Gas diffusion layer with enhanced pore structure and electrochemically deposited microporous layer and its preparing method

Abstract

A triple-layer gas diffusion layer (GDL) for proton exchange membrane (PEM) fuel cells comprises a macroporous substrate (MPS) made from multi-walled carbon nanotubes, polymethyl methacrylate as a pore-forming agent, and polytetrafluoroethylene as a binder, a first microporous layer (MPL) with carbon nanotubes and a hydrophobic binder, and a second MPL formed by electrochemical deposition of polyaniline. The MPS is fabricated by vacuum filtration of a suspension, followed by heat treatment to enhance porosity. The first MPL is deposited on the MPS, and the second MPL is added via a three-electrode system. This GDL is integrated into a membrane-electrode assembly with a treated membrane and platinum-on-carbon electrodes. The invention simplifies fuel cell design by managing water effectively across varying humidity levels, offering utility in energy applications.

Description

DescriptionTitle of Invention : Gas Diffusion Layer with Enhanced PoreStructure and Electrochemically Deposited Microporous Layer and its preparing methodTechnical Field

[0001] The present invention relates to the technical field of fuel cells, particularly to the gas diffusion layer (GDL) used in fuel cells and its manufacturing process.Background Art

[0002] The following background information may present examples of specific aspects of the prior art that, while expected to be helpful to further inform the reader as to more features of the prior art, is not to be seen as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon.

[0003] Previous efforts in this field have involved using GDLs composed of a macroporous substrate (MPS) and one or more thin coatings called the microporous layer (MPL).

[0004] Among the alternative pathways for producing clean energy, the use of fuel cells is a prominent option. Among the various types of fuel cells, Proton Exchange Membrane (PEM) fuel cells have gained attention. Due to their high energy conversion efficiency, quick start-up, simple design, low operating temperature, and environmental compatibility, they are considered a new power source for transportation and stationary / mobile applications. However, the widespread commercialization of PEM fuel cells is still limited due to their cost, performance, and durability.

[0005] A PEM fuel cell has a multi-layered structure and typically consists of anode and cathode flow fields and the Membrane Electrode Assembly (MEA). In fact, the MEA is the core component of the fuel cell system, comprising the anode and cathode Gas Diffusion Layers (GDLs), catalyst layers, and the proton exchange membrane.

[0006] The operation and design characteristics of PEM fuel cells, and consequently their performance, are closely related to the mass, heat, andcharge transfer within the cell components, with the GDL being one of the most critical elements. In other words, GDLs play essential roles, such as:

[0007] Uniformly distributing gaseous reactants across the active area of the electrodes.

[0008] Removing / retaining water and managing two-phase flow.

[0009] Providing electrical connectivity between the electrodes and bipolar plates.

[0010] Offering mechanical support for the MEA.

[0011] Gas diffusion layers typically consist of a macroporous substrate (MPS) and one or more thin coatings referred to as a microporous layer (MPL). The MPS is in direct contact with the flow channel and thus acts as a bridge for transferring mass, heat, and electricity. However, the MPL primarily manages multiphase flow.

[0012] Among the efforts to address the technical issue mentioned, i.e., improving water and two-phase flow management and thus increasing fuel cell performance, the use of multilayer GDLs with a gradient in hydrophobicity (or hydrophilicity) distribution or pore size is one such approach. This means that the hydrophobicity / hydrophilicity and pore size of the MPS and MPL(s) used in the production of the GDL differ.

[0013] In order to improve the performance of GDL and fuel cells under different operating conditions, Kitahara et al. proposed a bilayer MPL, where a hydrophilic layer (using PVA or TiO2) was applied over a hydrophobic layer (meaning the hydrophilic layer was after the catalyst layer). In low humidity, the bilayer MPL containing PVA or TiO2 showed better performance compared to conventional MPLs (those with a hydrophobic agent). However, the hydrophilicity of the PVA- containing MPL was very high, which negatively affected fuel cell performance in high humidity conditions (due to water flooding). Nevertheless, TiO2 improved performance under high humidity by providing an appropriate level of hydrophilicity to the hydrophilic layer. The role of the hydrophilic MPL in low humidity is to retain some moisture, helping to keep the membrane hydrated; the hydrophobic MPL prevents water from being removed from the hydrophilic MPL by dry air or oxygen. In high humidity, the hydrophilic layer aids in the rapid removal of water from the catalyst layer. However, if the hydrophilicity of this layeris too high, it retains water, does not facilitate proper water removal, and causes flooding.

[0014] One of the documents in this field is Chinese Patent Application No. CN1 1 1 146467A . In this document, various carbon powders, absolute ethyl alcohol, and a hydrophobic agent are used to prepare an MPL slurry, and two MPLs with different pore sizes are coated onto the MPS, with the pore size increasing from the catalyst layer towards the MPS. This feature has been reported to be beneficial for better and faster water discharge in high humidity / high current density and reduced mass transfer losses.

[0015] To regulate water within the fuel cell under high temperatures and low relative humidity, Chinese Application Pat. No. CN1 16632272A proposes a bilayer gas diffusion layer (GDL). This design incorporates a commercially available hydrophobic macroporous substrate (MPS) paired with a hydrophilic microporous layer (MPL) composed of carbon nanotubes, acetylene black, and perfluorosulfonic acid resin.Summary of Invention

[0016] The specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. The figures of the drawings are not drawn to scale.

