A Pt / Ag / g-C3N4 catalytic electrode and its preparation method and application

Abstract

The present invention belongs to the field of direct methanol fuel cells, and specifically relates to a Pt / Ag / g-C3N4 catalytic electrode, a preparation method thereof, and an application thereof. The Pt / Ag / g-C3N4 catalytic electrode comprises an inert electrode and Pt / Ag / g-C3N4 immobilized on the inert electrode. The present invention first immobilizes Ag / g-C3N4 on the inert electrode by a drop coating method, and then immobilizes Pt on the electrode by electroplating using the coordination effect of Pt and g-C3N4, thereby obtaining a Pt / Ag / g-C3N4 catalytic electrode. The Pt / Ag / g-C3N4 catalytic electrode provided by the present invention not only has a simple preparation method and mild and controllable reaction conditions, but also has good stability and catalytic activity. It can be directly used as an electrocatalytic anode of a methanol fuel cell for the catalytic oxidation of methanol. It is easy to use and has good promotion prospects.

Description

Technical Field

[0001] The present invention belongs to the field of direct methanol fuel cells, and in particular relates to a Pt / Ag / g-C3N4 catalytic electrode and a preparation method and application thereof. Background Art

[0002] In recent years, fuel cells have attracted widespread attention due to their high efficiency and low pollution levels. Direct methanol fuel cells (DMFCs), with their high energy density, low operating temperature, and low pollutant emissions, are considered an excellent energy conversion device. However, widespread production of DMFCs still faces many obstacles. For example, slow electrode kinetics lead to ultra-high potentials, making the reaction difficult to carry out. At low temperatures, more precious metal catalysts are required to convert the fuel into H2 and CO2, which increases the cost of the catalyst. Therefore, it is extremely important to develop fuel cell catalysts with good catalytic activity, high stability, and low cost.

[0003] Currently, the most widely used and most effective anode catalyst in direct methanol fuel cells is platinum (Pt)-based catalyst. However, the commercial application of DMFC is restricted by the low reserves, high cost, and easy poisoning of metal Pt. Therefore, in order to reduce the cost of catalysts and improve the activity and stability of catalysts, researchers mainly optimize Pt-based catalysts from the following two aspects: (1) combining Pt metal with other metals to develop Pt-based bimetallic catalysts, such as Pt / Au, Pt / Pd, Pt / Ni, Pt / Ru, and Pt / Ag; (2) selecting catalyst supports with good conductivity, large surface area, and reasonable pore structure. Among them, semiconductor materials are considered to be a promising type of support for Pt-based catalysts due to their strong support-metal interaction, excellent physical and chemical properties, and co-catalytic activity.

[0004] Graphitic carbon nitride (g-C3N4), a polymer semiconductor, offers advantages such as high thermal and chemical stability, low cost, strong corrosion resistance, a high nitrogen content, and ample anchor sites. It can be used as an excellent catalyst support material. The interaction between nitrogen and metal atoms, such as platinum, can effectively improve the catalytic activity of platinum. However, due to the insufficient extension of the π-conjugated system contained in g-C3N4, its conductivity as a support material is relatively weak. Therefore, its conductivity must be enhanced through doping or modification when used in direct methanol fuel cells.

[0005] Patent publication number CN109351364A discloses a method for preparing a graphene / graphite-like carbon nitride / palladium nanoparticle multi-level nanostructure composite material and its application. The goal is to address the current technical issues of low catalytic activity and small specific surface area for methanol oxidation. The preparation method includes: 1. preparing a graphene oxide solution, a Na2PdCl4 solution, and a g-C3N4 dispersion; 2. preparing an electrolyte; and 3. electrodeposition. While this method can form a multi-level nanostructure with a large specific surface area on the substrate of a working electrode, it still suffers from poor stability of the multi-level nanostructure and insignificant improvement in the working electrode's catalytic performance for methanol oxidation. Summary of the Invention

[0006] To address the aforementioned issues with the prior art, the present invention provides a Pt / Ag / g-C3N4 catalytic electrode and a method for preparing the same. By sequentially modifying and immobilizing Ag / g-C3N4 and Pt on an inert electrode, the electrode is endowed with excellent conductivity and catalytic activity, enabling its application in direct methanol fuel cells.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] A Pt / Ag / g-C3N4 catalytic electrode comprises an inert electrode and Pt / Ag / g-C3N4 immobilized on the inert electrode.

