CN114959788B - Preparation of an oxygen-friendly metal-doped network PdH/C and its application in the electrocatalytic oxidation of ethanol - Google Patents

Abstract

The invention discloses the preparation of an oxygen-friendly metal-doped network PdH/C and its application in the electrocatalytic oxidation of ethanol. It is synthesized by a simple one-step method. The resulting M-PdH/C nanocatalyst can be used under environmental conditions. It exists stably and has a complex network structure, which can expose more active sites and improve catalytic performance. The introduction of cheap oxygen-loving metals not only reduces costs, but also enables the M-PdH/C nanocatalyst prepared in the present invention to exhibit higher mass activity and resistance to toxicity compared with commercial Pd/C.

Description

Preparation of an oxygen-friendly metal-doped network-like PdH/C and its application in ethanol electrocatalysis Applications in oxidation

Technical field

The invention relates to the field of electrocatalysis of fuel cells, and in particular to the preparation of an oxygen-friendly metal-doped network-like PdH/C and its application in the electrocatalytic oxidation of ethanol.

Background technique

Direct ethanol fuel cell (DEFC) is a green energy device that uses ethanol as fuel and can directly convert chemical energy into electrical energy. Compared with other alcoholic fuels, ethanol has attracted widespread attention because of its abundant sources and low toxicity. As an anode catalyst, palladium (Pd) shows superior potential in alkaline media. Current research focuses on developing a high-performance, low-cost Pd-based catalyst.

Some studies have found that introducing other oxygen-loving metals or non-metals into Pd will change its electronic structure, which will help promote the further oxidation of toxic intermediates and improve its catalytic performance accordingly. Hydrogen atoms are one example. Early palladium hydride (PdH) was obtained in a high-pressure hydrogen atmosphere or by adding borohydride, but the resulting PdH structure was unstable and the hydrogen in the palladium lattice was easily released under ambient conditions, which limited its use. Exploration in the field of electrocatalysis. Recent research has found that certain solvents can release hydrogen in situ under specific conditions, and the prepared PdH structure is relatively stable. For example, stable PdH nanocubes were successfully prepared through N,N-dimethylformamide (DMF). It promotes its methanol electrocatalytic oxidation performance under alkaline conditions, but weakens its anti-toxicity against carbon monoxide (CO); some researchers also synthesized it by repeatedly adding hydrazine solution (N ₂ H ₄ ) to Pd nanocubes. PdH nanocatalyst was added to enhance the activity and stability of formic acid oxidation. The structure and composition of a catalyst largely influence its activity and selectivity. A large-area structure can expose more active sites and improve its catalytic activity; the synergistic effect between different components can also change the catalyst's ability to adsorb and desorb molecules during the reaction process. Therefore, on the premise of ensuring catalytic performance, replacing precious metals with some cheap metals is an effective strategy to save costs. Most of the PdH nanocatalysts reported in the literature are based on particles, but PdH with a network structure has not been reported yet.

Based on the above problems, designing a PdH nanocatalyst with high activity, high toxicity resistance, and low cost has important industrial application significance.

Contents of the invention

The present invention aims to provide a preparation of oxygen-friendly metal-doped network PdH/C and its application in the electrocatalytic oxidation of ethanol to improve the activity and stability of Pd-based catalysts.

The preparation method of oxygen-friendly metal-doped network-like PdH/C of the present invention includes the following steps:

Step 1: Place palladium acetylacetonate (Pd(acac) ₂ ) and the oxygen-loving metal precursor in a glass bottle, add the solvent 1-octadecene and amine solution, and dissolve with ultrasonic to form a uniformly dispersed solution;

Step 2: Place the glass bottle from Step 1 in an oil bath, heat it from room temperature to 150°C to 190°C and react for 4 to 8 hours;

Step 3: After the reaction is completed, cool to room temperature naturally, wash with a mixed solution of ethanol and cyclohexane, and centrifuge several times to finally obtain an M-PdH nanocatalyst with a network structure (M=Fe, Co, Ni, Bi) ;

Step 4: Place the activated carbon in cyclohexane for ultrasonic dispersion, add the M-PdH nanocatalyst obtained in step 3, continue ultrasonic dispersion, wash and centrifuge with acetic acid and cyclohexane, and dry to obtain M with a network structure. -PdH/C nanocatalyst. The loading amount of precious metal Pd is between 15% and 20%.