[0017] Gas diffusion layers (GDLs) are produced and used in both single-layer and multilayer forms. Single-layer GDLs consist of a macroporous substrate (MPS), while multilayer GDLs are made by coating the MPS with one or more microporous layers (MPL). In fact, the MPL is added to the MPS to enhance performance. It is worth noting that commercially available MPS can bepurchased from various companies such as Toray Industries, Avcarb Material Solutions, Freudenberg Performance Materials, and others, in different forms such as carbon paper and carbon cloth.

[0018] In most previous patents and research articles, commercially available MPS has been purchased and then coated with MPL(s) using various methods. However, in this invention, a film of multi-walled carbon nanotubes, known as bucky paper, has been developed as the MPS to be used as a single-layer GDL (or MPS

[0019] One of the main challenges of using bucky paper as MPS in fuel cells is its unsuitable porosity, mean pore size, and pore size distribution, which can cause severe mass transfer losses and two-phase flow management issues. To address this challenge, this invention employs PMMA to modify the porosity and pore size of the bucky paper (as previously detailed), which represents an innovative approach to producing MPS using carbon nanotubes.

[0020] Thus, in this invention, the MPS itself has been designed and produced, whereas in other patents, MPS is usually commercially purchased for manufacturing multilayer GDLs. The GDL developed in this invention not only delivers significantly better performance than the commercial sample (309.2% higher power density at 60°C and 10% relative humidity) but also maintains nearly constant power density when the relative humidity is reduced from 100% to 10%. This characteristic enables the elimination or reduction of humidification devices in fuel cells, thereby decreasing system size and cost and accelerating the commercialization of fuel cells.) within the fuel cell.

[0021] This invention employs an efficient electrochemical method for polymerization and synthesis of the second MPL. Compared to conventional methods used in other patents for MPL synthesis and coating, the electrochemical method is simpler, cleaner, and more cost-effective while ensuring precise control over the thickness and morphology of the formed polymeric MPL film. Moreover, unlike most other patents, this invention also includes the production of MPS , ultimately yielding a triple-layer GDL with graded hydrophobicity / hydrophilicity, thickness, and pore size distribution.

[0022] This invention relates to a method for producing a gas permeable layer, particularly a gas diffusion layer (GDL) with improved electrical conductivity, porosity, and mechanical stability, suitable for use in electrochemical devices such as fuel cells, electrolyzers, and sensors. The method involves the synthesis of a multi-layered structure comprising a microporous substrate (MPS), a first microporous layer (MPL), and a second conductive microporous layer (MPL) formed via electrochemical polymerization. The process is designed to optimize the layer's gas permeability, electrical resistance, and durability under operational conditions.

[0023] Detailed Steps of the Method:

[0024] Preparation of the Microporous Substrate (MPS):

[0025] A suspension is prepared by dispersing deionized water, sodium dodecyl sulfate (SDS) as a surfactant, polytetrafluoroethylene (PTFE) as a binder, multiwalled carbon nanotubes (MWCNTs) as a conductive filler, and polymethyl methacrylate (PMMA) as a sacrificial pore-forming agent. The suspension is homogenized using ultrasonic agitation to ensure uniform dispersion of components.

[0026] The resulting suspension is poured onto a membrane filter (e.g., polycarbonate or PTFE membrane) and subjected to vacuum filtration to form a thin film. This film is designated as the microporous substrate (MPS).

[0027] Formation of the First Microporous Layer (MPL):

[0028] A second suspension is prepared using deionized water, SDS, PTFE, and MWCNTs. This suspension is poured onto the MPS produced in step (a), which acts as a membrane filter, and vacuum filtration is performed to deposit the first MPL onto the MPS. This step ensures a uniform distribution of conductive and hydrophobic properties across the layer.

[0029] Drying and Separation of the Two-Layer Assembly:

[0030] The two-layer assembly (MPS + first MPL) is dried at ambient temperature (20-25 °C) for 12-24 hours to remove residual moisture. After drying, the assembly is carefully separated from the membrane filter to avoid mechanical damage.

[0031] Heat Treatment for Porosity Enhancement:

[0032] The two-layer assembly is heat-treated at 400 °C in an inert atmosphere (e.g., nitrogen or argon) for 1-2 hours. This step thermally decomposes the PMMA, creating a highly porous structure with increased pore size and improved gas permeability. The PTFE and MWCNTs remain intact, ensuring mechanical stability and electrical conductivity.

[0033] Preparation of the Electrolyte for Electrochemical Deposition:

[0034] An electrolyte solution is prepared using deionized water, sulfuric acid (H2SO4), and distilled aniline monomer. The concentrations of sulfuric acid and aniline in the electrolyte are maintained at 0.5 M and 0.1 M, respectively, to ensure optimal electrochemical polymerization conditions.

[0035] Electrochemical Deposition of Polyaniline (Second MPL):

[0036] The two-layer assembly produced in step (d) is used as the working electrode in a three-electrode electrochemical system. The system includes:

[0037] A platinum (Pt) electrode as the auxiliary electrode.

[0038] A silver / silver chloride (Ag / AgCI) electrode in saturated potassium chloride (KCI) solution as the reference electrode.

[0039] The electrochemical deposition of aniline is carried out at a constant potential (e.g., 0.8 V vs. Ag / AgCI) in a water and ice bath maintained at 0 °C to control the reaction kinetics and prevent overheating. This process results in the formation of a thin, conductive polyaniline film on the working electrode, which serves as the second MPL. The final product is a three-layer gas diffusion layer (GDL) with enhanced electrical and structural properties.

