A Pt-Ni-rGO / CFP integrated electrode and its fabrication method

Abstract

This invention discloses a Pt-Ni-rGO / CFP integrated electrode and its preparation method. The preparation method of the embodiment includes the following steps: (1) quantitatively coating a GO suspension onto the CFP surface, drying it, and then thermally reducing it to obtain an rGO / CFP support; (2) using the rGO / CFP support as the working electrode, placing it in an electrodeposition solution containing a platinum precursor, a nickel precursor, and a conductive ammonium salt, and loading Pt-Ni alloy nanoparticles onto the rGO / CFP support using cyclic voltammetry to obtain a Pt-Ni-rGO / CFP integrated electrode; (3) subjecting the Pt-Ni-rGO / CFP integrated electrode to heat treatment in a reducing atmosphere; wherein the heat treatment temperature is 300–450℃, and the time is 3–5 h. The Pt-Ni-rGO / CFP integrated electrode prepared by this invention exhibits good MOR catalytic activity and stability, and the noble metal loading is significantly reduced.

Description

Technical Field

[0001] This invention relates to an integrated Pt-Ni-rGO / CFP electrode for methanol oxidation reaction (MOR) and its preparation method. Background Technology

[0002] A fuel cell is an energy conversion device that directly converts the chemical energy stored in fuel and oxidant into electrical energy. Because fuel cells can directly convert chemical energy into electrical energy without going through a heat engine process and are not limited by the Carnot cycle, they have advantages such as high energy conversion efficiency, no noise, and no pollution, and are becoming an ideal energy utilization method.

[0003] Direct methanol fuel cells (DMFCs) are electrochemical devices that output energy by consuming methanol. Like other fuel cells, DMFCs also face the challenge of high loadings of precious metals such as Pt in the catalyst. Therefore, it is necessary to provide a method to reduce the Pt content in the catalyst and improve its performance by increasing atom utilization. Pt-Ni alloys exhibit optimal binding activity for reaction intermediates such as OH* in the MOR reaction. Therefore, Pt-Ni alloys are a promising catalyst for the methanol oxidation reaction (MOR).

[0004] In existing technologies, the preparation of PtNi alloy MOR catalysts typically involves impregnating Pt and Ni precursors onto a support, followed by heat treatment under a reducing atmosphere to obtain PtNi alloy particles. During MOR electrode fabrication, a binder is required to fix the MOR catalyst powder onto CFP (carbon paper), resulting in some PtNi alloy particles being covered by the binder, thus leading to low utilization of the PtNi alloy nanoparticles in the catalyst. Summary of the Invention

[0005] The main objective of this invention is to provide an integrated MOR electrode with good catalytic activity, stability, and low noble metal loading, as well as its preparation method.

[0006] To achieve the aforementioned main objectives, a first aspect of the present invention provides a method for preparing an integrated Pt-Ni-rGO / CFP electrode using an electrochemical method combined with thermal treatment, comprising the following steps:

[0007] (1) A quantitative GO suspension was coated onto the CFP surface, dried, and then thermally reduced to obtain the rGO / CFP carrier;

[0008] (2) Using the rGO / CFP support as the working electrode, it is placed in an electrodeposition solution containing platinum precursor, nickel precursor and conductive ammonium salt. Pt-Ni alloy nanoparticles are loaded on the rGO / CFP support by cyclic voltammetry to obtain an integrated Pt-Ni-rGO / CFP electrode.

[0009] (3) The Pt-Ni-rGO / CFP integrated electrode is placed in a reducing atmosphere for heat treatment; wherein the heat treatment temperature is 300-450℃ and the time is 3-5h.

[0010] Preferably, when preparing the electrodeposition solution, a predetermined mass of conductive ammonium salt and pH adjuster (e.g., boric acid) is first dissolved in water, and then a predetermined mass of platinum precursor and nickel precursor are added to it. This can make the prepared integrated electrode have better MOR electrocatalytic performance.

