A low-load Rh-based fuel cell anode catalyst, its preparation method and application

Abstract

This invention discloses a low-load Rh-based fuel cell anode catalyst, its preparation method, and its application, belonging to the field of battery anode material technology. The preparation method of the low-load Rh-based fuel cell anode catalyst includes the following steps: mixing 2-methylimidazole with methanol to obtain solution A; mixing Zn(NO3)2·6H2O with methanol to obtain solution B; adding solution A to solution B to obtain a mixed solution; a first heat treatment to obtain a reaction precipitate; washing with methanol; a first vacuum drying treatment to obtain ZIF-8; and a second heat treatment to obtain NC. 950 The mixture was mixed with deionized water to obtain a suspension; an aqueous RhCl3 solution was added dropwise to the suspension for adsorption treatment, followed by a second vacuum drying treatment and heat treatment to obtain a low-load Rh-based fuel cell anode catalyst. The catalyst prepared by this invention exhibits higher HOR activity and stability than commercial Pt / C catalysts under alkaline conditions, and also has cost advantages and potential for large-scale synthesis.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material technology, and particularly relates to a low-load Rh-based fuel cell anode catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen possesses advantages such as high calorific value, high energy density, and zero pollution from combustion products, making it an effective alternative to fossil fuels and the ideal environmentally friendly energy carrier for preventing climate change and meeting the ever-growing global energy demand. Fuel cells, electrochemical devices that convert the chemical energy of hydrogen into electrical energy, are considered a key driver of hydrogen technology.

[0003] Currently, proton exchange membrane fuel cells (PEMFCs) are the most widely used type of fuel cell, used in applications such as stationary fuel cells and fuel cell electric vehicles. PEMFC technology is based on rapid oxygen reduction (ORR) and hydrogen oxidation (HOR) reactions catalyzed by noble metal catalysts, such as platinum (Pt) coupled to a proton exchange membrane (PEM), exhibiting fast reaction kinetics and good durability. However, in terms of commercialization, PEMFC technology remains constrained by high cost. The proton exchange membranes and ionomers used in PEMFCs necessitate their use in acidic environments, which are generally corrosive to the materials. Therefore, it is essential to use noble metal catalysts stable under acidic conditions, perfluorinated ionomers, and acid-resistant bipolar plates.

[0004] In contrast, anion exchange membrane fuel cells (AEMFCs) show promise as an economical alternative to PEMFCs because they can utilize non-precious metal (NPM) catalysts, hydrocarbon membranes, and inexpensive metal bipolar plates, significantly reducing fuel cell costs. Current research indicates that using non-precious metal catalysts at the cathode of AEMFCs can achieve excellent ORR catalytic performance. However, the HOR process at the anode remains heavily reliant on platinum group metal (PGM) catalysts, as the activity and stability of NPM catalysts still lag significantly behind commercially available Pt / C catalysts. In particular, the HOR kinetics of PGM catalysts under alkaline conditions are slow, with reaction rates often 2-3 orders of magnitude lower than under acidic conditions (the reason for this phenomenon is currently unclear, but some studies suggest it may be related to the variation of the hydrogen binding energy of PGMs with ambient pH).

[0005] Therefore, it is of great significance to design anode catalysts that can maintain high activity and stability under alkaline conditions. Furthermore, the PGM content of AEMFC anode catalysts should be as low as possible to further reduce their actual operating costs. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a low-load Rh-based fuel cell anode catalyst, its preparation method, and its application. Under alkaline conditions, it exhibits higher HOR activity and stability than commercial Pt / C catalysts, and also has cost advantages and the potential for large-scale synthesis.

[0007] To achieve the above objectives, the present invention provides a method for preparing a low-load Rh-based fuel cell anode catalyst, comprising the following steps:

[0008] (1) 2-Methylimidazole is mixed with methanol to obtain solution A; Zn(NO3)2·6H2O is mixed with methanol to obtain solution B;

[0009] (2) Add solution A obtained in step (1) to solution B obtained in step (1), stir, and obtain a mixed solution;

[0010] (3) Place the mixed solution described in step (2) into a stainless steel high-pressure reactor lined with polytetrafluoroethylene, perform a first heating treatment, centrifuge, and obtain the reaction precipitate;

[0011] (4) The reaction precipitate described in step (3) was washed three times with methanol and then subjected to vacuum drying to obtain ZIF-8.

