Multilayer porous transport layer for membrane electrode assembly and method of making same

Abstract

A multi-layer porous transport layer (PTL) comprising a first layer comprising a first surface and a second surface opposite the first surface, the first layer being made of one or more first particles, and a second layer comprising a first surface and a second surface opposite the first surface, the second layer being made of one or more second particles, the second surface of the second layer is attached to the first surface of the first layer, the second layer being made of one or more second particles.

Description

[0001] The information provided in this section is presented to generally summarize the context of the present disclosure. The work of the presently named inventors, to the extent it is described in this background section, and the descriptions of aspects that can not have been eligible for prior art at the time of submission, are neither expressly nor impliedly admitted to be prior art against the present disclosure. TECHNICAL FIELD

[0002] The present invention relates generally to a membrane electrode assembly, and more particularly to a porous transport layer. BACKGROUND

[0003] Electrolyzers are devices that perform electrolysis, a process that uses electricity to split water into oxygen and hydrogen gas, which can be used as fuel in vehicles such as cars. Electrolyzers are composed of an anode and a cathode separated by an electrolyte. Electrolyzers can include a membrane electrode assembly (MEA), which facilitates the electrochemical reactions needed to produce split water and separate the product hydrogen gas from the product oxygen gas. On the anode side of the MEA, water is electrochemically oxidized into oxygen and protons. The protons diffuse through the membrane and are electrochemically reduced into hydrogen on the cathode side. Catalysts on each side are able to carry out the reactions, and the membrane allows protons to pass through while maintaining gas separation. In this way, the correct level of voltage and current must be applied to the cell to enable the production of gas. Additionally, porous transport layers (PTLs) on each side help to remove the gas from the electrolyzer and provide good electrical conductivity for efficient electron conduction. The performance and durability of the MEA can be improved by optimizing the design and / or structure of the existing PTLs, and these shortcomings are addressed by one or more aspects of the present disclosure. SUMMARY

[0004] In one configuration, a multi-layered porous transport layer (PTL) is provided, including a first layer and a second layer, the first layer including a first surface and a second surface opposite the first surface, the first layer made of one or more first particles, the second layer including a first surface and a second surface opposite the first surface, the second surface of the second layer connected to the first surface of the first layer, the second layer made of one or more second particles.

[0005] The multi-layered PTL can include one or more of the following optional aspects. For example, the one or more second particles have a diameter that is less than a diameter of the one or more first particles. The one or more first particles and the one or more second particles are made of titanium.

[0006] According to at least one aspect, a multilayer PTL includes a protrusion barrier disposed between a first surface of a second layer and a second surface of a first layer. The protrusion barrier may include both one or more first particles and one or more second particles. The one or more first particles may interlock with the one or more second particles.

[0007] According to another aspect, the first layer includes a first thickness, the second layer includes a second thickness, and the first thickness is greater than the second thickness. The first thickness can be from 100 micrometers (μm) to 500 μm, and the second thickness can be from 10 μm to 100 μm.

[0008] According to at least one instance, some of the one or more second particles are embedded between some of the one or more first particles.

[0009] According to another example, the second layer has a lower surface roughness than the first layer.

[0010] In another configuration, a proton exchange membrane (PEM) electrolyzer is provided for producing hydrogen for use as vehicle fuel. The PEM electrolyzer includes a first distribution plate and a second distribution plate spaced apart from the first distribution plate, a membrane disposed between the first and second distribution plates, a cathode chamber disposed between the second distribution plate and the membrane, and an anode chamber disposed between the first distribution plate and the membrane. The anode chamber includes an anode catalyst layer disposed adjacent to the membrane and a multilayer porous transport layer (PTL) disposed between the anode catalyst layer and the first distribution plate. The multilayer PTL includes a first layer made of one or more first particles and a second layer made of one or more second particles fused with some of the one or more first particles.

[0011] The PEM electrolyzer may include one or more of the following optional aspects. For example, the diameter of the one or more second particles is smaller than the diameter of the one or more first particles. The one or more first particles may have a diameter of 50 micrometers (μm) to 100 μm, and the one or more second particles may have a diameter of 1 μm to 45 μm.

