A cathode catalyst slurry incorporating serine polybenzimidazole and a method of making the same

Abstract

The application discloses a cathode catalyst slurry with introduced serine polybenzimidazole and a preparation method thereof, and the preparation method comprises the following steps: step 1, serine and polybenzimidazole are used as reactants to generate a condensation reaction, and serine polybenzimidazole is obtained; and step 2, the serine polybenzimidazole, a binder and a catalyst are mixed to obtain the cathode catalyst slurry with introduced serine polybenzimidazole. According to the application, the ionomer serine polybenzimidazole is introduced into a cathode catalyst layer, in a high-temperature environment of a high-temperature proton exchange membrane fuel cell, the hydroxyl groups on the ionomer serine polybenzimidazole can be crosslinked with phosphoric acid, the phosphoric acid is fixed on the ionomer serine polybenzimidazole, the adsorption of the phosphoric acid to Pt active sites is reduced, meanwhile, the migration and loss of the phosphoric acid in the cathode catalyst layer are reduced, the distribution of the phosphoric acid in the catalyst layer is adjusted, the proton conduction of the phosphoric acid is improved, and the output power and stability of the HT-PEMFC are improved.

Description

Technical Field

[0001] This invention relates to the field of high-temperature proton exchange membrane fuel cells, and specifically to a cathode catalyst slurry incorporating serine polybenzimidazole and its preparation method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are highly efficient energy conversion devices with advantages such as high power density, environmental friendliness, renewable fuel, and wide applicability, thus possessing a very broad application prospect. PEMFCs are divided into low-temperature PEMFCs (LT-PEMFCs) primarily using Nafion membranes and high-temperature PEMFCs (HT-PEMFCs) primarily using phosphoric acid-doped polybenzimidazole membranes. PEMFCs operating at temperatures above 100°C are called high-temperature PEMFCs (HT-PEMFCs), with operating temperatures typically between 100-200°C. Compared to commercially available low-temperature PEMFCs, high-temperature PEMFCs offer advantages such as simpler hydrothermal management, stronger resistance to CO poisoning, and higher catalytic reactivity.

[0003] The membrane electrode assembly (MEA) is a core component of a high-temperature proton exchange membrane fuel cell (HT-PEMFC), and the catalyst layer within the MEA plays a crucial role in determining fuel cell performance as the site of chemical reactions. In conventional cathode catalyst layers, phosphoric acid covers the active sites of the Pt catalyst, hindering the transport of reactant gases to these sites. Furthermore, phosphoric acid in conventional cathode catalyst layers can migrate and leak out, leading to performance degradation. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of phosphoric acid covering Pt active sites and migration and loss in traditional cathode catalyst layers, and to provide a cathode catalyst slurry incorporating serine polybenzimidazole and its preparation method.

[0005] To achieve the above objectives, the present invention provides a method for preparing a cathode catalyst slurry incorporating serine polybenzimidazole, comprising the following steps: Step 1: Serine and polybenzimidazole are used as reactants to undergo a condensation reaction to obtain serine polybenzimidazole; Step 2: Mix the serine polybenzimidazole, binder and catalyst to obtain the cathode catalyst slurry incorporating serine polybenzimidazole.

[0006] Optionally, step 1 can be further described as follows: dissolving serine and polybenzimidazole in a dimethyl sulfoxide solution, heating the solution to 90°C-100°C, and reacting for 22-24 hours to obtain the serine polybenzimidazole.

[0007] Optionally, the mass ratio of serine to polybenzimidazole is 1:(1-5).

[0008] Optionally, in step 2, the binder is polytetrafluoroethylene, and the catalyst is a platinum-based catalyst or a platinum-based alloy catalyst.

[0009] Optionally, in step 2, the mass ratio of serine polybenzimidazole to binder is 1:(0.1-5).

[0010] Optionally, in step 2, the mass ratio of serine polybenzimidazole to catalyst is 1:(5-20).

