CN101259410A - A kind of method for preparing platinum catalyst by electrodeposition - Google Patents

Abstract

The invention relates to the preparation of a platinum catalyst for a direct methanol fuel cell. The electrodeposition method is used to conduct pulse electrodeposition of platinum in two stages, that is, the I stage uses a relatively large current for crystal nucleus formation, and the II stage uses a small current for crystal nucleus formation. The particle size of the prepared catalyst can be reduced by changing the applied electrical signal, so that the formed platinum particles are more dispersed, have a higher coverage rate, and a larger specific surface area, thereby reducing the platinum loading per unit area of the electrode. The amount improves its utilization rate and activity, while reducing the cost of the catalyst. The application of this method is simple and controllable. The prepared platinum catalyst can be applied not only to direct methanol fuel cells, but also to other fuel cell catalysts. In addition, this method can be extended to platinum-ruthenium co-deposition and other multi-element metal co-deposition.

Description

A kind of method for preparing platinum catalyst by electrodeposition

technical field

The invention relates to the fields of fuel cell and catalyst preparation, in particular to a method for preparing a platinum-based direct methanol fuel cell catalyst.

Background technique

Direct methanol fuel cell (DMFC) has attracted much attention due to its advantages of high energy conversion efficiency, no pollution, no noise, simple system structure, high specific energy and convenient fuel portability. One of the key materials of DMFC is the electrode catalyst, whose activity directly affects the performance of the battery. At present, the electrocatalysts used in DMFC all use platinum as the main component, but platinum is a precious metal with scarce resources, and its utilization rate and activity are not high enough to meet the requirements of DMFC commercial use. The position of the catalyst platinum particles must be in the area that can contact the reactants, electron conductors and proton conductors at the same time, that is, the three-phase reaction zone, because only in the three-phase reaction zone can effective diffusion of gas and water and protons and electrons be guaranteed. Efferent and incoming from the catalytic reaction site. In electrodes prepared by traditional chemical synthesis methods, many platinum particles become inactive Pt because they are not in the three-phase reaction zone. In order to overcome the above disadvantages and improve the utilization rate of noble metals, Pt prepared by electrodeposition is only deposited in the region with both electron conductivity and proton conductivity. This process can avoid the loss of active platinum sites, so that the deposited Pt is an effective catalyst, which improves the utilization rate of noble metals, that is, the catalytic activity of the noble metal catalyst Pt per unit mass, thereby reducing the cost of the electrode. Such as the report of Kyoung Hwan Choi, et.al., Electrode fabrication for proton exchange membrane fuel cells by pulse electrodeposition, J.Power Sources 75 (1998) 230, but adopt two electrode system to carry out pulse electrodeposition to prepare platinum catalyst, there is Platinum has the disadvantages of high cost and low controllability as an anode. Another example is the invention of CN1947835A "a method for preparing a catalyst for direct methanol fuel cell by pulse electrodeposition", which proposes a method of directly depositing Pt on the activated carbon black/ionic emulsion carrier, although it has a slightly higher methanol electrolysis rate than the commercial catalyst. Oxidation catalytic activity, but the particle size is in the range of 100-300nm, and the dispersion and coverage rate are not high. To improve its catalytic methanol electrooxidation performance, the particle size needs to be reduced, the dispersion and coverage rate need to be improved, and the activity needs to be further enhanced. .

Contents of the invention

The purpose of the present invention is to make up for the deficiency of the above method, by performing pulse electrodeposition platinum in two stages, that is, the I stage adopts a large current for crystal nucleus formation, and the II stage adopts a small current for crystal nucleus growth, so that the formed The platinum particles are more dispersed, the coverage is higher, and the size is further reduced, and the specific surface area is larger, thereby reducing the platinum load per unit area of the electrode, improving the utilization rate and activity of platinum, and reducing the cost of the catalyst. The application method is simple and controllable .

The present invention comprises following implementation steps:

混合液，按照每毫升乙醇加入5～8毫克的比例，将经过酸化处理的活性炭Vulcan XC-72置于乙醇中，再加入

溶液(5wt.％)超声分散30～60分钟，形成碳浆，保证

溶液与乙醇悬浮液的质量百分比为100∶1～100∶5；1. Configure ethanol containing activated carbon and

Mixed liquid, according to the ratio of 5-8 mg per ml of ethanol, put the acidified activated carbon Vulcan XC-72 in ethanol, and then add

The solution (5wt.%) is ultrasonically dispersed for 30-60 minutes to form a carbon slurry, ensuring

The mass percentage of solution and ethanol suspension is 100:1～100:5;

2. Pipette 150-300 μL of the above-mentioned carbon slurry per square centimeter and drop it on the surface of the treated glassy carbon, graphite, carbon paper, carbon cloth and other catalyst substrates. Dry for 4-10 hours to prepare the working electrode used in the electrodeposition process.