[0009] As a preferred embodiment of the above technical solution, the inert electrode is any one of a glassy carbon electrode, a platinum electrode, and a gold electrode.

[0010] The preparation method of the Pt / Ag / g-C3N4 catalytic electrode comprises the following steps:

[0011] (1) Preparation of g-C3N4:

[0012] The precursor is placed in a muffle furnace and calcined for 1 to 5 hours. After the calcination, it is cooled to room temperature. The calcined product is ground, washed, and dried in sequence to obtain g-C3N4.

[0013] (2) Preparation and immobilization of Ag / g-C3N4:

[0014] S1. Preparation of Ag / g-C3N4: 10-200 mg g-C3N4 was dispersed in 30-60 mL water, and then 0.1-10 mg AgNO3 was added. The mixture was ultrasonicated for 10-60 min to obtain a photolyzed solution, which was then irradiated under visible light for 10-300 min. After the reaction, the solution was centrifuged, and the precipitate at the bottom was washed and dried to obtain Ag / g-C3N4.

[0015] S2. Immobilization of Ag / g-C3N4: 1-5 mg of Ag / g-C3N4 was dispersed in 1-10 mL of anhydrous ethanol and ultrasonicated for 20-60 min to obtain an Ag / g-C3N4 dispersion. The Ag / g-C3N4 dispersion was then dropped onto an inert electrode and allowed to dry naturally to obtain an Ag / g-C3N4 modified electrode.

[0016] (3) Preparation of Pt / Ag / g-C3N4 catalytic electrode:

[0017] H2PtCl6 was dissolved in 1MH2SO4 solution to obtain H2PtCl6 solution; then the Ag / g-C3N4 modified electrode was placed in the H2PtCl6 solution for electrodeposition to obtain a Pt / Ag / g-C3N4 catalytic electrode.

[0018] In the above technical solution, the chronoamperometry is used to deposit Pt onto the Ag / g-C3N4 electrode. The content and distribution of Pt in the catalyst are mainly regulated by changing the deposition time, and the coordination effect between Pt and carbon and nitrogen in g-C3N4 is utilized to achieve uniform and stable immobilization of Pt on the catalytic electrode.

[0019] As a preferred embodiment of the above technical solution, in step (1), the precursor is one or more of cyanamide, dicyandiamide, melamine, and urea.

[0020] As a preferred embodiment of the above technical solution, in step (1), the specific process of calcination is: heating from room temperature to 500-800°C at a heating rate of 1-10°C / min, and then keeping at 500-800°C for 1-5h.

[0021] As a preferred embodiment of the above technical solution, the preparation of the Ag / g-C3N4 dispersion in step (2) S2 also includes adding 0.5 to 4 mg of naphthol crystals, in order to stably modify the g-C3N4 on the inert electrode.

[0022] As a preferred embodiment of the above technical solution, in step (2) S2, the specific preparation process of the Ag / g-C3N4 modified electrode is: use a microinjector to draw 20μL of Ag / g-C3N4 dispersion droplets each time on the inert electrode, wait for it to dry naturally, and then repeat the addition 3 to 5 times.

[0023] As a preferred embodiment of the above technical solution, in step (3), the concentration of the H2PtCl6 solution is 1 to 5 mmol / L.

[0024] As a preferred embodiment of the above technical solution, in step (3), the specific parameters of the electrodeposition are: deposition at a potential of -0.4 to -0.2 V for 120 to 900 s.

[0025] Another object of the present invention is to use the above-mentioned Pt / Ag / g-C3N4 catalytic electrode as an electrocatalytic anode of a methanol fuel cell for catalytic oxidation of methanol.

