Cerium oxide controllable modification of noble metal-based porous carbon catalyst, preparation method and application

Abstract

The application discloses a cerium oxide controllable modified noble metal-based porous carbon catalyst and a preparation method. The porous carbon catalyst is loaded with cerium oxide particles in and out of the pores of the porous carbon. The cerium oxide particles loaded in the pores are not less than 40% of the total loading amount of the cerium oxide particles, the mass ratio of the loaded cerium / carbon is 0.2:1-0.5:1, and the pore volume of the porous carbon used for loading is 0.4-1 cm 3 / g. The preparation method comprises the following steps: a first step of dispersing a cerium source precursor and a noble metal-based porous carbon catalyst and impregnating the porous carbon pores; a second step of reacting the cerium source in and out of the pores of the porous carbon to generate cerium oxide and complete the loading; and a third step of separating and purifying the modified catalyst from the reaction solution. The application realizes the limitation of the controllable proportion of cerium oxide particles in the pore structure of the noble metal-based porous carbon catalyst, avoids the migration and slow dissolution of the cerium oxide particles, can quickly eliminate the free radicals generated in the power generation reaction process, and improves the stability and service life of the fuel cell.

Description

Technical Field

[0001] This invention relates to the field of fuel cell catalyst technology, specifically to a cerium oxide-modified noble metal-based porous carbon catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy is considered the best carrier for addressing the seasonal fluctuations of renewable energy. Proton exchange membrane fuel cells (PEMFCs), as the optimal device for converting hydrogen energy into electricity, have become an ideal power source to replace internal combustion engines. Due to their advantages in mass power density and start-up speed, fuel cells are geared towards the future development of heavy-duty vehicles (HDVs). To promote the commercialization of fuel cells in HDVs, durability is a crucial indicator that needs to be addressed. Japan's New Energy and Industrial Technology Development Organization (NEDO) has proposed that fuel cell lifespan reach 50,000 hours by 2030. Among the key components of fuel cells, the proton exchange membrane and the ionomers in the catalyst layer are susceptible to damage from free radical attacks during operation, weakening the hydrogen barrier effect and degrading proton conductivity, resulting in serious durability problems.

[0003] In existing technologies, free radical scavengers, such as cerium oxide, are often added to eliminate free radicals generated during operation. However, because cerium oxide is prone to loss due to potential migration, its free radical scavenging ability is weakened. Furthermore, the dissolution of cerium ions can lead to ion exchange with ionomers, causing a decrease in the proton conductivity of the ionomers. Therefore, it is necessary to develop technologies that effectively limit cerium oxide migration and dissolution, extend the effective time of cerium oxide, and further improve the stability and lifespan of fuel cells. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, this invention proposes a cerium oxide-modified noble metal-based porous carbon catalyst, its preparation method, and its application. In this invention, cerium oxide is loaded into the pores of a porous support. The confinement effect of the pores can effectively prevent the migration of cerium oxide particles and slow down the dissolution of cerium ions. The cerium oxide loaded on the carbon support is close to the electrochemical reaction sites, which can quickly remove free radicals generated during power generation and effectively improve the stability and service life of the fuel cell.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides a cerium oxide-modified noble metal-based porous carbon catalyst, wherein cerium oxide particles are supported both inside and outside the pores of the porous carbon, with the amount of cerium oxide particles supported inside the pores not less than 40% of the total cerium oxide particle loading in the porous carbon catalyst. The cerium / carbon mass ratio of the porous carbon catalyst is 0.2:1 to 0.5:1, and the pore volume of the porous carbon used for support is 0.4 cm³. 3 / g~1cm 3 / g.

[0008] In some embodiments, the noble metal-based particles are selected from those that can provide electrochemical reactivity.

[0009] In some embodiments, the material of the noble metal-based particles may be any of the following:

[0010] An alloy of any one or more precious metals;

[0011] An alloy containing a precious metal element and at least one non-precious metal element;

[0012] Noble metal oxynitrides.

[0013] A second aspect of the present invention provides a method for preparing the porous carbon catalyst described in any embodiment of the first aspect of the present invention, comprising:

[0014] The first step is to fully disperse the cerium source precursor and the noble metal-based porous carbon catalyst and impregnate them in the porous carbon pores.

[0015] The second step involves reacting the cerium source inside and outside the pores of the porous carbon to generate cerium oxide, thus completing the loading process.

[0016] The third step involves separating and purifying the modified catalyst from the reaction solution to obtain the cerium oxide-modified noble metal-based porous carbon catalyst.

[0017] In some embodiments, the impregnation process in the first step is carried out in an inert atmosphere and a set vacuum level is maintained.

[0018] In some embodiments, the vacuum level is set to -0.1 MPa to -0.02 MPa.

[0019] In some embodiments, the second step specifically includes: adding an alkaline solution dropwise under stirring conditions to adjust the pH, obtaining a mixed dispersion, and reacting the cerium source inside and outside the pores of the porous carbon at a preset reaction temperature to generate cerium oxide, thereby completing the loading.

[0020] In some embodiments, the pH is controlled between 10 and 14.