[0040] Post-Treatment of the Three-Layer GDL:

[0041] The triple layer GDL is removed from the electrolyte solution and thoroughly washed with a dilute sulfuric acid solution (e.g., 0.1 M H2SO4) to remove any unreacted aniline monomer or oligomers. The washed GDL is then dried at ambient temperature or in a vacuum oven at 60-80 °C for 2-4 hours to ensure complete removal of residual solvents.Technical Problem

[0042] The performance of polymer electrolyte membrane fuel cells (PEMFCs) largely depends on effective two-phase flow management, which involves maintaining an optimal balance between water removal for efficient reactant transfer and water retention for adequate hydration of membrane and electrocatalyst site. If the water content (humidity) within the fuel cell is insufficient, proton conductivity in the membrane and catalyst layer decreases, leading to increased ohmic losses. Conversely, excessive water accumulation can cause flooding within the fuel cell, resulting in mass transfer losses.

[0043] Among the various components of a fuel cell, gas diffusion layers (GDLs) play a crucial role in managing two-phase flow within the system. However, due to the complex interplay between water management and reactant transfer, most GDLs are optimized for specific operating conditions, performing well only at either high or low relative humidity levels. However, for fuel cells to be fully viable for commercial applications, GDLs must be designed to function effectively under a wide range of operating conditions, including both high and low relative humidity.

[0044] Ideally, a GDL should be designed to maintain a nearly constant performance across various levels of humidity — an essential goal that is achieved with the GDL developed in this invention. The unique characteristics of the GDL in this patent allow for the reduction or even elimination of humidification devices in fuel cells, thereby reducing system volume and cost while accelerating fuel cell commercialization. When an effective balance between water retention and removal is achieved, both ohmic losses and mass transfer limitations are minimized, significantly enhancing fuel cell performance.

[0045] Additionally, considering the critical role of GDLs in fuel cells, their exclusive production by a few advanced countries, and their high costs, domestic production of these layers is essential for localization efforts. Therefore, the objective of this invention is to develop a gas diffusion layer capable of delivering consistent performance under varying operating conditions, contributing to both the commercialization and localization of fuel cell technology.

[0046] Finally, it is important to note that these high-cost layers are not limited to fuel cell applications alone; they are also widely used in various electrochemical cells such as electrodialysis systems, batteries, breath alcohol analyzers, and more.Advantageous Effects of Invention

[0047] The present invention modifies the porosity, mean pore size, and pore size distribution of bucky paper using PMMA, addressing mass transfer losses and two-phase flow issues in fuel cells.

[0048] The developed gas diffusion layer (GDL) delivers 309.2% higher power density at 60°C and 10% relative humidity compared to commercial samples.

[0049] The power density remains nearly constant even when relative humidity is reduced from 100% to 10%, reducing the need for humidification devices.

[0050] By minimizing or eliminating humidification devices, the invention decreases fuel cell system size and cost, accelerating commercialization.

[0051] The electrochemical method for synthesizing the second microporous layer (MPL) is simpler, cleaner, and more cost-effective while ensuring precise control over thickness and morphology.

[0052] Unlike most patents that use commercially purchased MPS, this invention designs and produces its own MPS using bucky paper made from multi-walled carbon nanotubes.

[0053] The invention yields a triple-layer GDL with graded hydrophobicity / hydrophilicity, thickness, and pore size distribution, enhancing fuel cell efficiency.Brief Description of Drawings

[0054] [Fig.1 presents field-emission scanning electron microscope (FE-SEM) images of MPS with and without PMMA.

[0055] Fig.2 shows the results related to the pore size distribution of the produced MPSs.

[0056] Fig. 3 presents the Fourier Transform Infrared (FTIR) spectroscopy spectrum of the triple-layer GDL.

[0057] Fig. 4 shows scanning electron microscope (SEM) images that reveal the morphological properties of the microporous layer (MPL) produced by electrochemical deposition of polyaniline.

[0058] Fig.5 shows the cyclic voltammograms for the triple-layer GDL and illustrates the redox behavior of the polyaniline layer and confirm its electrochemical activity

[0059] Fig.6 shows the potential-time curve recorded during the electrochemical deposition process of polyaniline on the dual-layer GDL.

[0060] Fig.7 illustrates the performance curves (polarization curves) of the membrane electrode assembly (MEA) fabricated with a commercial GDL (Toray TGP-H-060).

[0061] Fig.8 shows the polarization curves of the fuel cell containing an MEA made with the triple-layer GDL developed in this invention.

[0062] Fig. 9 shows the performance of the three-layer GDL produced in the present invention at low relative humidities at a temperature of 60°C.

[0063] Fig.10&11 show, the performance of the triple-layer GDL developed in this invention is compared with a commercial GDL at 100% and 10% relative humidity.

[0064] Fig.12 compares the power density of MEAs fabricated with commercial and three-layer GDL under different operating conditions.]Description of Embodiments

[0065] A) MPS Fabrication

[0066] An MPS was fabricated using multi-walled carbon nanotubes (MWCNTs) (diameter: 10-20 nm, length: 30 pm, purity: 98%), sodium dodecyl sulfate (SDS) as a dispersant, polymethyl methacrylate (PMMA) as a pore-forming agent, and polytetrafluoroethylene (PTFE) as a binder. The details of the fabrication process are provided below. It should be noted that other materials such as graphite, acetylene black, graphene, graphene oxide, reduced graphene oxide, carbon black, etc., can be used instead of carbon nanotubes. Additionally, PTFE can be replaced with fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), perfluorinated polyether (PFPE), polydimethylsiloxane (PDMS), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), and similar materials.