In step 1, the oxygen-loving metal precursor is selected from Fe(acac) ₂ , Co(acac) ₂ , Ni(acac) ₂ or Bi(OAc) ₃ , preferably Bi(OAc) ₃ .

In step 1, the concentration of Pd(acac) ₂ in the system is 2 mg/mL, and the concentration of the oxygen-loving metal precursor is 0.1 mg/mL to 1 mg/mL. Further preferably, the optimal concentration of Bi(OAc) ₃ is 0.24 mg/mL.

In step 1, the amine solution is oleylamine; and the volume ratio of oleylamine to 1-octadecene is 3:2. For example, the volume of oleylamine is 3mL and the volume of 1-octadecene is 2mL.

The application of the oxygen-friendly metal-doped network PdH/C nanocatalyst of the present invention is to be used as a catalyst in the process of electrocatalytic oxidation of ethanol under alkaline conditions.

Specifically, a standard three-electrode system was used, with a platinum electrode as the counter electrode, a Hg/HgO electrode as the reference electrode, and a glassy carbon electrode coated with a meshed M-PdH/C nanocatalyst as the working electrode. The electrolyte contains a mixed solution of 1 mol/L KOH and 1 mol/LC ₂ H ₅ OH, which is purified by nitrogen gas until it is saturated before testing. Cyclic voltammetry testing was performed at a scan rate of 0.05V/s in the potential range of -0.9~0.3V, and compared with commercial Pd/C to explore its mass activity and anti-toxicity; and at -0.13V ( Stability test for 5000 seconds relative to Hg/HgO) potential.

The beneficial effects of the present invention are reflected in:

Under the solvothermal synthesis method, M-PdH/C nanocatalysts with a network structure were successfully prepared by adding palladium acetylacetonate and oxygen-loving metal precursors to the amine and 1-octadecene systems. The complex network structure can expose more active sites, and the introduction of cheap oxygen-loving metals not only reduces the preparation cost, but its synergistic effect with palladium further improves its ethanol oxidation performance under alkaline conditions. At the same time, the introduction of oxygen-loving metals also improves the catalyst's resistance to toxic intermediates (such as CO), indicating that it has superior stability in the electrocatalytic oxidation process.

Description of the drawings

The technical solution of the present invention will be further described below with reference to the accompanying drawings and examples. It should be noted that these drawings do not limit the scope of the present invention, but are only used as an explanation of the technical solution of the present invention.

Figure 1a is a transmission electron microscope image (TEM) of the PdH nanocatalyst prepared in Example 1, and Figure 1b is the corresponding X-ray diffraction image (XRD).

Figure 2a is the cyclic voltammogram (CV) of the PdH/C nanocatalyst prepared in Example 1 and commercial Pd/C in 1mol/LKOH solution, Figure 2b is the two in 1mol/LKOH and 1mol/LC ₂ H ₅ CV diagram in OH mixed solution.

Figure 3 is a chronoamperometric curve of the PdH nanocatalyst prepared in Example 1 and commercial Pd/C in a mixed solution of 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH.

Figure 4a is a TEM image of the Bi-PdH nanocatalyst prepared in Example 2, and Figure 4b is an XRD comparison chart of the PdH in Example 1 and the Bi-PdH nanocatalyst in Example 2.

Figure 5 is the X-ray photoelectron spectrum (XPS) of the Bi-PdH nanocatalyst prepared in Example 2.

Figure 6a is the CV diagram of the Bi-PdH/C nanocatalyst prepared in Example 2 and commercial Pd/C in 1 mol/LKOH solution. Figure 6b is the CV chart of the two in 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH mixed solution. CV diagram.

Figure 7 is a chronoamperometric curve of the PdH/C nanocatalyst prepared in Example 2 and commercial Pd/C in a mixed solution of 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH.

Figure 8a is the CV diagram of the Bi-PdH/C nanocatalyst prepared in Example 3 and commercial Pd/C in 1 mol/LKOH solution. Figure 8b is the CV chart of the two in 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH mixed solution. CV diagram.