[0012] (5) The ZIF-8 grinding described in step (4) is subjected to a second heating treatment in a N2 atmosphere and then naturally cooled to obtain NC. 950 ;

[0013] (6) The NC described in step (5) 950 Mix with deionized water and sonicate to obtain a suspension;

[0014] (7) While continuously stirring, add the RhCl3 aqueous solution to the suspension in step (6) for adsorption treatment, collect the black solid, perform a second vacuum drying treatment, and heat treatment in an H2 / Ar mixed atmosphere to obtain a low-load Rh-based fuel cell anode catalyst.

[0015] Preferably, the ratio of 2-methylimidazole to methanol in step (1) is 0.616 g: 15 mL; the ratio of Zn(NO3)2·6H2O to methanol in step (1) is 0.488 g: 30 mL.

[0016] Preferably, the stirring temperature in step (2) is 25°C, the stirring speed is 600 rpm, and the stirring time is 30 min.

[0017] Preferably, in step (3), the temperature of the first heating treatment is 120°C and the time of the first heating treatment is 4 hours; in step (3), the temperature of the centrifugation is 25°C, the speed of the centrifugation is 9000 rpm, and the time of the centrifugation is 5 minutes.

[0018] Preferably, in step (4), the temperature of the first vacuum drying treatment is 60°C, the time of the first vacuum drying treatment is 12h, and the vacuum degree of the first vacuum drying treatment is 0.08MPa.

[0019] Preferably, the particle size requirement for grinding in step (5) is 400 mesh; the second heating treatment in step (5) specifically involves heating to 950°C at a heating rate of 5°C / min, and then continuing to heat at 950°C for 2 hours.

[0020] Preferably, the NC in step (6) 950 The ratio of the ultrasonic treatment to deionized water is 50 mg: 4 mL; the ultrasonic treatment temperature in step (6) is 25 °C, the ultrasonic treatment frequency is 40 kHz, the ultrasonic treatment power is 300 W, and the ultrasonic treatment time is 10 min.

[0021] Preferably, the concentration of the RhCl3 aqueous solution in step (7) is 2.5 mg / mL, and the amount of the RhCl3 aqueous solution used is 1 mL; the adsorption treatment temperature in step (7) is 25°C, and the adsorption treatment time is 24 h; the second vacuum drying treatment temperature in step (7) is 60°C, the second vacuum drying treatment time is 24 h, and the vacuum degree of the second vacuum drying is 0.08 MPa; the volume content of H2 in the H2 / Ar mixed atmosphere in step (7) is 7%; the heat treatment temperature in step (7) is 200°C, and the heat treatment time is 2 h.

[0022] The present invention also provides a low-load Rh-based fuel cell anode catalyst prepared by the aforementioned preparation method.

[0023] The present invention also provides the application of the low-load Rh-based fuel cell anode catalyst or the low-load Rh-based fuel cell anode catalyst prepared by the preparation method in the preparation of anion exchange membrane fuel cells.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] 1) This invention uses a simple adsorption-thermal reduction process to uniformly load Rh single atoms and ultra-small Rh nanoparticles onto nitrogen-doped porous carbon. The synthesis process is simple, and the carbon support used is inexpensive and readily available, which can be further mass-produced.

[0026] 2) The low-load Rh-based fuel cell anode catalyst (Rh N / S-NC) prepared by this invention uses extremely low amounts of precious metals, with an Rh mass content of only 0.45 wt%. Furthermore, it exhibits excellent catalytic activity in the alkaline HOR conversion process, with a kinetic current density as high as 10.48 mA / cm².-2 It has 2.3 times the strength of commercial Pt / C, while also exhibiting excellent cycle durability and long-term stability.

[0027] 3) The Rh N / S-NC prepared in this invention was used as an anode catalyst in an actual AEMFC testing system, with a concentration of only 0.02 mg. Rh cm -2 Under precious metal loading conditions, applying a normal 0.65V battery operating voltage provides 0.62A cm⁻¹. -2 The fuel cell system exhibits high current density and peak power density, particularly after normalizing the PPD value to the amount of precious metal in the anode, demonstrating a mass activity as high as 25.7 W mg. PGM -1 It is superior to most AEMFC anode catalysts currently studied and has the potential to reduce the amount of precious metals used and the operating cost of AEMFC. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the preparation process of RhN / S-NC of the present invention;

[0030] Figure 2 ZIF-8 and NC prepared for this invention 950 Transmission electron microscope (TEM) images of RhN / S-NC, where a is a TEM image of ZIF-8 with a scale bar of 100 nm, and b is a TEM image of NC. 950 Transmission electron microscope image of , scale bar is 50 nm; c is transmission electron microscope image of Rh N / S-NC, scale bar is 50 nm.

[0031] Figure 3 The image shows the energy-scattered X-ray elemental mapping distribution of RhN / S-NC prepared in this invention, where a is a high-angle annular dark-field scanning transmission electron microscope image of the selected region with a scale bar of 200 nm, b is the Rh elemental distribution, c is the C elemental distribution, and d is the N elemental distribution.

