A method for preparing a fuel cell membrane electrode and its application in a fuel cell system

Abstract

The present invention discloses a method for preparing a fuel cell membrane electrode and its application in a fuel cell system, the preparation method comprising the following steps: using electrostatic spinning technology to construct a proton conduction skeleton network with high connectivity and high working condition adaptability in the membrane electrode catalyst layer on the cathode side, wherein the skeleton slurry includes one or more of PFSA ionomer resin, silicon oxide particles, polymer carrier and dispersing solvent; and then spraying the catalyst slurry on the formed proton conduction skeleton by electrostatic spraying. The catalytic layer has high proton conduction capacity, high catalyst utilization rate and high tolerance to relatively dry working conditions, a large electrochemical active area, and can still maintain high proton conductivity and performance output at low humidity, while saving the humidification cost in the fuel cell stack, avoiding complex water management problems, greatly improving the fuel cell power generation performance and adaptability to a variety of relatively dry working conditions, and reducing the stack power generation cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery membrane electrodes, and in particular relates to a method for preparing a fuel cell membrane electrode and its application in a fuel cell system. Background Art

[0002] In the membrane electrode of a proton exchange membrane fuel cell, oxygen reaches the reaction site on the cathode side and undergoes an ORR reaction to generate O 2- , hydrogen enters the anode side and undergoes HRR reaction to generate H + The ionomer network on the cathode side passes through the proton exchange membrane and reaches the cathode side reaction site, where it reacts with the generated O 2- Combined with generated water, the battery power generation process is completed. In this process, the proton transmission resistance in the ionomer network on the cathode side is large, which is an important source of overpotential loss in low-load cathode fuel cells. In principle, the transmission of protons in the ionomer network is achieved by the hydrophilic and hydrophobic phase separation of the ionomer. At present, the commercial ionomer is perfluorosulfonic acid type (PFSA), which consists of a hydrophobic main chain (-CF 4 ) and hydrophilic side chain sulfonic acid groups. Its hydrophobic main chain provides mechanical strength for the ionomer skeleton, while the sulfonic acid groups provide a place for proton conduction. The free volume of PFSA aggregates into mutually cross-linked nanoscale pores, with sulfonic acid (SO 3 -H + ) group. In the presence of water, the hydrogen ions form hydronium ions, so that the hydrogen ions are separated from the sulfonic acid side chain. When there is enough water in the pores, the hydronium ions can be transported in the water phase of the pores.

[0003] Therefore, ensuring the continuity of the cathode catalyst layer ionomer network and ensuring its full hydration are the keys to achieving its proton conduction. However, on the one hand, the traditional spraying method or hot pressing method cannot specifically construct a continuous ionomer network when preparing the membrane electrode, and its construction is heavily dependent on the characteristics of the slurry dispersion; on the other hand, achieving full hydration of the cathode side ionomer requires heavy reliance on cathode gas humidification treatment, which results in the cathode side often requiring a complex humidification system and water source, which increases the system operating costs, improves the system use conditions, and also leads to complex water management problems. Through this patented design, while increasing the continuity of the cathode catalyst layer proton transport network, the system can operate normally and stably without external humidification equipment and under relatively dry conditions, which is of great value for the high-performance power supply of fuel cells in special scenarios.

[0004] The Chinese patent application number CN2023102746896 proposes a self-humidifying fuel cell membrane electrode and its preparation method. Specifically, a layer of nano-oxide self-humidifying functional layer is first stacked between the cathode catalyst layer / proton exchange membrane and between the anode catalyst layer / proton exchange membrane, and then the anode and cathode catalyst layers are sprayed on the functional layers to form a self-humidifying membrane electrode. The patent achieves the capture of fuel cell water through the self-humidifying functional layer, thereby reducing the cost of external humidification equipment.

[0005] Although the solution proposed in the above patent can indeed achieve self-humidification of fuel cells and avoid serious degradation of battery performance under relatively dry conditions, the introduction of functional layers on both sides of the anode and cathode lengthens the transmission path of reactants and protons. At the same time, the main construction materials of the newly added functional layers are nano-alumina, nano-silicon oxide and other particles, and the intrinsic proton conductivity of these particles is low, which increases the additional proton and oxygen gas phase transmission resistance. On the other hand, the method of constructing a self-humidification functional layer does not solve the problem of poor continuity of the proton network in the catalytic layer. The continuity of the proton transmission network still heavily depends on the intrinsic dispersion of the catalyst slurry in the electrostatic spraying and hot pressing process.