[0026] In summary, the present invention has the following beneficial effects:

[0027] 1. The present invention first uses a drop coating method to solidify Ag / g-C3N4 on an inert electrode, and then uses electrodeposition to solidify Pt on the electrode by utilizing the coordination effect between Pt and g-C3N4 to obtain a Pt / Ag / g-C3N4 catalytic electrode; in this electrode, Pt / Ag has good electrocatalytic activity and g-C3N4 has good photocatalytic activity, and Ag, as a good conductor, can also enhance the conductivity of the solid carrier. The three work together to improve the electrode catalytic oxidation performance.

[0028] 2. The Pt / Ag / g-C3N4 catalytic electrode provided by the present invention not only has a simple preparation method and mild and controllable reaction conditions, but also has good stability and catalytic activity. It can be directly used as the electrocatalytic anode of a methanol fuel cell for the catalytic oxidation of methanol. It is easy to use and has good promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 TEM images of g-C3N4 (A) and Ag / g-C3N4 (B) prepared in Example 1;

[0030] Figure 2 is the HRTEM image of Pt / Ag / g-C3N4 prepared in Example 1;

[0031] Figure 3 CV comparison chart of the Pt / Ag / g-C3N4 catalytic electrode in Example 1, the Pt / g-C3N4 catalytic electrode in Comparative Example 1, and the Pt / C catalytic electrode in Comparative Example 2 in a solution containing 1.0 mol / L CH3OH+0.5 mol / L H2SO4, with a scan rate of 100 mV / s;

[0032] Figure 4 is based on Figure 3 J obtained from CV data in f / J b Value comparison chart;

[0033] Figure 5 CV comparison of the Pt / g-C3N4 catalytic electrodes prepared by adding different amounts of AgNO3 in Examples 1 and Examples 4 to 7 in a solution containing 1.0 mol / L CH3OH + 0.5 mol / L H2SO4, with a scan rate of 100 mV / s;

[0034] Figure 6These are chronoamperograms of the Pt / Ag / g-C3N4 catalytic electrode in Example 1, the Pt / g-C3N4 catalytic electrode in Comparative Example 1, and the Pt / C catalytic electrode in Comparative Example 2 in a solution containing 1.0 mol / L CH3OH + 0.5 mol / L H2SO4, with a scanning voltage of 0.6 V and a scanning time of 1200 s. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below with reference to specific embodiments. However, the specific details of the embodiments are only for the purpose of illustrating the present invention and do not represent all the technical methods under the concept of the present invention. Therefore, they should not be understood as limiting the overall technical solution of the present invention.

[0036] Example 1

[0037] A method for preparing a Pt / Ag / g-C3N4 catalytic electrode comprises the following steps:

[0038] (1) Preparation of g-C3N4:

[0039] 10 g of urea was calcined in a muffle furnace at a heating rate of 5 °C / min from room temperature to 550 °C, and then kept at 550 °C for 2 h. After the calcination, the product was cooled to room temperature, and the calcined product was ground, washed, and dried to obtain g-C3N4.

[0040] (2) Preparation and immobilization of Ag / g-C3N4:

[0041] S1. Preparation of Ag / g-C3N4: 100 mg of g-C3N4 was dispersed in 50 mL of water, and then 0.6 mg of AgNO3 was added. The solution was ultrasonicated for 30 min to obtain a photolyzed solution, which was then irradiated under visible light for 30 min. After the solution was irradiated, the solution was centrifuged, and the precipitate at the bottom was washed and dried to obtain Ag / g-C3N4.

[0042] S2. Immobilization of Ag / g-C3N4: 1 mg of Ag / g-C3N4 was dispersed in 2 mL of anhydrous ethanol, and then 1 mg of naphthol crystals was added. The mixture was ultrasonicated for 30 min to obtain an Ag / g-C3N4 dispersion. 20 μL of the Ag / g-C3N4 dispersion was then dropped onto the glassy carbon electrode using a microinjector. After the dispersion was allowed to dry naturally, the addition was repeated three times to obtain an Ag / g-C3N4 modified electrode.

