Anode Catalyst Layer of Membrane Electrode Assembly and Preparation Method Thereof

The present disclosure generally relates to an anode catalyst layer for a membrane electrode assembly and preparation methods thereof. More specifically, the present disclosure relates to an anode catalyst layer for a membrane electrode assembly including an anode catalyst, an ionomer solution, a multidimensional carbon material, and multi-walled carbon nanotubes in specific proportions, and a preparation method thereof, as well as a membrane electrode assembly prepared using the anode catalyst layer and a preparation method thereof.

Due to the strong sterilization power of ozone and its characteristic that leaves no residual pollution, ozone has been widely used in fields, such as food preservation, medical treatment, and water treatment. The current methods for ozone generation mainly include PEM (proton exchange membrane) water electrolysis, ultraviolet method, and high-voltage discharge method. The PEM water electrolysis method only requires the supply of direct current voltage and pure water to obtain high concentrations of ozone. In contrast, the UV method and high-voltage discharge method produce lower concentrations of ozone and generate by-products harmful to human health, thus gradually being replaced by the PEM water electrolysis method.

Since hydrogen may be produced from renewable energy sources and is almost pollution-free when in use, hydrogen is globally recognized as one of the ideal energy carriers. Currently, steam reforming of hydrocarbons or alcohols may be used for large-scale hydrogen production. However, due to the high production costs, there is still an urgent need to develop low-cost hydrogen production technologies. The PEM water electrolysis method may directly decompose water into hydrogen and oxygen, and the required energy may be obtained from renewable sources, such as solar energy. Therefore, there is increasing research on hydrogen production using the PEM water electrolysis method.

Currently, ozone and hydrogen are mostly produced separately by different methods. However, the PEM water electrolysis method may be used to produce both gases simultaneously, along with oxygen, resulting in the production of three gases. In the existing technology of the PEM water electrolysis method, membrane electrode technology is mostly used. The membrane electrode assembly used in membrane electrode technology includes an anode catalyst electrode, an electrolyte membrane, and a cathode catalyst electrode. Given the issues of insufficient stability and low electrolytic performance of membrane electrode technology, the composition of these three components greatly affects the overall performance of the membrane electrode assembly, with the material of the anode catalyst being the most critical. Commonly used materials for the anode catalyst include tin-antimony-nickel alloy (NATO), glassy carbon, lead dioxide, platinum-tantalum oxide, and boron-doped diamond, with lead dioxide being the most effective material for gas production.

However, since lead dioxide is a ceramic and very brittle, improper handling may easily cause the lead dioxide electrode to break. Furthermore, lead dioxide is prone to aging, leading to a decline in electrochemical activity, which results in a less-than-ideal operational lifespan. Additionally, lead dioxide requires a high voltage to produce ozone and cannot operate under low voltage conditions due to its material and kinetic characteristics. The poor conductivity of lead dioxide also significantly affects its performance during power interruptions. Moreover, after the power is restored, lead dioxide cannot recover to the performance levels prior to the interruption.

In view of the above, to address the issues of poor mass transfer effects and voltage fluctuation impacts in existing anode catalyst layers, the present disclosure provides an anode catalyst layer for a membrane electrode assembly and preparation methods thereof. This anode catalyst layer is made by combining specific proportions of lead dioxide (or a mixture with lead tetroxide) with ionomer solution, multidimensional carbon materials, and multi-walled carbon nanotubes. This combination enhances the electrochemical activity and structural strength of the anode catalyst layer, thus improving the overall efficiency and stability of the membrane electrode assembly in electrolysis applications.

According to a first aspect of the present disclosure, an anode catalyst layer for a membrane electrode assembly is provided. The anode catalyst layer for the membrane electrode assembly may include: 30-43 wt % of an anode catalyst; 10-20 wt % of an ionomer solution; 0.02-0.04 wt % of a multidimensional carbon material; and 0.3-0.4 wt % of a multi-walled carbon nanotube; wherein the anode catalyst is PbO, PbO, or a combination thereof.

In an implementation of the first aspect of the present disclosure, the anode catalyst layer for the membrane electrode assembly may further include: 2-6 wt % of a hydrophobic solution; 3-10 wt % of an acidic solution; and 30-40 wt % of deionized water.

In an implementation of the first aspect of the present disclosure, the anode catalyst may be a combination of PbOand PbOin a weight ratio from 10:1 to 1:10.

In an implementation of the first aspect of the present disclosure, the multidimensional carbon material may be graphene, graphene oxide, reduced graphene oxide, or any combination thereof.