[0021] In some embodiments, the preset reaction temperature is set to 30°C to 70°C.

[0022] In some embodiments, the third step specifically includes: filtering the product obtained in the second step, removing weakly durable ionic components, removing weakly durable nonionic components, and drying it to obtain the cerium oxide controllable modified noble metal porous carbon catalyst.

[0023] The weakly durable ionic components are unreacted ionic substances on the catalyst surface and ionic substances generated during the oxide formation process.

[0024] The weakly durable nonionic component consists of cerium oxide that is attached to the outside of the porous carbon pores and is easily detached, and cerium oxide particles that are not attached to the porous carbon.

[0025] By removing weakly durable ions and non-ionic components, ensuring that no ionic substances exist on the catalyst, and ensuring that the cerium oxide supported on the catalyst carbon support is mainly present in the pores, the durability effect is extended over a long period of time.

[0026] In some embodiments, the removal of weakly durable ionic components and the removal of weakly durable nonionic components both employ a combination of deionized water washing and vacuum filtration.

[0027] In some embodiments, the removal of weakly durable nonionic components further includes applying mechanical vibration and stirring without damaging the catalyst particles.

[0028] A third aspect of the present invention provides a hydrogen fuel cell, the hydrogen fuel cell comprising an electrode catalyst layer, the electrode catalyst layer comprising a porous carbon catalyst according to any embodiment of the first aspect of the present invention and / or a porous carbon catalyst prepared according to any embodiment of the second aspect of the present invention.

[0029] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0030] Existing technologies often incorporate free radical scavengers, such as cerium oxide, to eliminate free radicals generated during operation. However, cerium oxide suffers from potential migration and loss, which weakens its free radical elimination ability. Furthermore, the dissolution of cerium ions leads to ion exchange with ionomers, reducing the proton conductivity of the ionomers. This invention supports cerium oxide within the pores of a porous carbon catalyst. This catalyst is used to fabricate the anode catalyst layer, which is then used to construct a hydrogen fuel cell. After endurance testing under idling conditions, the increase in the hydrogen leakage current density of the proton exchange membrane and the increase in the proton conduction resistance of the catalyst layer are reduced. This can be attributed to the following: during endurance testing, the dissolution and migration of cerium ions affect the loss of its free radical elimination effect. Additionally, the sulfonate groups of the perfluorosulfonic acid polymer exchange with the dissolved cerium ions, affecting proton conductivity. By confining cerium oxide particles within the pore structure of the noble metal-based porous carbon catalyst, migration of cerium oxide particles is prevented and dissolution is slowed. Moreover, cerium oxide is located adjacent to free radical generation sites, enabling real-time elimination of free radicals generated during the power generation reaction, further improving the stability and lifespan of the fuel cell. Attached Figure Description

[0031] Figure 1 The XPS results of the cerium oxide controllably modified noble metal-based porous carbon catalyst prepared in the embodiments of the present invention are shown. Figures a and b are the full spectrum results and fine elemental spectra of Ce in Example 1, and figures c and d are the full spectrum results and fine elemental spectra of Ce in Example 2.

[0032] Figure 2 Figures a and b in the figure are the isothermal adsorption results of nitrogen before and after loading in Example 1 of the present invention, respectively;

[0033] Figure 3 The voltage decay rate during the durability test process of Examples 3, 4, Comparative Example 2, and Comparative Example 3 of the present invention;

[0034] Figure 4 The variation of hydrogen leakage current density at the start and end points of the durability tests conducted on Examples 3, 4, Comparative Example 2 and Comparative Example 3 of the present invention.

[0035] Figure 5 The variation of catalyst layer proton conduction resistance at the start and end points during proton conduction resistance tests of Examples 3, 4, Comparative Examples 2 and 3 of the present invention;

[0036] Figure 6 The polarization curve variations at the endurance start and end points during power generation performance testing of Examples 3, 4, Comparative Example 2, and Comparative Example 3 of the present invention are shown.

[0037] Figure 7To ensure the endurance start and end points for power generation performance testing of Examples 3, 4, Comparative Examples 2, and 3 of the present invention are at 1 A·cm -2 Voltage variation under current density. Detailed Implementation

[0038] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. Similar elements in different embodiments are referred to by related similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0039] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0040] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this application.

[0041] The first aspect of this invention provides a cerium oxide-modified noble metal-based porous carbon catalyst, in which cerium oxide particles are supported both inside and outside the pores of the porous carbon. The amount of cerium oxide particles supported inside the pores is not less than 40% of the total cerium oxide particle loading in the porous carbon catalyst. The cerium / carbon mass ratio of the catalyst is 0.2:1 to 0.5:1, and the pore volume of the porous carbon used for support is 0.4 cm³. 3 / g~1cm 3 / g, noble metal-based particles are used to provide electrochemical reactivity.

