CN103643219A - Preparation method of boron-doped diamond film electrode taking porous titanium as matrix - Google Patents

Abstract

The invention discloses a method for preparing a boron-doped diamond film electrode with porous titanium as a matrix, which is characterized in that the titanium matrix is a porous titanium material with a porosity of 20-50%, and hot wire chemical vapor deposition equipment is used. Preparation of Porous Ti-based BDD Electrodes by Second-Order Boron Concentration Controlled Chemical Vapor Deposition. This method controls the generation of TiC by adjusting the boron source concentration at different stages of the chemical vapor deposition process, that is, using high boron doping to suppress the formation of TiC in the initial stage, improving the bonding force between the substrate and the film, and reducing the boron source concentration in the later stage of the reaction. Low boron doping. The diamond crystal grains of the porous titanium-based BDD electrode prepared by the invention are uniform and dense, the porous titanium substrate is completely covered by the diamond film, and has good stability and a wide potential window.

Description

A kind of preparation method of boron-doped diamond film electrode with porous titanium as substrate

technical field

The invention belongs to the technical field of electrode materials, and in particular relates to a method for preparing a boron-doped diamond thin film electrode (BDD) by chemical vapor deposition on a porous titanium substrate using a second-order boron concentration control method.

Background technique

Among many known anode materials, boron-doped diamond film electrode (BDD) has the characteristics of wide potential window, low background current, good electrochemical stability, strong corrosion resistance, and surface is not easy to be polluted. The electrode material with the highest oxygen potential (E° _OH/H2O = 2.80V vs. SHE) has broad application prospects in electrooxidation, electrosynthesis, electroanalysis, supercapacitors, electrochemical sensors, etc. Due to the good electrical conductivity, high mechanical strength and cheap price of metal titanium (Ti), DSA (dimensionally Stable Anodes) type titanium-based BDD electrodes (Ti/BDD) are expected to be used in commercial processes.

At present, the research on Ti/BDD electrodes mainly focuses on two aspects: one is the preparation and optimization; the other is the application in wastewater treatment. However, these works are basically based on flat titanium-based BDD electrodes, which have the disadvantages of low space-time yield and poor mass transfer effect. If the electrode matrix structure is improved, since the electrode activity is related to its geometric factors, the change of its surface morphology and the increase of the specific surface area will improve the electrode performance.

Porous Ti is a new type of product of titanium metal. It is generally prepared by powder metallurgy technology. It has a porosity of 20-50%. It is honeycomb-shaped. Porosity, pore size, pore morphology, pore distribution, and mechanical properties. Porous titanium has many excellent properties, such as large specific surface area, good electrical and thermal conductivity, high mechanical strength, low price and good stability. If BDD electrodes can be prepared on porous titanium, then this kind of BDD electrode based on porous titanium will have a larger specific surface area than ordinary flat titanium-based BDD electrodes, which will significantly improve the surface utilization of the electrode, which is conducive to the application in field of electrocatalysis and electrochemical energy storage.

Ti/BDD electrodes are generally prepared by chemical vapor deposition. By controlling the preparation conditions (such as pressure, methane concentration, temperature, etc.), high-quality, different-scale (micron, nanometer) BDD films can be obtained on titanium substrates. However, it is very difficult to deposit a BDD film on a porous titanium substrate. In addition to solving the problem of cracking and peeling caused by the different thermal expansion coefficients of the two, and ensuring a good bonding force between the porous titanium substrate and the BDD film, BDD is also required. The membranes are uniformly dispersed on the inner and outer surfaces of the porous titanium matrix, showing a complete three-dimensional porous structure. Diamond nucleation and growth on porous titanium substrates is a very complex process, in which the entire growth process on the surface and inside of porous titanium should be considered. In addition, since the growth rate of diamond in different parts of porous titanium is different, in order to prevent the diamond film from cracking or peeling off from the substrate surface, the continuity between the substrate surface and the film in the hole must be considered. The bonding strength between diamond and titanium substrate is related to the titanium carbide (TiC) formed on its surface, and the formation of TiC will reduce the thermal stress gap between the diamond film and the substrate. However, if the content of TiC is high, its loose and porous structure is likely to cause the immersion of the electrolyte and cause the electrode film to fall off. Chinese patent CN102864482A uses the method of anodic oxidation to form a passivation layer on the surface of the substrate that can effectively prevent the formation of titanium carbide, thereby improving the adhesion characteristics of the diamond film and the porous titanium substrate, but the passivation film formed on the surface of the titanium base has poor conductivity. Its electron transport properties may be affected.