[0011] Preferably, the potential range of the cyclic voltammetry method is -0.8V to 0.5V.

[0012] Furthermore, the scanning speed of the cyclic voltammetry is 0.01–0.03 V / s, and the number of cycles is 1–5.

[0013] Preferably, the platinum precursor is potassium chloroplatinate and the nickel precursor is nickel chloride; the mass ratio of nickel chloride to potassium chloroplatinate can be 250-400:1, preferably 300-350:1.

[0014] Preferably, the conductive ammonium salt is ammonium chloride.

[0015] Preferably, the temperature of thermal reduction in step (1) is 700-900℃ and the time is 1-2h; the thermal reduction atmosphere can be an argon / hydrogen (Ar / H2) mixed atmosphere.

[0016] Preferably, the pH of the electrodeposition solution is less than 3; wherein, boric acid can be used to adjust the pH of the electrodeposition solution. When the pH of the electrodeposition solution is less than 3, the nickel and platinum metals in the solution can be better co-deposited on the carrier surface and form an alloy.

[0017] Preferably, before quantitatively coating the CFP surface with the GO suspension, the CFP is first immersed in aqua regia for a predetermined time, then washed and dried.

[0018] A second aspect of the present invention relates to an integrated Pt-Ni-rGO / CFP electrode prepared by the above-described method.

[0019] The embodiments of the present invention have the following beneficial effects:

[0020] (1) Pt-Ni alloy nanoparticles are used as the catalytic active component of the electrode. The addition of Ni can not only reduce the content of Pt, but also change its electronic structure through synergistic effect after forming an alloy with Pt, thereby increasing its catalytic activity.

[0021] (2) Pt-Ni alloy nanoparticles are directly loaded onto rGO / CFP supports to form an integrated MOR electrode by cyclic voltammetry. This method is not only simple and convenient, but also improves the dispersibility and utilization of Pt-Ni alloy nanoparticles and reduces the required amount of precious metal loading.

[0022] (3) Before heat treatment, Pt-Ni alloy nanoparticles are uniformly dispersed on the rGO / CFP support. Heat treatment of the electrode at a relatively low thermal reduction temperature of 300-450℃ can change the morphology and element distribution of the Pt-Ni alloy nanoparticles, causing Pt elements to segregate to the surface of the nanoparticles, thereby further improving its catalytic performance.

[0023] (4) After CFP is treated with aqua regia, the oxygen-containing functional groups on the carbon fiber surface will be enriched. These functional groups can not only make the bond between rGO and the carbon paper as a support carrier tighter, providing better conductivity and mass transport performance, but also provide more nucleation sites for the growth of Pt-Ni alloy nanoparticles and promote the uniform distribution of Pt-Ni alloy nanoparticles.

[0024] To more clearly illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0025] Figure 1 This is the CV curve of Pt-Ni alloy nanoparticles deposited by cyclic voltammetry in an embodiment of the present invention;

[0026] Figure 2 These are XRD patterns of the Pt-Ni-rGO / CFP integrated electrode before and after heat treatment in Example 1;

[0027] Figure 3 a and b are FE-SEM and HR-TEM images of the Pt-Ni-rGO / CFP integrated electrode before heat treatment in Example 2, respectively.

[0028] Figure 4 a and b are FE-SEM and HR-TEM images of the Pt-Ni-rGO / CFP integrated electrode after heat treatment in Example 2, respectively.

[0029] Figure 5 This is a comparison chart of the methanol oxidation cyclic voltammetry (CV) curves of the integrated electrodes prepared in Examples 1-3 and Comparative Example 1;

[0030] Figure 6 This is a comparison of the cyclic voltammetry (CV) curves of methanol oxidation after heat treatment of the Pt-Ni-rGO / CFP integrated electrode under different temperature conditions;

[0031] Figure 7 The graphs show the chronoamperometry (it) curves of methanol oxidation for the integrated electrodes prepared in Example 2 and Comparative Example 1.