3. A three-electrode system is composed of a working electrode, a counter electrode and a reference electrode, wherein the working electrode is the electrode prepared in step 2, the counter electrode is a platinum electrode, the reference electrode is a saturated calomel electrode (SCE), and the electrolyte contains The mixed solution of 0.5mol·L ^-1 H ₂ SO ₄ and 0.5～2mmol·L ^-1 H ₂ PtCl ₆ with 0～10 ^-3 mM additives, the pulse electrodeposition is carried out in two stages for pulse electrodeposition of platinum, the first stage is in Deposition is performed for 30-120s at a larger peak current density of 12-36mA·cm ^-2 , and a smaller peak current density of 4-10mA·cm ^-2 is used in the second stage. The current on-off time ratio t _off /t _on is 1.5-6:1, and the total deposition electricity is 1-2.5 C·cm ^-2 . The electrodeposition temperature is 20-60°C. During the electrodeposition process, argon was introduced into the solution.

The optimal choice of the additive is 10 ^-5 ~ 10 ^-3 mM, wherein the additive is selected from one of polyethylene glycol (PEG), lead acetate (LA), polyvinylpyrrolidone (PVP) and citric acid.

The advantage of the present invention is that there is no need to change the process method, only by changing the applied electrical signal, the crystal grains of the prepared catalyst can be reduced, so that the formed platinum particles are more dispersed, the coverage rate is higher, and the specific surface area is larger, thereby reducing The platinum load per unit area of the electrode is increased, its utilization rate and activity are improved, and the cost of the catalyst is reduced at the same time, and the application method is very simple. The prepared platinum catalyst can be applied not only to direct methanol fuel cells, but also to other fuel cell catalysts. In addition, this method can be extended to platinum-ruthenium co-deposition and other multi-element metal co-deposition.

Description of drawings

Fig. 1 is the 50,000 times magnified scanning electron microscope morphology of the catalyst synthesized in Example 2.

Fig. 2 is the 50,000 times magnified scanning electron microscope morphology of the catalyst synthesized in Example 3.

Fig. 3 is the cyclic voltammetry curve of the methanol catalytic electro-oxidation of the catalyst synthesized in Example 1.

Fig. 4 is the cyclic voltammetry curve of the methanol catalytic electro-oxidation of the catalyst synthesized in Example 2.

Fig. 5 is the cyclic voltammetry curve of the methanol catalytic electro-oxidation of the catalyst synthesized in Example 3.

Fig. 6 is the cyclic voltammetry curve of methanol catalytic electrooxidation of platinum catalyst synthesized by pulse electrodeposition under the condition of no segmental electrodeposition and constant peak current density of 6 mA·cm ^-2 .

Detailed ways

In 0.5mol·L ^-1 H ₂ SO ₄ +1.0mol·L ^-1 CH ₃ OH solution, the potential is between 0 and 0.75V, and the sweep rate is 10mV·s ^-1 for cyclic voltammetry. Argon was passed through the electrolyte for 20 min before the cyclic voltammetry experiment to eliminate the influence of dissolved oxygen in the solution. Take the cyclic voltammetry curve after three consecutive weeks of curve overlap. The test temperature is 30°C. The electrochemical performance of electrodes prepared by electrodeposition under different conditions was compared by comparing the currents corresponding to different electrodes at the same potential.

Example 1:

溶液与乙醇悬浮液的质量百分比为100∶1；取75μL滴到处理好的玻碳电极(面积0.28cm²)表面上；待乙醇蒸发完后，将电极50℃真空干燥7h，制得电沉积过程中所使用的工作电极，对电极为铂电极，参比电极为饱和甘汞电极(SCE)，以下所述电位均相对于SCE。电解液为0.5mol·L^-1H₂SO₄+2.0mmol·L^-1H₂PtCl₆。脉冲电沉积分两个阶段进行脉冲电沉积铂，I阶段在峰值电流密度12mA·cm^-2下沉积120s，II阶段的峰值电流密度为8mA·cm^-2，总的沉积电量为1.2C·cm^-2，电流的通断时间比t_off/t_on为300ms∶100ms，电沉积温度为20℃。电沉积过程中向溶液中通入氩气。Weigh 50 mg of acidified Vulcan XC-72 into 10 mL of ethanol, add 100 μL of Solution (5wt.%, density 45mgNafion/mL) was ultrasonically dispersed for 60 minutes, mixed evenly to form a carbon slurry,

The mass percentage of solution and ethanol suspension is 100:1; take 75 μL and drop it on the surface of the treated glassy carbon electrode (area 0.28cm ² ); after the ethanol is evaporated, dry the electrode in vacuum at 50°C for 7 hours to obtain electrodeposition The working electrode used in the process, the counter electrode is a platinum electrode, and the reference electrode is a saturated calomel electrode (SCE). The potentials described below are all relative to SCE. The electrolyte solution is 0.5mol·L ^-1 H ₂ SO ₄ +2.0mmol·L ^-1 H ₂ PtCl ₆ . The pulse electrodeposition is divided into two stages for pulse electrodeposition of platinum. In the first stage, the peak current density is 12mA·cm ^-2 for 120s. In the second stage, the peak current density is 8mA·cm ^-2 , and the total deposition electricity is 1.2C·cm ^-2 , the current on-off time ratio t _off /t _on is 300ms:100ms, and the electrodeposition temperature is 20°C. During the electrodeposition process, argon was introduced into the solution.