According to a second aspect of the present disclosure, a method for preparing an anode catalyst layer for a membrane electrode assembly is provided. The method may include: mixing 30-40 wt % of deionized water with an ionomer solution, a hydrophobic solution, and an acidic solution to form a first mixture; adding 30-43 wt % of an anode catalyst, a multi-walled carbon nanotube, and a multidimensional carbon material to the first mixture to form a second mixture; rotating the second mixture at 15000-18000 rpm for 30-50 minutes to form a homogeneous coating; and applying the homogeneous coating to a transfer substrate and drying at 25-30° C. for 10-15 minutes.

In an implementation of the second aspect of the present disclosure, the ionomer solution may be 10-20 wt %, the hydrophobic solution may be 2-6 wt %, the acidic solution may be 3-10 wt %, the multi-walled carbon nanotube may be 0.3-0.4 wt %, and the multidimensional carbon material may be 0.02-0.04 wt %.

In an implementation of the second aspect of the present disclosure, the multi-walled carbon nanotubes and the multidimensional carbon materials may be first prepared as a mixed powder before being added to the first mixture, wherein the mixed powder may be prepared by first mixing the multi-walled carbon nanotubes and the multidimensional carbon materials with an ethylene glycol aqueous solution in a 1:1 weight ratio, then subjecting the mixture to ultrasonic vibration for 2 hours followed by stirring at a constant temperature of 80° C. for 24 hours, and finally, the powder may be extracted by centrifugation and dried at 80° C. for 12 hours.

According to a third aspect of the present disclosure, a membrane electrode assembly including the above anode catalyst layer is provided.

According to a fourth aspect of the present disclosure, a method for preparing a membrane electrode assembly is provided. The method may include: sequentially stacking a cathode catalyst electrode, a solid electrolyte membrane, and the above anode catalyst layer to form the membrane electrode assembly; and hot-pressing the membrane electrode assembly at 120-140° C. under 20-60 kgf/cmfor 2 minutes.

According to a fifth aspect of the present disclosure, a method for preparing a membrane electrode assembly is provided. The method may include: mixing 30-40 wt % of deionized water with an ionomer solution, a hydrophobic solution, and an acidic solution to form a first mixture; adding 30-43 wt % of an anode catalyst, a multi-walled carbon nanotube, and a multidimensional carbon material to the first mixture to form a second mixture; rotating the second mixture at 15000-18000 rpm for 30-50 minutes to form a homogeneous coating; applying the homogeneous coating to a transfer substrate and drying at 25-30° C. for 10-15 minutes to form an anode catalyst layer; sequentially stacking a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly; hot-pressing the membrane electrode assembly at 120-140° C. under 20-60 kgf/cmfor 2 minutes; and removing the transfer substrate.

In an implementation of the fifth aspect of the present disclosure, the anode catalyst layer may have a loading per unit area of 30-60 mg/cm.

In an implementation of the fifth aspect of the present disclosure, the ionomer solution may be 10-20 wt %, the hydrophobic solution may be 2-6 wt %, the acidic solution may be 3-10 wt %, the multi-walled carbon nanotube may be 0.3-0.4 wt %, and the multidimensional carbon material may be 0.02-0.04 wt %.

The following description contains specific information about illustrative implementations of the present disclosure. The accompanying drawings and their detailed descriptions in the present disclosure are only for these illustrative implementations. However, the present disclosure is not limited to these illustrative implementations. Those skilled in the art will recognize other variations and implementations of the present disclosure.

Terms such as “at least one implementation,” “an implementation,” “multiple implementations,” “different implementations,” “some implementations,” “the present implementation,” etc., may indicate that the described implementations of the present disclosure may include specific features, compositions, or characteristics, but not every possible implementation of the present disclosure must include the specific features, compositions, or characteristics. Furthermore, repeated use of phrases such as “in an implementation,” “in the present implementation” does not necessarily refer to the same implementation, although they may. Moreover, the use of phrases such as “implementation” in association with “the present disclosure” does not mean that all implementations of the present disclosure must include the specific features, compositions, or characteristics, and should be understood as “at least some implementations of the present disclosure” include the stated specific features, compositions, or characteristics.

The terms “first,” “second,” “third,” etc. in the specification and the above drawings of the present disclosure are only used to distinguish different objects, not to describe a specific order.