[0032] Figure 8 This is a comparison of the methanol oxidation (MOR) CV curves of the integrated electrodes prepared in Comparative Examples 2 and 3.

[0033] Figure 9 a and b are FE-SEM images of the integrated electrodes prepared in Comparative Examples 2 and 3, respectively. Detailed Implementation

[0034] Numerous specific details are set forth in the following description to provide a thorough understanding of the invention; however, the invention may also be implemented using other variations or substitutions. Therefore, other possible implementations that can be discerned by those skilled in the art based on the embodiments described herein are all within the scope of protection of this invention.

[0035] Example 1: Pt-Ni(350A)-rGO / CFP

[0036] The carbon paper was pretreated in aqua regia for 24 hours, then removed, washed with ultrapure water, and dried to obtain the pretreated carbon paper.

[0037] 6 mg of GO was dispersed in 3 mL of anhydrous ethanol and sonicated for 4 hours to obtain a GO suspension of 2 mg / mL.

[0038] The GO suspension was evenly drop-coated onto both sides of the pretreated carbon paper and dried at room temperature to obtain GO / CFP.

[0039] GO / CFP was placed in a quartz boat and thermally reduced at 800℃ under an Ar / H2 atmosphere for 1 h to obtain the rGO / CFP support.

[0040] First, weigh 40 mg of NH4Cl and 370 mg of H3BO3 and dissolve them in 30 ml of ultrapure water. Then, dissolve approximately 11 mg of K2PtCl6 and 1500 mg of NiCl2·6H2O in the same 30 ml of water to obtain an electrodeposition solution with a K2PtCl6 concentration of 0.75 mM and a NiCl2 concentration of 25 mM. The pH of this electrodeposition solution is less than 3.

[0041] The electrodeposition solution was transferred to an electrolytic cell. The prepared rGO / CFP support was clamped at the front end of a clip as the working electrode (the exposed area of ​​the CFP on one side was 1 cm × 1 cm). A graphite rod was used as the counter electrode and an Ag / AgCl electrode as the reference electrode. Cyclic voltammetric electrodeposition was performed at room temperature. The starting potential of the cyclic voltammetric electrodeposition was -0.8 V, the final potential was 0.5 V, and the scan rate was 20 mV / s. After two cycles, the working electrode was removed from the clip and repeatedly washed with ultrapure water to remove the electrodeposition solution from the surface. Then, it was placed in a drying oven at 60 °C and vacuum dried for 1 h to obtain an integrated Pt-Ni-rGO / CFP electrode.

[0042] The Pt-Ni-rGO / CFP integrated electrode was placed in a quartz tube and heat-treated at 350°C for 3 hours under an Ar / H2 atmosphere to obtain the electrode product, which was marked as Pt-Ni(350A)-rGO / CFP.

[0043] Example 2: Pt-Ni(400A)-rGO / CFP

[0044] The difference between Example 2 and Example 1 is that in Example 2, the Pt-Ni-rGO / CFP integrated electrode was heat-treated at 400°C for 3 hours, and the resulting electrode product was marked as Pt-Ni(400A)-rGO / CFP.

[0045] Example 3: Pt-Ni(450A)-rGO / CFP

[0046] The difference between Example 3 and Example 1 is that in Example 3, the Pt-Ni-rGO / CFP integrated electrode was heat-treated at 450°C for 3 hours, and the resulting electrode product was marked as Pt-Ni(450A)-rGO / CFP.

[0047] Comparative Example 1: Pt-Ni-rGO / CFP

[0048] The difference between Comparative Example 1 and Example 1 is that the Pt-Ni-rGO / CFP integrated electrode was not heat-treated in Comparative Example 1.

