite sides of the flow plate may include a flow field or channels formed therein. The flow field or channels formed in each side of the plate may be machined, hydroformed, or etched in a respective side of the flow plate. The flow fields or channels formed on each side of the flow plate may be included for adjacent electrochemical cells included in a stack of electrochemical cells. Specifically, the flow field on one side of the flow plate may be configured for a first cell (e.g., the anode flow field of the first cell) while the opposite side of the flow plate may be configured for the second, adjacent cell of the stack (e.g., the cathode flow field of the second cell). In certain examples, the flow field configuration on one side of the plate for the anode flow field of the first cell may be a same configuration as the second side of the plate for the cathode flow field of the second cell. Alternatively, as discussed above, the anode flow field may have a different configuration than the cathode flow field. As such, the flow field configuration on one side of the plate for the anode flow field of the first cell may be a different configuration than the second side of the plate for the cathode flow field of the second cell.

[0113] As described herein, an increase in performance (e.g., electrochemical efficiency, power, durability) of an electrochemical cell may be obtained with narrower channels and wider lands. For a fixed flow field width, number of channels, channel width, and land width are dependent on each other. Additionally, channel depth may be determined in consideration of pressure drop requirements, with deeper channels allowing for smaller pressure drops. Channel based flow field designs with narrow and deep channels and wide lands can be manufactured by machining, which can use micro-machining end mills, speedforming, or groove-milling.

[0114] One or more embodiments of the disclosure may be referred to herein, individually and / or collectively, by the term "invention" merely for convenience and withoutintending to voluntarily limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, are apparent to those of skill in the art upon reviewing the description. As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. As used herein, "for example," "for instance," "such as," or "including" are meant to introduce examples that further clarify more general subject matter. Unless otherwise expressly indicated, such examples are provided only as an aid for understanding embodiments illustrated in the present disclosure and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed embodiment.

[0115] The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b) and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

[0116] It is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is understood that the following claims including all equivalents are intended to define the scope of the disclosure. The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the disclosure.

Claims

CLAIMS1. A flow field for an electrochemical cell, the flow field comprising: a plurality of channels configured to transfer fluid to or receive fluid from an adjacent layer of the electrochemical cell; and a plurality of lands configured to abut the adjacent layer of the electrochemical cell, each land of the plurality of lands separating two adjacent channels of the plurality of channels, wherein each channel comprises a first side wall, a second side wall, and a back wall, wherein the back wall extends between the first side wall and the second side wall, wherein the first side wall extends between the back wall and a first adjacent land, and wherein the second side wall extends between the back wall and a second adjacent land, wherein a width of each land of the plurality of lands is larger than a width of each channel of the plurality of channels, wherein the width of each land refers to a distance between one end of the respective land at a side wall of a first channel and an opposite second end of the respective land at a side wall of a second adjacent channel, and wherein the width of each channel refers to a largest distance between the first side wall and the second side wall of the respective channel at an opening of the respective channel.

2. The flow field of claim 1, wherein a width of each land of the plurality of lands is a same land width, and wherein a width of each channel of the plurality of channels is a same channel width.

3. The flow field of claim 1, wherein a ratio of an average width of each land of the plurality of lands divided by an average width of each channel of the plurality of channels is in a range of 2 to 10.

4. The flow field of claim 1, wherein a ratio of an average width of each land of the plurality of lands divided by an average width of each channel of the plurality of channels is in a range of 10 to 1000.

5. The flow field of claim 1, wherein the width of each channel of the plurality of channels is 1 millimeter (mm) or less.

6. The flow field of claim 1, wherein a depth of each channel of the plurality of channels is greater than the width of each channel of the plurality of channels.

7. The flow field of claim 6, wherein the depth of each channel of the plurality of channels is a same channel depth.

8. The flow field of claim 1, wherein the flow field is an anode flow field of the electrochemical cel I, and wherein the adjacent layer is a porous transport layer.

9. The flow field of claim 1, wherein the flow field is a cathode flow field of the electrochemical cel I, and wherein the adjacent layer is a gas diffusion layer.

10. The flow field of claim 1, wherein a width of the back wall of each channel is less than the width of each channel between the first side wall and the second side wall of the respective channel at the opening of the respective channel.

11. The flow field of claim 10, wherein a difference between the width of the back wall of each channel and the width of each channel at the opening of the respective channel provides a channel slope or curvature of greater than 90 degrees and less than 100 degrees defines as an angle between the back wall and the respective side wall.