[0043] (3) Preparation of Pt / Ag / g-C3N4 catalytic electrode:

[0044] H2PtCl6 was dissolved in 1MH2SO4 solution to obtain a 5mmol / LH2PtCl6 solution; then the Ag / g-C3N4 modified electrode was placed in the H2PtCl6 solution and deposited at a potential of -0.2V for 180s to obtain a Pt / Ag / g-C3N4 catalytic electrode.

[0045] Figure 1 TEM images of g-C3N4 (A) and Ag / g-C3N4 (B) prepared in Example 1. As can be seen from Figure A, the prepared g-C3N4 has a lamellar structure with a large number of wrinkles on the surface, thereby increasing its specific surface area, which is beneficial to the loading of Pt and Ag; Figure 1 As can be seen in Figure B, a large number of Ag nanoparticles are evenly distributed on the flake-like g-C3N4.

[0046] Figure 2 This is the HRTEM image of Pt / Ag / g-C3N4 prepared in Example 1. It can be seen from the figure that g-C3N4 has no lattice fringes and has an amorphous morphology; the insets are enlarged images of Ag and Pt, respectively, and their lattice spacings are 0.25nm and 0.19nm, corresponding to the Ag (111) crystal plane and Pt (200) crystal plane, respectively.

[0047] Example 2

[0048] A method for preparing a Pt / Ag / g-C3N4 catalytic electrode comprises the following steps:

[0049] (1) Preparation of g-C3N4:

[0050] 10 g of melamine was calcined in a muffle furnace at a heating rate of 10 °C / min from room temperature to 500 °C, and then kept at 500 °C for 5 h. After the calcination, the product was cooled to room temperature, and the calcined product was ground, washed, and dried to obtain g-C3N4.

[0051] (2) Preparation and immobilization of Ag / g-C3N4:

[0052] S1. Preparation of Ag / g-C3N4: 150 mg of g-C3N4 was dispersed in 60 mL of water, and then 0.6 mg of AgNO3 was added. The solution was ultrasonicated for 60 min to obtain a photolyzed solution, which was then irradiated under visible light for 120 min. After the solution was irradiated, the solution was centrifuged, and the precipitate at the bottom was washed and dried to obtain Ag / g-C3N4.

[0053] S2. Immobilization of Ag / g-C3N4: 3 mg of Ag / g-C3N4 was dispersed in 5 mL of anhydrous ethanol, and then 2 mg of naphthol crystals were added. The mixture was ultrasonicated for 45 min to obtain an Ag / g-C3N4 dispersion. 20 μL of the Ag / g-C3N4 dispersion was then dropped onto the glassy carbon electrode using a microinjector. After the dispersion was allowed to dry naturally, the addition was repeated 5 times to obtain an Ag / g-C3N4 modified electrode.

[0054] (3) Preparation of Pt / Ag / g-C3N4 catalytic electrode:

[0055] H2PtCl6 was dissolved in 1MH2SO4 solution to obtain a 3mmol / LH2PtCl6 solution; then the Ag / g-C3N4 modified electrode was placed in the H2PtCl6 solution and deposited at a potential of -0.4V for 360s to obtain a Pt / Ag / g-C3N4 catalytic electrode.

[0056] Example 3

[0057] A method for preparing a Pt / Ag / g-C3N4 catalytic electrode comprises the following steps:

[0058] (1) Preparation of g-C3N4:

[0059] 10 g of urea was calcined in a muffle furnace at a heating rate of 5 °C / min from room temperature to 600 °C, and then kept at 600 °C for 1.5 h. After the calcination, the product was ground, washed, and dried to obtain g-C3N4.

[0060] (2) Preparation and immobilization of Ag / g-C3N4:

[0061] S1. Preparation of Ag / g-C3N4: 200 mg of g-C3N4 was dispersed in 50 mL of water, and then 0.6 mg of AgNO3 was added. The solution was ultrasonicated for 30 min to obtain a photolyzed solution, which was then irradiated under visible light for 300 min. After the reaction, the solution was centrifuged, and the precipitate at the bottom was washed and dried to obtain Ag / g-C3N4.