[0011] Optionally, the specific steps of step 2 are as follows: Step 2.1: Disperse the adhesive in water and a surfactant solution to obtain an adhesive solution; Step 2.2: Disperse the catalyst in a solvent to obtain a catalyst solution; Step 2.3: Mix the serine polybenzimidazole, binder solution and catalyst solution to obtain the cathode catalyst slurry incorporating serine polybenzimidazole.

[0012] Optionally, the surfactant may be FC-4430 or FC-003.

[0013] The present invention also provides a cathode catalyst slurry incorporating serine polybenzimidazole, comprising an ionomer, a binder, and a catalyst; wherein the ionomer is serine polybenzimidazole, the binder is polytetrafluoroethylene, and the catalyst is a platinum-based catalyst or a platinum-based alloy catalyst.

[0014] The present invention also provides a proton exchange membrane fuel cell membrane electrode, comprising a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer, wherein the cathode catalyst layer and the anode catalyst layer are disposed on both sides of the proton exchange membrane, and the cathode catalyst layer is made of the above-mentioned cathode catalyst slurry.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention introduces ionomer serine polybenzimidazole into the cathode catalyst layer. Under the high-temperature environment of a high-temperature proton exchange membrane fuel cell (HT-PEMFC), the hydroxyl groups on the ionomer serine polybenzimidazole can crosslink with phosphoric acid, fixing the phosphoric acid on the ionomer serine polybenzimidazole. This reduces the adsorption of phosphoric acid on Pt active sites, while also mitigating the migration and loss of phosphoric acid in the cathode catalyst layer. This regulates the distribution of phosphoric acid in the catalyst layer, improves the proton conduction of phosphoric acid, and enhances the output power and stability of the HT-PEMFC. Attached Figure Description

[0016] Figure 1These are the polarization characteristic curves of the membrane electrodes prepared from the catalyst slurries of Examples 1-3 and the comparative examples.

[0017] Figure 2 These are the cyclic voltammetry curves of the membrane electrodes prepared from the catalyst slurries of Examples 1-3 and the comparative examples. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] As described in the background section, in conventional membrane electrode cathode catalyst layers, phosphoric acid covers the active sites of the Pt catalyst, hindering gas transport to these sites. Furthermore, phosphoric acid in conventional cathode catalyst layers can migrate and leak out, leading to performance degradation in the battery.

[0020] To address the issues of phosphoric acid covering Pt active sites and migrating away in traditional cathode catalyst layers, this invention condenses serine and polybenzimidazole (OPBI) to obtain the ionomer serine polybenzimidazole (SerPBI), which is then introduced into the cathode catalyst layer. Since the hydroxyl groups of the ionomer SerPBI can crosslink with phosphoric acid under high-temperature conditions, the phosphoric acid is immobilized on the ionomer SerPBI, effectively reducing the adsorption of phosphoric acid at Pt active sites and minimizing its migration and loss, thus regulating the distribution of phosphoric acid in the cathode catalyst layer.

[0021] Specifically, the present invention provides a method for preparing a cathode catalyst slurry incorporating serine polybenzimidazole, the method comprising: Step 1: Serine and polybenzimidazole are used as reactants to undergo a condensation reaction to obtain serine-polybenzimidazole. The reaction formula is as follows:

[0022] Step 2: Mix the serine polybenzimidazole, binder and catalyst to obtain the cathode catalyst slurry incorporating serine polybenzimidazole.

[0023] In some embodiments, the binder is polytetrafluoroethylene (PTFE), the surfactant is FC-4430 or FC-003, and the catalyst is a platinum-based catalyst (such as Pt / C) or a platinum alloy catalyst (such as PtCo / C).

[0024] A certain mass of serine polybenzimidazole was dissolved in dimethyl sulfoxide (DMSO) to obtain a serine polybenzimidazole solution. The serine polybenzimidazole solution was mixed with a binder solution and a catalyst solution to obtain the cathode catalyst slurry incorporating serine polybenzimidazole.