[0012] According to at least one aspect, the multilayer PTL further includes a penetration barrier layer comprising some of one or more first particles and some of one or more second particles. Some of the one or more second particles may be embedded between some of the one or more first particles.

[0013] According to another aspect, the second layer has a lower surface roughness than the first layer.

[0014] According to at least one example, the multilayer PTL has an arithmetic mean height (Ra) of 3.0 μm to 6 μm, and the second layer is configured to be in substantially contact with the anode catalyst layer.

[0015] According to yet another configuration, a method for manufacturing a multilayer porous transport layer (PTL) is provided, the method comprising providing a first layer having one or more first particles, applying a slurry having one or more second particles onto the first layer, drying the slurry on the first layer, and fusing the slurry onto the first layer such that at least some of the one or more second particles are fused to the one or more first particles.

[0016] The method may include one or more of the following optional aspects or steps. For example, applying a slurry having one or more second particles to a first layer also includes mixing one or more second particles with water, a solvent, and a binder.

[0017] According to another aspect, fusing the slurry onto the first layer also includes sintering the slurry and the first layer at a temperature above 600 degrees Celsius (°C) and below 1400 degrees Celsius (°C). Attached Figure Description

[0018] The accompanying drawings described herein are for illustrative purposes only for the selected configurations and are not intended to limit the scope of this disclosure.

[0019] Figure 1 This is a front perspective view of a vehicle according to the principles of the present invention;

[0020] Figure 2 This is a side view schematic diagram of a membrane electrode assembly (MEA) according to the principles of the present invention;

[0021] Figure 3 yes Figure 2 A close-up side view of a portion of the MEA;

[0022] Figure 4 This is a graph comparing the performance of a single porous transport layer (PTL) with that of a multilayer PTL, based on the principles of this disclosure; and

[0023] Figure 5 This is a flowchart of a method for manufacturing a multilayer PTL based on the principles of this disclosure.

[0024] In all the accompanying drawings, the corresponding reference numerals denote the corresponding parts. Detailed Implementation

[0025] The example configuration will now be described more fully with reference to the accompanying drawings. The example configuration is provided so that this disclosure will be thorough and will fully communicate the scope of this disclosure to those skilled in the art. Specific details, such as examples of specific components, apparatus, and methods, are set forth to provide a thorough understanding of the configuration of this disclosure. It will be apparent to those skilled in the art that specific details are not required, the example configuration may be embodied in many different forms, and the specific details and example configuration should not be construed as limiting the scope of this disclosure.

[0026] The terminology used herein is for the purpose of describing a particular exemplary configuration only and is not restrictive. As used herein, the singular articles “a” and “the” may also be intended to include plural forms unless the context clearly indicates otherwise. The terms “comprising,” “including,” and “having” are inclusive and therefore specify the presence of features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0027] When an element or layer is referred to as “on another element or layer,” “joined to,” “connected to,” “attached to,” or “linked to” another element or layer, it may be directly on, joined to, attached to, or linked to the other element or layer, or there may be intermediate elements or layers present. Conversely, when an element is referred to as “directly on another element or layer,” “directly joined to,” “directly connected to,” “directly attached to,” or “directly linked to” another element or layer, there may be no intermediate elements or layers present. Other terms used to describe relationships between elements should be interpreted in a similar manner (e.g., “between” vs. “directly between,” “adjacent” vs. “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0028] In this document, the terms “first,” “second,” “third,” etc., may be used to describe various elements, components, regions, layers, and / or parts. These elements, components, regions, layers, and / or parts should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or part from another. Unless the context clearly indicates otherwise, terms such as “first,” “second,” and other numerical terms do not imply order or sequence. Therefore, without departing from the teachings of the example configuration, the first element, component, region, layer, or part discussed below may be referred to as the second element, component, region, layer, or part.

[0029] In this application, including the following definitions, the term "module" may be replaced by the term "circuit". The term "module" may refer to, be part of, or include the following: application-specific integrated circuit (ASIC); digital, analog, or mixed analog / digital discrete circuit; digital, analog, or mixed analog / digital integrated circuit; combinational logic circuit; field-programmable gate array (FPGA); processor (shared, dedicated, or grouped) that executes code; memory (shared, dedicated, or grouped) that stores code executed by the processor; other suitable hardware components that provide the described functionality; or some or all of the foregoing, such as in a system-on-a-chip.