[0062] S2. Immobilization of Ag / g-C3N4: 5 mg of Ag / g-C3N4 was dispersed in 8 mL of anhydrous ethanol, and then 4 mg of naphthol crystals were added. The mixture was ultrasonicated for 60 min to obtain an Ag / g-C3N4 dispersion. 20 μL of the Ag / g-C3N4 dispersion was then dropped onto the glassy carbon electrode using a microinjector. After the dispersion was allowed to dry naturally, the addition was repeated four times to obtain an Ag / g-C3N4 modified electrode.

[0063] (3) Preparation of Pt / Ag / g-C3N4 catalytic electrode:

[0064] H2PtCl6 was dissolved in 1MH2SO4 solution to obtain 2mmol / LH2PtCl6 solution; then the Ag / g-C3N4 modified electrode was placed in the H2PtCl6 solution and deposited at a potential of -0.3V for 480s to obtain a Pt / Ag / g-C3N4 catalytic electrode.

[0065] Examples 4 to 7

[0066] The same as Example 1, the only difference is that the amount of AgNO3 added in the preparation and immobilization of Ag / g-C3N4 is different; specifically, 0.2 mgAgNO3 is added in Example 4, 0.4 mgAgNO3 is added in Example 5, 0.8 mgAgNO3 is added in Example 6, and 1.0 mgAgNO3 is added in Example 7.

[0067] Comparative Example 1

[0068] A method for preparing a Pt / g-C3N4 catalytic electrode comprises the following steps:

[0069] (1) Preparation of g-C3N4:

[0070] 10 g of urea was calcined in a muffle furnace at a heating rate of 5 °C / min from room temperature to 550 °C, and then kept at 550 °C for 2 h. After the calcination, the product was cooled to room temperature, and the calcined product was ground, washed, and dried to obtain g-C3N4.

[0071] (2) Immobilization of g-C3N4:

[0072] 1 mg g-C3N4 was dispersed in 2 mL of anhydrous ethanol, and then 1 mg of naphthol crystals was added. The mixture was ultrasonicated for 30 min to obtain a g-C3N4 dispersion. 20 μL of the g-C3N4 dispersion was then dropped onto a glassy carbon electrode using a microinjector. After the sample was allowed to dry naturally, the addition was repeated three times to obtain a g-C3N4 modified electrode.

[0073] (3) Preparation of Pt / g-C3N4 catalytic electrode:

[0074] H2PtCl6 was dissolved in 1MH2SO4 solution to obtain a 5mmol / LH2PtCl6 solution; then the g-C3N4 modified electrode was placed in the H2PtCl6 solution and deposited at a potential of -0.2V for 180s to obtain a Pt / g-C3N4 catalytic electrode.

[0075] Comparative Example 2

[0076] A method for preparing a Pt / C catalytic electrode comprises the following steps:

[0077] First, 1 mg of commercial carbon was taken, ground and ultrasonically dispersed in 2 mL of anhydrous ethanol, and then 1 mg of naphthol crystals was added and ultrasonicated for 30 minutes to obtain a commercial carbon dispersion; then 20 μL of the commercial carbon dispersion was aspirated by a microinjector and dropped on a glassy carbon electrode each time. After it was naturally dried, the addition was repeated 3 times to obtain a commercial carbon electrode; then, H2PtCl6 was dissolved in 1MH2SO4 solution to obtain a 5 mmol / LH2PtCl6 solution; then the commercial carbon electrode was placed in the H2PtCl6 solution and deposited at a potential of -0.2 V for 180 seconds to obtain a Pt / C catalytic electrode.

[0078] Figure 3 The CV curves of the Pt / Ag / g-C3N4 catalytic electrode in Example 1, the Pt / g-C3N4 catalytic electrode in Comparative Example 1, and the Pt / C catalytic electrode in Comparative Example 2 in a solution containing 1.0 mol / L CH3OH + 0.5 mol / L H2SO4 are shown in the figure at a scan rate of 100 mV / s. As can be seen from the figure, the current density of Pt / Ag / g-C3N4 is 14.82 mA / cm -2 , respectively Pt / g-C3N4 (current density of 4.96 mA / cm -2 ) and commercial Pt / C (current density of 2.04 mA / cm -2 ), indicating that the Pt / Ag / g-C3N4 electrode has good catalytic activity for methanol oxidation.

