Boron-doped Diamond Electrode with Ultra-high Specific Surface Area, and Preparation Method Therefor and Application Thereof

Abstract

A boron-doped diamond electrode with an ultra-high specific surface area, and a preparation method therefor and the application thereof are provided. The boron-doped diamond electrode includes a substrate and an electrode working layer arranged on a surface thereof, the substrate is polysilicon or monocrystal silicon with a high specific surface area, and the electrode working layer is a boron-doped diamond layer. The polysilicon with a high specific surface area is obtained by anisotropIc etching and/or isotropic etching, and the monocrystal silicon with a high specific surface area is obtained by anisotropic etching. The boron-doped diamond layer includes a highly conductive layer, a corrosion-resistant layer, and a strongly electrocatalytically active layer, which have different boron contents. Compared with a traditional plate electrode, the present disclosure has a low cost and an extremely high specific surface area, provides a larger current intensity with a lower current density, and has broad application prospects.

Claims

1. A boron-doped diamond electrode with an ultra-high specific surface area, comprising a substrate and an electrode working layer, wherein a surface of the substrate is covered by the electrode working layer, the substrate is a_polysilicon with a high specific surface area or a_monocrystal silicon with a high specific surface area; the electrode working layer is a boron-doped diamond layer; the polysilicon with Ha JJthe high specific surface area is obtained by carrying out an anisotropic etching and/or an isotropic etching on a surface of the polysilicon; and the monocrystal silicon with the high specific surface area is obtained by carrying out the anisotropic etching on a surface of the monocrystal silicon.

2. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 1, wherein the substrate is the polysilicon with the high specific surface area; the polysilicon with the high specific surface area is obtained by carrying out the isotropic etching on a polysilicon the surface of the polysilicon; the substrate is in a shape of a column, a cylinder or a flat plate; and the substrate is a three-dimensional continuous network structure, a two-dimensional continuous network structure., or a two-dimensional closed flat plate structure.

3. The boron-doped diamond electrode with theultra-high specific surface area according to claim 1 wherein the boron-doped diamond layer comprises a boron-doped diamond highly conductive layer, a boron-doped diamond corrosion-resistant layer, and a boron-doped diamond strongly electrocatalytically active layer, and the boron-doped diamond highly conductive layer, the boron-doped diamond corrosion-resistant layer, and the boron-doped diamond strongly electrocatalytically active layer have different boron contents and are successively deposited on the substrate surface of the substrate.

4. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 3, wherein in the boron-doped diamond highly conductive layer, a B/C is 20000 ppm-33333 ppm in an atomic ratio; in the boron-doped diamond corrosion-resistant layer, a B/C is 0 ppm-10000 ppm in the atomic ratio; and in the boron-doped diamond strongly electrocatalytically active layer, a B/C is 10000 ppm-20000 ppm in the atomic ratio.

5. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 3 wherein the boron-doped diamond layer has a thickness of 5 nm-2 mm; the boron-doped diamond strongly electrocatalytically active layer accounts for 40%-60% of the boron-doped diamond layer in the thickness; and micro holes and/or sharp cones are distributed on a surface of the boron-doped diamond layer.