The term “include(s)” and any of its variations in the specification and the above drawings of the present disclosure are intended to cover a non-exclusive inclusion, explicitly indicating an open-ended inclusion or relationship of the stated combinations, groups, series, and equivalents. For example, a process, method, system, product, or equipment that includes a series of steps or modules is not limited to the listed steps or modules, but may optionally include unlisted steps or modules, or may optionally include other steps or modules inherent to these processes, methods, products, or equipment.

Additionally, for the purpose of interpretation and not limitation, specific details such as functional entities, technologies, protocols, standards, etc. are elaborated to provide an understanding of the described technology. In other examples, detailed descriptions of well-known methods, techniques, systems, architectures, etc. are omitted for brevity.

The present disclosure provides an anode catalyst layer for a membrane electrode assembly, which may include 30-43 wt % of anode catalysts, 10-20 wt % of ionomer solution, 0.02-0.04 wt % of multidimensional carbon materials, and 0.3-0.4 wt % of multi-walled carbon nanotubes. The anode catalyst layer for the membrane electrode assembly of the present disclosure may further include 2-6 wt % of hydrophobic solution, 3-10 wt % of acidic solution, and 30-40 wt % of deionized water.

In some implementations, the anode catalyst may be lead dioxide (PbO), lead tetroxide (PbO), or a combination thereof. In a preferred implementation, the anode catalyst may be a combination of lead dioxide and lead tetroxide in a weight ratio from 10:1 to 1:10.

In some implementations, the ionomer solution may be a perfluorosulfonic acid (PFSA) polymer (such as Nafion®), tetrafluoroethylene-perfluoro (3-oxa-4-pentenesulfonic acid) copolymer, short-side-chain perfluorinated sulfonic acid/PTFE copolymer in the SOH form, or any combination thereof.

In some implementations, the multidimensional carbon material may be graphene, graphene oxide, reduced graphene oxide, or any combination thereof.

In some implementations, the hydrophobic solution may be polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) dispersion, polydimethylsiloxane (PDMS), or any combination thereof.

In some implementations, the acidic solution may be sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, or any combination thereof.

The present disclosure also provides a method for preparing the anode catalyst layer for a membrane electrode assembly, which is mainly by preparing the anode catalyst layer according to the above weight percentages of each material. The specific preparation may include: (a) taking the 30-40 wt % of deionized water, and sequentially adding the ionomer solution, the hydrophobic solution, and the acidic solution to form a first mixture; (b) sequentially adding the 30-43 wt % of anode catalysts, the multi-walled carbon nanotubes, and the multidimensional carbon materials to the first mixture to form a second mixture; (c) rotating the second mixture at 15000-18000 rpm for 30-50 minutes to form a homogeneous coating; and (d) applying the homogeneous coating to a transfer substrate and drying at 25-30° C. for 10-15 minutes.

In some implementations, the ionomer solution may account for 10-20 wt % of the total weight. In some implementations, the hydrophobic solution may account for 2-6 wt % of the total weight. In some implementations, the acidic solution may account for 3-10 wt % of the total weight. In some implementations, the multi-walled carbon nanotubes may account for 0.3-0.4 wt % of the total weight. In some implementations, the multidimensional carbon material may account for 0.02-0.04 wt % of the total weight.

In some implementations, the multi-walled carbon nanotubes and the multidimensional carbon materials may be first prepared as a mixed powder before being added to the first mixture. The mixed powder may be prepared by first mixing the multi-walled carbon nanotubes and the multidimensional carbon materials with an ethylene glycol aqueous solution in a 1:1 weight ratio, then subjecting the mixture to ultrasonic vibration for 2 hours followed by stirring at a constant temperature of 80° C. for 24 hours, and finally, the powder may be extracted by centrifugation and dried at 80° C. for 12 hours.

In some implementations, the transfer substrate may be glass fiber paper, polyimide (Kapton), polytetrafluoroethylene sheet (Teflon sheet), aluminum foil, or any combination thereof.

The present disclosure also provides a membrane electrode assembly, which mainly includes the above anode catalyst layer containing materials in specific weight percentages. The membrane electrode assembly of the present disclosure may be based on solid polymer electrolyte technology, where an anode catalyst layer and a cathode catalyst layer are attached to both sides of a solid electrolyte to form a membrane electrode assembly.

In some implementations, the solid electrolyte may be a polymer membrane with proton transmission capability, for example, the solid electrolyte may be a perfluorinated sulfonic acid polymer membrane (such as Nafion, Aciplex), a partially fluorinated sulfonated polymer membrane (such as BAM3G™), a non-fluorinated sulfonated polymer membrane (such as sulfonated polyimide, sulfonated aromatic backbone, polystyrene), or related or derived composite structures. In some implementations, the cathode catalyst layer may be an electrode composed of platinum-based (Pt/C) or molybdenum-based (Co—MoS) catalysts combined with porous and gas-liquid diffusion transport substrates such as carbon cloth, titanium felt, or titanium plate.