[0049] Comparative Example 2: Pt-Ni(SWP)-rGO / CFP

[0050] The carbon paper was pretreated in aqua regia for 24 hours, then removed, washed with ultrapure water, and dried to obtain the pretreated carbon paper.

[0051] 6 mg of GO was dispersed in 3 mL of anhydrous ethanol and sonicated for 4 hours to obtain a GO suspension of 2 mg / mL.

[0052] The GO suspension was evenly drop-coated onto both sides of the pretreated carbon paper and dried at room temperature to obtain GO / CFP.

[0053] GO / CFP was placed in a quartz boat and thermally reduced at 800℃ under an Ar / H2 atmosphere for 1 h to obtain the rGO / CFP support.

[0054] First, weigh 40 mg of NH4Cl and 370 mg of H3BO3 and dissolve them in 30 ml of ultrapure water. Then, dissolve approximately 11 mg of K2PtCl6 and 1500 mg of NiCl2·6H2O in the same 30 ml of water to obtain an electrodeposition solution with a K2PtCl6 concentration of 0.75 mM and a NiCl2 concentration of 25 mM. The pH of this electrodeposition solution is less than 3.

[0055] The electrodeposition solution was transferred to an electrolytic cell, and the prepared rGO / CFP support was clamped at the front end of the clip as the working electrode (the exposed area of ​​one side of the CFP is 1cm×1cm). A graphite rod was used as the counter electrode and an Ag / AgCl electrode was used as the reference electrode. Electrodeposition was performed at room temperature: First, a constant potential of -0.35V (nucleation potential) was applied to the surface of the working electrode and held for 0.05s to generate Pt-Ni crystal nuclei; then, the crystal nuclei were grown using a square wave pulse method. The low potential of the square wave pulse was -0.8V, the high potential was 0.5V, the frequency was 10Hz, and the square wave pulse deposition time was 120s.

[0056] After electrodeposition, the working electrode is removed from the clip and repeatedly rinsed with ultrapure water to remove the electrodeposition solution from the surface. Then it is placed in a drying oven at 60°C and vacuum dried for 1 hour. The resulting electrode is labeled as Pt-Ni(SWP)-rGO / CFP.

[0057] Comparative Example 3: Pt-Ni(SWP-A)-rGO / CFP

[0058] The difference between Comparative Example 3 and Comparative Example 2 is that the electrode after vacuum drying in Comparative Example 3 was subjected to heat treatment under the same conditions as in Example 2, and the resulting electrode product was marked as Pt-Ni(SWP-A)-rGO / CFP.

[0059] Structural and morphological analysis of the embodiments and comparative examples

[0060] Figure 1 The scan curves for Pt-Ni alloy nanoparticle deposition using cyclic voltammetry in this invention show the potential windows for various metal depositions, which can be inferred from the peaks in the negative scan portion of the cyclic voltammetry. When synthesizing Pt-Ni alloy nanoparticles using cyclic voltammetry, the reduction peaks at approximately -0.3 V and 0.25 V (relative to RHE) correspond to the co-deposition of Pt and Ni in the electrodeposition solution, indicating that Pt and Ni were electrochemically deposited on the CFP surface.

[0061] Figure 2These are the XRD patterns of the Pt-Ni-rGO / CFP integrated electrode prepared in Example 1 before and after heat treatment. The XRD pattern of the electrode before heat treatment is labeled as Pt-Ni-rGO / CFP, and the XRD pattern of the electrode after heat treatment is labeled as Pt-Ni(400A)-rGO / CFP.

[0062] like Figure 2 As shown, there are two obvious high-intensity peaks near approximately 26.4° and 54.5° in the two spectra before and after heat treatment. These two diffraction peaks correspond to the (002) and (004) planes of rGO on the CFP surface, respectively. Among them, the full width at half maximum (FWHM) of Pt-Ni(400A)-rGO / CFP is smaller than that of Pt-Ni-rGO / CFP, which indicates that the crystal size of rGO increases after heat treatment.