[0042] Furthermore, when the amount of cerium oxide supported in the pores is low, the quenching effect on free radicals generated by noble metals within the pores is weak, and the restriction effect on the loss of cerium oxide with potential migration is also limited, resulting in an insignificant effect on increasing the reaction time of cerium oxide. Therefore, in the embodiments of the present invention, the amount of cerium oxide particles supported in the pores is limited to no less than 40% of the total cerium oxide particle loading in the porous carbon catalyst. In principle, all cerium oxide particles can be supported in the pores of the porous carbon, that is, the cerium oxide particles supported in the pores account for 40% to 100% of the total cerium oxide particle loading in the porous carbon catalyst, preferably set at 40% to 70%.

[0043] Furthermore, the pore size, pore volume, and BET specific surface area of ​​cerium oxide deposited within the pores can be calculated using nitrogen isothermal adsorption curves before and after loading, and the differences between the two can be analyzed. Since cerium oxide loaded outside the pores is prone to migration and dissolution, losing its durability, this embodiment of the invention loads a certain amount of cerium oxide particles inside the pores of porous carbon to improve durability. The confinement effect of the pores effectively slows down the dissolution of cerium ions. The cerium oxide loaded on the carbon support is adjacent to the electrochemical reaction sites, which can quickly remove free radicals generated during power generation, effectively improving the stability and lifespan of the fuel cell.

[0044] Furthermore, the cerium / carbon mass ratio used in this embodiment of the invention indicates the cerium oxide loading, calculated by measuring the cerium content and carbon mass ratio using X-ray photoelectron spectroscopy (XPS). If the cerium / carbon mass ratio is too small, the amount of cerium oxide is insufficient, and free radicals generated during the aging process will occupy free radical capturing sites, resulting in incomplete free radical capture and causing aging. Therefore, the cerium / carbon mass ratio is preferably greater than 0.2:1. If the cerium / carbon mass ratio is too large, the amount of cerium oxide is excessive, causing excessive cerium oxide to cover the catalyst, resulting in the electrochemically active noble metal alloy being covered, affecting the supply of reactant gases and proton transport. Therefore, the cerium / carbon mass ratio should preferably be less than 0.5:1. Therefore, in this embodiment of the invention, the cerium / carbon mass ratio is set to 0.2:1 to 0.5:1.

[0045] Furthermore, the pore volume defined in this embodiment refers to the volume of the pores within the carbon support, excluding the volume of interparticle packing. The pore volume is calculated using the adsorption branch of the nitrogen adsorption isotherm via the BJH method. If the pore volume is too small, it is not conducive to the loading of cerium oxide within the pores; therefore, the pore volume should not be less than 0.4 cm³. 3 / g; If the pore volume is too large, it will increase the risk of ionomers intruding into the pores, leading to catalyst poisoning and reduced activity. Therefore, the pore volume should not exceed 1 cm³. 3 / g. Therefore, in this embodiment of the invention, the pore volume of the porous carbon used for support is set to 0.4cm³. 3 / g~1cm 3 / g.

[0046] Furthermore, in this embodiment of the invention, the noble metal-based particles are not particularly limited as long as they can catalyze the hydrogen oxidation and oxygen reduction reactions. Examples of materials that can be used as noble metal-based particles include:

[0047] a. Noble metals (Pt, Pd, Rh, Ir, Au, Ag, Ru, Os, etc.), which can be one noble metal or an alloy of multiple noble metals;

[0048] b. Alloys containing precious metal elements and one or more non-precious metal elements (Fe, Co, Cr, V, Ti, Ni, etc.);

[0049] c. Noble metal oxynitrides.

[0050] The second aspect of this invention provides a method for preparing a cerium oxide-modified noble metal-based porous carbon catalyst, comprising the following steps:

[0051] The first step is to fully disperse the cerium source precursor and catalyst and impregnate them in porous carbon pores;

[0052] The second step involves reacting the cerium source inside and outside the pores of the porous carbon to generate cerium oxide, thus completing the loading process.

[0053] The third step involves separating and purifying the modified catalyst from the reaction solution to obtain a cerium oxide-modified noble metal-based porous carbon catalyst.

[0054] In some embodiments, the first step specifically involves: fully dissolving the cerium source precursor in a solvent, adding a noble metal-based porous carbon catalyst, stirring and dispersing it evenly, and maintaining a vacuum after replacing the inert gas.

[0055] Furthermore, the cerium source precursor in the first process is selected from substances that can generate cerium oxide through reaction, specifically at least one of cerium nitrate hexahydrate, cerium sulfate tetrahydrate, and cerium chloride.

[0056] Furthermore, the amount of cerium source used in the first step is calculated based on the mass of cerium element, and the mass ratio of cerium source to porous carbon is between 0.2:1 and 0.5:1. If the ratio is too low, the cerium / carbon mass ratio after loading will be too low, resulting in insufficient free radical capture capacity. Therefore, the ratio is preferably above 0.2:1. If the ratio is too high, the cerium / carbon mass ratio after loading will be too high, causing excessive cerium oxide to cover the catalyst, resulting in the electrochemically active noble metal alloy being covered, affecting the supply of reactant gases and the transport of protons. Therefore, the ratio is preferably below 0.5:1.