The present disclosure also provides a method for preparing a membrane electrode assembly, including: (a) sequentially stacking a cathode catalyst electrode (or layer), a solid electrolyte membrane, and the above anode catalyst layer (or electrode) to form a membrane electrode assembly; and (b) hot-pressing the membrane electrode assembly at 120-140° C. under 20-60 kgf/cmfor 2 minutes.

In some implementations, the method for preparing the membrane electrode assembly of the present disclosure may more specifically include: (a) taking the 30-40 wt % of deionized water, and sequentially adding the ionomer solution, the hydrophobic solution, and the acidic solution to form a first mixture; (b) sequentially adding the 30-43 wt % of anode catalysts, the multi-walled carbon nanotubes, and multidimensional carbon materials to the first mixture to form a second mixture; (c) rotating the second mixture at 15000-18000 rpm for 30-50 minutes to form a homogeneous coating; (d) applying the homogeneous coating to a transfer substrate and drying at 25-30° C. for 10-15 minutes to form an anode catalyst layer; (e) sequentially stacking a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly; (f) hot-pressing the membrane electrode assembly at 120-140° C. under 20-60 kgf/cmfor 2 minutes; and (g) removing the transfer substrate.

In some implementations, the ionomer solution may account for 10-20 wt % of the total weight. In some implementations, the hydrophobic solution may account for 2-6 wt % of the total weight. In some implementations, the acidic solution may account for 3-10 wt % of the total weight. In some implementations, the multi-walled carbon nanotubes may account for 0.3-0.4 wt % of the total weight. In some implementations, the multidimensional carbon material may account for 0.02-0.04 wt % of the total weight.

In some implementations, the anode catalyst layer may have a loading per unit area of 30-60 (mg/cm), which may be adjusted based on practical requirements, such as electrode lifespan and gas concentration. In some preferred implementations, the anode catalyst layer may have a loading per unit area of 35 (mg/cm).

The following provides further description of the present disclosure through several examples, but the present disclosure is not limited to these examples.

1.1 Test Group: Preparing Membrane Electrode Assembly with Graphene as a Multidimensional Carbon Material

Take 37 wt % of deionized water, and sequentially add 20 wt % of PFSA Dispersion ionomer solution (e.g., Nafion®), 4 wt % of PTFE hydrophobic solution, and 6 wt % of 0.5M sulfuric acid solution. Then sequentially add 32 wt % of commercially available 97% lead dioxide (Thermo Scientific; product NO: 217535000), 0.32 wt % of multi-walled carbon nanotubes, and 0.035 wt % of graphene. Spin a container filled with the mixture by a centrifuge at 18000 rpm for 30 minutes to form a homogeneous coating, apply the homogeneous coating to a transfer substrate, dry the homogeneous coating with the substrate at 30° C. for 10 minutes to form the anode catalyst layer. Next, sequentially stack a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly, where the anode catalyst layer has a loading per unit area of 35 (mg/cm). Then hot-press the membrane electrode assembly at 135° C. under 25 kgf/cmfor 2 minutes, and remove the transfer substrate to complete the membrane electrode assembly, hereinafter referred to as Pb+M+G.

1.2 Test Group: Preparing Membrane Electrode Assembly with Graphene Oxide as a Multidimensional Carbon Material

Take 37 wt % of deionized water, and sequentially add 20 wt % of PFSA Dispersion ionomer solution (e.g., Nafion®), 4 wt % of PTFE hydrophobic solution, and 6 wt % of 0.5M sulfuric acid solution. Then sequentially add 32 wt % of commercially available 97% lead dioxide (Thermo Scientific; product NO: 217535000), 0.32 wt % of multi-walled carbon nanotubes, and 0.035 wt % of graphene oxide. Spin a container filled with the mixture by a centrifuge at 18000 rpm for 30 minutes to form a homogeneous coating, apply the homogeneous coating to a transfer substrate, dry the homogeneous coating with the substrate at 30° C. for 10 minutes to form the anode catalyst layer. Next, sequentially stack a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly, where the anode catalyst layer has a loading per unit area of 35 (mg/cm). Then hot-press the membrane electrode assembly at 135° C. under 25 kgf/cmfor 2 minutes, and remove the transfer substrate to complete the membrane electrode assembly, hereinafter referred to as Pb+M+GO.