[0030] The term "code" as used above can include software, firmware, and / or microcode, and can refer to programs, routines, functions, classes, and / or objects. The term "shared processor" includes a single processor that executes some or all of the code from multiple modules. The term "group processor" includes processors that, in combination with additional processors, execute some or all of the code from one or more modules. The term "shared memory" covers a single memory that stores some or all of the code from multiple modules. The term "group memory" includes memory that, in combination with additional memory, stores some or all of the code from one or more modules. The term "memory" can be a subset of the term "computer-readable medium." The term "computer-readable medium" does not include transient electrical and electromagnetic signals propagating through the medium and can therefore be considered tangible and non-transitory memory. Non-limiting examples of non-transitory memory include tangible computer-readable media, which include non-volatile memory, magnetic memory, and optical memory.

[0031] The apparatus and methods described in this application can be implemented, in whole or in part, by one or more computer programs executed by one or more processors. The computer program includes processor-executable instructions stored on at least one non-transitory tangible computer-readable medium. The computer program may also include and / or depend on stored data.

[0032] A software application (i.e., a software resource) can refer to computer software that instructs a computing device to perform a task. In some examples, a software application may be referred to as an "application," "app," or "program." Example applications include, but are not limited to, system diagnostic applications, system management applications, system maintenance applications, word processing applications, spreadsheet applications, messaging applications, media streaming applications, social networking applications, and game applications.

[0033] Non-transitory memory can be a physical device used to temporarily or permanently store programs (e.g., instruction sequences) or data (e.g., program state information) for use by a computing device. Non-transitory memory can be volatile and / or non-volatile addressable semiconductor memory. Examples of non-volatile memory include, but are not limited to, flash memory and read-only memory (ROM) / programmable read-only memory (PROM) / erasable programmable read-only memory (EPROM) / electrically erasable programmable read-only memory (EEPROM) (e.g., commonly used in firmware, such as boot programs). Examples of volatile memory include, but are not limited to, random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), phase-change memory (PCM), and magnetic disks or magnetic tapes.

[0034] These computer programs (also referred to as programs, software, software applications, or code) include machine instructions for a programmable processor and can be implemented using high-level procedural and / or object-oriented programming languages ​​and / or assembly / machine languages. As used herein, the terms “machine-readable medium” and “computer-readable medium” refer to any computer program product, non-transitory computer-readable medium, apparatus, and / or device (e.g., disk, optical disk, memory, programmable logic device (PLD)) used to provide machine instructions and / or data to a programmable processor, including machine-readable media that receive machine instructions as machine-readable signals. The term “machine-readable signal” refers to any signal used to provide machine instructions and / or data to a programmable processor.

[0035] Various implementations of the systems and techniques described herein can be implemented in digital electronic and / or optical circuits, integrated circuits, specially designed ASICs (Application-Specific Integrated Circuits), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include implementations in one or more computer programs executable and / or interpretable on a programmable system, which includes at least one programmable processor, which may be dedicated or general-purpose, coupled to receive data and instructions from a storage system, at least one input device, and at least one output device, and to transmit data and instructions to the storage system, at least one input device, and at least one output device.

[0036] The processes and logical flows described in this specification can be executed by one or more programmable processors (also known as data processing hardware) that execute one or more computer programs to perform functions by manipulating input data and generating output. The processes and logical flows can also be executed by special-purpose logic circuitry (e.g., FPGAs (Field-Programmable Gate Arrays) or ASICs (Application-Specific Integrated Circuits)). As an example, processors suitable for executing computer programs include both general-purpose and special-purpose microprocessors, as well as any one or more processors of any type of digital computer. Typically, a processor receives instructions and data from read-only memory or random access memory, or both. The basic elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Typically, a computer will also include one or more mass storage devices (e.g., magnetic disks, magneto-optical disks, or optical disks) for storing data, or operatively coupled to receive data from or transfer data to, or both. However, a computer does not need to have such devices. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and memory devices, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks or removable disks; magneto-optical disks; and CD-ROMs and DVD-ROMs. Processors and memory may be supplemented by or incorporated into dedicated logic circuitry.