12. The flow field of claim 1, wherein the flow field, when positioned within the electrochemical cell, is configured to operate with 200 mV or less of pure resistive loss when operating of at least at least 3 Amps / cm2, at least 4 Amps / cm2, at least 5 Amps / cm2, at least 6 Amps / cm2, at least 7 Amps / cm2, at least 8 Amps / cm2, at least 9 Amps / cm2, at least 10 Amps / cm2, at least 11 Amps / cm2, at least 12 Amps / cm2, at least 13 Amps / cm2, at least 14Amps / cm2, at least 15 Amps / cm2, at least 16 Amps / cm2, at least 17 Amps / cm2, at least 18Amps / cm2, at least 19 Amps / cm2, at least 20 Amps / cm2, at least 25 Amps / cm2, at least 30Amps / cm2, in a range of 1-30 Amps / cm2, in a range of 3-20 Amps / cm2, in a range of 3-15Amps / cm2, in a range of 3-10 Amps / cm2, or in a range of 10-20 Amps / cm2.

13. The flow field of claim 1, wherein the flow field, when positioned within the electrochemical cell, is configured to transfer 0.05-1 mL of water through the electrochemical cell per Amp per min.

14. An electrochemical cell comprising: a flow field as claimed in any of claims 1-13; a membrane; and a porous layer positioned between the flow field and the membrane.

15. The electrochemical cell of claim 14, further comprising: an additional flow field positioned on an opposite side of the membrane from the flow field; and an additional porous layer positioned between the additional flow field and the membrane, wherein the additional flow field comprises: an additional plurality of channels configured to transfer fluid to or receive fluid from the additional porous layer of the electrochemical cell; and an additional plurality of lands configured to abut the additional porous layer of the electrochemical cell, each land of the additional pluralityof lands separating two adjacent channels of the additional plurality of channels, wherein each channel comprises a first side wall, a second side wall, and a back wall, wherein the back wall extends between the first side wall and the second side wall, wherein the first side wall extends between the back wall and a first adjacent land, and wherein the second side wall extends between the back wall and a second adjacent land, wherein a width of each land of the additional plurality of lands is larger than a width of each channel of the additional plurality of channels, wherein the width of each land refers to a distance between one end of the respective land at a side wall of a first channel and an opposite second end of the respective land at a side wall of a second adjacent channel, and wherein the width of each channel refers to a largest distance between the first side wall and the second side wall of the respective channel at an opening of the respective channel.

16. The electrochemical cell of claim 15, wherein a width of each land of the additional plurality of lands is a same land width, and wherein a width of each channel of the additional plurality of channels is a same channel width.

17. The electrochemical cell of claim 15, wherein the flow field is an anode flow field of the electrochemical cell, wherein the porous layer is a porous transport layer, wherein the additional flow field is a cathode flow field of the electrochemical cell, and wherein the additional porous layer is a gas diffusion layer.

18. The electrochemical cell of claim 17, wherein a sum of a number of channels and a number of lands within the anode flow field is greater than a sum of a number of channels and a number of lands within the cathode flow field.

19. The electrochemical cell of claim 17, wherein each channel within the anode flow field has a centerline symmetry with a respective channel in the cathode flow field.

20. The electrochemical cell of claim 17, wherein a centerline of each channel within the anode flow field is offset from a centerline of a respective channel in the cathode flow field.

21. The electrochemical cell of claim 17, wherein each channel within the anode flow field is aligned opposite from a respective land in the cathode flow field, and wherein each channel within the cathode flow field is aligned opposite from a respective land in the anode flow field.

22. The electrochemical cell of claim 14, wherein the electrochemical cell is configured to operate with 200 mV or less of pure resistive loss when operating of at least at least 3 Amps / cm2, at least 4 Amps / cm2, at least 5 Amps / cm2, at least 6 Amps / cm2, at least 7 Amps / cm2, at least 8 Amps / cm2, at least 9 Amps / cm2, at least 10 Amps / cm2, at least 11Amps / cm2, at least 12 Amps / cm2, at least 13 Amps / cm2, at least 14 Amps / cm2, at least 15Amps / cm2, at least 16 Amps / cm2, at least 17 Amps / cm2, at least 18 Amps / cm2, at least 19Amps / cm2, at least 20 Amps / cm2, at least 25 Amps / cm2, at least 30 Amps / cm2, in a range of1-30 Amps / cm2, in a range of 3-20 Amps / cm2, in a range of 3-15 Amps / cm2, in a range of 3- 10 Amps / cm2, or in a range of 10-20 Amps / cm2.

23. The electrochemical cell of claim 14, wherein the electrochemical cell is configured to transfer 0.05-1 m L of water through the electrochemical cell per Amp per min.

24. An electrochemical system comprising: a plurality of electrochemical cells stacked on top of one another, wherein each electrochemical cell within the plurality of electrochemical cells comprises a flow field and an additional flow field as claimed in any of claims 14-23.

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