[0032] Figure 4 The images are high-angle annular dark-field scanning transmission electron microscope images of the RhN / S-NC prepared in this invention with aberration correction, where a is the image under a 20 nm scale, b is the image under a 10 nm scale, and c is the image under a 5 nm scale.

[0033] Figure 5 The images shown are transmission electron microscope (TEM) images of RhNP-NC prepared in Comparative Example 1. In the images, a is a TEM image of RhNP-NC with a scale bar of 50 nm, b is a high-angle annular dark-field scanning TEM image of RhNP-NC with a scale bar of 50 nm, and c is a further magnified atomic-resolution scanning TEM image with a scale bar of 2 nm.

[0034] Figure 6 The energy-scattered X-ray elemental mapping distribution of RhNP-NC prepared for Comparative Example 1 is shown in a. a. high-angle annular dark-field scanning transmission electron microscope image of the selected region, with a scale bar of 200 nm; b. Rh elemental distribution; c. C elemental distribution; d. N elemental distribution.

[0035] Figure 7 The images shown are transmission electron microscope (TEM) images of Rh SA-NC prepared in Comparative Example 2. In the images, a is a TEM image of Rh SA-NC with a scale bar of 50 nm, b is a high-angle annular dark-field scanning TEM image of Rh SA-NC with a scale bar of 50 nm, and c is a further magnified atomic-resolution scanning TEM image with a scale bar of 2 nm.

[0036] Figure 8 The energy-scattered X-ray elemental mapping distribution of Rh SA-NC prepared for Comparative Example 2 is shown in the figure. In the figure, a is the high-angle annular dark-field scanning transmission electron microscope image of the selected region with a scale bar of 200 nm, b is the Rh elemental distribution, c is the C elemental distribution, and d is the N elemental distribution.

[0037] Figure 9 The RhN / S-NC prepared for this invention, the Rh NP-NC prepared in Comparative Example 1, and the Rh SA-NC and NC prepared in Comparative Example 2 are all included. 950 X-ray diffraction pattern;

[0038] Figure 10 The high-resolution XPS spectra of Rh 3d and N1s of the Rh N / S-NC prepared in this invention, the Rh NP-NC prepared in Comparative Example 1, and the RhSA-NC prepared in Comparative Example 2 are shown, where a is the high-resolution XPS spectrum of Rh 3d and b is the high-resolution XPS spectrum of N1s.

[0039] Figure 11The following are fine structure analysis diagrams of Rh K-edge X-ray absorption, where a is the absorption edge energy diagram, b is the Fourier transform extended X-ray absorption fine structure spectrum, c is the R-space EXAFS curve of Rh N / S-NC prepared in this invention, d is the R-space EXAFS curve of Rh SA-NC prepared in Comparative Example 2, e is the K-space EXAFS curve of Rh N / S-NC prepared in this invention, and f is the K-space EXAFS curve of Rh SA-NC prepared in Comparative Example 2.

[0040] Figure 12 The HOR polarization curve is shown in a 0.1M KOH solution saturated with H2 at a rotation speed of 1600 rpm.

[0041] Figure 13 Fit the HOR Tafel plot of the dynamic current density to the Butler-Volmer equation;

[0042] Figure 14 HOR polarization curves of RhN / S-NC prepared by this invention at different rotation speeds;

[0043] Figure 15 The Koutecky-Levich fitting plot shows the relationship between the overpotential of 50mV and the overpotential of 50mV.

[0044] Figure 16 The linear fitting curve for the micro-polarization region;

[0045] Figure 17 The HOR polarization curves of the RhN / S-NC prepared in this invention before and after 2000 CV cycles in H2-saturated 0.1M KOH;

[0046] Figure 18 After 2000 CV cycles, the j of the Rh N / S-NC prepared in this invention g@50mV j k Histogram of j0 changes;

[0047] Figure 19 The current-time chronocurrent response graph is shown for a 0.1M KOH solution saturated with H2 at 0.05V (vs. RHE).