6. A method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 1 comprising the following steps: step I.sub.: pretreating the substrate carrying out the anisotropic etching or/and the isotropic etching on a surface of a polysilicon substrate material to obtain the polysilicon with the high specific surface area; and canying out the anisotropic etching on a surface of a monocrystal silicon substrate material to obtain the monocrystal silicon with the high specific surface area, step II: planting seed crystals on the substrate surface of the substrate placing the polysilicon with H al l the high specific surface area or the monocrystal silicon with the high specific surface area obtained in the step 1 in a suspension containing mixed particles of a nanocrystal diamond and/or a_microcrystal diamond, and carrying out an ultrasonic treatment and a_ drying to obtain the polysilicon with the high specific surface area or the monocrystal silicon with the high specific surface area with the nanocrystal diamond and/or the microcrystal diamond adsorbed on the surface of the polysilicon and the surface of the monocrvstal silicon: step III: depositing the boron-doped diamond layer placing the polysilicon with the high specific surface area or the monocrystal silicon with the high specific surface area obtained in the step II in a chemical vapor deposition furnace, injecting a carbon containing gas and a boron containing gas, and sequentially carrying out three stages of a deposition to obtain the boron-doped diamond layer, wherein during -a first stage of the deposition, the boron containing gas is controlled to account for 0.03%-0.05% of a total mass flow of a gas in the chemical vapor deposition furnace; during a second stage of the deposition, the boron containing gas is controlled to account for 0%-0.015% of the total mass flow of the gas in the chemical vapor deposition furnace, and during a. third stage of the deposition, the boron containing gas is controlled to account for 0.015%-0.03% of the total mass flow of the gas in the chemical vapor deposition furnace; and step IV: ahigh-temperature treatment carrying out a heat treatment on the polysilicon with the high specific surface area or the monocrystal silicon with the high specific surface area with the boron-doped diamond layer deposited, wherein a temperature of the heat treatment temperature is 400° C.-1200° C., a time of the heat treatment is 5 min-110 min, apressure in the chemical vapor deposition furnace is 10 Pa-10.sup.5 Pa, and an atmosphere of the heat treatment contains an etching gas.

7. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 6, wherein in the step 1, a specific process of carrying out the anisotropic etching on the surface of .the polysilicon substrate material is: soaking the polysilicon substrate material in an anisotropic etching solution at 20° C.-90° C. for 10 min- 180 min, and cleaning and drying the polysilicon substrate material; and the anisotropic etching solution is one of: a sodium hydroxide solution, a potassium hydroxide solution, a mixed solution of sodium hydroxide and sodium hypochlorite, a tetramethyl ammonium hydroxide solution, a mixed solution of tetramethyl ammonium hydroxide and isopropanol, a mixed solution of the tetramethyl ammonium hydroxide and polyethylene glycol octyl phenyl ether, a mixed solution of the tetramethyl ammonium hydroxide and ammonium persulfate, a_mixed solution of the tetramethyl ammonium hydroxide, the polyethylene glycol octyl phenyl ether, and the isopropanol, a mixed solution of ethylenediamine, pyrocatechol, and water, and ethylenediamine phosphoquinone.

8. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 6, wherein in the step 1, a specific process of carrying out the isotropic etching on the surface of the polysilicon substrate material is: soaking the polysilicon substrate material in an isotropic etching solution at 0° C.-90° C. for 10 s-130 min, and cleaning and drying the polysilicon substrate material; and the isotropic etching solution is one of a mixed solution of hydrofluoric acid and nitric acid, a_mixed solution of the hydrofluoric acid, the nitric acid, and acetic acid, and a inixed solution of the hydrofluoric acid and the acetic acid.

9. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 6, wherein in the step 11, a mass fraction of the mixed particles in the suspension containing the mixed particles of the nanocrystal diamond and/or the microcrystal diamond mixed particles is 0.01%-0.05%; in the step 11, a time of the ultrasonic treatment is 5 min-30 min; in the step III, the carbon containing gas accounts for 0.5%-10.0% of the total mass flow of the gas in the chemical vapor deposition furnace during the three stages of the deposition; and in the step III, the first stage of the deposition is carried out at 600° C.- 1000° C. and 10.sup.5 Pa- 10.sup.4 Pa for less than or equal to 18 h; the second stage of the deposition is carried out at 600° C.-1000° C. and 10.sup.3 Pa-10.sup.4 Pa for less than or equal to 18 h; and the third stage of the deposition is carried out at 600° C.-1000° C. and 10.sup.3 Pa-10.sup.4 Pa for less than or equal to 18 h.