[0006] The Chinese patent application number CN2023102466607 proposes a nanofiber catalyst layer membrane and fuel cell membrane electrode based on electrospinning and a preparation method thereof. Specifically, a polymer carrier is used as one of the raw materials, and then combined with electrospinning to form a membrane with a certain strength; the prepared electrode can show higher voltage performance at the same current density.

[0007] The solution proposed in the above patent is to prepare a new membrane electrode through electrospinning technology, with the aim of improving catalyst utilization, and it is found that the electrode exhibits higher mass transfer performance. This method does not solve the proton conductivity problem of the membrane electrode under relatively dry conditions, nor does it improve the continuity of the proton transport ionomer network in the catalyst layer.

[0008] The Chinese patent application number CN2014106962575 proposes a method for preparing a non-imidyl ionic liquid with proton conductivity functionalization of a cationic sulfonic acid group. Specifically, 1,4-butane sultone, trimethylamine aqueous solution and sulfuric acid solution are reacted, and the obtained product is loaded in a fuel cell membrane electrode; the prepared electrode exhibits higher proton conductivity, thereby improving the battery power generation performance.

[0009] The above patent proposes a solution to enhance the proton transport in the cathode of the catalyst layer by relying on a new type of ionic liquid. This method does not solve the proton transport problem of fuel cells under relatively dry conditions, does not have self-humidification characteristics, and still heavily relies on external humidification of reactants to achieve proton conduction in the cathode catalyst layer. It also does not purposefully construct a continuous proton transport skeleton network in the catalyst layer, and the continuity of the proton transport network is still highly dependent on the intrinsic dispersion characteristics of the slurry. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a method for preparing a fuel cell membrane electrode and its application in a fuel cell system.

[0011] The present invention is achieved through the following technical solutions.

[0012] The present invention provides a method for preparing a fuel cell membrane electrode, comprising the following steps:

[0013] S1: preparing slurry A, slurry B and slurry C respectively;

[0014] S2: coating the slurry C on the substrate, and then stacking and hot-pressing the slurry C together with the proton exchange membrane to obtain an anode catalyst layer;

[0015] S3: Use slurry A to spray on the membrane electrode to obtain a membrane electrode containing a skeleton network, spray slurry B on the side of the half membrane electrode with the skeleton network to form a cathode catalyst layer, and finally dry the membrane electrode to obtain a battery membrane electrode.

[0016] Preferably, the method for preparing the slurry A comprises the following steps: uniformly mixing a Nafion solution containing 10-40% solid content of perfluorosulfonic acid resin, polyethylene oxide, ethanol and nano-silicon oxide, and ball milling for at least 24 hours to obtain the slurry A.

[0017] Preferably, the preparation method of slurry B and slurry C comprises the following steps: uniformly mixing a Nafion solution containing 10-30% solid content of perfluorosulfonic acid resin, a Pt / C catalyst, isopropanol and deionized water to obtain a mixed slurry, and then obtaining cathode catalyst slurry B and anode catalyst slurry C.

[0018] Preferably, in step S2, the slurry C is evenly coated on a Teflon substrate using a doctor blade method, cut to a suitable size and stacked on a hot press together with a proton exchange membrane, the hot pressing temperature is controlled to be 70-120°C, the pressure is 0.2-0.8MPa for hot pressing, and the hot pressing time is controlled to be no more than 6 minutes to obtain a half-membrane electrode containing an anode catalyst layer.

[0019] Preferably, in step S3, slurry A is heated at 0.2-0.6 ml h -1The flow rate is sent to the spinneret, and a voltage of 10-20 kV is applied between the spinneret and the collector; the half-side membrane electrode containing the anode catalyst layer obtained in step S2 is placed 10-25 cm below the tip of the spinneret, and spinning is performed thereon to form a skeleton network.

[0020] Preferably, in step S3, a microinjection needle pump is used to inject slurry B at a rate of 0.1-0.4 ml min -1 The flow rate is injected into the electrostatic nozzle, the cathode containing the anode catalyst layer and the half-membrane electrode containing the skeleton network is placed upward, 10-30 cm below the tip of the electrostatic nozzle, and slurry B is sprayed thereon to complete the preparation of the cathode catalyst layer structure; and it is dried in a vacuum oven at a temperature of 30-50°C for not less than 3 hours.

[0021] Preferably, the solid concentration of the perfluorosulfonic acid resin is 3-9wt%, the concentration of polyethylene oxide is 0.05-0.2wt%, the concentration of nano-silicon oxide is 1-7%, and the ball milling is carried out on a ball mill using zirconium oxide beads for at least 24 hours.