[0048] Figure 20 The polarization and power density curves of the AEMFC prepared by this invention as the battery anode catalyst under H2 / O2 inlet conditions are compared with the PGM utilization of different anode catalysts. In the figure, a is the polarization and power density curve under H2 / O2 inlet conditions, and b is the comparison of PGM utilization of different anode catalysts. Detailed Implementation

[0049] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0050] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0051] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0052] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0053] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0054] The experimental materials used in this invention were sourced as follows: 2-methylimidazole was purchased from Shanghai Mairui Chemical Technology Co., Ltd.; methanol was purchased from Beijing Tongguang Fine Chemical Co., Ltd.; Zn(NO3)2·6H2O was purchased from Xilong Scientific Co., Ltd.; a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene was purchased from Beijing Yalunda Machinery Equipment Co., Ltd., model KH-100; a tubular electric heating furnace was purchased from Tianjin Zhonghuan Electric Furnace Co., Ltd., model SK-G06123K; RhCl3 was purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd.; PVP-40 was purchased from Shanghai Yuanye Biotechnology Co., Ltd.; NaOH was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; anhydrous ethanol was purchased from Beijing Tongguang Fine Chemical Co., Ltd.; rhodium acetylacetone was purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd.; and DMF was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0055] Example 1

[0056] (1) 0.616g of 2-methylimidazole (2-MIM) was mixed with 15mL of methanol and stirred until completely dissolved to obtain solution A; 0.488g of Zn(NO3)2·6H2O was mixed with 30mL of methanol and stirred until completely dissolved to obtain solution B;

[0057] (2) Quickly add solution A to solution B, stir at 25°C and 600 rpm for 30 min to obtain a mixed solution;

[0058] (3) Place the mixed solution in a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, heat it at 120℃ for 4 hours, and centrifuge at 25℃ and 9000rpm for 5 minutes to obtain the reaction precipitate.

[0059] (4) The reaction precipitate was washed three times with methanol, dried under vacuum of 0.08 MPa and 60°C for 12 hours to obtain ZIF-8.

[0060] (5) ZIF-8 powder was ground to 400 mesh and transferred to a ceramic boat, which was then placed in a tubular electric heating furnace for a second heating treatment in a flowing N2 atmosphere. The second heating treatment specifically involved heating to 950°C at a heating rate of 5°C / min, followed by continuous heating at 950°C for 2 hours. After natural cooling, the black powder was collected to obtain NC. 950 ;

[0061] (6) 50mg NC 950 Dispersed in 4 mL of deionized water, and ultrasonically treated with parameters of 25℃, 40kHz, 300W, and 10 min to obtain a suspension.

[0062] (7) Under continuous stirring, 1 mL of a 2.5 mg / mL RhCl3 aqueous solution was added dropwise to the suspension. Adsorption treatment was performed at 25°C for 24 h. The black solid was collected and dried under a second vacuum of 0.08 MPa at 60°C for 24 h. The black solid after the second vacuum drying was then placed in a ceramic boat and placed in a tubular electric heating furnace. Heat treatment was performed at 200°C for 2 h in an H2 / Ar mixed atmosphere (H2 volume content 7%) to obtain the low-load Rh-based fuel cell anode catalyst, RhN / S-NC. Figure 1 The diagram shown is a schematic of the preparation process of RhN / S-NC.

[0063] Comparative Example 1

[0064] 0.616g of 2-methylimidazole (2-MIM) was mixed with 15mL of methanol and stirred until completely dissolved to obtain solution A; 0.488g of Zn(NO3)2·6H2O was mixed with 30mL of methanol and stirred until completely dissolved to obtain solution B; solution A was quickly added to solution B and stirred at 25℃ and 600rpm for 30min to obtain a mixed solution; (3) the mixed solution was placed in a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and subjected to a first heat treatment at 120℃ for 4h, followed by a second heat treatment at 25℃. Centrifuge at 9000 rpm for 5 min to obtain the reaction precipitate; wash the precipitate three times with methanol, and perform a first vacuum drying treatment at 60℃ for 12 h under a vacuum of 0.08 MPa to obtain ZIF-8; grind ZIF-8 into 400 mesh powder, transfer it to a ceramic boat, place it in a tubular electric heating furnace, and perform a second heating treatment in a flowing N2 atmosphere. The second heating treatment specifically involves heating to 950℃ at a heating rate of 5℃ / min, and then maintaining the temperature at 950℃ for 2 h. After natural cooling, collect the black powder to obtain NC. 950 ;

[0065] In beaker A, 0.229 g of PVP-40 was dissolved in 22.5 mL of deionized water, and 2.5 mL of RhCl3 aqueous solution (20 mM) was added to the PVP-40 aqueous solution. In beaker B, 2.08 g of NaOH and 4 mL of anhydrous ethanol were dissolved in 22.5 mL of water, stirred until homogeneous, and then poured into beaker A, with continuous stirring. Subsequently, the Rh nanoparticles (black solid, denoted as RhNPs) were collected by centrifugation and washed three times with water. The washed RhNPs and 50 mg of NC were then... 950 Disperse the mixture evenly in 5 mL of deionized water and stir until the liquid is completely evaporated. After drying overnight under a vacuum of 0.08 MPa and a temperature of 60 °C, collect RhNP-NC.