[0037] To provide interaction with a user, one or more aspects of this disclosure can be implemented on a computer having a display device for displaying information to the user, such as a CRT (cathode ray tube), LCD (liquid crystal display) monitor, or touchscreen, and optional keyboard and pointing devices, such as a mouse or trackball, through which the user can provide input to the computer. Other types of devices can also be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including sound, speech, or tactile input. Additionally, the computer can interact with the user by sending documents to and receiving documents from the device used by the user; for example, by sending web pages to a web browser on the user's client device in response to a request received from a web browser.

[0038] refer to Figure 1The document provides an illustrative example of a vehicle 100, such as a fuel cell vehicle or a fuel cell electric vehicle. Vehicle 100 includes a fuel cell stack 102 configured to receive and utilize gaseous reactants (e.g., hydrogen) as fuel. A proton exchange membrane (PEM) electrolyzer is provided below, and it can be configured to split water into oxygen and hydrogen. The hydrogen produced by the PEM electrolyzer can be used as fuel in vehicle 100 or as fuel in stationary power stations, mobile charging stations, or any other suitable application.

[0039] The porous transport layer (PTL) of a membrane electrode assembly (MEA) can be a fundamental component of a PEM electrolyzer. For example, the PTL can help remove oxygen generated by reactions within the PEM electrolyzer and the PTL, and provide good conductivity for efficient electron conduction. As addressed by one or more aspects of this disclosure, different configurations of the PTL are desirable to improve the performance and durability of the MEA.

[0040] refer to Figure 2 This document provides an illustrative configuration of a PEM electrolyzer 10. The PEM electrolyzer 10 includes a first distribution plate 12 and a second distribution plate 14 spaced apart from the first distribution plate 12. The first distribution plate 12 and the second distribution plate 14 may also be referred to as bipolar plates. The first distribution plate 12 includes an inlet 16 and an outlet 18, the inlet 16 being configured to receive fluid and transport fluid into the PEM electrolyzer 10, and the outlet 18 being configured to receive fluid and transport fluid out of the PEM electrolyzer 10. The first distribution plate 12 may include an inner surface 20, which includes a flow field pattern 22 having one or more channels 24. The second distribution plate 14 includes one or more outlets 26, which are configured to receive fluid and transport fluid out of the PEM electrolyzer 10. The second distribution plate 14 may include an inner surface 28, which includes a flow field pattern 30 having one or more channels 32. In this illustrative configuration, the inner surface 28 of the second distribution plate 14 faces the inner surface 20 of the first distribution plate 12. According to one aspect, the flow field structure 30 of the second distribution plate 14 may be different from the flow field structure 22 of the first distribution plate 12.

[0041] The PEM electrolyzer 10 may also include external circuitry 33, which includes a power supply 34 (e.g., a DC power supply, a battery, etc.) that is communicatively connected to the first distribution plate 12 and the second distribution plate 14.

[0042] Continue to refer to Figure 2The PEM electrolyzer 10 includes an MEA 35 having a proton exchange membrane (i.e., a membrane) 36 disposed between a first distribution plate 12 and a second distribution plate 14. The membrane 36 may have a first side or surface 38 facing the inner surface 20 of the first distribution plate 12 and a second side or surface 40 facing the inner surface 28 of the second distribution plate 14.

[0043] The PEM electrolyzer 10 may further include an anode chamber 42 disposed between the first distribution plate 12 and the membrane 36. More specifically, the anode chamber 42 may be disposed between the inner surface 20 of the first distribution plate 12 and the first side 38 of the membrane 36. Additionally, the PEM electrolyzer 10 may include a cathode chamber 44 disposed between the second distribution plate 14 and the membrane 36. More specifically, the cathode chamber 44 may be disposed between the inner surface 28 of the second distribution plate 14 and the second side 40 of the membrane 36.