Figure 9 is a chronoamperometric curve of the Bi-PdH/C nanocatalyst prepared in Example 3 and commercial Pd/C in a mixed solution of 1 mol/L KOH and 1 mol/LC ₂ H ₅ OH.

Figure 10a is the CV diagram of the Bi-PdH/C nanocatalyst prepared in Example 4 and commercial Pd/C in 1 mol/LKOH solution. Figure 10b is the CV chart of the two in 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH mixed solution. CV diagram.

Figure 11 is a chronoamperometric curve of the Bi-PdH/C nanocatalyst prepared in Example 4 and commercial Pd/C in a mixed solution of 1 mol/L KOH and 1 mol/LC ₂ H ₅ OH.

Figure 12 is a CV comparison chart of the M-PdH/C (M=Fe, Co, Ni) nanocatalyst prepared in Example 5 in a mixed solution of 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH.

Detailed ways

The technical solution of the present invention will be further described below with reference to specific examples. It should be noted that the following specific descriptions of the examples are only used to illustrate the synthesis, characterization and performance of the catalyst and should not be understood as a limitation of the present invention. Limitations, those embodiments not directly mentioned in this article may still be obtained by combining these technical solutions.

Example 1:

This example prepares a network-like PdH/C nanocatalyst without oxygen-loving metal doping, including the following steps:

1. Weigh 10 mg of Pd(acac) ₂ into a glass bottle, add 2 mL of 1-octadecene and 3 mL of oleylamine, close the small cap tightly, and sonicate for about 20 minutes until the precursor is completely dissolved to form a uniform mixture.

2. Place the above mixture in an oil bath, heat it from room temperature to 170°C, and keep it for 6 hours.

3. After the reaction is completed, cool to room temperature naturally, wash with a mixed solution of cyclohexane and ethanol, collect the product by centrifugation at 9300 rpm, repeat the operation three times, and dissolve the obtained product in 5 mL of cyclohexane for later use.

4. Weigh 8.0mg of activated carbon into a centrifuge tube, add 5mL of cyclohexane and sonicate for 30 minutes to disperse the activated carbon evenly.

5. Add the product obtained in step 3 to the activated carbon dispersed in step 4, continue ultrasonic for 1 hour, centrifuge, wash with acetic acid and cyclohexane, and finally wash once with cyclohexane. The product is dried to obtain networked PdH/C nanoparticles. catalyst.

Figure 1a is a TEM image of the PdH nanocatalyst prepared in Example 1. It can be seen that the sample exhibits an intertwined network structure. Figure 1b is the XRD pattern of the PdH nanocatalyst prepared in Example 1. It can be seen that the XRD diffraction peak of the sample has an obvious negative shift relative to the metal Pd (JCPDS: 46-1043), indicating the formation of PdH, and the diffraction peak of The negative shift can be attributed to the introduction of hydrogen which expands the lattice of Pd.

Figure 2a is the cyclic voltammetry curve of the PdH/C nanocatalyst prepared in Example 1 and commercial Pd/C in 1mol/LKOH solution; Figure 2b is the mixture of the two in 1mol/L KOH and 1mol/LC ₂ H ₅ OH From the cyclic voltammetry curve in the solution, it can be seen that compared with commercial Pd/C (0.77Amg _Pd ^-1 ), PdH/C nanocatalysis has a higher mass activity, reaching 3.80Amg _Pd ^-1 , which is about the commercial Pd/C (0.77Amg Pd -1 ). 5.0 times that of Pd/C, indicating that the PdH/C nanocatalyst prepared in Example 1 has better ethanol oxidation performance.

Figure 3 is a chronoamperometric curve of the PdH/C nanocatalyst prepared in Example 1 and commercial Pd/C in a mixed solution of 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH. Compared with commercial Pd/C, Example 1 The prepared PdH/C nanocatalyst still has a higher current density after 5000 seconds of stability test, indicating that it has higher stability in the electrocatalytic oxidation process.

