Electrodeposition preparation method of Pt / Co4N nanowire catalyst for ammoxidation

Abstract

The invention discloses an electro-deposition preparation method for a Pt / Co4N nanowire catalyst for ammoxidation. The preparation method comprises the following steps: dissolving Co (NO3) 2.6 H2O, NH4F and CO (NH2) 2 in H2O to obtain a pink solution; putting the pink solution into an electric heating constant-temperature oil bath pan, heating to obtain purple flocculent liquid, and centrifugally drying to obtain Co4N powder; the method comprises the following steps: adding Co4N powder into an H2O solution containing Nafion and isopropanol to prepare uniform printing ink; and dropwise adding the printing ink to the surface of an electrode, and scanning the electrode in H2O containing H2PtCl6. 6H2O and Na3C6H5O7. H2O for three circles under the potential of-0.8 to 0.4 V through a cyclic voltammetry method to obtain the Pt / Co4N nanowire catalyst. The method is characterized in that the Pt / Co4N nanowire catalyst for ammoxidation is synthesized through solvothermal and electro-deposition methods. The catalyst not only has remarkable ammonia oxidation catalytic performance, but also is good in stability, small in dosage, low in energy consumption and high in yield, and low-cost large-scale production and preparation can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of novel functional nanomaterials, and particularly relates to an electrodeposition method for preparing a Pt / Co 4 N nanowire catalyst for ammonia oxidation. Background Art

[0002] With the increasing global energy demand and the increasingly severe environmental problems, developing green and efficient energy carriers has become an important way to solve the energy crisis. As a green and renewable energy, ammonia has the advantages of high energy density and low carbon emissions, and is an important part of the future energy system. Ammonia can not only be directly used as a fuel in ammonia-oxygen fuel cells, but also can be used as a storage and transportation carrier for hydrogen energy, showing great application potential. In ammonia-oxygen fuel cells, ammonia is converted into electrical energy through an electrochemical oxidation reaction (AOR), which has the advantages of low-temperature operation and long life. However, the oxidation reaction of ammonia is limited by the high energy barrier formed by the nitrogen-nitrogen bond, and its reaction efficiency is restricted. In addition, the poisoning effect of the adsorbed intermediate * N on the electrode during the reaction often leads to rapid deactivation of the catalyst. These problems seriously restrict the performance of the ammonia oxidation reaction. Platinum (Pt)-based noble metal nanomaterials exhibit excellent catalytic performance in the ammonia oxidation reaction and can efficiently promote the reaction at a lower potential. By synthesizing and optimizing Pt-based catalysts, the efficiency of ammonia oxidation can be further improved, providing key technical support for the efficient utilization of ammonia energy. Therefore, while improving the activity of Pt-based catalysts, effectively reducing the Pt dosage is of great significance for the efficient and wide application of ammonia energy.

[0003] As is well known, metal nitrides have shown broad application prospects in the field of electrocatalysis due to their excellent electronic conductivity, structural stability, and unique electronic structure. Especially the cobalt nitride (Co 4 N) nanowire structure has a highly ordered conductive network and abundant surface active sites, which is conducive to promoting rapid charge migration and enhancing interfacial reaction kinetics, making it an ideal electrocatalytic support material. Considering the high catalytic performance of Pt in AOR, depositing it uniformly on the surface of Co 4 N in the form of an ultrathin layer is expected to significantly improve the catalytic efficiency and maximize the atomic utilization rate of Pt. However, there is no report in the existing literature on using the electrodeposition method to construct an ultrathin Pt layer on the surface of Co 4 N nanowires. The electrodeposition method has outstanding advantages such as precise controllability, simple operation, and strong adaptability, and can effectively adjust the deposition thickness and uniformity of Pt, thereby maximizing the atomic utilization rate of Pt and constructing an efficient and cost-controllable Pt / Co 4 N ammonia oxidation catalytic system. Therefore, developing a simple electrodeposition method to prepare a Pt / Co with both high activity and high Pt atomic utilization rate 4N nanowire catalysts are crucial. Summary of the Invention

[0004] To avoid the deficiencies of the prior art, the present invention provides an electrodeposition preparation method for Pt / Co 4 N nanowire catalysts for ammonia oxidation.

[0005] One of the objectives of the present invention is to provide a simple and feasible method for electrodepositing a Pt layer.

[0006] Another objective of the present invention is to provide a Pt / Co 4 N nanowire catalyst for ammonia oxidation.