10. A method of a use of the boron-doped diamond electrode with the ultra-high specific surface area according to claim 1, wherein the boron-doped diamond electrode is used in an electrochemical oxidation treatment of a wastewater, a sterilization and a disinfection of a various daily water, a removal of organic pollutants, or ozone generators, or electrochemical biosensors.

11. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 2, wherein the boron-doped diamond layer comprises a boron-doped diamond highly conductive layer, a boron-doped diamond corrosion-resistant layer, and a boron-doped diamond strongly electrocatalytically active layer, and the boron-doped diamond highly conductive layer, the boron-doped diamond corrosion-resistant layer, and the boron-doped diamond strongly electrocatalytically active layer have different boron contents and are successively deposited on the surface of the substrate.

12. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 11, wherein in the boron-doped diamond highly conductive layer, a B/C is 20000 ppm-33333 ppm in an atomic ratio; in the boron-doped diamond corrosion-resistant layer, a B/C is 0 ppm-10000 ppm in the atomic ratio; and in the boron-doped diamond strongly electrocatalytically active layer, a B/C is 10000 ppm-20000 ppm in the atomic ratio.

13. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 11, wherein the boron-doped diamond layer has a thickness of 5 .Math.m-2 mm; the boron-doped diamond strongly electrocatalytically active layer accounts for 40%-60% of the boron-doped diamond layer in the thickness, and micro holes and/or sharp cones are distributed on a surface of the boron-doped diamond layer.

14. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 4, wherein the boron-doped diamond layer has a thickness of 5 .Math.m-2 mm; the boron-doped diamond strongly electrocatalytically active layer accounts for 40%-60% of the boron-doped diamond layer in the thickness; and micro holes and/or sharp cones are distributed on a surface of the boron-doped diamond layer.

15. The boron-doped diamond electrode with the ultra-high specific surface area according to claim 12, wherein the boron-doped diamond layer has a thickness of 5 .Math.m-2 mm; the boron-doped diamond strongly electrocatalytically active layer accounts for 40%-60% of the boron-doped diamond layer in the thickness; and micro holes and/or sharp cones are distributed on a surface of the boron-doped diamond layer.

16. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 6, wherein the substrate is the polysilicon with the high specific surface area; the polysilicon with the high specific surface area is obtained by carrying out the isotropic etching on the surface of the polysilicon; the substrate is in a shape of a column, a cylinder, or a flat plate; and the substrate is a three-dimensional continuous network structure, a two-dimensional continuous network structure, or a two-dimensional closed flat plate structure.

17. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 6, wherein the boron-doped diamond layer comprises a boron-doped diamond highly conductive layer, a boron-doped diamond corrosion-resistant layer, and a boron-doped diamond strongly electrocatalytically active layer, and the boron-doped diamond highly conductive layer, the boron-doped diamond corrosion-resistant layer, and the boron-doped diamond strongly electrocatalytically active layer have different boron contents and are successively deposited on the surface of the substrate.

18. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 17, wherein in the boron-doped diamond highly conductive layer, a B/C is 20000 ppm-33333 ppm in an atomic ratio; in the boron-doped diamond corrosion-resistant layer, a B/C is 0 ppm-10000 ppm in the atomic ratio; and in the boron-doped diamond strongly electrocatalytically active layer, a B/C is 10000 ppm-20000 ppm in the atomic ratio.

19. The method for preparing the boron-doped diamond electrode with the ultra-high specific surface area according to claim 17, wherein the boron-doped diamond layer has a thickness of 5 .Math.m-2 mm; the boron-doped diamond strongly electrocatalytically active layer accounts for 40%-60% of the boron-doped diamond layer in the thickness; and micro holes and/or sharp cones are distributed on a surface of the boron-doped diamond layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 shows the morphology of a polysilicon substrate subjected to anisotropic etching in Example 1.

[0056] FIG. 2 shows the morphology of a polysilicon substrate subjected to isotropic etching in Example 2.