[0025] In some embodiments, the mass ratio of serine polybenzimidazole to binder is 1:(0.1-5).

[0026] The technical solution of the present invention will be further described below with reference to the embodiments.

[0027] Example 1 This embodiment provides a method for preparing a cathode catalyst slurry incorporating serine polybenzimidazole, the method comprising: (1) Preparation of serine polybenzimidazole solution: Ten parts by mass of polybenzimidazole were dissolved in dimethyl sulfoxide to obtain a polybenzimidazole solution at a dissolution temperature of 60°C for 6 hours. Then, five parts by mass of serine were added to the polybenzimidazole solution to undergo a condensation reaction to obtain a serine polybenzimidazole solution at a reaction temperature of 100°C for 24 hours.

[0028] (2) Preparation of catalyst slurry: A certain mass of polytetrafluoroethylene (PTFE) was dispersed in deionized water, and a certain mass of surfactant FC-4430 was dissolved in dimethyl sulfoxide (DMSO). The two were mixed to obtain a PTFE solution. A certain mass of PtCo / C catalyst was then dispersed in DMSO to obtain a PtCo / C catalyst solution. Then, 20 parts by mass of the PTFE solution and 5 parts by mass of the serine polybenzimidazole solution were added to 100 parts by mass of the PtCo / C catalyst solution to obtain the cathode catalyst slurry incorporating serine polybenzimidazole in this embodiment.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that the serine polybenzimidazole solution is 10 parts by mass.

[0030] Example 3 The difference between this embodiment and Embodiment 1 is that the serine polybenzimidazole solution is 15 parts by weight.

[0031] Example 4 The difference between this embodiment and Embodiment 1 is that the polytetrafluoroethylene solution is 25 parts by mass.

[0032] Example 5 The difference between this embodiment and Embodiment 1 is that the reaction temperature of serine and polybenzimidazole is 95°C.

[0033] Example 6 This embodiment provides a membrane electrode prepared using the catalyst slurry of Example 1, and its preparation method is as follows: The catalyst slurry from Example 1 was uniformly sprayed onto the surface of the cathode gas diffusion layer using an ultrasonic spraying method, with the Pt catalyst loading controlled at 0.4-0.6 mg / cm³. 2After drying, a cathode gas diffusion electrode is obtained. A polybenzimidazole proton exchange membrane and an anode gas diffusion electrode are taken and hot-pressed onto both sides of the polybenzimidazole proton exchange membrane to prepare a membrane electrode. The active area of ​​the membrane electrode is 4 cm². 2 The hot pressing temperature is 160℃ and the time is 6 minutes. The hot-pressed membrane electrode is placed in a constant temperature and humidity cabinet for storage and later use.

[0034] The cathode gas diffusion layer comprises a support layer (150 μm thick) and a microporous layer (30 μm thick). The support layer is carbon paper or carbon cloth, and the microporous layer comprises carbon powder and PTFE, with a carbon powder loading of 2 mg / cm³. 2 The PTFE content in the microporous layer is 10%-30%. The cathode gas diffusion layer is prepared using the following method: Vulcan XC-72 toner and PTFE emulsion were mixed, and an appropriate amount of ethanol was added. The mixture was ultrasonically stirred to obtain a slurry, which was then coated onto the surface of commercially available Torray carbon paper. The toner loading and PTFE content were then determined by weighing. Finally, the mixture was placed in a muffle furnace and heat-treated at 340°C for 30 minutes. After cooling to room temperature, a cathode gas diffusion layer was obtained.

[0035] The aforementioned anode gas diffusion electrode mainly comprises an anode gas diffusion layer and an anode catalyst layer. The anode gas diffusion layer is identical to the aforementioned cathode gas diffusion layer. The anode catalyst layer is primarily composed of a catalyst and PTFE, wherein the catalyst is Pt / C, and the loading of the noble metal Pt is 0.1-0.3 mg / cm³. 2 The PTFE content is 10%-30%. The anode catalyst layer is prepared using the following method: Weigh a certain amount of Pt / C catalyst, add a small amount of deionized water to wet it, stir and disperse it evenly, then add a certain amount of PTFE water-alcohol solution, and ultrasonically disperse it evenly to obtain a catalyst slurry; use ultrasonic spraying to uniformly coat the slurry onto the microporous surface of the anode gas diffusion layer to obtain the anode catalyst layer.