[0022] Preferably, in the mixed slurry, the solid content is set to 0.1-0.4%, the mass ratio of Pt / C catalyst to ionomer resin is 1:0.1-0.6; in the dispersion solvent composed of isopropanol and deionized water, the mass ratio of isopropanol to deionized water is 4-9:1.

[0023] A fuel cell system comprises a fuel cell membrane electrode prepared by a fuel cell membrane electrode preparation method.

[0024] Preferably, the fuel cell system includes a proton exchange membrane fuel cell stack, a hydrogen path system and an air path system.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention solves the problem that the membrane electrode of a proton exchange membrane fuel cell prepared by a conventional method has a lower power generation capacity or even battery deactivation due to lower proton conductivity under relatively dry operating conditions. Figure 2As shown, the proton exchange membrane fuel cell membrane electrode prepared by the traditional method will experience a dramatic performance decline when the reactant gas supply humidity is lower than 50% RH, so that when the gas supply humidity drops below 10% RH, the battery peak power will drop rapidly as the battery operation time increases, and the battery deactivation problem will occur after a period of constant current operation. In contrast, the membrane electrode performance of the proton conductive hydrophilic skeleton network with high operating condition adaptability constructed by this method is significantly weakened in dependence on the reactant gas supply humidity. Although the performance decreases slightly with the change of gas supply humidity, the decrease is much smaller than the former; at the same time, even under dry reactant gas supply conditions, the battery maintains a relatively high output power and maintains a stable output power during the constant current operation monitoring period. Therefore, the present invention can maintain a relatively high power output level of the fuel cell membrane electrode under relatively dry conditions or even extremely dry conditions.

[0027] 2. The present invention solves the problem that the continuity of the ionomer network providing proton conductivity on the cathode side of the membrane electrode of a proton exchange membrane fuel cell prepared by a conventional method is seriously dependent on the intrinsic dispersion of the cathode catalyst slurry. Figure 3 As shown, compared with the proton exchange membrane fuel cell membrane electrode prepared by the traditional method, in the cathode catalyst layer constructed by the present invention, protons can be conducted along the artificially constructed continuous skeleton network, thereby significantly improving its ECSA due to the improvement of the continuity of the proton conduction channel, and the catalyst utilization rate is more than 2.4 times that of the traditional catalyst layer.

[0028] 3. The present invention greatly simplifies the fuel cell system, omits the reaction gas humidification system and other equipment, and solves the flooding problem of the traditional fuel cell membrane electrode under high current conditions, greatly simplifying the system complexity and equipment cost. Figure 5 , 6 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The constant current of the battery membrane electrode prepared by the method for preparing the fuel cell membrane electrode of the present invention is 0.8A / cm 2 Schematic diagram of voltage monitoring results;

[0030] Figure 2 The constant current of the battery membrane electrode prepared by the existing technology is 0.8A / cm 2 Schematic diagram of voltage monitoring results;

[0031] Figure 3 This is the membrane electrode cyclic voltammetry test diagram

[0032] Figure 4 It is a schematic diagram of the preparation method of the present invention;

[0033] Figure 5It is a schematic structural diagram of a fuel cell system including a battery membrane electrode of the present invention;

[0034] Figure 6 It is a structural schematic diagram of a fuel cell system in the prior art. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0036] Example:

[0037] like Figures 1 to 5 As shown, a method for preparing a fuel cell membrane electrode comprises the following steps:

[0038] S1: preparing slurry A, slurry B and slurry C respectively;

[0039] S2: coating the slurry C on the substrate, and then stacking it together with the proton exchange membrane on a hot press to obtain an anode catalyst layer and a membrane electrode, which is a Nafion proton exchange membrane;

[0040] S3: Use slurry A to spray on the membrane electrode to obtain a membrane electrode containing a skeleton network, spray slurry B on the side of the half membrane electrode with the skeleton network to form a cathode catalyst layer, and finally dry the membrane electrode to obtain a battery membrane electrode.

[0041] The preparation method of the slurry A comprises the following steps: uniformly mixing a DuPont D-2020 Nafion solution containing 10-40% solid content of perfluorosulfonic acid resin, polyethylene oxide, ethanol and nano-silicon oxide, and ball milling for at least 24 hours to obtain slurry A. Slurry A is an electrospinning slurry. In this embodiment, a 20% DuPont D-2020 Nafion solution is preferably used, and ball milling is performed for 24 hours.