[0044] MEA 35 may include an anode catalyst layer 46 and a multilayer porous transport layer (PTL) 48, both disposed within the anode chamber 42. Typically, the anode catalyst layer 46 may be configured to decompose and / or separate water molecules. The anode catalyst layer 46 may include a first or inner surface 50 and a second or outer surface 52 opposite to the inner surface 50. Figure 1 and Figure 2 As shown, the inner surface 50 can be attached to or directly adjacent to the first side 38 of the membrane 36. According to one aspect, the anode catalyst layer 46 can be made of, for example, iridium ruthenium oxide, iridium oxide, iridium black, or platinum black.

[0045] Reference Figure 1 and 2 The multilayer PTL 48 may include a first or outer layer 54 and a second or inner layer (i.e., a low-protrusion layer) 56. The first layer 54 may include a first or inner surface 58 and a second or outer surface 60. The second layer 56 may include a first or inner surface 62 and a second or outer surface 64. Figure 2 As shown, the first layer 54 can be disposed between the second layer 56 and the first distribution plate 12, and the second layer 56 can be disposed between the anode catalyst layer 46 and the first layer 54. More specifically, refer to Figure 2 The outer surface 60 of the first layer 54 is bonded to the inner surface 20 of the first distribution plate 12, the inner surface 58 of the first layer 54 is bonded to the outer surface 64 of the second layer 56, and the inner surface 62 of the second layer 56 is bonded to the first side 38 of the membrane 36. According to one aspect, the first layer 54 may have a first thickness between 100 micrometers (μm) and 500 μm, and the second layer 56 may have a second thickness between 10 μm and 100 μm.

[0046] Reference Figure 3The first layer 54 comprises one or more first particles 66, and the second layer 56 comprises one or more second particles 68. According to one aspect, both the one or more first particles 66 and the one or more second particles 68 may be made of titanium, but the one or more first particles 66 are larger than the one or more second particles 68. For example, the diameter of the one or more first particles 66 may range from 50 to 100 μm, and the diameter of the one or more second particles 68 may range from 1 to 45 μm. The multilayer PTL 48 may have an arithmetic mean height (Ra) of 3.0 to 6 μm, and preferably less than 3.8 μm. Additionally or alternatively, the multilayer PTL may have a maximum height (i.e., the distance between the highest peak and the lowest valley) of 20 to 22 μm, and preferably less than 21.2 μm. Therefore, at least a portion of the multilayer PTL 48 includes a low surface roughness, which may be desirable, for example, for reducing interfacial contact resistance.

[0047] The use of particles with smaller diameters increases the interfacial contact between the multilayer PTL 48 and the anode catalyst layer 46. Additionally, the use of smaller diameter particles helps prevent the anode catalyst layer 46 and / or membrane 36 from penetrating or intruding into the multilayer PTL 48. Preventing and / or avoiding penetrating is desirable for improving the durability of the MEA 35. Additionally or alternatively, refer to... Figure 4 Increasing the interfacial contact between the multilayer PTL 48 and the anode catalyst 46 is desirable to improve the electrical properties of the multilayer PTL 48.

[0048] Refer again Figure 3 The multilayer PTL 48 may further include a transition region or intrusion barrier layer 70, wherein one or more of the one or more second particles 68 are embedded between and / or interlocked with one or more first particles 66. The intrusion barrier 70 may be desired to reduce the intrusion of the anode catalyst layer 46 and / or the membrane 36 into the first layer 54 and / or the second layer 56 of the multilayer PTL 48. The protrusion barrier 70 may include a thickness 71 greater than or equal to the second thickness of the second layer 56.

[0049] Refer again Figure 2MEA 35 may include a cathode catalyst layer 72 and a gas diffusion layer 74 disposed in the cathode chamber 44. The cathode catalyst layer 72 includes a first or inner surface 76 and a second or outer surface 78 spaced apart from the inner surface 76. According to one aspect, the cathode catalyst layer 72 may contain, for example, platinum black or platinum supported on a carbon catalyst. The gas diffusion layer 74 may include a first or inner surface 80 and a second or outer surface 82. In this illustrative configuration, the outer surface 82 of the gas diffusion layer 74 is disposed adjacent to the inner surface 28 of the second distribution plate 14, the inner surface 80 of the gas diffusion layer 74 is coupled to and / or disposed adjacent to the outer surface 78 of the cathode catalyst layer 72, and the inner surface 76 of the cathode catalyst layer 72 is coupled to and / or disposed adjacent to the second side 40 of the membrane 36.