[0057] Furthermore, the solvent selected in the first step is capable of fully dissolving the cerium source precursor, facilitating subsequent catalyst dispersion, and achieving a set surface tension so that the precursor solution can fully wet the liquid system within the porous carbon pores. Specifically, at least one of water, ethanol, isopropanol, and n-butanol can be selected.

[0058] Furthermore, the combination and minimum amount of solvents in the first step should be sufficient to fully dissolve the cerium source precursor. The optimal combination and amount should be selected based on the type of cerium source. Preferably, the solvent combination and amount should ensure uniform dispersion of the catalyst system. Further preferably, the solution combination and amount should achieve a set surface tension to ensure sufficient wetting of the porous carbon pores by the precursor solution.

[0059] Furthermore, the inert gas used in the first step is used to reduce side reactions in the reaction system and to maintain an inert atmosphere for safety. Specifically, at least one of argon, helium, nitrogen, and carbon dioxide can be selected. Inert gas replacement is completed by evacuating the original gas atmosphere from the reaction system and then introducing inert gas for a certain period. The evacuation and inert gas introduction time is preferably 3-5 minutes, and the number of replacements is selected based on the optimal evacuation and gas replacement time.

[0060] Furthermore, the vacuum degree in the first step refers to the vacuum state in the sealed reaction system. If the vacuum degree is too high, the gas in the porous carbon cannot be discharged, and the cerium source precursor solution cannot completely wet the porous carbon, resulting in an excessively low proportion in the pores during subsequent loading processes. Therefore, the vacuum degree is preferably -0.1 MPa to -0.02 MPa.

[0061] In some embodiments, the second step (loading step) specifically involves: adding an alkaline solution dropwise under stirring conditions to adjust the pH, obtaining a mixed dispersion, and allowing the cerium source to react inside and outside the pores of the porous carbon for a certain period of time at a preset reaction temperature to generate cerium oxide, thereby completing the loading.

[0062] Furthermore, the alkaline solution used in the second step provides an alkaline reaction system, enabling the cerium source precursor to react and generate cerium oxide. The alkaline solution can be prepared from at least one of sodium hydroxide and potassium hydroxide. The amount of alkaline solution used is determined based on the actual volume of the reaction system, with the optimal amount chosen to ensure uniform dispersion after dropwise addition.

[0063] Furthermore, the pH value of the reaction system in the second step will affect the particle size of the cerium oxide produced by the reaction. The particle size of cerium oxide needs to be controlled so that it can be carried into the pores. The pH value is preferably 10 to 14.

[0064] Furthermore, the preset reaction temperature used in the second step affects the formation rate of cerium oxide. If the temperature is too high, the reaction rate is too fast, and the generated cerium oxide is prone to agglomeration, resulting in larger cerium oxide particle sizes, which is not conducive to its loading into the pores. Therefore, the preset reaction temperature should not be higher than 70℃. On the other hand, if the temperature is too low, the reaction cannot overcome the reaction energy barrier and cannot occur. Therefore, the preset reaction temperature should not be lower than 30℃. Thus, the preset reaction temperature used in the second step is preferably set to 30℃~70℃.

[0065] Furthermore, in the second step, if the reaction time is too short, it is difficult to completely generate cerium oxide; if the reaction time is too long, the economics of the synthesis method will be affected, and there may be a risk of side reactions. The specific reaction time should be selected based on the state of the reaction system, such as temperature, pH, and the concentration of materials in the reaction solution.

[0066] In some embodiments, the third step (post-processing step) specifically involves: filtering the product obtained in the second step, removing weakly durable ionic components, removing weakly durable nonionic components, and drying it to obtain a cerium oxide controllable modified noble metal porous carbon catalyst.

[0067] Furthermore, in the third step, the catalyst generated in the reaction is initially separated from the reaction solution by vacuum filtration. Optionally, the filter paper used for vacuum filtration is a nitrocellulose filter membrane, specifically model: Whatman7182-002, 0.2μm.

[0068] Furthermore, in the third step, the weakly durable ionic components refer to unreacted ionic substances on the catalyst surface and ionic substances generated during oxide formation. These ionic components do not contribute to durability and will, in subsequent fuel cell applications, undergo ion exchange with the sulfonic acid groups of the ionomer, reducing the ionic conductivity of the polymer. The removal of these weakly durable ionic components can be achieved using a combination of deionized water washing and vacuum filtration. The optimal process is selected based on the number of washes, the intensity of vacuum filtration, and the final treatment time, combined with the content of the weakly durable ionic components in the reaction system. The washing endpoint is when the filtrate is neutral. Whether the ionic substances have been completely removed can be detected by measuring the resistivity of the filtrate, i.e., the resistivity should be close to the resistivity of the deionized water used in the example (>18.3 MΩ·cm).

