Method for preparing palladium nano-film hydrogen sensor

Abstract

The invention discloses a method for preparing a palladium nano-film hydrogen sensor, and belongs to the field of sensor preparation. The invention discloses a method for preparing a palladium nano-film hydrogen sensor. The method comprises the following steps: step 1, carrying out surface pretreatment on an aluminum sheet; secondly, the aluminum sheet is subjected to electrochemical polishing; thirdly, the aluminum sheet is subjected to primary oxidation; 4, performing secondary oxidation on the aluminum sheet, and forming a regular porous aluminum oxide layer on the surface of the aluminum sheet; 5, carrying out a pore expansion experiment on the porous aluminum oxide layer; step 6, removing the aluminum substrate layer and the barrier layer and fishing out the film, specifically, step 7, coating the film through electron beam evaporation equipment; 8, preparing a microelectrode, and then completing electrical connection and packaging; rapid aging and failure of the sensor caused by embrittlement, cracking or peeling due to substrate limitation and strong lattice stress are avoided, the whole preparation process is simplified, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensor preparation, and particularly relates to a method for preparing a palladium nanomembrane hydrogen sensor. BACKGROUND

[0002] The existing palladium nanomembrane preparation methods can be roughly summarized as follows: One is a template-assisted method, which prepares a palladium nanocolumn array membrane by using a template technology. First, a suitable template material is selected to form the required holes or micro-nano structures. Then, palladium nanocolumns or nanostructures are deposited in the template through chemical reduction or electrochemical deposition technology. Finally, the palladium nanocolumn array membrane is obtained by removing the template (such as chemical dissolution or mechanical peeling). Although this method can better control the shape and size of the palladium nanocolumns, the selection and removal process of the template may affect the quality and uniformity of the final palladium nanomembrane.

[0003] The second method is a self-assembly method, which spontaneously assembles palladium nanoparticles or palladium nanowires into an array structure by using a surfactant or organic ligand to guide the arrangement of the palladium nanoparticles or nanowires. This method has the advantages of mild preparation conditions and simple operation, but the structural order and consistency of the palladium nanocolumn array are affected by the properties of the material itself and the preparation conditions, resulting in poor repeatability of the preparation.

[0004] The last method is a nano-sculpting method, which carves palladium material through nanoscale processing technology (such as focused ion beam, electron beam etching, etc.) to form a palladium nanocolumn array. This method can accurately control the size and arrangement of the palladium nanocolumns, but the processing process is complex, time-consuming, and costly.

[0005] The existing technology faces many problems. First, the selection and preparation of the template limit the diversity of material types and structures. The step of removing the template may damage the nanocolumn array and reduce product quality. The process may involve harmful chemicals, posing environmental and safety risks. The efficiency is low and the cost is relatively high in large-scale production. The structural order and uniformity of the self-assembly method depend on the subtle conditions of the self-assembly process, and the repeatability and controllability are poor. Sometimes additional chemical treatment steps are needed to stabilize the structure, increasing complexity. The distribution of the obtained nanocolumns is not compact enough, affecting the performance of the sensor. The method is sensitive to environmental conditions and the preparation process is easily disturbed by external factors. The nano-sculpting method is costly because it involves expensive professional equipment and consumables. The processing flow is complex, requiring professional technical support and high-level operation expertise. The production speed is slow, making it difficult to meet the demand for large-scale rapid production. The amount of material loss is large, and the effective material utilization rate is low.

[0006] The porous alumina film is used as a permanent substrate, and the template removal step is not needed, so that the film structure is not damaged, and the high specific surface area of the palladium nanofilm enhances the contact efficiency with hydrogen, thereby improving the response speed. SUMMARY

[0007] The application aims to solve the problems in the prior art and provides a method for preparing a palladium nanofilm hydrogen sensor.

[0008] To achieve the above-mentioned purpose, the application adopts the following technical scheme: A method for preparing a palladium nanofilm hydrogen sensor comprises the following steps: Step one, surface pretreatment of an aluminum sheet; Step two, electrochemical polishing of the aluminum sheet; Step three, primary oxidation of the aluminum sheet; Step four, secondary oxidation of the aluminum sheet to form a regular porous alumina layer on the surface thereof; Step five, pore expansion experiment of the porous alumina layer; Step six, removal of the aluminum substrate layer and the barrier layer and fishing of the film, and the specific steps are as follows: A, pretreatment of the porous alumina layer; B, drying after smearing a shielding layer on one side of the pretreated porous alumina layer; C, cutting according to the size of the glass substrate to be pasted, floating the side with the porous alumina layer upward in a CuCl2 and HCl mixed solution, fishing out the porous alumina layer after ensuring that the aluminum substrate layer is completely removed, and then placing the porous alumina layer in Milli-Q water for floating; D, floating the porous alumina layer with the removed aluminum substrate and the shielding layer protection in a phosphoric acid solution to remove the barrier layer existing at the bottom of the alumina layer; E, taking out the residual phosphoric acid solution floating in the Milli-Q water, and then placing it in an acetone solution to remove the shielding layer, and thus obtaining the porous alumina film; Step seven, film plating by an electron beam evaporation device; Step eight, preparation of a microelectrode, and then electrical connection and packaging.