Contents of the invention

The purpose of the present invention is to address the above problems and disclose a method for preparing porous titanium-based BDD electrodes by chemical vapor deposition using a second-order boron concentration control method. The method controls the generation of TiC by adjusting the boron source concentration at different stages of the chemical vapor deposition process In the initial stage, use high boron doping to suppress the formation of TiC, improve the bonding force between the substrate and the film, and reduce the concentration of boron source in the later stage of the reaction for low boron doping, so that the preparation has a large specific surface area, good conductivity and stability. Three-dimensional porous titanium-based BDD electrode materials with other advantages.

Technical scheme of the present invention is:

A method for preparing a boron-doped diamond film electrode with porous titanium as a substrate, at least comprising the following steps:

Step 1: Soak porous titanium with a porosity of 20-50% in hot sodium hydroxide aqueous solution to fully remove oil, then ultrasonically clean the degreased porous titanium with water, put it in 10% hydrochloric acid solution, and heat to a slight boil state until the solution gradually becomes light purple, ultrasonically cleaned with deionized water, and then placed in deionized water for protection;

Step 2: Use the porous titanium treated in the above steps as the substrate, the tantalum wire as the hot wire, methane and hydrogen as the gas source, and trimethyl borate as the boron source. In the methane and hydrogen atmosphere, use the hot wire chemical vapor deposition method Growth of boron-doped diamond film; boron doping is to make H ₂ pass into trimethyl borate (B(OCH ₃ ) ₃ ) solution to enter the reaction system in the form of B(OCH ₃ ) ₃ /H ₂ , carbon, hydrogen, boron The proportion of B(OCH ₃ ) ₃ /H ₂ is controlled by the flow rate of methane, hydrogen, and B(OCH ₃ ) ₃ /H ₂ . B(OCH ₃ ) ₃ /H ₂ adopts low flow rate, and the total sample growth time is controlled at 5-10 hours, among which the growth time at high flow rate is 1.5-3 hours, and the growth time at low flow rate is controlled at 3.5-7 hours.

The flow control ratio of methane, hydrogen, and B(OCH ₃ ) ₃ /H ₂ described in step 2 is: in the initial stage of boron-doped diamond film growth, methane flow rate (sccm): hydrogen flow rate (sccm): B (OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 1:100:3, in the late stage of the reaction, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 1 :100:0.5～1.5

The process parameters of the hot filament chemical vapor deposition method in the second step are: the distance between the sample holder and the filament is 5-10mm, the temperature of the filament is 2000-2500°C, the temperature of the substrate is 650-850°C, and the reaction pressure is 3-10mm. 4kPa.

Beneficial effect:

The porous titanium-based boron-doped diamond film electrode prepared by the present invention has uniform and dense diamond grains, the porous titanium substrate is completely covered by the diamond film, including the inner and outer surfaces of the pores, and the diamond film has no cracks or incomplete appearance. High boron doping inhibits the formation of TiC, increases the bonding force between the substrate and the film, and is beneficial to improve the stability of the electrode. When the boron concentration is low, the growth rate of the diamond grains is accelerated, which is manifested as a BDD electrode with a wider width. potential window.

Description of drawings

Figure 1 is a scanning electron microscope image of a BDD film prepared on a porous titanium substrate. Figure 1a is a Ti substrate without BDD deposition, and Figure 1b is a BDD thin film electrode prepared on a porous Ti substrate, and the inset is a sample image under low magnification.

Fig. 2 is a SEM image of various parts of the boron-doped diamond film electrode. Among them, Figure 2a is the hole part of the electrode, Figure 2b is the contact part of titanium particles, Figure 2c is the inner surface of the BDD electrode, and Figure 2d is the sample under high magnification.