[0067] To fabricate the MPS, 52.8 mg of multi-walled carbon nanotubes, 66.7 mg of polymethyl methacrylate (PMMA), and 1 wt% SDS were dispersed in 52.8 mg ofdeionized water. The mixture was stirred using an ultrasonic probe for 20 minutes to obtain a homogeneous suspension. PMMA was added as a pore-forming agent to increase porosity and the meanpore size of the MPS. When PMMA is subjected to heat, it undergoes thermal decomposition, leaving behind pores that enhance the porosity and mean pore size of the MPS.

[0068] Next, 15 mg of a 30 wt% PTFE emulsion (equivalent to 10 wt% relative to the carbon nanotubes) was added to the suspension and further sonicated for 15 minutes.

[0069] In the second stage, the resulting suspension was poured onto a mixed cellulose ester (MCE) filtration membrane and vacuum-filtered to form a thin film, known as bucky paper, with a thickness of 190 pm, which constitutes the MPS. Notably, the thickness of the fabricated MPS in this invention can be adjusted by modifying the concentration of carbon nanotubes and PMMA.

[0070] In this invention, the MPS is first fabricated, and after placing the first MPL on top of it (details provided later), the dual-layer GDL (comprising MPS and the first MPL) is placed in a furnace at 400°C for 30 minutes. Finally, adding the second MPL produces a three-layer GDL.

[0071] To investigate the effect of PMMA on the properties of MPS, a single-layer GDL (i.e., a gas diffusion layer consisting solely of MPS) was also fabricated. The fabrication process followed the same steps as mentioned in the previous paragraph, with the only difference being that after vacuum filtration, the resulting thin film (MPS) was first dried at room temperature for 24 hours and then placed in a furnace at 400°C for 30 minutes.

[0072] Additionally, to compare and evaluate the impact of PMMA, an MPS sample was fabricated under similar conditions but without PMMA.

[0073] The pores within the GDL are classified into three categories based on size:

[0074] Micropores: Pores with a radius smaller than 50 nm

[0075] Mesopores: Pores with a radius between 50 and 7000 nm

[0076] Macropores: Pores with a radius larger than 7000 nm

[0077] It is important to note that these ranges may vary slightly in different reports.

[0078] Figure (1 ) presents field-emission scanning electron microscope (FE-SEM) images of MPS with and without PMMA. Based on these images, the effect of PMMA on pore formation is clearly evident. Additionally, mercury porosimetry was used to analyze the pore structure.

[0079] The results related to the pore size distribution of the produced MPSs are presented in Figure (2). According to the results, by using the pore-forming agent, the meanpore size of the produced MPS increased by 141 times, from 0.07 pm to 9.87 pm.

[0080] In this invention, a triple-layer GDL is fabricated using two MPLs with different structures and properties, as detailed below.

[0081] Fabrication of the First MPL and Its Deposition on MPS

[0082] To fabricate the first MPL and deposit it on MPS, the following steps were taken:

[0083] Dispersion Process:

[0084] 14 mg of multi-walled carbon nanotubes (MWCNTs) and 1 wt% SDS were dispersed in 14 mL of deionized water using ultrasonication for 20 minutes.

[0085] A PTFE emulsion (20 wt% relative to MWCNTs) was then added to the suspension and ultrasonicated for an additional 15 minutes to achieve a homogeneous mixture.

[0086] Deposition on MPS:

[0087] The resulting suspension was deposited onto the MPS fabricated in the previous stage.

[0088] After vacuum filtration, the first MPL formed on top of the MPS.

[0089] Drying and Heat Treatment:

[0090] The resulting dual-layer GDL was dried at room temperature and then heated in a furnace at 400°C for 30 minutes.

[0091] The thickness of the first MPL was measured to be approximately 30 pm.

[0092] Alternative Materials and Deposition Methods

[0093] Instead of MWCNTs, alternative materials such as graphite, acetylene black, graphene, graphene oxide, reduced graphene oxide, carbon black, etc. can be used.

[0094] Instead of PTFE, other binders like fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), perfluorinated polyether (PFPE), polydimethylsiloxane (PDMS), polyvinylpyrrolidone (PVP), and polyvinylidene fluoride (PVDF) can be utilized. Alternative deposition methods for the first MPL include manual brushing, doctor blade coating, screen printing, and more. It is important to note that the thickness of the first MPL can be adjusted by modifying the MWCNT and PMMA concentration in the suspension.

[0095] To synthesize the second microporous layer (MPL) and integrate it onto the dual-layer GDL fabricated in the previous stage, electrochemical deposition of a conductive polymer (polyaniline) was employed. The porous structure and unique intrinsic properties of polyaniline make it an excellent candidate for applications in proton exchange membrane (PEM) fuel cells and GDLs. Whereas MPL, developed in this invention, demonstrates a dual pore size distribution, spanning from micropores to macropores, leading to enhanced gas permeability and mass transport efficiency. Pore size distribution analysis reveals a dramatic improvement, wherein the dual-porosity structure extends across micropore and macropore regions, improving gas diffusion capabilities. The average pore size of the gas permeability layer increased 141 times, from 0.07 pm to 9.87 pm, significantly optimizing fluid transport and reactant accessibility in applications such as fuel cells and gas diffusion electrodes.

[0096] This novel gas permeability layer offers superior mass transport properties, enhanced permeability, and tailored pore structures, making it highly suitable for advanced energy and filtration applications.