[0042] The preparation method of the slurry B and slurry C comprises the following steps: uniformly mixing a DuPont D-2020Nafion solution containing 10-30% solid content of perfluorosulfonic acid resin, a Pt / C catalyst, isopropanol, and deionized water to obtain a mixed slurry, and then obtaining a cathode catalyst slurry B and an anode catalyst slurry C. Slurry B is a cathode catalyst layer slurry, and slurry C is an anode catalyst layer slurry. In this embodiment, a 20% DuPont D-2020Nafion solution is preferred.

[0043] In step S2, the slurry C is evenly coated on the Teflon substrate by a doctor blade method, cut to a suitable size and stacked on a hot press together with the proton exchange membrane to be prepared, and the hot pressing temperature is controlled to be 70-120°C, the pressure is 0.2-0.8MPa for hot pressing, and the hot pressing time is controlled to be no more than 6min to obtain a half-side membrane electrode containing an anode catalyst layer. In this embodiment, the preferred hot pressing temperature is 100°C, the pressure is 0.5MPa, and the hot pressing time is 5min.

[0044] In step S3, slurry A is added at 0.2-0.6 ml h -1 The flow rate is sent to the spinneret, and a voltage of 10-20 kV is applied between the spinneret and the collector; the half-side membrane electrode containing the anode catalyst layer obtained in step S2 is placed 10-25 cm below the tip of the spinneret, and spinning is performed thereon to form a proton conductive hydrophilic skeleton network with high working condition adaptability. This step is an electrospinning technology. In this embodiment, a voltage of 15 kV is preferably applied and placed 15 cm below the tip of the spinneret.

[0045] In step S3, a microinjection needle pump is used to inject slurry B at a rate of 0.1-0.4 ml min -1 The flow rate is injected into the electrostatic spray head, and the cathode of the half-side membrane electrode containing the anode catalyst layer and the cathode high working condition adaptability proton conductive hydrophilic skeleton network is placed upward, 10-30cm below the tip of the electrostatic spray head, and slurry B is sprayed on it to complete the preparation of the cathode catalyst layer structure. This step is an electrostatic spraying method. In this embodiment, 0.2ml min is preferred. -1 Flow rate, placed 19cm below the tip of the electrostatic nozzle.

[0046] In step S3, the mixture is dried in a vacuum oven at a temperature of 30-50°C for no less than 3 hours to completely volatilize the dispersed solvent in the cathode and anode catalyst layers. In this embodiment, the preferred drying temperature is 40°C and the drying time is 3.5 hours.

[0047] In the preparation method of slurry A, the solid concentration of the perfluorosulfonic acid resin is 3-9wt%, the concentration of polyethylene oxide is 0.05-0.2wt%, the concentration of nano-silicon oxide is 1-7%, and the 1mm particle size zirconium oxide beads are used for ball milling on a ball mill for at least 24h. In this embodiment, the solid concentration of the perfluorosulfonic acid resin is preferably 6wt%, the concentration of polyethylene oxide is 0.1wt%, the concentration of nano-silicon oxide is 4%, and the 1mm particle size zirconium oxide beads are used for ball milling on a ball mill for 25h.

[0048] In the preparation method of slurry B and slurry C, in the mixed slurry, the solid content of the dry weight of the Pt / C catalyst + perfluorosulfonic acid resin is set to 0.1-0.4%, and the mass ratio of the catalyst to the ionomer resin is 1:0.1-0.6; in the dispersion solvent composed of isopropanol and deionized water, the mass ratio of isopropanol to deionized water is 4-9:1. In this embodiment, the solid content of the dry weight of the Pt / C catalyst + perfluorosulfonic acid resin is preferably set to 0.2%, and the mass ratio of the Pt / C catalyst to the ionomer resin is 1:0.33; in the dispersion solvent composed of isopropanol and deionized water, the mass ratio of isopropanol to deionized water is 7:1.

[0049] A fuel cell system comprises a fuel cell membrane electrode prepared by a fuel cell membrane electrode preparation method. A fuel cell power generation system comprises a proton exchange membrane fuel cell stack, a hydrogen path system and an air path system.

[0050] The anode and cathode are set on the proton exchange membrane fuel cell stack, and the gas inlet and outlet are set on the anode and cathode. The anode gas inlet is connected to the hydrogen path system through a pipeline, and a pressure control valve is set on the pipeline. After the reaction is completed, the exhaust gas is discharged from the anode gas outlet; the cathode gas inlet is connected to the air path system through a pipeline, and a pressure control valve is set on the pipeline. After the reaction is completed, the exhaust gas is discharged from the cathode gas outlet. Compared with the traditional structure, equipment such as the reaction gas humidification system is omitted.