Fig. 3 is the cyclic voltammogram of the porous titanium-based BDD electrode in 0.5mol/L H ₂ SO ₄ solution, the scanning range is -1.1-2.7V, and the scanning speed is 100mV/s.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1

(1) The porous titanium matrix with a pore size of 15mm×15mm×1mm and a porosity of 60 μm and a porosity of 32% (measured by mercury porosimetry) is soaked in an aqueous NaOH solution with a mass fraction of 10% to fully deoil it, and degrease it with water. After ultrasonic cleaning of the final porous titanium substrate, put it into a beaker filled with 10% hydrochloric acid solution and heat it to a slight boiling state. Stir continuously until the solution gradually becomes light purple. Use deionized water to ultrasonically clean the porous titanium substrate for 5 minutes and rinse it clean. Then put it in deionized water for protection;

(2) The porous titanium processed in step (1) is used as the substrate, the tantalum wire is used as the hot wire, methane and hydrogen are used as the gas source, and trimethyl borate is used as the boron source. In the methane and hydrogen atmosphere, hot wire chemical vapor deposition is used. Method for growing boron-doped diamond film;

(3) The distance between the sample holder and the filament is 8mm, the filament temperature is 2200°C, and the substrate temperature is 750°C;

(4) Use a gas flowmeter to control the proportion of each gas and the amount of boron doping during the electrode preparation process. During the reaction process, the flow rate of hydrogen is always controlled at 300 sccm, the total pressure of the system is 4kPa, and the growth time of the sample is controlled at 6h;

(5) In the initial stage of boron-doped diamond film growth, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 1:100:3, and the growth time is 2 hours , in the late stage of the reaction, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 1:100:0.5, and the growth time was controlled at 4 hours.

The morphology of the porous titanium-based BDD electrode is characterized by SEM, as shown in Figure 1 and Figure 2. The prepared porous titanium-based boron-doped diamond film electrode has uniform and dense diamond grains, and the porous titanium matrix is completely covered by the diamond film, including pores. The inner and outer surfaces of the diamond film have no cracks or incomplete appearance; the electrochemical properties are tested by cyclic voltammetry. Figure 3 is the cyclic voltammogram of the porous titanium-based BDD electrode in 0.5mol/L H ₂ SO ₄ solution, and its potential The window is 3.4V, and the oxygen evolution potential reaches 2.4V.

Example 2

(1) The porous titanium matrix with a pore size of 15mm×15mm×1mm and a porosity of 60 μm and a porosity of 32% (measured by mercury porosimetry) is soaked in an aqueous NaOH solution with a mass fraction of 10% to fully deoil it, and degrease it with water. After ultrasonic cleaning of the final porous titanium substrate, put it into a beaker filled with 10% hydrochloric acid solution and heat it to a slight boiling state. Stir continuously until the solution gradually becomes light purple. Use deionized water to ultrasonically clean the porous titanium substrate for 5 minutes and rinse it clean. Then put it in deionized water for protection;

(2) The porous titanium processed in step (1) is used as the substrate, the tantalum wire is used as the hot wire, methane and hydrogen are used as the gas source, and trimethyl borate is used as the boron source. In the methane and hydrogen atmosphere, hot wire chemical vapor deposition is used. Method for growing boron-doped diamond film;

(3) The distance between the sample holder and the filament is 8mm, the filament temperature is 2200°C, and the base temperature is 750°C;

(4) Use a gas flow meter to control the proportion of each gas and the amount of boron doping during the electrode preparation process. During the reaction process, the flow rate of hydrogen is always controlled at 296 sccm, the total pressure of the system is 4kPa, and the growth time of the sample is controlled at 7h;

(5) In the initial stage of boron-doped diamond film growth, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 3:296:8, and the growth time is 2 hours , in the late stage of the reaction, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 3:296:3, and the growth time was controlled at 5 hours.

The morphology of the porous titanium-based BDD electrode was characterized by SEM. The prepared porous titanium-based boron-doped diamond film electrode has uniform and dense diamond grains, and the porous titanium matrix is completely covered by the diamond film, including the inner and outer surfaces of the pores. There are no cracks or defects in the film; the electrochemical properties are tested by cyclic voltammetry, the potential window is 3.4V, and the oxygen evolution potential is 2.4V.