[0097] The electrochemical deposition of aniline is typically conducted using a three- electrode system, comprising a reference electrode, an auxiliary electrode, and a working electrode. The process involves the anodic oxidation of the aniline monomer in an aqueous electrolyte solution containing strong acids (e.g., sulfuric acid, hydrochloric acid, or nitric acid) as dopants. This oxidation results in the formation of a conductive polymer film on the working electrode.

[0098] When an appropriate potential is applied to the working electrode, the oxidation process initiates with the generation of a radical cation. The polymerization mechanism proceeds as follows: the monomer oxidizes to form a radical cation, which then reacts with another radical cation to create a dimer. This dimer, adsorbed on the electrode surface, undergoes further oxidation, producing another radical cation that reacts with additional monomers. This cyclic process continues, leading to the growth of a polymer film on the working electrode surface.

[0099] The electrochemical deposition can be performed using various techniques, including potentiostatic, galvanostatic, and cyclic voltammetry methods, each offering precise control over the polymerization process and the properties of the resulting polymer film.

[0100] Aniline oxidizes over time, leading to changes in its properties. Therefore, it must be distilled before use, which was done by vacuum distillation of aniline. Subsequently, to produce the second microporous layer (MPL), electrochemical deposition of aniline was carried out in a three-electrode system. In this system, a platinum electrode, an Ag / AgCI / (KCI, sat) electrode, and a dual-layer GDL (produced in the previous step) were used as the auxiliary electrode, reference electrode, and working electrode, respectively. This process was performed in a solution containing deionized water, sulfuric acid, and aniline using the galvanostatic method at a constant current of 20 mA / s for 20 minutes. The concentrations of sulfuric acid and aniline in the solution were 0.5 M and 0.1 M, respectively. The experiment was designed such that only one side of the duallayer GDL was coated with polyaniline. It is worth noting that before starting the process, the solution was deoxygenated by bubbling nitrogen gas for 30 minutes, and nitrogen was continuously passed over the solution during the process. Additionally, to enhance the electrical conductivity of the polyaniline film formed on the dual-layer GDL, the process was conducted in an ice-water bath at 0°C.

[0101] Polyaniline can exist in different forms depending on its oxidation state, known as leucoemeraldine, emeraldine, and pernigraniline. Leucoemeraldine refers to the fully reduced form, emeraldine is the semi-oxidized form, and pernigraniline is the fully oxidized form of polyaniline. The only conductive form of polyaniline is emeraldine salt, which is obtained by doping or protonating emeraldine. Aftercompleting the experiment, the dual-layer GDL coated with the polyaniline film (triple-layer GDL) was removed from the polymerization solution, washed with 0.5 M sulfuric acid, and then dried overnight in a vacuum oven at 60°C to finally produce the triple-layer GDL. The thickness of the second MPL was measured to be approximately 5 pm. The final thickness of the triple-layer GDL was about 225 pm. However, it is possible to produce triple-layer GDLs with different thicknesses by adjusting the thickness of the MPS and MPLs through increasing the concentration of the materials used (carbon nanotubes, PMMA, and aniline) or modifying the process duration.

[0102] To investigate and confirm the formation of a polyaniline film on the dual-layer GDL, Fourier Transform Infrared (FTIR) spectroscopy was used. The FTIR spectrum of the triple-layer GDL is presented in Figure (3). The bands at 1628 cm-1and 1463 cm-1correspond to the stretching vibrations of the quinonoid ring and the benzenoid ring, respectively. The peaks at 1245 cm-1and 1228 cm-1are attributed to the bending vibrations of aromatic N-C amines and the stretching vibrations of C-N+ in the polarons structure, indicating the presence of protonated and conductive polyaniline. The signal observed at 3426 cm-1is assigned to the stretching vibration of H-N. The peaks at 2928 cm-1and 2858 cm-1are related to the CH3 and CH2 groups. Therefore, by comparing the FTIR spectrum, the production of polyaniline can be confirmed.

[0103] According to the results of the scanning electron microscope images shown in Figure (4), MPL produced by electrochemical deposition of polyaniline is porous and has an amorphous structure.

[0104] To investigate the electrochemical behavior (oxidation-reduction) of the triplelayer GDL, cyclic voltammetry (CV) was performed within a potential range of 0.2 V to 1 V (relative to Ag / AgCI / KCI(sat)) with a scan rate of 20 mV / s in a 1 M sulfuric acid solution. In this test, a platinum electrode, Ag / AgCI / (KCI,sat) reference electrode, and triple-layer GDL were used as the auxiliary electrode, reference electrode, and working electrode, respectively. Prior to the process, the solution was deoxygenated with nitrogen for 30 minutes, and nitrogen was continuously bubbled through the solution during the process. The voltammograms for the triple-layer GDL are presented in Figure (5). The peak structure is consistent with what has been previously demonstrated. The firstanodic peak at approximately 0.38 V indicates the conversion from leucoemeraldine to emeraldine, which is recognized as the most conductive form of polyaniline. The second peak around 0.67 V corresponds to the oxidation of emeraldine and its conversion to pernigraniline. The redox couples at 0.75 V and 0.35 V are related to the reverse of these transformation processes. Despite the presence of carbon nanotubes in the GDL structure, no additional peaks are observed in the voltammograms, indicating the lack of electrochemical activity of the carbon nanotubes.

[0105] Additionally, in Figure (6), the potential-time curve during the polyaniline deposition process on the dual-layer GDL is presented. As can be seen, a sharp increase in potential is observed in the initial moments, which then stabilizes at a nearly constant value. This sharp increase is due to the oxidation of aniline present in the electrolyte solution.