[0063] Furthermore, both Pt-Ni-rGO / CFP and Pt-Ni(400A)-rGO / CFP spectra show four diffraction peaks at 40.5°, 46.5°, 68.2°, and 84.1°, which are shifted to higher angles by about 1.6° relative to the standard PDF card for Pt, confirming that platinum and nickel have been alloyed on the electrode surface.

[0064] Furthermore, the content of the two metals on the integrated electrode prepared in the examples was characterized by ICP. The results showed that the atomic ratio of Pt to Ni in the prepared electrode was about 2.17:1. In addition, some nickel existed in the form of nickel oxide or nickel hydroxide. Therefore, the alloy formed by platinum and nickel was denoted as Pt3Ni.

[0065] Figure 3 In Example 2, images a and b are respectively FE-SEM and TEM images of the Pt-Ni-rGO / CFP integrated electrode before heat treatment. It can be seen that the Pt-Ni alloy nanoparticles are uniformly dispersed on the rGO / CFP support, with an average particle size of 22.9 nm. Figure 4 In Figures a and b, respectively, are the FE-SEM and TEM images of the Pt-Ni-rGO / CFP integrated electrode after heat treatment at 400℃ in Example 2. It can be seen that after heat treatment, the Pt-Ni alloy nanoparticles that are close to each other fuse together, and segregation occurs on the surface of the nanoparticles. The Pt with higher catalytic activity moves to the surface of the nanoparticles, which not only increases the atomic utilization of Pt, but also protects the Ni in it, thereby significantly improving the catalytic activity of the electrode.

[0066] MOR electrocatalytic performance testing of electrodes in examples and comparisons

[0067] Test conditions: The test was conducted using a three-electrode system in a N2-saturated solution of 2 mol / L CH3OH + 0.5 mol / L KOH; the reference electrode was an Ag / AgCl electrode, and the counter electrode was a graphite rod electrode.

[0068] Comparative analysis of the MOR catalytic performance of electrodes at different heat treatment temperatures

[0069] Figure 5 This is a comparison of the methanol oxidation (MOR) CV curves of the integrated electrodes prepared in Examples 1-3 and Comparative Example 1. Example 1 is labeled Pt-Ni(350A)-rGO / CFP, Example 2 is labeled Pt-Ni(400A)-rGO / CFP, Example 3 is labeled Pt-Ni(450A)-rGO / CFP, and Comparative Example 1 is labeled Pt-Ni-rGO / CFP.

[0070] As can be seen from the figure, the Pt-Ni-rGO / CFP integrated electrode exhibits a significant increase in mass current density after heat treatment at 350℃, 400℃, and 450℃. The Pt-Ni(400A)-rGO / CFP electrode with the highest mass current density is obtained at a heat treatment temperature of 400℃. This indicates that heat treatment at this temperature can effectively improve the methanol electro-oxidation (MOR) activity of the electrode, and 400℃ is the optimal temperature for heat treatment.

[0071] Figure 6 This is a comparison of cyclic voltammetry (CV) curves of methanol oxidation for the integrated Pt-Ni-rGO / CFP electrode before and after heat treatment at 400℃, 550℃, 700℃, and 1100℃. The untreated electrode sample is labeled Pt-Ni-rGO / CFP (untreated), the sample treated at 400℃ is labeled Pt-Ni-rGO / CFP-400, the sample treated at 550℃ is labeled Pt-Ni-rGO / CFP-550, the sample treated at 700℃ is labeled Pt-Ni-rGO / CFP-700, and the sample treated at 1100℃ is labeled Pt-Ni-rGO / CFP-1100. Figure 6 It can be seen that when the heat treatment temperature of the Pt-Ni-rGO / CFP integrated electrode is above 550℃, its MOR electrocatalytic activity unexpectedly decreases.