[0069] Furthermore, in the third step, the weakly durable nonionic component refers to cerium oxide adhering to the pores of the carbon support and easily detaching, as well as cerium oxide particles not adhering to the carbon support. This component dissolves during the durability process and migrates with the electric field, which is detrimental to the long-term durability effect. The removal of the nonionic component can be achieved through a combination of deionized water washing and vacuum filtration. An enhanced separation operation can be employed, applying mechanical vibration and stirring without damaging the catalyst particles, allowing the weakly durable nonionic component to detach from the catalyst and enter the filtrate. A suitable filter membrane pore size ensures that cerium oxide particles flow out with the filtrate without catalyst loss. The optimal process is selected based on the specific number of water washes, the intensity of vacuum filtration, the enhanced separation operation, and the final treatment time, combined with the content of the weakly durable nonionic component in the reaction system.

[0070] Furthermore, the drying process in the third step involves using a vacuum oven to remove the water adhering to the catalyst surface after washing. The drying temperature should be set within a suitable range. If the drying temperature is too high, side reactions caused by the temperature may affect the catalyst activity; therefore, the drying temperature should not exceed 100℃. If the drying temperature is too low, the water will be difficult to remove quickly; therefore, the drying temperature should not be lower than 60℃. The optimal drying time should be selected based on the drying temperature. To ensure safety and prevent catalyst ignition, a certain inert gas atmosphere (such as nitrogen) must be maintained during the pressure recovery process after drying.

[0071] The third aspect of this invention relates to the application of a cerium oxide-modified noble metal-based porous carbon catalyst in hydrogen fuel cells. The hydrogen fuel cells of this invention use at least the catalyst of this invention as the catalyst for the anode catalyst layer. The composition of the anode catalyst layer (e.g., platinum loading, type of ionomer, ionomer-to-carbon mass ratio (I / C ratio), etc.) is not particularly limited, and the optimal values ​​can be selected according to the application purpose. The structure outside the anode catalyst layer is also not particularly limited, and the optimal configuration can be selected according to the purpose. It should be noted that the catalyst involved in this invention can also be used as a catalyst on the cathode catalyst layer side.

[0072] A noble metal-based porous carbon catalyst was prepared by controllably modifying a cerium oxide layer to form an anode catalyst layer. This catalyst layer was then used to fabricate a hydrogen fuel cell. After endurance testing under idling conditions, the increase in hydrogen leakage current density of the proton exchange membrane and the increase in proton conduction resistance of the catalyst layer were reduced. This can be attributed to the following reasons: during endurance testing, the dissolution and migration of cerium ions affect the loss of its free radical elimination effect. Furthermore, the sulfonate ions of the perfluorosulfonic acid polymer exchange with the dissolved cerium ions, affecting proton conduction. By confining cerium oxide particles within the pore structure of the noble metal-based porous carbon catalyst, migration of cerium oxide particles is prevented and dissolution is slowed. Additionally, cerium oxide is adjacent to free radical generation sites, enabling real-time elimination of free radicals generated during the power generation reaction, further improving the stability and lifespan of the fuel cell.

[0073] The following describes specific embodiments and comparative examples of the present invention:

[0074] 1. Catalyst Preparation

[0075] 1.1 Example 1

[0076] 0.2 g of cerium nitrate hexahydrate was dissolved thoroughly in 50 mL of deionized water by stirring. 0.35 g of platinum-based porous carbon catalyst (platinum loading 50%) was added. The mixture was stirred continuously under these conditions to ensure uniform dispersion. The reaction system was sealed and evacuated for 3 min, then purged with nitrogen for 3 min, repeated three times. The vacuum was adjusted to -0.05 MPa and maintained throughout the reaction. While stirring, 1 mol / L sodium hydroxide solution was added dropwise to adjust the pH to 13, completing the addition within 30 min to obtain a mixed dispersion. The reaction system was heated to 50 °C and reacted for 30 min. After cooling to room temperature, the reaction mixture was filtered through a Whatman 7182-002 0.2 μm membrane to separate the catalyst from the reaction solution, and the final product was collected. For the removal of weakly durable ionic components, under continuous vacuum filtration (vacuum degree: -0.05 MPa), the sample was washed three times with deionized water. The filtrate was neutral, with a resistivity >18.3 MΩ·cm, and the filter residue was obtained. For the removal of weakly durable nonionic components, 50 mL of deionized water was added to the obtained filter residue, followed by ultrasonication for 10 min and mechanical stirring for 10 min to remove the weakly durable nonionic components from the catalyst into the water. Under continuous vacuum filtration (vacuum degree: -0.05 MPa), the sample was washed three times with deionized water to complete the treatment steps. The sample was then dried in a vacuum oven at 60 °C for 24 h under a nitrogen atmosphere to obtain a cerium oxide-modified platinum-based porous carbon catalyst.

[0077] 1.2, Example 2

[0078] The difference between this embodiment and Example 1 is that the carbon catalyst used is a platinum-based solid carbon catalyst. The rest are the same as in Example 1, and will not be repeated here.

[0079] 1.3 Comparative Example 1

[0080] Platinum-based porous carbon catalysts without cerium oxide support were used directly for the preparation of fuel cell membrane electrodes, with a platinum loading of 50%.