[0050] During operation, water (H2O) 84 or another fluid is introduced into the PEM electrolyzer 10 through inlet 16, allowing water 84 to flow through the flow field structure 22 and through one or more channels 24. The water 84 moves through multiple PTL layers 48 and reacts with the anode catalyst layer 46 to form oxygen (O2) 86 and positively charged hydrogen ions (H+). + (i.e., protons) 88. Anode chamber 42 can be configured to carry out a reaction represented by the following formula:

[0051] 2H₂O→O₂+4H⁺++4e -

[0052] Electrons 90 flow through external circuit 33, while hydrogen ions 88 selectively cross membrane 36 to move to cathode chamber 44. In cathode chamber 44, hydrogen ions 88 combine with electrons 90 from external circuit 33 to form hydrogen gas (H2). Cathode chamber 44 can be configured to carry out a reaction represented by the following equation:

[0053] 4H + +4e - →2H2

[0054] refer to Figure 5 A flowchart of a method 100 for manufacturing a multilayer porous transport layer is provided.

[0055] At 110, a first layer 54 of a multilayer PTL can be provided, including a first particle 66.

[0056] At 120°, the slurry can be applied to the inner surface 62 of the first layer 54. In some configurations, the slurry may be in the form of an ink containing second particles 68. According to one aspect, the slurry may contain titanium particles, water, solvent, and / or binder. The titanium particles used in the slurry may have a diameter of 1-45 μm and may be in the form of, for example, powder, flakes, or fibers. The binder may be made of polytetrafluoroethylene (PTFE), perfluoropolyether (PFPE), polyvinylidene fluoride (PVDF), peracetic acid (PAA), cellulose hydrocarbon, etc.

[0057] At 130, the slurry on the inner surface 62 of the first layer 54 can be dried.

[0058] At 140, the slurry can be fused to the first layer 54 to form the second layer 56. For example, sintering can be used to fuse or otherwise bond the slurry to the first layer 54. For example, the slurry and the first layer 54 can be sintered at a temperature greater than 600 degrees Celsius (°C) and less than 1400°C.

[0059] Many embodiments have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of this disclosure. Therefore, other embodiments are within the scope of the appended claims.

[0060] The foregoing description is provided for illustrative purposes. It is not intended to be exhaustive or limiting of this disclosure. Elements or features of a particular configuration are generally not limited to that particular configuration, but are interchangeable where applicable and can be used in selected configurations even if not specifically shown or described. They can also be varied in many ways. Such variations should not be considered as departing from this disclosure, and all such modifications are intended to be included within the scope of this disclosure.

Claims

1. A multi-layered porous transport layer (PTL) comprising: a first layer, the first layer including a first surface and a second surface opposite the first surface, the first layer made of one or more first particles; and a second layer, the second layer including a first surface and a second surface opposite the first surface, the second surface of the second layer connected to the first surface of the first layer, the second layer made of one or more second particles.

2. The multi-layered PTL of claim 1, wherein a diameter of the one or more second particles is less than a diameter of the one or more first particles.

3. The multi-layered PTL of claim 2, wherein the one or more first particles and the one or more second particles are made of titanium.

4. The multi-layered PTL of claim 1, further comprising a protruding barrier disposed between the first surface of the second layer and the second surface of the first layer.

5. The multi-layered PTL of claim 4, wherein the protruding barrier includes both the one or more first particles and the one or more second particles.

6. The multi-layered PTL of claim 5, wherein the one or more first particles interlock with the one or more second particles.

7. The multi-layered PTL of claim 1, wherein the first layer includes a first thickness and the second layer includes a second thickness, the first thickness greater than the second thickness.

8. The multi-layered PTL of claim 7, wherein the first thickness is 100 pm to 500 pm and the second thickness is 10 pm to 100 pm.

9. The multi-layered PTL of claim 1, wherein some of the one or more second particles are embedded between some of the one or more first particles.

10. The multi-layered PTL of claim 1, wherein the second layer has a lower surface roughness than the first layer.

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