Example 2:

This example prepares a bismuth-doped network Bi-PdH/C nanocatalyst, including the following steps:

1. Weigh 10 mg Pd(acac) ₂ and 1.2 mg Bi(OAc) ₃ into a glass bottle, add 2 mL 1-octadecene and 3 mL oleylamine, close the small cap tightly, and sonicate for about 20 minutes until the precursor is completely dissolved. Form a homogeneous mixture.

2. Place the above mixture in an oil bath, heat it from room temperature to 170°C, and keep it for 6 hours.

3. After the reaction is completed, cool to room temperature naturally, wash with a mixed solution of cyclohexane/ethanol, collect the product by centrifugation at 9300 rpm, repeat the operation three times, and dissolve the obtained product in 5 mL of cyclohexane for later use.

4. Weigh 8.0mg of activated carbon into a centrifuge tube, add 5mL of cyclohexane and sonicate for 30 minutes to disperse the activated carbon evenly.

5. Add the product obtained in step 3 to the activated carbon dispersed in step 4, continue ultrasonic for 1 hour, centrifuge, wash with acetic acid and cyclohexane, and finally wash once with cyclohexane. After drying the product, the Bi-PdH/C network is obtained Nanocatalyst.

Figure 4a is a TEM image of the Bi-PdH nanocatalyst prepared in Example 2. It can be seen that the sample still exhibits an intertwined network structure. Figure 4b is an XRD comparison chart of the PdH in Example 1 and the Bi-PdH nanocatalyst in Example 2. The XRD diffraction peak positions of the two are basically the same.

Figure 5 is an XPS image of the Bi-PdH nanocatalyst prepared in Example 2. It can be seen that the bismuth element exists in the catalyst. Combining the XRD and TEM images shows that we have successfully prepared a Bi-PdH nanocatalyst with a network structure.

Figure 6a is the cyclic voltammetry curve of the Bi-PdH/C nanocatalyst prepared in Example 2 and commercial Pd/C in 1mol/LKOH solution; Figure 6b is the cyclic voltammogram of the two in 1mol/LKOH and 1mol/LC ₂ H ₅ OH From the cyclic voltammetry curve in the mixed solution, it can be seen that compared with commercial Pd/C (0.77Amg _Pd ^-1 ), Bi-PdH/C nanocatalysis has a higher mass activity, reaching 8.02Amg _Pd ^-1 . It is about 10.4 times that of commercial Pd/C, indicating that the PdH/C nanocatalyst prepared in Example 2 has better ethanol oxidation performance.

Figure 7 is a chronoamperometric curve of the Bi-PdH/C nanocatalyst prepared in Example 2 and commercial Pd/C in a mixed solution of 1 mol/L KOH and 1 mol/LC ₂ H ₅ OH. Compared with commercial Pd/C, The Bi-PdH/C nanocatalyst prepared in Example 2 still has a higher current density after a stability test of 5000 seconds, indicating that it has higher stability during the electrocatalytic oxidation process.

Example 3:

The Bi-PdH/C nanocatalyst was prepared according to the method described in Example 2, keeping other conditions unchanged and only changing the mass of Bi(OAc) ₃ to 2.4 mg.

Figure 8a is the cyclic voltammetry curve of the Bi-PdH/C nanocatalyst prepared in Example 3 and commercial Pd/C in 1mol/LKOH solution; Figure 8b is the cyclic voltammogram of the two in 1mol/LKOH and 1mol/LC ₂ H ₅ OH From the cyclic voltammetry curve in the mixed solution, it can be seen that compared with commercial Pd/C (0.77Amg _Pd ^-1 ), Bi-PdH/C nanocatalysis has a higher mass activity, reaching 6.30Amg _Pd ^-1 . It is 8.1 times that of commercial Pd/C, indicating that the PdH/C nanocatalyst prepared in Example 3 has better ethanol oxidation performance.

Figure 9 is a chronoamperometric curve of the Bi-PdH/C nanocatalyst prepared in Example 3 and commercial Pd/C in a mixed solution of 1 mol/L KOH and 1 mol/LC ₂ H ₅ OH. Compared with commercial Pd/C, The Bi-PdH/C nanocatalyst prepared in Example 3 still has a higher current density after a stability test of 5000 seconds, indicating that it has higher stability during the electrocatalytic oxidation process.