[0066] Comparative Example 2

[0067] 0.55 g Zn(NO3)2·6H2O and 60 mg rhodium acetylacetonate were dissolved in 30 mL methanol. Simultaneously, 0.66 g 2-methylimidazole was dissolved in 15 mL methanol. The two solutions were mixed and stirred continuously for 30 min, then poured into a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 120 °C for 4 h. After cooling, a light yellow precipitate was obtained by centrifugation and washed three times with methanol and DMF, respectively. The light yellow solid was dried under a vacuum of 0.08 MPa at 60 °C, placed in a ceramic boat, and then heated to 900 °C in a tube furnace under N2 atmosphere at a heating rate of 5 °C / min and held for 3 h. After cooling, RhSA-NC was collected.

[0068] Experimental Example 1

[0069] ZIF-8 and NC prepared in Example 1 were observed under a transmission electron microscope (TEM). 950 The distribution of Rh, C, and N on the material surface was observed using energy-scattered X-rays (EDX) and Rh N / S-NC, and the sample surface was observed under aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC HAADF-STEM).

[0070] like Figure 2 a, Figure 2 b and Figure 2 As shown in c, Rh N / S-NC ( Figure 2 As shown in c), it maintains the relationship with NC. 950 ( Figure 2 (as shown in b) and ZIF-8 ( Figure 2 The same dodecahedral framework structure as shown in Figure a).

[0071] like Figure 3 a, Figure 3 b, Figure 3 c and Figure 3 As shown in Figure d, the energy-scattered X-ray elemental mapping image shows that Rh, C, and N are uniformly dispersed on the surface of the RhN / S-NC material.

[0072] like Figure 4 a, Figure 4 b, Figure 4 As shown in Figure c, under aberration-corrected high-angle annular dark-field scanning transmission electron microscope, ultra-small Rh nanoparticles can be observed on the surface of the Rh N / S-NC sample. The particle size distribution is relatively uniform, with an average diameter (AD) of only 2.03 nm. Upon further magnification, isolated Rh single atoms are dispersed within a similar spatial distance around the Rh nanoparticles (corresponding to the 0.22 nm lattice fringes of the Rh(111) crystal plane), as shown by the highlighted dashed circles.

[0073] The Rh NP-NC prepared in Comparative Example 1 and the Rh SA-NC prepared in Comparative Example 2 were observed under a transmission electron microscope (TEM). The elemental distribution on the material surface was observed using energy-scattered X-rays (EDX). The sample surface was observed under an aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC HAADF-STEM).

[0074] like Figure 5 a, Figure 5 b and Figure 5 As shown in c, Figure 6 a, Figure 6 b, Figure 6 c and Figure 6 As shown in Figure d, the Rh NPs prepared in Comparative Example 1 are easily annealed in NC.950 While some aggregation occurs on the surface, a distribution of Rh nanoparticles around 2 nm is still visible; similarly, a lattice with a width of 0.22 nm was measured, corresponding to the (111) crystal plane of Rh. Rh SA-NC prepared using a typical host-guest strategy, such as... Figure 7 a, Figure 7 b and Figure 7 As shown in c, Figure 8 a, Figure 8 b, Figure 8 c and Figure 8 As shown in d, the results show that no metal agglomeration can be observed on its surface, and isolated Rh single atoms can be identified in HAADF-STEM at atomic resolution.

[0075] like Figure 9 As shown, the Rh N / S-NC prepared in Example 1, the Rh NP-NC prepared in Comparative Example 1, and the Rh SA-NC and NC prepared in Comparative Example 2 are compared. 950 The powder X-ray diffraction (PXRD) results showed no significant differences, with only two broad peaks appearing near 2θ = 24° and 43°, corresponding to the (002) and (101) crystal planes of amorphous carbon, respectively. In particular, no diffraction peaks of any Rh crystalline phase were observed in the PXRD results of Rh N / S-NC, Rh NP-NC, and Rh SA-NC, indicating that the Rh species in the prepared catalysts were well dispersed on the surface of the carbon material without severe agglomeration.

[0076] The Rh metal content of the prepared materials was tested by inductively coupled plasma optical emission spectrometry (ICP-OES). The results for Rh N / S-NC, Rh NP-NC, and Rh SA-NC were 0.45 wt%, 0.63 wt%, and 0.07 wt%, respectively.