[0106] To investigate the wettability of the GDL surface, the sessile drop method was used,. According to the results, the contact angle of the triple-layer GDL was calculated to be around 70°, indicating the hydrophilic nature of the second MPL, which is made of polyaniline. For this reason, the MPL containing polyaniline was used as the second MPL, close to the catalyst layer, to utilize this hydrophilic property to enhance the performance of the fuel cell, the results of which will be presented later. As previously mentioned, both the MPS and the first MPL are highly hydrophobic, with the hydrophobic agent content in the first MPL (20% by weight) being higher than in the MPS (10%).

[0107] According to the results, the through-plane and in-plane electrical resistance of the triple-layer GDL were calculated to be 2.56 m£ .cm2 and 5.93 mQ.cm, respectively.

[0108] In order to investigate the performance of the fabricated GDL in the fuel cell and compare it with the commercial GDL, it is necessary to prepare a membraneelectrode assembly (MEA), the details of which are discussed below. It is important to note that during preparation of the membrane-electrode assembly, the second MPL is closer to the electrocatalyst.

[0109] Membrane Preparation:

[0110] Typically, Nation membranes are treated by hydrogen peroxide and acid solutions to remove their organic impurities and protonation. It is important to note that other similar membranes can also be used in the Membrane Electrode Assembly (MEA), and mentioning Nation does not limit fuel cells to this membrane alone.

[0111] For membrane preparation, a Nation 1 17 membrane was cut to 3 cm x 3 cm and treated sequentially in the following solutions at 80°C for 1 hour each:

[0112] 3% w / w H2O2solution

[0113] Deionized water

[0114] 0.5 M sulfuric acid

[0115] Deionized water

[0116] Finally, the membrane was dried in an oven at 80°C for several hours.

[0117] Catalyst Ink Preparation:

[0118] Another step in MEA preparation is the preparation of the catalyst ink. The ink was prepared using:

[0119] 40% w / w platinum on carbon (Pt / C)

[0120] 5% w / w Nation ionomer

[0121] Isopropanol

[0122] Deionized water

[0123] The Nation ionomer content was chosen as 25% and 30% w / w for the cathode and anode, respectively,

[0124] Isopropanol was added at 20% w / w of deionized water. During ink preparation, the Pt / C powder was first wetted with deionized water, followed by the addition of Nation solution and isopropanol to avoid combustion reactions

[0125] Catalyst Coating:

[0126] The Pt / C loading was targeted at 0.4 mg / cm2and 0.3 mg / cm2for the cathode and anode, respectively.

[0127] Hot Pressing:

[0128] After preparing the Nation membrane and the anode / cathode electrodes, hot pressing was the final step in MEA preparation. The electrodes were aligned with the Nation membrane and pressed at 130°C and 60 bar for 2 minutes to form the final MEA.

[0129] To evaluate the performance of the MEAs, a Biologic-FCT-150s fuel cell test station was used. This device features spiral flow channels with an active area of 5 cm2

[0130] The performance of the MEA fabricated with the commercial GDL (Toray TGP-H-060) at a temperature of 60°C, a pressure of 1 bar, and various relative humidity (RH) levels is shown in Figure (7). In the commercial sample, the maximum power density has decreased from approximately 121 mW / cm2to 68 mW / cm2, and the limiting current density from 498 mA / cm2to 292 mA / cm2as the relative humidity (RH) reduces from 100% to 20%. The reasons for this behavior can be summarized as follows:

[0131] With decreasing RH, the ohmic resistance of the membrane increases. In other words, at higher RH levels, the membrane absorbs more water, resulting in more ionic clusters or channels being filled with water. Consequently, protons can easily transport through these water-filled clusters or ionic channels within the membrane, leading to lower membrane resistance.

[0132] With decreasing RH, the charge transfer resistance within the electrocatalyst increases, and the kinetics of electrochemical reactions in the fuel cell decrease. In fact, as RH decreases, the wettability of the reaction zone within the catalyst layer decreases, and as the ionomer (Nation) dries out, the proton transport rate decreases.

[0133] With decreasing RH, the charge transfer resistance at the triple-phase boundary increases. In fact, as the relative humidity decreases, the ionomer in the catalyst layer dries out, the solubility of reactant gases (especially oxygen) decreases, and as a result, the fuel cell performance declines. Additionally, the reduction in RH leads to increased mass transfer losses, which further contributes to the reduction in the limiting current density.

[0134] The performance of the fuel cell including MEA made with the triple-layer GDL developed in this invention is shown in Figure (13) at a temperature of 60°C, apressure of 1 bar, and different humidity levels. According to the results, the maximum power density and limiting current density were approximately 257.23 mW / cm2and 767 mA / cm2, respectively, at 100% relative humidity.

[0135] As evident, the triple-layer GDL developed in this invention exhibits nearly stable performance with decreasing RH, which is a significant advantage for the commercialization of gas diffusion layers. In fact, the performance of a PEM fuel cell largely depends on achieving an appropriate balance between water removal for efficient reactant transfer and water retention for effective membrane hydration. However, due to the interplay between water management and reactant transfer, most GDLs are only optimized for specific operating conditions.

[0136] GDLs must be developed while simultaneously considering the range of operating conditions they may encounter to fully commercialization of fuel cells. Therefore, an ideal GDL should be designed to maintain relatively stable performance across a wide range of relative humidity levels. The triple-layer GDL in this invention meets this requirement, meaning it effectively retains or removes water (moisture) as needed, essentially functioning as a self-drying or selfhumidifying layer depending on the conditions.