[0036] The polybenzimidazole proton exchange membrane has a thickness of 10-40 μm and a phosphoric acid doping content of 200 wt%-400 wt%. The polybenzimidazole proton exchange membrane is prepared using the following method: The dried polybenzimidazole membrane was cut to a specific size. The cut membrane was then immersed in 85 wt% phosphoric acid at 120°C for 60 minutes. Excess phosphoric acid was blotted off the membrane surface with filter paper, and the membrane was quickly weighed to calculate the phosphoric acid doping level. The phosphoric acid doping level was determined by the mass ratio of phosphoric acid to polybenzimidazole resin (mass of doped phosphoric acid / original mass of the polybenzimidazole membrane). The acid immersion process was repeated until the phosphoric acid doping level reached 400 wt%.

[0037] Comparative Example The difference between this comparative example and Example 1 is that no serine polybenzimidazole solution was added to the catalyst slurry.

[0038] The catalyst slurries of Examples 1-3 and the comparative examples were uniformly sprayed onto the surface of the cathode gas diffusion layer using an ultrasonic spraying method. After drying, the cathode gas diffusion electrode was obtained. Each cathode gas diffusion electrode was then further fabricated into a high-temperature proton exchange membrane fuel cell.

[0039] According to GB / T 20042.5-2009, polarization curves were tested on each high-temperature proton exchange membrane fuel cell. The specific operating conditions were: single cell operating temperature of 160℃, anode feed of pure hydrogen, cathode feed of atmospheric pressure oxygen, and cathode / anode feed ratio of 1 / 1.

[0040] According to GB / T 20042.5-2009, cyclic voltammetry tests were conducted on various high-temperature proton exchange membrane fuel cells. The specific operating conditions were as follows: the single cell operating temperature was 160℃, the anode was fed with pure hydrogen, the cathode was fed with nitrogen at atmospheric pressure, and the cathode / anode feed ratio was 1 / 1.

[0041] See Figure 1 The polarization characteristic curves of the high-temperature proton exchange membrane fuel cells of Examples 1-3 and the comparative example of the present invention were obtained. As can be seen from the graphs, at 0.1 A / cm... 2 The membrane electrode voltages for Examples 1, 2, 3, and the comparative example of the present invention were measured to be 0.716V, 0.712V, 0.723V, and 0.710V, respectively. The fuel cell power densities for Examples 1, 2, 3, and the comparative example of the present invention were measured to be 71.6 mW / cm². -2 71.2mW cm -2 72.3mW cm -2 71.0mW cm -2 At 0.5A / cm 2 At that time, the membrane electrode voltages corresponding to Examples 1, 2, 3, and the comparative example of the present invention were measured to be 0.605V, 0.597V, 0.597V, and 0.579V, respectively. The fuel cell power densities corresponding to Examples 1, 2, 3, and the comparative example of the present invention were measured to be 302.5 mW / cm². -2 298.5 mW cm -2 298.5 mW cm -2 289.5mW cm -2 .

[0042] At low current densities, the membrane electrode polarization losses of the high-temperature proton exchange membrane fuel cells prepared in Examples 1-3 and the comparative example are comparable. At high current densities, the membrane electrode polarization losses of Examples 2-3 are smaller than those of the high-temperature proton exchange membrane fuel cells prepared in the comparative example, while the membrane electrode polarization loss of Example 1 is slightly larger than that of the comparative example. This indicates that when the proportion of SerPBI is larger, the power density of the fuel cell is greater and the performance is better.