Example 3

(1) The porous titanium substrate with a size of 15mm×15mm×1mm, a pore size of 100μm, and a porosity of 27% (measured by mercury porosimetry) is soaked in an aqueous NaOH solution with a mass fraction of 10% to fully deoil it, and degrease it with water. After ultrasonic cleaning of the final porous titanium substrate, put it into a beaker filled with 10% hydrochloric acid solution and heat it to a slight boiling state. Stir continuously until the solution gradually becomes light purple. Use deionized water to ultrasonically clean the porous titanium substrate for 5 minutes and rinse it clean. Then put it in deionized water for protection;

(2) The porous titanium processed in step (1) is used as the substrate, the tantalum wire is used as the hot wire, methane and hydrogen are used as the gas source, and trimethyl borate is used as the boron source. In the methane and hydrogen atmosphere, hot wire chemical vapor deposition is used. Method for growing boron-doped diamond film;

(3) The distance between the sample holder and the filament is 8mm, the filament temperature is 2200°C, and the substrate temperature is 750°C;

(4) Use a gas flowmeter to control the proportion of each gas and the amount of boron doping during the electrode preparation process. During the reaction process, the flow rate of hydrogen is always controlled at 300 sccm, the total pressure of the system is 4kPa, and the growth time of the sample is controlled at 6h;

(5) In the initial stage of boron-doped diamond film growth, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 1:100:3, and the growth time is 2 hours , in the late stage of the reaction, methane flow rate (sccm): hydrogen flow rate (sccm): B(OCH ₃ ) ₃ /H ₂ flow rate (sccm) = 1:100:1.5, and the growth time was controlled at 4 hours.

The morphology of the porous titanium-based BDD electrode was characterized by SEM. The prepared porous titanium-based boron-doped diamond film electrode has uniform and dense diamond grains, and the porous titanium matrix is completely covered by the diamond film, including the inner and outer surfaces of the pores. The film has no cracks or defects; the electrochemical properties are tested by cyclic voltammetry, the potential window is 3.4V, and the oxygen evolution potential reaches 2.4V.

Claims (3)

1. a preparation method for the boron-doped diamond film electrode that the POROUS TITANIUM of take is matrix, is characterized in that at least comprising the following steps:

Step 1: the porous titanium material that is 20～50% by porosity soaks abundant oil removing with hot aqueous sodium hydroxide solution, then water is totally put into 10% hydrochloric acid soln by the porous titanium material ultrasonic cleaning after oil removing and is heated to slight boiling condition, be gradually lilac to solution, with deionized water ultrasonic cleaning be totally placed in deionized water, protect standby;

Step 2: using handled porous titanium material in above-mentioned steps as substrate, tantalum wire is heated filament, and methane and hydrogen are source of the gas, and trimethyl borate is boron source, in methane and hydrogen atmosphere, adopts hot-wire chemical gas-phase deposition method growth boron-doped diamond film;

Wherein, the doping of boron is to make H ₂pass into trimethyl borate (B (OCH ₃) ₃) solution is with B (OCH ₃) ₃/ H ₂form enters in reaction system;

The ratio of carbon, hydrogen, boron is by methane, hydrogen, B (OCH ₃) ₃/ H ₂flow proportional control, at the starting stage of boron-doped diamond film growth, B (OCH ₃) ₃/ H ₂adopt large flow control condition, at reaction later stage B (OCH ₃) ₃/ H ₂adopt low discharge, total time of sample grown is controlled at 5～10 hours, and wherein large flow growth time is 1.5～3 hours, and it is 3.5～7 hours that low discharge growth time is controlled.

2. a kind of preparation method of take the boron-doped diamond film electrode that POROUS TITANIUM is matrix according to claim 1, its feature is at the methane described in described step 2, hydrogen, B (OCH ₃) ₃/ H ₂flow control ratio be: in the starting stage of boron-doped diamond film growth, methane flow rate (sccm): hydrogen flow rate (sccm): B (OCH ₃) ₃/ H ₂flow velocity (sccm)=1:100:3, in reaction later stage, methane flow rate (sccm): hydrogen flow rate (sccm): B (OCH ₃) ₃/ H ₂flow velocity (sccm)=1:100:0.5～1.5.

3. a kind of preparation method of take the boron-doped diamond film electrode that POROUS TITANIUM is matrix according to claim 1, it is characterized in that: the hot-wire chemical gas-phase deposition method processing parameter in described step 2 is: the distance between sample carrier and filament is 5～10mm, filament temperature is 2000～2500 ℃, base reservoir temperature is at 650～850 ℃, and reaction pressure is 3～4kPa.

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