[0137] Stability of performance with changing relative humidity is a very important point. The reasons for this performance can be summarized as follows:

[0138] As mentioned earlier, effective water retention at lower relative humidity levels is essential for achieving optimal performance. At low relative humidity, the hydrophilic nature of the second MPL enhances water retention and increases the back-diffusion of the produced water from the cathode to the anode, thereby increasing membrane and reaction zone humidity and improving performance. Additionally, the small mean pore size of the first MPL (determined to be approximately 70 nm based on mercury porosimetry results) contributes to greater water retention by increasing the capillary pressure required for water removal, which further enhances performance.

[0139] At higher relative humidity levels, the hydrophilicity of the second MPL facilitates water removal from the catalyst layer and improves the permeability of the produced water.The hydrophilic layer enhances water dispersion over the catalyst layer, increasing the number of water flow pathways to transfer excesswater from the catalyst layer to the first MPL. Additionally, due to the significant difference in mean pore size between the first MPL (70 nm) and the MPS (9.87 pm), which creatscapillary pressure gradient, and the higher PTFE content in the first MPL compared to the MPS (20% vs. 10%), the produced water is efficiently transferred from the first MPL to the MPS. This process effectively prevents water flooding. Ultimately, these combined effects reduce mass transfer losses and enhance fuel cell performance.

[0140] The MPLs in the triple-layer GDL act as thermal barriers, increasing membrane temperature. At low relative humidity, a higher membrane temperature can lead to drying, but the hydrophilic MPL retains water, preventing fuel cell performance degradation. Additionally, at higher relative humidity, the increased membrane temperature prevents excessive water saturation of the electrocatalyst by removing water in vapor form which reduces mass transfer losses and thereby enhances fuel cell performance.

[0141] In Figures (10) and (1 1 ), the performance of the triple-layer GDL developed in this invention is compared with a commercial GDL at 100% and 10% relative humidity. As evident, the triple-layer GDL has demonstrated significantly better performance than the commercial sample across different relative humidity levels.

[0142] In fact, the triple-layer GDL provides superior performance due to the presence of the MPL and its beneficial properties. Additionally, the design used in its production has caused to a reduction in both mass transfer and ohmic losses.

[0143] It is also important to note that placing the MPL on the MPS reduces the contact resistance between the components of the triple-layer GDL, which in turn decreases ohmic losses and improves overall performance of fuel cell.

[0144] The above embodiments as described are only illustrative, and not intended to limit the technique approaches of the present invention. Although the present invention is described in details referring to the preferable embodiments, those skilled in the art will understand that the technique approaches of the present invention can be modified or equally displaced without departing from the protective scope of the claims of the present invention. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article“a” or “an” does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.Industrial Applicability

[0145] The present invention, a triple-layer gas diffusion layer (GDL) for use in proton exchange membrane (PEM) fuel cells, demonstrates significant industrial applicability through its practical utility and adaptability in various industrial settings. The GDL, consisting of a macroporous substrate (MPS), a hydrophobic first microporous layer (MPL), and a hydrophilic second MPL, is designed to enhance fuel cell performance by improving efficiency and stability under diverse operating conditions. Its self-drying and self-wetting properties allow it to manage water effectively without the need for external humidification devices, simplifying fuel cell system design and reducing production costs.

[0146] This invention is well-suited for industrial applications in the manufacture of PEM fuel cells, which are utilized across sectors such as automotive, stationary power generation, and portable electronics. By optimizing gas permeability and mass transport, the GDL offers a competitive advantage over conventional designs, making it valuable for producing high-performance fuel cells for hydrogen-powered vehicles, backup power systems, and compact electronic devices. Additionally, its enhanced properties extend its potential use to advanced energy systems and filtration applications, such as gas separation or purification processes, broadening its industrial relevance.

[0147] The fabrication process involves straightforward techniques — such as forming the MPS and first MPL from suspensions of multi-walled carbon nanotubes with a pore-forming agent and binder, followed by electrochemical deposition of a conductive polymer for the second MPL — using standard industrial equipment and materials. This process is scalable and flexible, allowing manufacturers to adapt the GDL to specific requirements by varying material compositions or deposition methods. The ability to incorporate alternative materials further enhances its versatility for industrial production.

[0148] By reducing system complexity, improving fuel cell efficiency, and supporting sustainable energy solutions, the triple-layer GDL provides economic and environmental benefits, aligning with industry demands for cost-effective and eco-friendly technologies. Consequently, the invention is capable of being produced and applied in industries including energy, transportation, and manufacturing, fulfilling the requirements for industrial applicability, i

Claims

AMENDED CLAIMS received by the International Bureau on January 29, 2026 (29.01 .2026)Claims

1. [Amended} Gas diffusion layer with enhanced pore structure and electrochemically deposited microporous layer comprising:(a) a macroporous substrate (MPS) formed by synthesizing a porous electrically conductive structure comprising(i) an electrically conductive carbon material selected from multiwalled carbon nanotubes and other conductive carbon materials,(ii) a polymeric pore-forming agent comprising polymethyl methacrylate (PMMA), and(iii) a polymeric binder comprising a fluoropolymer, wherein the MPS is fabricated by forming a dispersion comprising the electrically conductive carbon material, the PMMA, and the polymeric binder, followed by filtration and thermal treatment such that the PMMA is thermally decomposed to generate pores, wherein the MPS has a thickness of about 190 pm, and wherein a mean pore size of the MPS is increased by at least one order of magnitude relative to an MPS fabricated without PMMA and is tunable by adjusting the concentrations of the electrically conductive carbon material and the PMMA;(b) a first microporous layer disposed directly on the MPS, the first MPL comprising an electrically conductive carbon material and a hydrophobic polymeric binder, wherein the first MPL has a thickness of about 30 pm and a mean pore size in the nanometer range that is smaller than the mean pore size of the MPS; and(c) a second microporous layer disposed on the first MPL and configured to face a catalyst layer in an assembled fuel cell, the second MPL comprising a hydrophilic, electrically conductive polymer formed by electrochemical deposition of polyaniline, wherein the second MPL has a thickness of about 5 pm and exhibits a dual pore size distribution extending from micropores to macropores; wherein the MPS, the first MPL, and the second MPL collectively define a triple-layer gas diffusion layer having coordinated gradients in pore size, hydrophobicity and hydrophilicity, and layer thickness,wherein the coordinated gradients are configured to establish substantially stable power density over a relative humidity range from 10% to 100%.