[0057] FIG. 3 shows the morphology of a polysilicon substrate subjected to anisotropic etching first and then isotropic etching in Example 3.

[0058] FIG. 4 is the structure of an ozone generator in Example 3, wherein: 1. Shell, 2. Gland, 3. Electrode holder, and 4. Electrode assembly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example 1

[0059] First, anisotropic etching was carried out on the surface of a polysilicon substrate material. The polysilicon substrate material was soaked in a 10 M KOH solution as the anisotropic etching solution at 80° C. for 60 min, and then cleaned and dried to obtain step-like polysilicon with a high specific surface area, the shape of which is shown in FIG. 1.

[0060] The etched polysilicon was placed in a suspension of nanocrystal and microcrystal diamond mixed particles, and subjected to ultrasonic vibration for 30 min to obtain the polysilicon substrate with diamond grains adsorbed on the surface.

[0061] The substrate was put into a chemical vapor deposition furnace. The distance between a hot wire and the substrate surface was kept at 9 mm. A hydrogen gas flow rate was adjusted and kept at 97 sccm during the heating process, and methane and borane were injected into the furnace to start deposition at a temperature of 850° C. and a pressure of 3 kPa in a mixed atmosphere of B.sub.2H.sub.4, CH.sub.4 and H.sub.2. When a highly conductive layer was deposited, the gas ratio was B.sub.2H.sub.6— CH.sub.4— H.sub.2═1.0 sccm: 3.0 sccm: 97 sccm, and the deposition time was 3 h; when a corrosion resistant layer was deposited, the gas ratio was B.sub.2H.sub.6— CH.sub.4— H.sub.2═0.2 sccm: 3.0 sccm: 97 sccm, and the deposition time was 3 h; and when a strongly electrocatalytically active layer was deposited, the gas ratio was B.sub.2H.sub.6— CH.sub.4— H.sub.2═0.6 sccm: 3.0 sccm: 97 sccm, and the deposition time was 6 h.

[0062] The resulting electrode material was put into a tubular furnace, and subjected to heat treatment in the air. The temperature was set and kept at 750° C. for 20 min. After high temperature oxidation, the electrode surface appeared some tapered shape.

[0063] The electrode was assembled and its performance was tested with a three electrode system. The results showed that the oxygen evolution potential was 1.82 V, the hydrogen evolution potential was -0.60 V, the potential window was 2.42 V, and the background current was 83.42 .Math.A/cm.sup.2.

[0064] It can be seen from the above data that the polysilicon substrate subjected to anisotropic etching has excellent electrochemical performance and favorable electrode reversibility.

Example 2

[0065] Except that a polysilicon substrate was subjected to isotropic etching in Example 2, other conditions were the same as in Example 1. First, isotropic etching was carried out on the surface of a polysilicon substrate material in an analytical pure HF and HNO.sub.3 mixed solution in a volume ratio of HF— HNO.sub.3═3:1 as an isotropic etching solution. The polysilicon substrate material was soaked in the isotropic etching solution for 2 min at room temperature for etching, and then cleaned and dried to obtain pits and micro holes composited polysilicon with a high specific surface area, the shape of which is shown in FIG. 2.

[0066] The subsequent preparation process was the same as that of Example 1. The electrode performance was tested, and the results showed that the oxygen evolution potential was 2.37 V, the hydrogen evolution potential was -0.55 V, the potential window was 2.92 V, and the background current was 39.71 .Math.A/cm.sup.2.

[0067] It can be seen from the above data that the polysilicon substrate subjected to isotropic etching has excellent electrochemical performance and favorable electrode reversibility. When the electrode was used for degrading reactive blue 19 for 3 h, the decolority

[0068] removal rate was 100%, the TOC removal rate was 55%, and the energy consumption was 36 kW h.