[0081] 2. Preparation of fuel cells

[0082] 2.1 Example 3

[0083] The preparation of the fuel cell in this embodiment includes the following steps:

[0084] Step 1: Preparation of the catalyst layer

[0085] The anode-side catalyst layer was prepared using the catalyst prepared in Example 1. The ionomer was a commercially available 25% Aquivion solution from Solvay (a perfluorosulfonic acid PFSA ionomer dispersion, trade name: D79-25BS, with an ion exchange equivalent of 790 g / mol); the solvent was a mixture of water and isopropanol at a water-to-alcohol mass ratio of 1.3:1; the slurry solid content was 10%; and the I / C ratio (mass ratio of ion exchange resin to catalyst in the catalyst layer) was set to 1. After uniform dispersion by mechanical stirring, the anode slurry was obtained. A commercially available platinum-cobalt catalyst from TKK (trade name 36E52, platinum loading 46%) was used as the cathode catalyst. The ionomer, solvent, and water-to-alcohol ratio were consistent with the anode slurry; the slurry solid content was 15%; and the I / C ratio was set to 1.1. A doctor blade coating process was used, controlling the wet film thickness by controlling the doctor blade spacing. After drying, the catalyst layer was prepared. The platinum loading of the anode-side catalyst layer was 0.03 mg / cm³. 2 The platinum-cobalt loading of the cathode-side catalyst layer is 0.18 mg / cm³. 2 .

[0086] Step 2, Membrane Electrode Assembly

[0087] The proton exchange membrane used was a 10μm membrane produced by Shandong Dongyue Group. The anode-side catalyst layer and the cathode-side catalyst layer prepared in step 1 were transferred onto both sides of the proton exchange membrane. The gas diffusion layer, the gold-plated current collector, and the graphite parallel flow field plate (using channels and ribs with a width and depth of 0.4mm) were assembled in sequence to complete the preparation of a single cell of fuel cell. The tested activity range was 1cm×2cm.

[0088] 2.2, Example 4

[0089] The difference between this embodiment and Example 3 is that the anode-side catalyst layer in this embodiment is made using the catalyst prepared in Example 2. The rest of this embodiment is the same as that in Example 3, and will not be repeated here.

[0090] 2.3 Comparative Example 2

[0091] The difference between this comparative example and Example 3 is that, in preparing the anode-side catalyst layer slurry using the catalyst obtained in Comparative Example 1, a cerium oxide dispersion (20% by mass of cerium oxide) was added in addition to the catalyst, and the mass ratio of the dispersion to the added catalyst was 1:1. All other aspects are consistent with Example 3 and will not be repeated here.

[0092] 2.4 Comparative Example 3

[0093] The difference between this comparative example and Example 1 is that the anode-side catalyst layer in this comparative example was prepared using the catalyst prepared in Comparative Example 1. The rest of this comparative example is the same as that in Example 3, and will not be repeated here.

[0094] 3. Validation of the embodiments of the present invention:

[0095] 3.1 First, the characterization and testing methods used in this invention will be described:

[0096] 3.1.1 The characterization and testing methods used for the prepared catalyst are as follows:

[0097] 1) Element mass percentage

[0098] The X-ray photoelectron spectroscopy (XPS) of the supported catalyst was measured, and the mass percentage of each element was quantified based on the spectrum integration.

[0099] 2) Pore size, pore volume, and BET specific surface area

[0100] Nitrogen adsorption isotherms of the catalyst before and after loading were measured, and the pore size, pore volume and BET specific surface area were calculated based on the obtained nitrogen adsorption isotherms.

[0101] 3) Load-bearing ratio inside the borehole

[0102] The loading ratio inside the pores can be obtained by using elemental surface scanning in transmission mode of a scanning transmission microscope to obtain the amount of cerium, and then using elemental surface scanning in secondary mode to obtain the amount of cerium outside the pores, thus obtaining the distribution ratio of cerium oxide inside and outside the pores.

[0103] 3.1.2 The characterization and testing methods used for the prepared fuel cell are as follows:

[0104] 1) Durability test

[0105] Idle operating condition durability testing was conducted according to DOE recommended procedures. The system operated under constant open-circuit conditions with the following parameters: hydrogen atmosphere at 1 L / min at the anode, air atmosphere at the cathode at 1 L / min, single-cell temperature of 90°C, humidified anode and cathode atmospheres at 30% RH (relative humidity), anode back pressure of 150 kPa (gauge pressure), and cathode back pressure of 100 kPa (gauge pressure).

[0106] The initial membrane electrode sample was subjected to constant open-circuit conditions for 45 hours as one cycle. After each cycle, power generation performance, hydrogen leakage current density, and catalyst layer proton conductivity were tested to comprehensively evaluate the degradation of the membrane electrode during the durability test. During the durability test, the open-circuit potential variation was continuously monitored.

[0107] 2) Hydrogen leakage current density test

[0108] The leakage hydrogen current density was measured from open circuit to 0.6V using a linear voltammetric scan method at a scan rate of 20mV / s. The test conditions were as follows: the anode was in a hydrogen atmosphere with a flow rate of 0.07L / min, the cathode was in a nitrogen atmosphere with a flow rate of 0.166L / min, the single cell temperature was 80℃, both anode and cathode gas atmospheres were humidified with 90%RH, and the back pressure was 0 (gauge pressure).