Example 2:

溶液(5wt.％，密度为45mgNafion/mL)超声分散40分钟，混合均匀，形成碳浆，

溶液与乙醇悬浮液的质量百分比为100∶4；取75μL滴到处理好的石墨电极(面积0.5cm²)表面上；待乙醇蒸发完后，将电极60℃真空干燥5h，制得电沉积过程中所使用的工作电极，对电极为铂电极，参比电极为饱和甘汞电极(SCE)。电解液为0.5mol·L^-1H₂SO₄+0.5mmol·L^-1H₂PtCl₆。脉冲电沉积分两个阶段进行脉冲电沉积铂，I阶段在峰值电流密度36mA·cm^-2下沉积60s，II阶段的峰值电流密度为6mA·cm^-2，总的沉积电量为1.2C·cm^-2，电流的通断时间比t_off/t_on为4s∶1s，电沉积温度为50℃。电沉积过程中向溶液中通入氩气。制得高分散的纳米级铂催化剂，如图1所示。直径约100nm左右的块状Pt粒子，比表面积很大，覆盖率高。Weigh 40 mg of acidified Vulcan XC-72 into 5 mL of ethanol, add 200 μL of

Solution (5wt.%, density 45mgNafion/mL) was ultrasonically dispersed for 40 minutes, mixed uniformly to form a carbon slurry,

The mass percentage of the solution and the ethanol suspension is 100:4; take 75 μL and drop it on the surface of the treated graphite electrode (area 0.5 cm ² ); after the ethanol is evaporated, the electrode is vacuum-dried at 60°C for 5 hours to obtain the electrodeposition process The working electrode, the counter electrode is a platinum electrode, and the reference electrode is a saturated calomel electrode (SCE). The electrolyte solution is 0.5mol·L ^-1 H ₂ SO ₄ +0.5mmol·L ^-1 H ₂ PtCl ₆ . The pulse electrodeposition is divided into two stages for pulse electrodeposition of platinum. In the first stage, the peak current density is 36mA·cm ^-2 for 60s. In the second stage, the peak current density is 6mA·cm ^-2 , and the total deposition electricity is 1.2C·cm ^-2 , the current on-off time ratio t _off /t _on is 4s:1s, and the electrodeposition temperature is 50°C. During the electrodeposition process, argon was introduced into the solution. A highly dispersed nanoscale platinum catalyst was prepared, as shown in Figure 1. Blocky Pt particles with a diameter of about 100nm have a large specific surface area and a high coverage.

Example 3:

溶液(5wt.％，密度为45mgNafion/mL)超声分散30分钟，混合均匀，形成碳浆，

溶液与乙醇悬浮液的质量百分比为100∶2；取100μL滴到处理好的石墨电极表面上；待乙醇蒸发完后，将电极60℃真空干燥5h，制得电沉积过程中所使用的工作电极，对电极为铂电极，参比电极为饱和甘汞电极(SCE)。电解液为0.5mol·L^-1H₂SO₄+1.0mmol·L^-1H₂PtCl₆+10^-5mmol·L^-1PEG(分子量为400)。脉冲电沉积分两个阶段进行脉冲电沉积铂，I阶段在峰值电流密度24mA·cm^-2下沉积90s，II阶段的峰值电流密度为10mA·cm^-2，总的沉积电量为12C·cm^-2，电流的通断时间比t_off/t_on为5s∶1s，电沉积温度为30℃。电沉积过程中向溶液中通入氩气。制得高分散、高覆盖率的纳米级铂催化剂，如图2所示。Pt粒子的形貌为直径约从20至100nm的块状，块上还有小的阶梯，比表面积非常大。Weigh 50 mg of acidified Vulcan XC-72 into 10 mL of ethanol, add 200 μL of

Solution (5wt.%, density 45mgNafion/mL) was ultrasonically dispersed for 30 minutes, mixed evenly to form a carbon slurry,

