Patent Application
20230047374
The subject matter disclosed herein relates generally to solid polymer electrolyte electrolyzers, fuel cells, unitized regenerative fuel cells (URFCs), and other electrochemical cells. More particularly, the subject matter disclosed herein relates to the design and construction of a bipolar plate flow field and porous transport layer of such devices.
As society and technologies change, the U.S. energy system is evolving from traditional fossil energy towards sustainable, affordable, and reliable energy sources. In this regard, water electrolysis based on the low-temperature solid polymer electrolyte membrane electrolyzer cells (PEMECs) is one of the most competitive hydrogen production candidates because PEMECs can be combined with intermittent renewable energy sources (e.g., geothermal, wind, solar, hydroelectricity) to realize carbon-free and high-purity hydrogen production.
PEMECs were typically constructed in a sandwich configuration, including end plates, current collectors, bipolar plates (BPs), porous transport layers (PTLs), and catalyst layers for both anode and cathode sides, as well as a solid polymer electrolyte membrane (PEM) serving as the electrolyte. PTLs play many roles in PEMECs, including electricity transfer, mass transfer, heat transfer and mechanical support, indicating the significance of the impact of PTLs' properties on the overall performance of PEMECs. According to the configuration of conventional PTLs, it can be divided into felt, mesh, foam and sintered powder plates. However, for the conventional PTLs, the pileup of microfibers or particles leads to large contact resistance and requires large thickness to ensure mechanical strength. To decrease the contact resistance and the material cost, thin/tunable liquid/gas diffusion layer (TTLGDL) can be used as a PTL, which can decrease the ohmic resistance and the PTL's thickness.
In addition, though, for both conventional PTLs and TTLGDLs, the transport of reactants/products relies on the existence of micropores inside PTLs or TTLGDLs. Due to the properties of flow fields and the sandwich structure of PEMECs, however, the micropores in PTLs or TTLGDLs are often blocked by the lands of the BP flow field, resulting in the impediment of reactant/product transport under the solid land area. In fact, it has been shown that gas accumulation under the land area is much larger than under the channel area. The excess gas accumulation under the land area can cause severe ohmic and mass transport issues and degrade the overall performance of PEMECs, especially under high current density. In some cases, mass transport limitations can be alleviated with increased water pumping rate, but such a solution presents a parasitic loss, decreasing overall system efficiency and ultimately increasing the cost of hydrogen production. Accordingly, it would be desirable to overcome the severe mass transport challenges under the land area of the BP flow field in such systems.
In accordance with this disclosure, devices, systems, and methods of producing improved fluid flow assemblies in solid polymer electrolyte electrolyzers, fuel cells, and unitized regenerative fuel cells are provided. In one aspect, a fluid flow assembly for a solid polymer electrolyte electrochemical cell is provided. The fluid flow assembly includes a bipolar plate (BP) flow field comprising an inlet, an outlet, and a plurality of discrete lands arranged within the flow field; and a liquid/gas diffusion layer positioned in fluid communication with the flow field between the inlet and the outlet, the liquid/gas diffusion layer comprising a solid substrate through which a plurality of pores is formed. In this arrangement, the BP lands can be arranged and configured such that the plurality of pores is substantially unobstructed by the BP lands.
In another aspect, a method for fabricating a fluid flow assembly porous transport layer for a solid polymer electrolyte electrochemical cell is provided. The method includes steps of positioning a plurality of discrete lands between an inlet and an outlet to define a bipolar plate flow field, and positioning a porous transport layer in fluid communication with the flow field between the inlet and the outlet. Specifically, positioning the porous transport layer can include arranging and configuring the BP lands such that the plurality of pores is substantially unobstructed by the BP lands.
In another aspect, a flow-enhanced liquid/gas diffusion layer design includes a solid substrate through which a plurality of pores is formed. This design introduces additional micro channels in the liquid/gas diffusion layers for improving its in-plane and through-plane transport ability. The configuration of micro channels could be parallel, wedge-shaped, or crossed, or their combinations. The amount, length, width, height, wedge angles, and crossed directions of micro channels are well-tunable, depending on the specific system design. The configuration of the micro channels could also include modifying the cross-section of the channels. The cross-section design can be inverted trapezoidal, where parameters of top width, bottom width, and height of channels are well-tunable. Specifically, the micro channels can be partially fabricated in coupling the lands of the bipolar plate flow field. Positioning the liquid/gas diffusion layer can include arranging and configuring the lands of bipolar plate flow field. In this arrangement, the water and gas transport are enhanced in both in-plane and through-plane directions and substantially unobstructed by the lands.
Although some of the aspects of the subject matter disclosed herein have been stated hereinabove, and which are achieved in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.