[0109] 3) Proton conduction resistance test

[0110] At 0.45V, the constant potential impedance spectrum was measured with a voltage excitation of 10mV and a measurement frequency range of 100kHz to 500mHz. The test conditions were as follows: the anode was in a hydrogen atmosphere with a flow rate of 0.07L / min, the cathode was in a nitrogen atmosphere with a flow rate of 0.166L / min, the single cell temperature was 80℃, the anode and cathode gas atmospheres were both humidified with 90%RH, and the back pressure was 0 (gauge pressure).

[0111] 4) Power generation performance

[0112] The voltage values ​​at different current points were measured in constant current mode to evaluate the power generation performance of the fuel cell. Test conditions: anode atmosphere was hydrogen, flow rate 1 L / min; cathode atmosphere was air, flow rate 2 L / min; single cell temperature was 80℃; both anode and cathode atmospheres were humidified at 90% RH; back pressure was 70 kPa (gauge pressure).

[0113] 3.2 The embodiments and comparative examples of the present invention were tested according to the characterization test methods described in 3.1. The test results are as follows:

[0114] 3.2.1 Regarding the prepared catalyst

[0115] 1) Element mass percentage

[0116] Figure 1 XPS images of Examples 1 and 2 used to prepare the anode-side catalyst layer are shown. The mass percentages of each element were calculated from the XPS images. Figure 1 Figures a and b in the figure show the full spectrum result and the detailed spectrum of Ce element in Example 1, respectively. Figure 1 Figures c and d in the figure show the full spectrum result and the fine spectrum of Ce element, respectively, of Example 2. Figure 1 The following information is known:

[0117] (1) Both Example 1 and Example 2 contained cerium after loading, indicating that cerium oxide was successfully loaded.

[0118] (2) The platinum-to-carbon mass ratio in Example 1 was 0.93:1, and the cerium-to-carbon mass ratio was 0.35:1;

[0119] (3) The platinum-carbon mass ratio in Example 2 was 1.06:1, and the cerium-carbon mass ratio was 0.33:1.

[0120] 2) Pore size, pore volume, and BET specific surface area

[0121] Figure 2 The image shows nitrogen isothermal adsorption-desorption images before and after loading in Example 1 for the preparation of the anode catalyst layer, along with pore size, pore volume, and BET specific surface area. The following can be observed:

[0122] (1) The BET specific surface area before loading in Example 1 was 318.99 m². 2 / g, the BET specific surface area after loading is reduced to 293.14m². 2 / g, this is because cerium oxide adheres to the catalyst, reducing the BET specific surface area;

[0123] (2) The pore size after loading in Example 1 decreased from 9.88 nm to 9.64 nm, indicating that cerium oxide was also partially loaded in the pores;

[0124] (3) The pore volume of the sample after loading in Example 1 increased from 0.54 m³. 3 / g reduced to 0.45m 3 / g, further illustrating the distribution of cerium oxide within the pores.

[0125] 3.2.2 Applications of fuel cells

[0126] 1) Durability test

[0127] Figure 3 The decay rate of open-circuit potential before and after durability testing is shown in Examples 3 and 4, and Comparative Examples 2 and 3. The following can be observed:

[0128] (1) According to the decay rate, the lower the decay rate, the better the durability effect. Example 3 is the best, followed by Example 4, then Comparative Example 2, and Comparative Example 3 is the worst.

[0129] (2) All samples with cerium oxide support have a certain durability improvement effect, and the durability improvement effect is the best when cerium oxide is supported in the pore.

[0130] 2) Hydrogen leakage current density test

[0131] Figure 4 The following can be observed by showing the changes in hydrogen leakage current density at the beginning and end of the durability test for Examples 3 and 4, and Comparative Examples 2 and 3:

[0132] (1) At the durability starting point, the hydrogen leakage current density of each sample is similar, indicating that the addition of cerium oxide has no significant effect on the initial hydrogen leakage current density of the proton exchange membrane.

[0133] (2) Durability endpoint: The less the change percentage, the better the durability effect. Example 3 is the best, followed by Example 4, then Comparative Example 2, and Comparative Example 3 is the worst. This shows that all samples with cerium oxide support have a certain durability improvement effect, and the durability improvement effect of cerium oxide support in the pore is the best.

[0134] 3) Proton conduction resistance test

[0135] Figure 5 The changes in proton conduction resistance of the catalyst layer at the durability start and end points are shown in Examples 3 and 4, and Comparative Examples 2 and 3. The following can be observed:

[0136] (1) Durability starting point: the proton conduction resistance of the catalyst layer of each sample is similar; indicating that the addition of cerium oxide did not affect the proton conduction ability of the catalyst layer.

[0137] (2) Durability endpoint, proton conduction resistance of catalyst layer, evaluated according to the percentage change, the smaller the increase value, the less the proton conduction capacity deteriorates. Comparative Example 3 is the best, followed by Example 3, then Comparative Example 2, and Example 4 is the worst. This shows that samples with cerium oxide support will have a certain impact on proton conduction capacity. However, cerium oxide support in the pores helps to reduce the dissolution and migration of cerium oxide and reduce the poisoning of ionomers.