[0077] like Figure 10 a and Figure 10 As shown in Figure b, the Rh 3d XPS spectrum of Rh N / S-NC can be deconvolved into four peaks, which are respectively attributed to Rh 0 3D 5 / 2 (307.1eV), Rh x+ 3D 5 / 2 (309.1eV), Rh 0 3D 3 / 2 (312.5eV) and Rh x+ 3D 3 / 2(313.8 eV) indicates that metallic and oxidized states coexist in Rh species. The content of genus-state Rh is significantly lower, with more Rh species likely losing electrons through chemical interactions such as coordination with nonmetals. Conversely, Rh species in Rh NP-NC mainly exist in the metallic state, with some oxidized Rh due to surface oxidation. However, due to the low Rh content and the shielding effect of the surrounding carbon framework in Rh SA-NC, only a relatively weak oxidation state signal (approximately 309.6 eV corresponding to Rh) can be observed. 3+ 3D 5 / 2 Approximately 314.3 eV corresponds to Rh 3+ 3D 3 / 2 High-resolution XPS spectra of N 1s revealed that the dominant forms of N species in the three different Rh samples were pyridine N and graphitic N, similar to the composition of the pyrolytic ZIF-8 material. As the most likely anchoring sites for single atoms, pyridine N and graphitic N in Rh N / S-NC and Rh SA-NC showed a negative shift of approximately 0.1 eV compared to Rh NP-NC, revealing potential electron transfer and interactions between Rh atoms and N sites.

[0078] like Figure 11 As shown, X-ray absorption fine structure (XAFS) analysis based on the Rh K-edge determines the true distribution and coordination environment of Rh atoms in Rh N / S-NC. Figure 11 As shown in Figure a, in the near-edge X-ray absorption spectrum of Rh N / S-NC, the absorption edge energy is higher than that of Rh foil and Rh NP-NC, but lower than that of Rh SA-NC and standard Rh₂O₃. This indicates that the valence state of Rh atoms in Rh N / S-NC is between 0 and +3, while in Rh NP-NC and Rh SA-NC it is closer to 0 and +3 valence, respectively, consistent with the XPS results above. Figure 11 The Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum shown in Figure b indicates that... The nearby Rh NP-NC main peak corresponds to the typical Rh-Rh bond in the Rh foil, while a similar scattering path appears in the Rh N / S-NC, confirming the interaction between Rh atoms in the nanoparticles. Simultaneously, due to Rh-O / N coordination, the Rh N / S-NC exhibits... A distinct scattering peak is observed at this location, and the weak peak of Rh NP-NC at this position may originate from the surface oxidation of Rh nanoparticles and their bonding with the nitrogen-doped carbon substrate. In contrast, for Rh SA-NC, only the Rh-O / N scattering path is observed, and no Rh-Rh bonds are present, confirming the atomic dispersion of Rh species in Rh SA-NC. Further, in R space (e.g., ... Figure 11 c and Figure 11 (as shown in d) and k-space ... Figure 11 China and Figure 11 As shown in f, EXAFS curves of Rh N / S-NC and Rh SA-NC were fitted respectively to obtain more accurate atomic coordination information and structural parameters. The fitting results for Rh N / S-NC show that... and The fitted curves for the main peaks are consistent with the experimental data, and are attributed to the first shell coordination of Rh-N (coordination number 3.8, interatomic distance ). Rh-N coordination in small nanoparticles. Rh SA-NC possesses a similar Rh-N coordination environment to Rh N / S-NC, with a coordination number of 4.2 and an interatomic distance of [missing information]. There is no Rh-Rh coordination.

[0079] Experimental Example 2

[0080] 1. Electrochemical testing

[0081] All electrochemical tests were performed using a standard three-electrode system via an electrochemical workstation (CHI760E). For the preparation of the catalyst ink-like dispersion, 2 mg of sample powder and 20 μL of Nafion solution were dispersed in 380 μL of ethanol and then sonicated for 30 min. In the polarization curve measurements below, the iR drop was compensated for to 90%. Multiple cyclic voltammetry (CV) scans were performed within the corresponding potential ranges to activate the catalyst prior to testing.

[0082] Use a loading of 0.25 mg cm -2 A rotating disk electrode (RDE, 5 mm in diameter) of the catalyst was used as the working electrode, while a graphite rod and a Hg / HgO electrode were used as the counter electrode and reference electrode, respectively. In a 0.1 M KOH electrolyte saturated with H2, the catalyst was subjected to an LSV reaction at 1 mV s⁻¹. -1 Polarization curves were obtained at the scan rate. HOR polarization curves at different rotational speeds (400, 900, 1600, 2500 rpm) were collected in the potential range of 0-0.3V (vs. RHE).