The features and advantages of the present subject matter will be more readily understood from the following detailed description which should be read in conjunction with the accompanying drawings that are given merely by way of explanatory and non-limiting example, and in which:
The present subject matter provides devices, systems, and methods of producing improved porous transport layers in solid polymer electrolyte electrolyzers, fuel cells, and unitized regenerative fuel cells. In one aspect, the present subject matter provides a flow field that maximizes mass transport in PEMECs, achieving excellent electrochemical activity without the need for high water pumping rate. Referring to
In this configuration, the flow field 110 is a pin-type flow field that is configured to provide fluid flow between an inlet 111 and an outlet 112, and a plurality of discrete lands 115 is arranged within the flow field 110 to distribute the fluid flow substantially uniformly through a plurality of flow channels 116 across the flow field 110. In some embodiments, the lands 115 are configured as substantially circular contact pillars. Alternatively, the flow field 110 can have any of a variety of configurations, including but not limited to a parallel flow field, a single serpentine flow field, a multiple serpentine flow field, an interdigitated flow field, and a cascade flow field. Regardless of the particular configuration, in some embodiments, the lands 115 can be arranged in a substantially staggered pattern that is configured to reduce large pressure drops and promote exchange in-between the flow channels 116.
In some embodiments, the PTL 120 of the PEMEC is positioned in fluid communication with the flow field 110 between the inlet 111 and the outlet 112. In some embodiments, the PTL 120 is a liquid/gas diffusion layer (LGDL) that is formed from a solid substrate 121 through which a plurality of pores 122 are formed. In this arrangement, the flow field 110 provides a desired supply of reactants to interior layers of the PEMEC through the pores 122 of the PTL 120. In combination with this structure, the architecture of the flow field 110 alleviates mass transport limitations because it addresses the lack of in-plane permeability of some PTLs, such as LGDLs.
In this regard, in some embodiments, ohmic losses can be reduced by constructing the flow field 110 and PTL 120 as a unitized component, and obstruction within the membrane and between the flow field 110 and PTL 120 can be reduced by configuring the flow field 110 to be substantially aligned with non-porous regions of the PTL 120. For example, in some embodiments, the pin design, pitch, and aspect-ratios of the flow field 110 can be adjusted to maximize porosity for a given configuration of the PTL 120, such as is shown in
In some embodiments, for example, each of the lands 115 of the flow field 110 is substantially aligned with portions of the substrate 121 between the pores 122 such that the plurality of pores 122 are substantially unobstructed by the lands 115 for a given configuration of the PTL 120. Such coordinated design of the components can enable superior electrochemical performance. In comparison to conventional parallel or serpentine flow field designs, which can obstruct a substantial portion of the underlying PTL 120 (e.g., with a porosity of 0.5 or less), a pin-type flow field 110 can be configured to align with the underlying PTL 120 so that the effective porosity is optimized (e.g., greater than about 0.88).
In a representative, non-limiting example, a pin type flow-field was fabricated and tested with a micro-patterned LGDL with 200 μm pores in diameter and catalyst-coated LGDL (CCLGDL) at standard operating conditions.
The 8c4 CCLGDL was geometrically identical to a micro-patterned LGDL with 200 μm pores in diameter but was meanwhile catalyst-coated. The additional catalyst loading on the CCLGDL enhanced sensitivity to the mass transport improvement made possible by the pin-type flow-field. This representative embodiment shows that substantial benefit can be realized for bare LGDL and CCLGDL constructions. In addition, a unitized pin-type flow field/LGDL combination can further reduce ohmic losses, yielding even better electrochemical performance and efficiency in polymer electrolyte water electrolyzers.
The configuration of the PTL 120 can further be designed to improve the mass transport, performance, and efficiency in electrolyzers and fuel cells. Referring to
As shown in
Depending on the desired distribution of fluid flow to the pores 122, the micro channels 125 can be arranged in a common direction, or the channels 125 can be arranged in different directions. Further, the length of each of the micro channels 125 can extend a distance sufficient to connect two pores or multiple pores in succession. In some embodiments, the micro channels 125 are sized to have a width that is substantially equal to a width of the pores 122 with which they are aligned. Alternatively, the width can be smaller or larger than the width of the pores 122. In any configuration, even though the lands 115 of the BP flow field 110 remain in contact with a surface of the FELGDL 120′, the micro channels 126 provide selective fluid flow beneath portions of the obstructed surface so that the active areas in each of the pores 122 are “open” to the reactions. As a result, the gas accumulation and pore blockage in un-modified LGDL configurations can be avoided to a great extent. The in-plane micro channels 125 can thus enhance the reactant/production transport of the whole active area including in areas corresponding to both the lands 115 and the flow channels 116 at the same time. Such a configuration for the FELGDL 120′ can further improve the operation of the polymer electrolyte water electrolyzer in which it is included. For example, in conventional systems, catalyst layers are coated on the PEM, and form catalyst-coated membranes (CCMs). By using the FELGDL 120′ as a PTL for such a system, improved performance can be achieved. Specifically, in one experimental configuration, a PTLs/CCM using anode catalysts having 3.0 mg Ir/cm2, the presently disclosed FELGDL can achieve a cell voltage of 1.86 V at the current density of 2 A/cm2. As shown in
Alternatively, in place of a conventional PTL/CCM configuration, there has been development in catalyst-coated liquid/gas diffusion layers (CCLGDLs) to promote improved catalyst utilization and PEMEC efficiency. Using the FELGDL 120′ in such a configuration can likewise provide improved performance. For example, in a CCLGDLs/PEM using anode catalysts having 0.26 mg Ir/cm2, test results are shown in
In some embodiments, the performance of the FELGDL 120′ can further be enhanced by modifying the configuration of the micro channels 125. As shown in
In some embodiments, this wedge-shaped configuration of the micro channels 125 is selectively provided only in regions of the FELGDL 120′ that are positioned beneath the lands 115 of the flow field 110, which are those areas in which flow enhancement is most desired as shown in
The wedge angle of the flow-enhancing micro channels 125 is well-tunable.