[0069] In addition, in this example, the effect of the mixed solutions of HF and HNO.sub.3 in different ratios (1:1, 2:1, 6:1) on the isotropic etching of the polysilicon substrate material was also investigated. The etching time was 2 min, and microstructure characterization found that:

[0070] the film surfaces prepared by all the mixed etching solutions were completely covered with diamond, the content of graphite phase was very small, and the diamond growth was well. The film diamond obtained with an etching solution in a mixing ratio of 1:1 has an uneven grain size and fewer pits. The film obtained with an etching solution in a mixing ratio of 6:1 has fewer pits and many deep holes with a smaller diameter. The BDD film obtained with an etching solution in a mixing ratio of 3:1 has the largest specific surface area.

[0071] The electrode was assembled and its performance was tested with a three electrode system. The results showed that when the etching solution was in a mixing ratio of HF— HNO3═1:1, the oxygen evolution potential was 2.20 V, the hydrogen evolution potential was -0.51 V, the potential window was 2.71 V, and the background current was 124.50 .Math.A/cm.sup.2; when the etching solution was in a mixing ratio of HF— HNO.sub.3═2:1, the oxygen evolution potential was 2.31 V, the hydrogen evolution potential was -0.53 V, the potential window was 2.84 V, and the background current was 33.43 .Math.A/cm.sup.2; when the etching solution was in a mixing ratio of HF— HNO.sub.3═3:1, the oxygen evolution potential was 2.37 V, the hydrogen evolution potential was -0.55 V, the potential window was 2.92 V, and the background current was 39.71 .Math.A/cm.sup.2; and when the etching solution was in a mixing ratio of HF— HNO.sub.3═6:1, the oxygen evolution potential was 2.22 V, the hydrogen evolution potential was -0.54 V, the potential window was 2.76 V, and the background current was 133.26 .Math.A/cm.sup.2. It can be seen from the above data that the BDD electrodes prepared with the four mixed etching solutions all have excellent electrochemical performance, where the electrode obtained with the etching solution in a mixing ratio of 3:1 has the highest oxygen evolution potential and the widest potential window, and has the best electrochemical performance in general.

Example 3

[0072] In Example 3, a step-like polysilicon substrate was first etched by anisotropic etching, and then subjected to isotropic etching. The etching parameters of the etching solution were the same as those in Examples 1 and 2. The morphology of the resulting polysilicon substrate is shown in FIG. 3.

[0073] Then, a BDD electrode was prepared by the same method as in Example 1, and the electrode performance was tested. The results showed that the oxygen evolution potential was 2.52 V, the hydrogen evolution potential was -0.63 V, the potential window was 3.15 V, and the background current was 12.62 .Math.A/cm.sup.2.

[0074] It can be seen from the above data that the polysilicon substrate subjected to anisotropic etching combined with isotropic etching has excellent electrochemical performance and favorable electrode reversibility.

[0075] The BDD electrode prepared in Example 3 was applied to an ozone generator, the structure of which is shown in FIG. 4, including a shell 1, a gland 2, an electrode holder 3, and an electrode assembly 4.

[0076] The BDD electrode prepared in Example 3 was used as an anode, and a titanium mesh was used as a cathode, the electrode assembly was formed with a perfluorinated ion membrane and installed in the ozone generator (FIG. 4). A constant current power supply was applied for trial operation, and the gas production performance of the ozone generator was tested. The results showed that the average ozone yield was 967 mg/h.

Comparative Example 1

[0077] Except that the first stage deposition was not carried out in Comparative Example 1, other conditions were the same as in Example 1. The electrode performance was tested, and the results showed that the oxygen evolution potential was 1.79 V, the hydrogen evolution potential was -0.58 V, the potential window was 2.37 V, and the background current was 292.71 .Math.A/cm.sup.2.

[0078] It can be seen that the electrode performance is obviously inferior to Example 1. The electrode has high resistance, which will increase the energy consumption greatly in the actual wastewater degradation process.