2. The gas diffusion layer of claim 1, wherein the PMMA in theMPS is thermally decomposed during heat treatment at 400°C for 30 minutes, increasing the mean pore size of the MPS by at least 141 times compared to an MPS fabricated without PMMA, and wherein the PTFE in the MPS is present at 10 wt% relative to the MWCNTs.

3. The gas diffusion layer of claim 1, wherein the MWCNTs in the MPS have a diameter of 10-20 nm, a length of 30 pm, and a purity of 98%, and are dispersed in deionized water with 1 wt% sodium dodecyl sulfate (SDS) as a dispersant using ultrasonication for at least 20 minutes.

4. The gas diffusion layer of claim 1, wherein the hydrophobic binder in the first MPL is PTFE present at 20 wt% relative to the MWCNTs, and the first MPL is deposited onto the MPS by vacuum filtration of a suspension comprising MWCNTs, PTFE, and SDS, followed by heat treatment at 400°C for 30 minutes.

5. The gas diffusion layer of claim 1, wherein the polyaniline in the second MPL is in its emeraldine salt form, formed by electrochemical deposition using a three-electrode system comprising a platinum auxiliary electrode, an Ag / AgCl / (KCl, sat) reference electrode, and the dual-layer GDL as the working electrode, in a solution of 0.5 M sulfuric acid and 0.1 M aniline at a constant current of 20 mA / s for 20 minutes.

6. The gas diffusion layer of claims 1 and 5, wherein the electrochemical deposition of polyaniline is conducted at 0°C in an ice-water bath, and the resulting triple-layer GDL is washed with 0.5 M sulfuric acid and dried in a vacuum oven at 60°C overnight.

7. The gas diffusion layer of claim 1, wherein the MPS, the firstMPL, or both further comprise a material selected from the group consisting of graphite, acetylene black, graphene, graphene oxide, reduced graphene oxide, and carbon black, as a substitute for or in addition to MWCNTs.

8. The gas diffusion layer of claim 1, wherein the binder in the MPS, the first MPL, or both is selected from the group consisting offluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), perfluorinated polyether (PFPE), polydimethylsiloxane (PDMS), polyvinylpyrrolidone (PVP), and poly vinylidene fluoride (PVDF), as a substitute for PTFE.

9. The gas diffusion layer claiml, wherein the first MPL is deposited onto the MPS by a method selected from the group consisting of manual brushing, doctor blade coating, and screen printing, as an alternative to vacuum filtration.

10. The gas diffusion layer of claim 1, wherein the triple-layer GDL has a total thickness of approximately 225 pm, a through-plane electrical resistance of approximately 2.56 mQ-cm2, and an inplane electrical resistance of approximately 5.93 mQ-cm wherein the second MPL exhibits a contact angle of approximately 70.

11. A method for producing the gas diffusion layer, comprising the steps of:(a) preparing a first suspension comprising deionized water, 1 wt % sodium dodecyl sulfate (SDS), 52.8 mg of multi-walled carbon nanotubes (MWCNTs), 66.7 mg of polymethyl methacrylate (PMMA), and 15 mg of a 30 wt% polytetrafluoroethylene (PTFE) emulsion, ultrasonicated for at least 20 minutes, casting the suspension onto a mixed cellulose ester (MCE) membrane filter, and vacuum filtering it to form a thin film as the MPS;(b) preparing a second suspension comprising deionized water, 1 wt% SDS, 14 mg of MWCNTs, and 20 wt% PTFE relative to the MWCNTs, ultrasonicated for at least 15 minutes, casting the suspension onto the MPS produced in step (a) as a filter, and vacuum filtering it to form the first MPL on the MPS, thereby producing a dual-layer structure;(c) drying the dual-layer structure produced in step (b) at room temperature for 24 hours and separating it from the MCE membrane filter;(d) heat treating the dual-layer structure produced in step (c) at 400°C for 30 minutes to thermally decompose the PMMA, increasing the porosity and average pore size of the MPS to approximately 9.87 pm;(e) preparing an electrolyte solution comprising deionized water, 0.5 M sulfuric acid, and 0.1 M distilled aniline monomer, deoxygenated by bubbling nitrogen gas for 30 minutes;(f) using the dual-layer structure produced in step (d) as the working electrode in a three-electrode system, with a platinum electrode as the counter electrode and an Ag / AgCl / (KCl, sat) electrode as the reference electrode, electrochemically depositing polyaniline onto the dual-layer structure by applying a constant current in the electrolyte prepared in step (e), forming the second MPL as a thin film of conductive polyaniline, thereby producing the triple-layer GDL; and(g) removing the triple-layer GDL produced in step (f) from the electrolyte solution, washing it with sulfuric acid, and drying it.

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