Example 4:

The Bi-PdH/C nanocatalyst was prepared according to the method described in Example 2, keeping other conditions unchanged and only changing the mass of Bi(OAc) ₃ to 0.6 mg.

Figure 10a is the cyclic voltammetry curve of the PdH/C nanocatalyst prepared in Example 4 and commercial Pd/C in 1mol/LKOH solution; Figure 10b is the mixed solution of the two in 1mol/LKOH and 1mol/LC ₂ H ₅ OH From ^the cyclic ^voltammetry _{curve in} 8.0 times that of Pd/C, indicating that the PdH/C nanocatalyst prepared in Example 4 has better ethanol oxidation performance.

Figure 11 is a chronoamperometric curve of the Bi-PdH/C nanocatalyst prepared in Example 4 and commercial Pd/C in a mixed solution of 1 mol/L KOH and 1 mol/LC ₂ H ₅ OH. Compared with commercial Pd/C, The Bi-PdH/C nanocatalyst prepared in Example 4 still has a higher current density after a stability test of 5000 seconds, indicating that it has higher stability during the electrocatalytic oxidation process.

Example 5:

The network-like PdH/C nanocatalyst doped with iron, cobalt, and nickel oxygen-loving metals was prepared according to the method described in Example 2. Keeping other conditions unchanged, only Bi(OAc) ₃ was replaced with 2.3 mg of Fe(acac). ₂ , 2.2 mg of Co(acac) ₂ , 2.0 mg of Ni(acac) ₂ .

Figure 12 is a comparison diagram of the cyclic voltammogram curves of the M-PdH/C (M=Fe, Co, Ni) nanocatalyst prepared in Example 5 in a mixed solution of 1 mol/LKOH and 1 mol/LC ₂ H ₅ OH. It can be seen that The catalysts prepared in Example 5 all have higher mass activity than commercial Pd/C, indicating that doping with other oxygen-loving metals can also enhance the ethanol oxidation performance of PdH/C nanocatalysts.

Claims (3)

1. The application of the network-shaped PdH/C nano catalyst doped with the oxophilic metal is characterized in that:

the network-shaped PdH/C nano catalyst doped with the oxophilic metal is used as a catalyst in the process of electrocatalytic oxidation of ethanol under an alkaline condition;

the network-shaped PdH/C doped with the oxophilic metal is prepared by the following steps:

step 1: placing palladium acetylacetonate and an oxophilic metal precursor into a glass bottle, adding a solvent 1-octadecene and an amine solution, and performing ultrasonic dissolution to form a uniformly dispersed solution;

step 2: placing the glass bottle in the step 1 in an oil bath pot, heating to 150-190 ℃ from room temperature, and reacting for 4-8 hours;

step 3: naturally cooling to room temperature after the reaction is finished, washing with a mixed solution of ethanol and cyclohexane, and centrifuging for several times to finally obtain the M-PdH nano catalyst with a network structure, wherein M=Fe, co, ni or Bi;

step 4: placing activated carbon into cyclohexane for ultrasonic dispersion, adding the M-PdH nano catalyst obtained in the step 3 into the cyclohexane, continuing ultrasonic dispersion uniformly, washing and centrifuging with acetic acid and cyclohexane, and drying to obtain the M-PdH/C nano catalyst with a network structure;

in step 1, the oxophilic metal precursor is selected from Fe (acac) ₂ 、Co(acac) ₂ 、Ni(acac) ₂ Or Bi (OAc) ₃ ；

In step 1, pd (acac) in the system ₂ The concentration of the precursor of the oxophilic metal is 2mg/mL, and the concentration of the precursor of the oxophilic metal is 0.1 mg/mL-1 mg/mL;

in the step 1, the amine solution is oleylamine.

2. The use according to claim 1, characterized in that:

the volume ratio of the amine solution to the 1-octadecene is 3:2.

3. The use according to claim 1, characterized in that:

using a standard three-electrode system, taking a platinum sheet electrode as a counter electrode, a Hg/HgO electrode as a reference electrode, and a glassy carbon electrode with a netlike M-PdH/C nano catalyst coated on the surface as a reference electrodeWorking electrode, electrolyte is formed by KOH and C ₂ H ₅ Mixed solution of OH.