1.3 Test Group: Preparing Membrane Electrode Assembly with Reduced Graphene Oxide as a Multidimensional Carbon Material

Take 37 wt % of deionized water, and sequentially add 20 wt % of PFSA Dispersion ionomer solution (e.g., Nafion®), 4 wt % of PTFE hydrophobic solution, and 6 wt % of 0.5M sulfuric acid solution. Then sequentially add 32 wt % of commercially available 97% lead dioxide (Thermo Scientific; product NO: 217535000), 0.32 wt % of multi-walled carbon nanotubes, and 0.035 wt % of reduced graphene oxide. Spin a container filled with the mixture by a centrifuge at 18000 rpm for 30 minutes to form a homogeneous coating, apply the homogeneous coating to a transfer substrate, dry the homogeneous coating with the substrate at 30° C. for 10 minutes to form the anode catalyst layer. Next, sequentially stack a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly, where the anode catalyst layer has a loading per unit area of 35 (mg/cm). Then hot-press the membrane electrode assembly at 135° C. under 25 kgf/cmfor 2 minutes, and remove the transfer substrate to complete the membrane electrode assembly, hereinafter referred to as Pb+M+RGO.

1.4 Control Group: Preparing Membrane Electrode Assembly without Multi-Walled Carbon Nanotubes or a Multidimensional Carbon Material

Take 37 wt % of deionized water, and sequentially add 20 wt % of PFSA Dispersion ionomer solution (e.g., Nafion®), 4 wt % of PTFE hydrophobic solution, and 6 wt % of 0.5M sulfuric acid solution. Then sequentially add 32 wt % of commercially available 97% lead dioxide (Thermo Scientific; product NO: 217535000), and 0.4-0.8 wt % of multi-walled carbon nanotubes (e.g., 0.6 wt % may be used). Spin a container filled with the mixture by a centrifuge at 18000 rpm for 30 minutes to form a homogeneous coating, apply the homogeneous coating to a transfer substrate, dry the homogeneous coating with the substrate at 30° C. for 10 minutes to form the anode catalyst layer. Next, sequentially stack a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly, where the anode catalyst layer has a loading per unit area of 35 (mg/cm). Then hot-press the membrane electrode assembly at 135° C. under 25 kgf/cmfor 2 minutes, and remove the transfer substrate to complete the membrane electrode assembly, hereinafter referred to as Pb+M.

Take 38 wt % of deionized water, and sequentially add 20 wt % of PFSA Dispersion ionomer solution (e.g., Nafion®), 4 wt % of PTFE hydrophobic solution, and 6 wt % of 0.5M sulfuric acid solution. Then sequentially add 32 wt % of commercially available 97% lead dioxide (Thermo Scientific; product NO: 217535000). Spin a container filled with the mixture by a centrifuge at 18000 rpm for 30 minutes to form a homogeneous coating, apply the homogeneous coating to a transfer substrate, dry the homogeneous coating with the substrate at 30° C. for 10 minutes to form the anode catalyst layer. Next, sequentially stack a cathode catalyst electrode, a solid electrolyte membrane, and the anode catalyst layer to form a membrane electrode assembly, where the anode catalyst layer has a loading per unit area of 35 (mg/cm). Then hot-press the membrane electrode assembly at 135° C. under 25 kgf/cmfor 2 minutes, and remove the transfer substrate to complete the membrane electrode assembly, hereinafter referred to as Pb.

The anode catalyst layers of the above membrane electrode assemblies Pb, Pb+M, Pb+M+G, Pb+M+GO, and Pb+M+RGO are observed using a scanning electron microscope, with results shown in, wherein lead dioxide is indicated by black dotted lines, multi-walled carbon nanotubes by black solid lines, and multidimensional carbon materials by black dashed lines.shows that the anode catalyst layer containing only lead oxide has a dense surface, which would reduce the reaction area.shows that the anode catalyst layer containing multi-walled carbon nanotubes has a lower density and a larger volume and forms a macroporous structure due to its cylindrical shape, which would result in high electrical conductivity and mass ratio.to E show that in the anode catalyst layers containing multidimensional conductive carbon materials, when used in conjunction with multi-walled carbon nanotubes, the multidimensional conductive carbon materials may cover the catalyst surface and enhance bonding ability, thus promoting the formation of microelectronic conduction channels between the microporous channels that are formed by the multi-walled carbon nanotubes, and further improving conductivity.