[0072] Figure 7 The figures show the chronocurrent (it) curves of the electrodes prepared in Example 2 and Comparative Example 1. As can be seen from the figures, the durability of the Pt-Ni(400A)-rGO / CFP integrated electrode in Example 2, which underwent heat treatment at 400℃, is significantly higher than that of the untreated Pt-Ni-rGO / CFP integrated electrode in Comparative Example 1. Specifically, after 6000 s of cycling, the current density of the Pt-Ni(400A)-rGO / CFP integrated electrode is still higher than that of the Pt-Ni-rGO / CFP integrated electrode, and approximately twice that of the latter. This demonstrates that the sample treated at a lower temperature has better methanol electro-oxidation durability.

[0073] Comparative analysis of the changes in MOR performance of electrodes prepared by different electrochemical methods after heat treatment

[0074] Figure 8 The graphs show the methanol oxidation (MOR) curves of the electrodes prepared in Comparative Example 2 and Comparative Example 3. As can be seen from the graphs, the catalytic performance of the electrode prepared in Comparative Example 2 actually decreased after heat treatment at 400℃. Figure 9 a and b are FE-SEM images of the electrodes prepared in Comparative Example 2 and Comparative Example 3, respectively. As can be seen from the figures, after heat treatment at 400℃, the surface of the Pt-Ni alloy nanoparticles of the electrode prepared in Comparative Example 2 did not produce Pt surface segregation as in the electrode of the example. Its structure and morphology changed from an irregular morphology with many high-index crystal planes to a regular spherical shape with fewer high-index crystal planes, which in turn led to a decrease in its catalytic performance after heat treatment.

[0075] In summary, in the embodiments of the present invention, Pt-Ni alloy nanoparticles are directly loaded onto the rGO / CFP support to form an integrated MOR electrode by cyclic voltammetry, which can improve the dispersibility and utilization rate of Pt-Ni alloy nanoparticles and effectively reduce the required amount of noble metal loading; furthermore, by heat-treating the integrated MOR electrode at a lower temperature, the catalytic activity and stability of the integrated MOR electrode can be significantly improved.

[0076] Although the present invention has been described above through specific embodiments, it should be understood that any equivalent changes made by those skilled in the art in accordance with the present invention without departing from the scope of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for fabricating an integrated Pt-Ni-rGO / CFP electrode, comprising the following steps: (1) A quantitative GO suspension was coated onto the CFP surface, dried, and then thermally reduced to obtain the rGO / CFP carrier. (2) The rGO / CFP support is used as the working electrode and placed in an electrodeposition solution containing platinum precursor, nickel precursor and conductive ammonium salt. Pt-Ni alloy nanoparticles are loaded on the rGO / CFP support by cyclic voltammetry to obtain an integrated Pt-Ni-rGO / CFP electrode. (3) The Pt-Ni-rGO / CFP integrated electrode is subjected to heat treatment in a reducing atmosphere; wherein, The heat treatment temperature is 300~450℃, and the time is 3~5h; The potential range of the cyclic voltammetry is -0.8 V to 0.5 V, the scan rate is 0.01 to 0.03 V / s, and the number of cycles is 1 to 5. The nickel precursor is nickel chloride, and the platinum precursor is potassium chloroplatinate; the mass ratio of nickel chloride to potassium chloroplatinate is 250~400:

1.

2. The preparation method according to claim 1, wherein, The conductive ammonium salt is ammonium chloride.

3. The preparation method according to claim 1, wherein, In step (1), the temperature for thermal reduction is 700–900℃, and the time for thermal reduction is 1–2 hours.

4. The preparation method according to claim 1, wherein, The pH of the electrodeposition solution is less than 3.

5. The preparation method according to claim 1, wherein, Before quantitatively coating the CFP surface with GO suspension, the CFP is immersed in aqua regia for a predetermined time, then washed and dried.

6. The Pt-Ni-rGO / CFP integrated electrode obtained by the preparation method according to any one of claims 1 to 5.

Images