[0083] Accelerated durability testing was conducted at 100 mV s in a potential range of 0–0.3 V (vs. RHE). -1 The catalyst underwent 2000 CV cycles at a scan rate. The LSV curves and time-current response were recorded after the CV cycles to assess the catalyst stability.

[0084] 2. Membrane Electrode Assembly (MEA) and AEMFC Testing

[0085] The synthesized RhN / S-NC, RhNP-NC, or RhSA-NC were used as anode catalysts (0.02 mg). Rh cm-2 ), and commercially available Pt / C (40wt%, Alfa Aesar) was used as the cathode catalyst (0.2mg). Pt cm -2 The catalyst and ionomer (PAP-TP-100) were ultrasonically dispersed in a mixture of deionized water and isopropanol (1:20 v / v) for 1 hour to prepare the catalyst ink. The resulting uniform ink was then sprayed onto both sides of a PAP-TP-85 membrane to prepare a membrane with a fixed area of ​​5 cm². 2 Catalyst coating (CCM) was prepared. The CCM was immersed in 3M KOH solution for 12 hours to promote anion exchange to OH-. - Then rinsed multiple times with deionized water to remove excess KOH. Subsequently, a rinsed CCM, fluorinated ethylene-propylene (FEP) gasket, GDL (SGL29BC), and a 5cm... 2 The flow field is assembled into a graphite bipolar plate and metal current collectors on each side of the MEA.

[0086] AEMFC performance testing was conducted on a Scribner 850e system equipped with a back pressure module. Test conditions: battery temperature 95°C, anode humidifier temperature 88°C, cathode humidifier temperature 97°C, H2 flow rate 0.5 L / min. -1 O2 flow rate is 1 L / min -1 The back pressure is symmetrical at 250 kPa.

[0087] The results are as follows Figures 12-16 As shown, Figure 12 The figure shows the HOR polarization curve recorded at 1600 rpm using a rotating disk electrode (RDE). The Rh N / S-NC achieved a polarization of 2.35 mA cm⁻¹ at an overpotential of 50 mV. -2 The high current density exceeds that of Pt / C (1.77 mA cm⁻¹). -2 ), Rh NP-NC (0.49mA cm) -2 ) and Rh SA-NC (0.11mA cm -2 ). And as Figure 13 The kinetic Tafel plots show that Rh N / S-NC exhibits a larger HOR kinetic current compared to commercial Pt / C and other Rh samples. Since the HOR process is mass-transfer controlled, the limiting current density obtained with Rh N / S-NC as a catalyst increases proportionally with rotational speed (e.g., ...). Figure 14 As shown). Figure 15 The figure shows the Koutecky-Levich equation fitting plot for RhN / S-NC. At an overpotential of 50mV, the reciprocal of the current density is linearly correlated with the reciprocal of the square root of the rotational speed. The resulting fitting slope is (4.05cm).2 mA -1 s -1 / 2 The result is close to the theoretical value, indicating that the expected two-electron HOR process occurred. Furthermore, the kinetic current density (jk) of Rh N / S-NC at a 50mV overpotential reaches 10.48 mA / cm². -2 It is a commercial Pt / C (4.56 mA cm⁻¹) -2 2.3 times that of ). For example Figure 16 The figure shows the linear fit of the micro-polarized region to determine the exchange current density (j0) of the material. Rh N / S-NC exhibits the largest j0 value, reaching 1.87 mA / cm. -2 Higher than Pt / C (1.16 mA / cm²). -2 ) and Rh NP-NC (0.23 mAcm -2 ), Rh SA-NC (0.18mAcm) -2 This reflects the excellent intrinsic HOR activity of the catalytic material.

[0088] like Figure 17 As shown, the performance parameters are compared after cyclic durability testing. After 2000 CV scans, the polarization curve of Rh N / S-NC shows almost no decay, while the half-wave potential (E) of Pt / C increases significantly. 1 / 2 The voltage increased by 19.7 mV. Furthermore, the geometric current density (j) at 50 mV... g@50mV ) not only did not decay, but even slightly increased, while j k j0 and j0 decay by only 2.5% and 1.6% respectively. For example... Figure 18 As shown, the long-term stability test of the catalytic materials was conducted using the chronoamperometry method. After continuous operation for 10 hours in H2-saturated 0.1M KOH at a potential of 0.05V (vs. RHE), the HOR current of Pt / C decreased significantly by nearly 50%, while RhN / S-NC showed only a slight loss of 7.3%. Figure 19 The results show that the prepared Rh N / S-NC material has excellent stability.