[0007] The Pt / Co 4 N nanowire catalyst for ammonia oxidation prepared by the present invention is prepared from cobalt hexahydrate nitrate (Co(NO 3 ), 2 ·6H 2 O), ammonium fluoride (NH 4 F), urea (CO(NH 2 ), 2 ), deionized water (H 2 O) as raw materials, and Co 4 N nanowires are prepared by a solvothermal method. Then, an ultrathin Pt layer is electrodeposited using chloroplatinic acid hexahydrate (H 2 PtCl 6 ·6H 2 O) and trisodium citrate (Na 3 C 6 H 5 O 7 ·H 2 O). The preparation process includes the following specific steps: 1. Dissolve 150 - 250 mg of Co(NO 3 ), 2 ·6H 2 O, 40 - 80 mg of NH 4 F, and 220 - 260 mg of CO(NH 2 ), 2 in 8 - 24 mL of H 2 O to obtain a pink solution; 2. Place the pink solution obtained in step 1 in an electrothermal constant temperature oil bath and heat it at 100 - 140 °C for 3 - 9 h to obtain a purple flocculent liquid, and then centrifuge and dry it to obtain Co 4 N powder; 3. Take 1 - 3 mg of Co 4The N powder was added to 400 μL of aqueous solution containing 6 μL of Nafion and 100 μL of isopropanol to prepare a homogeneous ink. 4. 14 μL of the ink obtained in Step 3 was dropped onto the electrode surface, and the electrode was placed in 100 - 150 mL of deionized water containing 400 - 600 mg of H 2 PtCl 6 ·6H 2 O and 50 - 150 mg of Na 3 C 6 H 5 O 7 ·H 2 O. After scanning three cycles by cyclic voltammetry at a potential of -0.8 to 0.4 V, the Pt / Co 4 N nanowire catalyst was obtained.

[0008] Advantages of the present invention: 1. The present invention provides an electrodeposition preparation method for an ammonia oxidation Pt / Co 4 N nanowire catalyst, that is, by solvothermal synthesis of dispersed Co 4 N nanowires, and then by a simple electrodeposition method to prepare dispersed Pt / Co 4 N nanowire catalyst. The preparation method is simple and easy to operate, does not require special equipment, and does not require complex and cumbersome steps after preparation. It is particularly suitable for batch preparation and is suitable for industrial-scale production and commercial applications; 2. The product prepared by the present invention is a dispersed Pt / Co 4 N nanowire catalyst, and the product morphology and size are uniform, and it can be prepared on a large scale and is easy to use; 3. The Pt / Co 4 N nanowire catalyst prepared by the present invention has a peak current density of 18.05 mA cm -1 at a scanning rate of 20 mV s -2 . Its catalytic performance and stability are significantly better than those of commercial Pt / C catalysts, and it has excellent ammonia oxidation catalytic performance and good stability; 4. The preparation of the present invention only requires ordinary equipment commonly used in laboratories, does not require special equipment, and the process is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings in the description of the embodiments or the prior art. However, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0010] Figure 1Pt / Co prepared according to the present invention 4 Transmission electron microscopy image of the Pt / Co

[0011] Figure 2 Pt / Co prepared according to the present invention 4 X-ray diffraction pattern of the Pt / Co

[0012] Figure 3 Pt / Co prepared according to the present invention 4 X-ray photoelectron spectroscopy of Pt4f, Co2p and N1s of the Pt / Co

[0013] Figure 4 Pt / Co prepared according to the present invention 4 Ammonia oxidation performance test chart of the Pt / Co and commercial Pt / C catalysts

[0014] Figure 5 Pt / Co prepared according to the present invention 4 Stability test chart of the Pt / Co Specific implementation method

[0015] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0017] Unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods; the reagents and materials, unless otherwise specified, can all be obtained commercially.

[0018] Example 1: Dissolve 200 mg of Co(NO 3 ) 2 ·6H 2 O, 60 mg of NH 4 F and 240 mg of CO(NH 2 ) 2 in 16 mL of H 2 O to obtain a pink solution; place the pink solution in an electrothermal constant temperature oil bath and heat it at 120 °C for 6 h to obtain a purple flocculent liquid, centrifuge and dry it to obtain Co 4 N powder; add 2 mg of Co 4 N powder to 400 µL of H2 Prepare a uniform ink in an O solution; drop 14 μL of the ink onto the electrode surface, and place the electrode in 125 mL of H 2 PtCl 6 ·6H 2 O and 100 mg of Na 3 C 6 H 5 O 7 ·H 2 O. After scanning three cycles at a potential of -0.8 to 0.4 V by cyclic voltammetry, a Pt / Co 2 N nanowire catalyst is obtained. 4 N nanowire catalyst.

[0019] Example 2: Dissolve 150 mg of Co(NO 3 ) 2 ·6H 2 O, 80 mg of NH 4 F, and 220 mg of CO(NH 2 ) 2 in 8 mL of H 2 O to obtain a pink solution; place the pink solution in an electrothermal constant-temperature oil bath and heat it at 100 °C for 12 h to obtain a purple flocculent liquid. After centrifugation and drying, Co 4 N powder is obtained; add 3 mg of Co 4 N powder to 400 μL of H 2 O solution containing 6 μL of Nafion and 100 μL of isopropanol to prepare a uniform ink; drop 14 μL of the ink onto the electrode surface, and place the electrode in 100 mL of H 2 containing 400 mg of H 6 PtCl 2 ·6H 3 O and 150 mg of Na 6 C 5 H 7 O 2 ·H 2 O. After scanning three cycles at a potential of -0.8 to 0.4 V by cyclic voltammetry, a Pt / Co 4 N nanowire catalyst is obtained.