The mass percentage of the solution and the ethanol suspension is 100:2; take 100 μL and drop it on the surface of the treated graphite electrode; after the ethanol is evaporated, the electrode is vacuum-dried at 60°C for 5 hours to obtain the working electrode used in the electrodeposition process , the counter electrode is a platinum electrode, and the reference electrode is a saturated calomel electrode (SCE). The electrolyte solution is 0.5mol·L ^-1 H ₂ SO ₄ +1.0mmol·L ^-1 H ₂ PtCl ₆ +10 ^-5 mmol·L ^-1 PEG (400 molecular weight). The pulse electrodeposition is divided into two stages for pulse electrodeposition of platinum. In the first stage, the peak current density is 24mA·cm ^-2 for 90s. In the second stage, the peak current density is 10mA·cm ^-2 , and the total deposition capacity is 12C·cm ^{-2 2.} The current on-off time ratio t _off /t _on is 5s:1s, and the electrodeposition temperature is 30°C. During the electrodeposition process, argon was introduced into the solution. A nanoscale platinum catalyst with high dispersion and high coverage was prepared, as shown in Figure 2. The morphology of Pt particles is a block with a diameter of about 20 to 100 nm, and there are small steps on the block, and the specific surface area is very large.

Carry out cyclic voltammetry test to the catalyst synthesized in the above examples 1-3 in methanol solution, the test results are shown in Figure 3, Figure 4, and Figure 5 respectively, and without segmental electrodeposition, the peak current density is constant at 6mA · cm ^-2 , a platinum catalyst (as shown in Figure 6 ) prepared with a deposition charge of 1.2C·cm ^-2 and a current on-off time ratio t _off /t _on of 4s:1s (as shown in Figure 6 ) was compared. It can be seen that compared with no segmented electrodeposition, the platinum catalyst prepared by segmented electrodeposition has a higher peak current density of methanol oxidation, and has a higher catalytic activity for methanol electrooxidation.

Example 4:

The process is similar to Example 3, but the electrolyte is 0.5mol·L ^-1 H ₂ SO ₄ +1.0mmol·L ^-1 H ₂ PtCl ₆ +10 ^-4 mmol·L ^-1 LA. The pulse electrodeposition is divided into two stages for pulse electrodeposition of platinum. The first stage is deposited at a peak current density of 24mA·cm ^-2 for 90s, the peak current density of the second stage is 6mA·cm ^-2 , and the total deposition electricity is 1.08C·cm ^-2 , the current on-off time ratio t _off /t _on is 5s: 1s to prepare a nanoscale platinum catalyst with high dispersion and high coverage.

Example 5:

The process is similar to Example 3, but the substrate is carbon paper, and the electrolyte is 0.5mol·L ^-1 H ₂ SO ₄ +10mmol·L ^-1 H ₂ PtCl ₆ +10 ^-4 mmol·L ^-1 PVP (molecular weight is 60000 ). The pulse electrodeposition is divided into two stages for pulse electrodeposition of platinum. The first stage is deposited at a peak current density of 24mA·cm ^-2 for 120s, the peak current density of the second stage is 4mA·cm ^-2 , and the total deposition electricity is 2.4C·cm ^-2 , the current on-off time ratio t _off /t _on is 5s: 1s to prepare a nanoscale platinum catalyst with high dispersion and high coverage.

Claims (5)

1. A method for preparing a platinum catalyst by electrodeposition, characterized in that a three-electrode system is composed of a working electrode, a counter electrode and a reference electrode, and the electrolyte is 0.5mol L ^-1 containing 0-10 ^-3 mM additive In the mixed solution ^of H ₂ SO ₄ and 0.5～2mmol·L ^-1 H ₂ PtCl ₆ , the pulse electrodeposition of platinum was carried out in two stages. Thereafter, the peak current density is 4-10mA·cm ^-2 , the total deposition electricity is 1-2.5C·cm- ² , the current on-off time ratio t _off /t _on is 1.5-6:1, and the electrodeposition temperature It is 20-60°C. 2. The method according to claim 1, wherein the additive is 10 ^-5 ~ 10 ^-3 mM, one selected from polyethylene glycol, lead acetate, polyvinylpyrrolidone, and citric acid. 3. The method according to claim 1, characterized in that the working electrode is first configured with ethanol containing activated carbon and

Mixed liquid, according to the ratio of 5-8 mg per ml of ethanol, put the acidified activated carbon Vulcan XC-72 in ethanol, and then add The solution (5wt.%) was ultrasonically dispersed for 30-60 minutes to form a carbon slurry; then pipette 150-300 μL of the above-mentioned carbon slurry per square centimeter and drop it on the surface of the catalyst substrate. °C for 4-10 hours in vacuum to prepare the working electrode used in the electrodeposition process. 4. The method of claim 3, wherein:

The mass percentage of the solution and the ethanol suspension is 100:1-100:5. 5. The method according to claim 3, wherein the catalyst substrate is one of glassy carbon, graphite, carbon paper, and carbon cloth.

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