[0138] 4) Power generation performance test

[0139] Figure 6 The polarization curves of Examples 3 and 4, and Comparative Examples 2 and 3, are shown to show the changes at the beginning and end of the durability test. 1A / cm is extracted. 2 The voltage values ​​are summarized in Figure 7 From this, we can know the following:

[0140] (1) Durability starting point, each sample at 1A / cm 2 The voltage values ​​are close to those of the fuel cell, indicating that the addition of cerium oxide did not cause a serious deterioration in the performance of the fuel cell.

[0141] (2) Durability endpoint: for each sample at 1A / cm 2 The voltage values ​​were evaluated according to the percentage change. The smaller the decrease, the better the durability effect. Example 3 was the best, followed by Comparative Example 2, then Example 4, and Comparative Example 3 was the worst. This shows that all samples with cerium oxide support have a certain durability improvement effect, and the durability improvement effect is the best when cerium oxide is supported in the pore.

[0142] In summary, this invention enables the controllable proportion of cerium oxide particles to be confined within the pore structure of a noble metal-based porous carbon catalyst, thereby preventing the migration of cerium oxide particles and slowing down dissolution. Furthermore, since cerium oxide is located close to free radical generation sites, it can eliminate free radicals generated during power generation in real time, effectively improving the stability and lifespan of fuel cells.

[0143] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

Claims

1. A cerium oxide-modified noble metal-based porous carbon catalyst for hydrogen fuel cells, characterized in that, Cerium oxide particles are supported both inside and outside the pores of the porous carbon catalyst. The amount of cerium oxide particles supported inside the pores is not less than 40% of the total cerium oxide particle loading in the porous carbon catalyst. The cerium / carbon mass ratio of the porous carbon catalyst is 0.2:1 to 0.5:1, and the pore volume of the porous carbon used for support is 0.4 cm³. 3 / g~1 cm 3 / g; The preparation steps of the porous carbon catalyst include: The first step is to fully disperse the cerium source precursor and the noble metal-based porous carbon catalyst and impregnate them in the porous carbon pores. The second step involves reacting the cerium source inside and outside the pores of the porous carbon to generate cerium oxide, thus completing the loading process. The third step involves separating and purifying the modified catalyst from the reaction solution to obtain the cerium oxide-modified noble metal-based porous carbon catalyst. The impregnation process in the first step is carried out in an inert atmosphere and the set vacuum level is maintained. The vacuum level is set between -0.1 MPa and -0.02 MPa; The second step includes: adding an alkaline solution dropwise under stirring conditions to adjust the pH, obtaining a mixed dispersion, and reacting the cerium source inside and outside the pores of the porous carbon at a preset reaction temperature to generate cerium oxide, thus completing the loading; pH should be controlled between 10 and 14; The preset reaction temperature is set to 30℃~70℃.

2. The porous carbon catalyst according to claim 1, characterized in that, The materials used for noble metal-based particles can be any of the following: An alloy of any one or more precious metals; An alloy containing a precious metal element and at least one non-precious metal element; Noble metal oxynitrides.

3. A method for preparing the porous carbon catalyst according to claim 1 or 2, characterized in that, include: The first step is to fully disperse the cerium source precursor and the noble metal-based porous carbon catalyst and impregnate them in the porous carbon pores. The second step involves reacting the cerium source inside and outside the pores of the porous carbon to generate cerium oxide, thus completing the loading process. The third step involves separating and purifying the modified catalyst from the reaction solution to obtain the cerium oxide-modified noble metal-based porous carbon catalyst. The impregnation process in the first step is carried out in an inert atmosphere and the set vacuum level is maintained. The vacuum level is set between -0.1 MPa and -0.02 MPa; The second step specifically includes: adding an alkaline solution dropwise under stirring conditions to adjust the pH, obtaining a mixed dispersion, and reacting the cerium source inside and outside the pores of the porous carbon at a preset reaction temperature to generate cerium oxide, thus completing the loading; pH should be controlled between 10 and 14; The preset reaction temperature is set to 30℃~70℃.

4. The preparation method according to claim 3, characterized in that, The third step specifically includes: filtering the product obtained in the second step, removing weakly durable ionic components, removing weakly durable nonionic components, and drying it to obtain the cerium oxide controllable modified noble metal porous carbon catalyst. The weakly durable ionic components are unreacted ionic substances on the catalyst surface and ionic substances generated during the oxide formation process. The weakly durable nonionic component consists of cerium oxide that is attached to the outside of the porous carbon pores and is easily detached, and cerium oxide particles that are not attached to the porous carbon.

5. The preparation method according to claim 4, characterized in that, Both the removal of weakly durable ionic components and the removal of weakly durable nonionic components employ a combination of deionized water washing and vacuum filtration.

6. A hydrogen fuel cell, characterized in that, The hydrogen fuel cell includes an electrode catalyst layer, which comprises a porous carbon catalyst according to claim 1 or 2 and / or a porous carbon catalyst prepared by any one of claims 3 to 5.

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