As shown in
As shown in
Alternatively, or in addition, referring to
Those having ordinary skill in the art will recognize that any of a variety of other adjustments of these parameters, either individually or in combinations together, can be made to correspondingly adjust the operation of the FELGDL 120′ according to the specific requirements of the fluid flow assembly 100.
Regardless of the particular structural configuration of the PTL 120/FELGDL 120′, in some embodiments, the material of the substrate can be modified to improve performance of the fluid flow assembly 100. In some embodiments, modification of the substrate can involve providing a surface coating on the PTL 120/FELGDL 120′, the surface coating comprising a material including but not limited to a nitride, a metal, a carbide, a composite, or any combination thereof. In addition, in some embodiments, the surface coating can be applied by any of a variety of processes, including but not limited to galvanizing, electrochemical coating, chemical vapor deposition, physical vapor deposition, conversion coating, thermal spraying, chemosynthesis, or any combination thereof.
In some particular embodiments, for example, modification of the substrate can involve nitridation on the substrate for nitride formation, which can be used to meet requirements of corrosion resistance that are sufficient to withstand the chemical and electrochemical corrosions from acidic/basic atmosphere and high voltage during cell operation, respectively. In some particular embodiments, for example, where a titanium-based substrate is used as the PTL 120/FELGDL 120′, modification of the substrate can involve nitridation on the titanium substrate for titanium nitride (TiNx) formation, where x is a value in a range of 0<x≤5.0. For example, x can be 0.3, 0.5, 2, 5 or any other value falling within this range, depending on the nitridation levels. In some embodiments, such a nitridation process is carried out under ammonia at any of a range of temperatures between about 600° C. and about 1000° C., including 600° C., 700° C., 800° C., 900° C., or 1,000° C. The nitride coating thickness can be dependent on the nitridation temperature and time, where a higher applied temperature and longer time can result in a thicker coating. For example, at 800° C., the TiNx coating thickness can be about 120 nm, which is sufficient to increase the electrical conductivity. Moreover, TiNx can provide further benefits of high electrical conductivity and excellent resistance to most chemicals, and is reported as an effective electronic structure modulator, which meets all the expectations for a promising substrate for catalysts used on an anode structure to facilitate the oxygen evolution reaction (OER).
In one example embodiment, the PTL 120/FELGDL 120′ is a thin/well-tunable liquid/gas diffusion layer (TTLGDL) that is fabricated from thin titanium foils with engineered thickness (e.g., ranging from about 25 to about 200 μm, including about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or 200 μm), pore shape (e.g., triangle, square, pentagon, hexagon, octagon, decagon, or combinations thereof), pore size (e.g., having a hydraulic diameter ranging from about 50 to about 400 μm, including about 50, 100, 150, 200, 250, 300, 350, or 400 μm), and porosity (e.g., ranging from about 20% to about 70%, including about 20, 30, 35, 40, 45, 50, 55, 60, 65, or 70%). As shown in
Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to “a cell” includes a plurality of such cells, and so forth.
Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently-disclosed subject matter.
As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.
As used herein, ranges can be expressed as from “about” one particular value, and/or to “about” another particular value. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.
The presently disclosed subject matter can be embodied in other forms without departure from the spirit and essential characteristics thereof. The embodiments described therefore are to be considered in all respects as illustrative and not restrictive. Although the present subject matter has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the present subject matter.
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/233,531, filed Aug. 16, 2021, the disclosure of which is incorporated herein by reference in its entirety.
This invention was made with government support under Grant Nos. EE0008426 and EE0008423 awarded by the Department of Energy. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63233531 | Aug 2021 | US |