[0043] See Figure 2 Cyclic voltammograms of the membrane electrodes of Examples 1-3 of this invention and the high-temperature proton exchange membrane fuel cell of the comparative example were obtained. Calculations showed that the electrochemical active area (ECSA) of Examples 1, 2, 3, and the comparative example was 89.9 m². 2 / g、69.6m 2 / g, 62.1m 2 / g, 57.8m 2 / g. Example 1 showed the highest ECSA content, indicating that the addition of SerPBI can regulate the phosphate distribution in the catalyst layer, thereby increasing the active surface area of ​​the catalyst.

[0044] In summary, this invention provides a cathode catalyst slurry incorporating serine-polybenzimidazole and its preparation method. Serine-polybenzimidazole is obtained by condensing serine and polybenzimidazole, and then introduced into the cathode catalyst layer. Since the hydroxyl groups of SerPBI can crosslink with phosphoric acid under high-temperature conditions, the phosphoric acid is immobilized on SerPBI, thereby effectively reducing the adsorption of phosphoric acid at Pt active sites and minimizing phosphoric acid migration and loss, thus regulating the distribution of phosphoric acid in the cathode catalyst layer.

[0045] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a cathode catalyst slurry incorporating serine-polybenzimidazole, characterized in that, Includes the following steps: Step 1: Serine and polybenzimidazole are used as reactants to undergo a condensation reaction to obtain serine polybenzimidazole; the specific steps of Step 1 are as follows: dissolve serine and polybenzimidazole in dimethyl sulfoxide solution, heat the solution to 90℃-100℃, and react for 22h-24h. Step 2: Mix the serine polybenzimidazole, binder and catalyst to obtain the cathode catalyst slurry incorporating serine polybenzimidazole.

2. The method for preparing the cathode catalyst slurry incorporating serine polybenzimidazole as described in claim 1, characterized in that, In step 1, the mass ratio of serine to polybenzimidazole is 1:(1-5).

3. The method for preparing the cathode catalyst slurry incorporating serine polybenzimidazole as described in claim 1, characterized in that, In step 2, the binder is polytetrafluoroethylene, and the catalyst is a platinum-based catalyst or a platinum-based alloy catalyst.

4. The method for preparing the cathode catalyst slurry incorporating serine polybenzimidazole as described in claim 1, characterized in that, In step 2, the mass ratio of the serine polybenzimidazole to the binder is 1:(0.1-5).

5. The method for preparing the cathode catalyst slurry incorporating serine polybenzimidazole as described in claim 1, characterized in that, In step 2, the mass ratio of the serine polybenzimidazole to the catalyst is 1:(5-20).

6. The method for preparing the cathode catalyst slurry incorporating serine polybenzimidazole as described in claim 1, characterized in that, The specific steps of step 2 are as follows: Step 2.1: Disperse the adhesive in water and a surfactant solution to obtain an adhesive solution; Step 2.2: Disperse the catalyst in a solvent to obtain a catalyst solution; Step 2.3: Mix the serine polybenzimidazole, binder solution and catalyst solution to obtain the cathode catalyst slurry incorporating serine polybenzimidazole.

7. The method for preparing the cathode catalyst slurry incorporating serine polybenzimidazole as described in claim 6, characterized in that, The surfactant is FC-4430 or FC-003.

8. A cathode catalyst slurry incorporating serine-containing polybenzimidazole, obtained by the preparation method as described in claim 1, characterized in that, It includes an ionomer, a binder, and a catalyst; the ionomer is serine polybenzimidazole, the binder is polytetrafluoroethylene, and the catalyst is a platinum-based catalyst or a platinum-based alloy catalyst.

9. A membrane electrode assembly for a proton exchange membrane fuel cell, characterized in that, It includes a proton exchange membrane, a cathode catalyst layer and an anode catalyst layer, wherein the cathode catalyst layer and the anode catalyst layer are disposed on both sides of the proton exchange membrane, and the cathode catalyst layer is made of the cathode catalyst slurry as described in claim 8.

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