[0079] Figure 4 Based on Figure 3 J obtained from CV data in f / J b The comparison chart of the values ​​shows that the J f / J b The value is 3.31, which is higher than 2.88 of Pt / g-C3N4 and 3.19 of Pt / C. f / J b The larger the value, the stronger the catalyst's ability to resist CO poisoning during the electrocatalytic oxidation of methanol. Therefore, Pt / Ag / g-C3N4 has a stronger ability to resist CO poisoning.

[0080] Figure 5 The CV comparison graphs of the Pt / g-C3N4 catalytic electrodes prepared with different amounts of AgNO3 in Example 1 and Examples 4-7 in a solution containing 1.0 mol / L CH3OH + 0.5 mol / L H2SO4 are shown. As can be seen from the graph, the Pt / g-C3N4 catalytic electrode prepared with 0.6 mg of AgNO3 in Example 1 has better catalytic activity.

[0081] Figure 6The chronoamperometry diagrams are shown for the Pt / Ag / g-C3N4 catalytic electrode in Example 1, the Pt / g-C3N4 catalytic electrode in Comparative Example 1, and the Pt / C catalytic electrode in Comparative Example 2 in a solution containing 1.0 mol / L CH3OH + 0.5 mol / L H2SO4. As can be seen from the figure, due to the accumulation of poisoned intermediates in the methanol oxidation reaction, the current of the three catalytic electrodes decreases rapidly within the first 100 seconds. Among the three catalytic electrodes, the current density of the Pt / Ag / g-C3N4 catalytic electrode decreases the slowest, and after 1200 seconds of operation, the limiting current density of the Pt / Ag / g-C3N4 catalytic electrode is much higher than the catalytic effects of the other two catalytic electrodes, indicating that the electrode has very superior stability.

Claims

1. A method for preparing a Pt / Ag / g-C3N4 catalytic electrode, comprising the following steps: (1) Preparation of g-C3N4: 10 g of urea was calcined in a muffle furnace at a heating rate of 5 °C / min from room temperature to 550 °C, then kept at 550 °C for 2 h. After cooling to room temperature, the calcined product was ground, washed, and dried to obtain g-C3N4. (2) Preparation and immobilization of Ag / g-C3N4: S1. Preparation of Ag / g-C3N4: 100 mg of g-C3N4 was dispersed in 50 mL of water, and then 0.6 mg of AgNO3 was added. The mixture was ultrasonicated for 30 min to obtain a photolyzed solution, which was then irradiated under visible light for 30 min. After the reaction, the solution was centrifuged, and the precipitate at the bottom was washed and dried to obtain Ag / g-C3N4. S2. Immobilization of Ag / g-C3N4: Disperse 1 mg of Ag / g-C3N4 in 2 mL of anhydrous ethanol, then add 1 mg of naphthol crystals and sonicate for 30 min to obtain an Ag / g-C3N4 dispersion. Then, use a microinjector to aspirate 20 μL of the Ag / g-C3N4 dispersion and drop it onto the glassy carbon electrode. After allowing it to dry naturally, repeat the addition three times to obtain an Ag / g-C3N4 modified electrode. (3) Preparation of Pt / Ag / g-C3N4 catalytic electrode: H2PtCl6 was dissolved in 1M H2SO4 solution to obtain a 5mmol / L H2PtCl6 solution; then the Ag / g-C3N4 modified electrode was placed in the H2PtCl6 solution and deposited at a potential of -0.2V for 180s to obtain a Pt / Ag / g-C3N4 catalytic electrode.

2. Use of the Pt / Ag / g-C3N4 catalytic electrode prepared by the method according to claim 1 as an electrocatalytic anode of a methanol fuel cell for catalytic oxidation of methanol.

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