[0020] Example 3: Dissolve 250 mg of Co(NO 3 ) 2 ·6H 2 O, 40 mg of NH 4 F, and 260 mg of CO(NH 2 ) 2Dissolved in 24 mL of H 2 O to obtain a pink solution; the pink solution was placed in an electrothermal constant temperature oil bath and heated at 140 °C for 3 h to obtain a purple flocculent liquid, which was centrifuged and dried to obtain Co 4 N powder; 1 mg of Co 4 N powder was added to 400 µL of H 2 O solution containing 6 µL of Nafion and 100 µL of isopropanol to prepare a uniform ink; 14 µL of the ink was dropped onto the electrode surface, and the electrode was placed in 150 mL of H 2 containing 600 mg of H 6 PtCl 2 ·6H 3 O and 50 mg of Na 6 C 5 H 7 O 2 ·H 2 O and scanned three cycles at a potential of -0.8 to 0.4 V by cyclic voltammetry to obtain the Pt / Co 4 N nanowire catalyst.

[0021] Figure 1 is the transmission electron microscopy image of the Pt / Co 4 N nanowire catalyst prepared in Example 1. It can be seen from Figure 1 that the synthesized Pt / Co 4 N nanowire catalyst has uniform thickness, with an average thickness of about 50 - 60 nm and is evenly dispersed.

[0022] Figure 2 is the X-ray diffraction pattern of the Pt / Co 4 N nanowire catalyst prepared in Example 1. It can be seen from Figure 2 that the Pt / Co 4 N nanowire catalyst corresponds to the diffraction peaks of Co 4 N and Pt.

[0023] Figure 3 (a-c) are the X-ray photoelectron spectra of Co2p, N1s, and Pt4f of the Pt / Co 4 N nanowire catalyst prepared in Example 1, indicating the coexistence of Co, N, and Pt.

[0024] Figure 4 is the ammonia oxidation performance test chart of the Pt / Co 4 N nanowire catalyst prepared in Examples 1 - 3 and the commercial Pt / C catalyst. It can be seen from Figure 4 that under the test conditions of 20 mV s -1 the Pt / Co 4The peak current density of the Pt / Co N nanowire catalyst is 18.05 mA cm -2 , which is significantly higher than that of the Pt / Co 4 N nanowire catalysts and commercial Pt / C catalysts prepared in Examples 2 and 3, indicating that the Pt / Co 4 N nanowire catalyst prepared in Example 1 has excellent ammonia oxidation performance.

[0025] Figure 5 Figure for the stability test of the Pt / Co 4 N nanowire catalyst prepared in Example 1. As can be seen from Figure 5 it, at a voltage of 0.68 V, after 12 hours of long-term testing, the current density still remains basically stable, only decaying to 73.8%. This indicates that the Pt / Co 4 N nanowire catalyst prepared in Example 1 has excellent stability.

[0026] Obviously, those skilled in the art can make various changes and modifications to the electrodeposition preparation method of a Pt / Co 4 N nanowire catalyst of the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A method for preparing a Pt / Co4N nanowire catalyst for ammonia oxidation by electrodeposition, comprising the following steps: Dissolve 150-250 mg Co(NO3)2·6H2O, 40-80 mg NH4F and 220-260 mg CO(NH2)2 in 8-24 mLH2O to obtain a pink solution; place the pink solution in an electric constant temperature oil bath and heat at 100-140 °C for 3-9 h to obtain a purple flocculent liquid, which is then centrifuged and dried to obtain Co4N powder; add 1-3 mg Co4N powder to 400 µL H2O solution containing 6 µL Nafion and 100 µL isopropanol to prepare a uniform ink; 14 µL of ink was dropped onto the electrode surface, and the electrode was subjected to cyclic voltammetry in 100-150 mL H2O containing 400-600 mg H2PtCl6·6H2O and 50-150 mg Na3C6H5O7·H2O, and then scanned three times at a potential of -0.8~0.4 V to obtain the Pt / Co4N nanowire catalyst.

2. The method for preparing the Pt / Co4N nanowire catalyst by electrodeposition according to claim 1, characterized in that: The amount of Co(NO3)2·6H2O used was 200 mg, the amount of NH4F used was 60 mg, the amount of CO(NH2)2 used was 240 mg, and the amount of water used to synthesize Co4N was 16 mL.

3. The method for preparing the Pt / Co4N nanowire catalyst by electrodeposition according to claim 1, characterized in that: The amount of Co4N used during electrodeposition was 2 mg, the amount of H2PtCl6·6H2O used was 500 mg, the amount of Na3C6H5O7·H2O used was 100 mg, and the amount of water used during electrodeposition was 125 mL.

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