[0051] The purpose of the present invention is to solve the problem that the proton conductive network on the cathode side of the membrane electrode obtained by the traditional preparation method is poor in continuity, the catalyst utilization rate is low, and at the same time, it is heavily dependent on the cathode reactant intake humidification system to achieve sufficient wetting of the ionomer in the membrane electrode, thereby achieving proton conduction. The present invention provides a new membrane electrode preparation method, which constructs a highly connected proton conductive network on the cathode side, so that the proton transmission that originally relied heavily on the dispersion of the slurry can be transmitted through an artificially constructed continuous skeleton network; at the same time, a hydrophilic skeleton network that can achieve product drainage recovery without external reactant humidification is constructed, which improves the tolerance of the fuel cell system to various dry conditions, and reduces the negative impact of humidity reduction on the proton transmission resistance in the membrane electrode under reaction conditions. This method is suitable for the preparation of membrane electrodes for proton exchange membrane fuel cells, so as to simultaneously achieve high catalyst utilization, high proton conductivity, and stable and high-performance fuel cell operation under relatively dry conditions.

Claims

1. A method for preparing a fuel cell membrane electrode, characterized in that: The following steps are involved: S1: preparing slurry A, slurry B and slurry C respectively; S2: coating the slurry C on the substrate, and then stacking and hot-pressing the slurry C together with the proton exchange membrane to obtain an anode catalyst layer; S3: Use slurry A to spin on the membrane electrode to obtain a membrane electrode containing a skeleton network, spray slurry B on the side of the half membrane electrode with the skeleton network to form a cathode catalyst layer, and finally dry the membrane electrode to obtain a battery membrane electrode; The preparation method of the slurry A comprises the following steps: uniformly mixing a Nafion solution containing a perfluorosulfonic acid resin with a solid content of 10-40%, polyethylene oxide, ethanol and nano-silicon oxide, and ball milling for at least 24 hours to obtain the slurry A; The preparation method of the slurry B and slurry C comprises the following steps: uniformly mixing a Nafion solution containing 10-30% solid content of perfluorosulfonic acid resin, a Pt / C catalyst, isopropanol, and deionized water to obtain a mixed slurry, and then obtaining a cathode catalyst slurry B and an anode catalyst slurry C; The solid content concentration of the perfluorosulfonic acid resin is 3-9wt%, the concentration of polyethylene oxide is 0.05-0.2wt%, and the concentration of nano-silicon oxide is 1-7%. The process is ball-milled on a ball mill using zirconium oxide beads for at least 24 hours.

2. A method for preparing a fuel cell membrane electrode according to claim 1, characterized in that: In the step S2, the slurry C is evenly coated on the Teflon substrate by a scraping method, cut to a suitable size and stacked on a hot press together with the proton exchange membrane, the hot pressing temperature is controlled to be 70-120°C, the pressure is 0.2-0.8MPa for hot pressing, and the hot pressing time is controlled to be no more than 6 minutes to obtain a half-side membrane electrode containing an anode catalyst layer.

3. A method for preparing a fuel cell membrane electrode according to claim 1, characterized in that: In step S3, slurry A is added at 0.2-0.6 ml h -1 The flow rate is sent to the spinneret, and a voltage of 10-20 kV is applied between the spinneret and the collector; the half-side membrane electrode obtained in step S2 is placed 10-25 cm below the tip of the spinneret, and spinning is performed thereon to form a skeleton network.

4. A method for preparing a fuel cell membrane electrode according to claim 1, characterized in that: In step S3, a microinjection needle pump is used to inject slurry B at a rate of 0.1-0.4 ml min -1 The flow rate is injected into the electrostatic nozzle, the cathode containing the anode catalyst layer and the half-membrane electrode containing the skeleton network is placed upward, 10-30 cm below the tip of the electrostatic nozzle, and slurry B is sprayed thereon to complete the preparation of the cathode catalyst layer structure; and it is dried in a vacuum oven at a temperature of 30-50°C for not less than 3 hours.

5. A method for preparing a fuel cell membrane electrode according to claim 1, characterized in that: In the mixed slurry, the solid content is set to 0.1-0.4%, the mass ratio of Pt / C catalyst to ionomer resin is 1:0.1-0.6; in the dispersion solvent composed of isopropanol and deionized water, the mass ratio of isopropanol to deionized water is 4-9:

1.

6. A fuel cell system, comprising a cell membrane electrode prepared by the preparation method according to any one of claims 1 to 5.

7. A fuel cell system according to claim 6, characterized in that: It includes a proton exchange membrane fuel cell stack, a hydrogen path system and an air path system.

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