[0089] like Figure 20 a and Figure 20 As shown in Figure b, the performance of RhN / S-NC as an anode catalyst in H2-O2AEMFC was further evaluated to meet practical production requirements. MEAs were prepared using RhN / S-NC (with Rh NP-NC and Rh SA-NC as comparisons), commercial Pt / C, and PAP-TP-85 as the anode catalyst, cathode catalyst, and anion exchange membrane, respectively. Figure 20As shown in Figure a, under conditions of 95°C, 250 kPa back pressure, and H2-O2 feed, the AEMFC with Rh N / S-NC as the anode can provide 0.62 A cm⁻¹ at a typical battery operating voltage of 0.65 V. -2 The current density is 1.13 A cm⁻¹. -2 It can achieve 515mW cm -2 High peak power density (PPD). Among them, the anode PGM load (0.02 mg) Rh cm -2 Only the cathode (0.2mg) Pt cm -2 The result of 1 / 10 of the original value is significant because it greatly reduces the cost of the anode catalyst while maintaining good AEMFC performance. The PPD of Rh N / S-NC was normalized by the amount of noble metal used in the anode and was... Figure 20 Compared to other MEAs shown in b, RhN / S-NC exhibits exceptionally high metal utilization and a mass activity as high as 25.7 W mg. PGM -1 Therefore, it has a very good prospect for practical application.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a low-load Rh-based fuel cell anode catalyst, characterized in that, Includes the following steps: (1) 2-Methylimidazole is mixed with methanol to obtain solution A; Zn(NO3)2·6H2O is mixed with methanol to obtain solution B; (2) Add solution A obtained in step (1) to solution B obtained in step (1), stir, and obtain a mixed solution; (3) Place the mixed solution described in step (2) in a stainless steel high-pressure reactor lined with polytetrafluoroethylene, perform a first heat treatment, centrifuge, and obtain the reaction precipitate; (4) The reaction precipitate described in step (3) is washed three times with methanol and then subjected to vacuum drying to obtain ZIF-8; (5) The ZIF-8 mentioned in grinding step (4) is subjected to a second heating treatment in N2 atmosphere and then naturally cooled to obtain NC. 950 ; (6) The NC described in step (5) 950 Mix with deionized water and sonicate to obtain a suspension; (7) While stirring continuously, add RhCl3 aqueous solution to the suspension in step (6) for adsorption treatment, collect the black solid, perform a second vacuum drying treatment, and heat treatment in an H2 / Ar mixed atmosphere to obtain a low-load Rh-based fuel cell anode catalyst. The ratio of 2-methylimidazole to methanol in step (1) is 0.616 g: 15 mL; the ratio of Zn(NO3)2·6H2O to methanol in step (1) is 0.488 g: 30 mL; In step (3), the temperature of the first heating treatment is 120°C and the time of the first heating treatment is 4 hours; in step (3), the temperature of the centrifugation is 25°C, the speed of the centrifugation is 9000 rpm, and the time of the centrifugation is 5 minutes. The grinding particle size requirement in step (5) is 400 mesh; the second heating treatment in step (5) is specifically: heating to 950°C at a heating rate of 5°C / min, and then continuing to heat at 950°C for 2 hours; The NC mentioned in step (6) 950 The mixing ratio with deionized water is 50 mg: 4 mL; The concentration of the RhCl3 aqueous solution in step (7) is 2.5 mg / mL, and the amount of RhCl3 aqueous solution used is 1 mL; the adsorption treatment temperature in step (7) is 25℃, and the adsorption treatment time is 24 h; the temperature of the second vacuum drying treatment in step (7) is 60℃, the second vacuum drying treatment time is 24 h, and the vacuum degree of the second vacuum drying is 0.08 MPa; the volume content of H2 in the H2 / Ar mixed atmosphere in step (7) is 7%; the temperature of the heat treatment in step (7) is 200℃, and the heat treatment time is 2 h.

2. The preparation method according to claim 1, characterized in that, The stirring temperature in step (2) is 25°C, the stirring speed is 600 rpm, and the stirring time is 30 min.

3. The preparation method according to claim 1, characterized in that, In step (4), the temperature of the first vacuum drying treatment is 60°C, the time of the first vacuum drying treatment is 12h, and the vacuum degree of the first vacuum drying treatment is 0.08MPa.

4. The preparation method according to claim 1, characterized in that, The ultrasonic treatment in step (6) is performed at a temperature of 25°C, a frequency of 40kHz, a power of 300W, and a duration of 10min.

5. The low-load Rh-based fuel cell anode catalyst prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the low-load Rh-based fuel cell anode catalyst as described in claim 5 or the low-load Rh-based fuel cell anode catalyst prepared by the preparation method as described in any one of claims 1 to 4 in the preparation of anion exchange membrane fuel cells.

Images