[0009] Preferably, in step one, during the pretreatment, the aluminum sheet is first cut into the required size, then the surface is cleaned with washing agent, then it is rinsed with tap water, cleaned with Milli-Q water several times, and then sequentially placed in Milli-Q water, alcohol and acetone solutions for ultrasonic treatment for 10-20 min, and then cleaned with Milli-Q water and dried with nitrogen.

[0010] Preferably, in step two, the pretreated aluminum sheet is cleaned with Milli-Q water by ultrasonic washing, then flattened by a tablet press, and then placed in a 1M NaOH solution at room temperature for 10-20 min until the dense oxide layer on the surface is removed, at which time the aluminum sheet is removed, rinsed with Milli-Q water and dried with nitrogen, and the aluminum sheet is ready for polishing; the polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate, the plate spacing is 4-6 cm, the polishing voltage is 15-25v, and the polishing time is 30-40 min.

[0011] Further, in step three, before the first oxidation, a thick shielding layer is applied to the back of the aluminum sheet and the part of the aluminum sheet that is in contact with the air, and then pre-oxidation is performed for 3 min, the acidic electrolyte for the first oxidation is 0.3M oxalic acid solution, the oxidation voltage is 36-45V, the oxidation temperature is 15±2℃, and the first oxidation time is 11-13h, after the first oxidation, a preliminary porous aluminum oxide layer is formed on the surface of the aluminum sheet.

[0012] Further, in step four, the preliminary porous aluminum oxide layer obtained after the first oxidation is removed as a sacrificial layer, at which time the aluminum sheet surface will leave regular grooves, which will be the basis for the second oxidation, the steps and parameters of the second oxidation are the same as those of the first oxidation, and then a relatively regular porous aluminum oxide layer is obtained, wherein the way to remove the preliminary porous aluminum oxide layer is: The aluminum sheet after the first oxidation is placed in a mixture of 12% phosphoric acid and 3.6% chromic acid, the volume ratio of phosphoric acid to chromic acid is 1:1, the reaction temperature is 60-70℃, and the reaction time is 6-12h, until a shiny aluminum sheet layer is obtained.

[0013] Preferably, in step five, the solution selected for hole expansion is a 5% phosphoric acid solution by mass fraction, and the hole expansion temperature is 30-35℃.

[0014] Further, in step six, the pretreatment operation is to repeatedly rinse the expanded porous aluminum oxide sheet with a large amount of acetone and Milli-Q water and dry it with nitrogen; the drying operation uses a 60℃ oven for 12-18 min; the temperature of the phosphoric acid solution is 28-35℃, and the mass fraction is 5%;.

[0015] Preferably, in step seven, the clean porous aluminum oxide film is fixed on the electron beam evaporation device, ensuring that it is stable and perpendicular to the evaporation source, then the palladium alloy material target is placed in the evaporation source position of the electron beam evaporation device, the electron beam evaporation device is started, and the energy and focusing position of the electron beam are adjusted so that it directly irradiates the palladium alloy material target, and the evaporation of the palladium alloy material begins, when the palladium alloy material coating reaches the predetermined thickness, the evaporation is stopped, and the porous aluminum oxide film is cooled to ensure that the coating is solidified and stable; The palladium alloy material is selected from one or more of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy and palladium-silver alloy, the mass fraction of nickel in the palladium-nickel alloy is 4-20%, and the predetermined thickness is preferably 50-100 nm.

[0016] Further, in step eight, the microelectrode is prepared on the silicon substrate by using a photolithography technology, the electrode material is any one of platinum or gold, and the electrode structure is an interlaced microelectrode structure.

[0017] Further, in step eight, the prepared palladium alloy material nanometer film is transferred to the substrate with the microelectrode by using a cold welding technology, the microelectrode is connected with the external circuit by using a platinum wire and a micro welding technology, the electrical connection is completed, and the microelectrode and the wire connection part are encapsulated by using epoxy resin.

[0018] Compared with the prior art, the method for preparing the palladium nanometer film hydrogen sensor has the following beneficial effects: 1. The method for preparing the palladium nanometer film hydrogen sensor, by using the ordered nanopore structure of the porous alumina and combining the electron beam evaporation plating technology, the palladium film with the nanometer structure is obtained, the response value and the response speed of the prepared palladium nanometer film hydrogen sensor are significantly improved, the test range is increased, the sensitivity to hydrogen is higher, and compared with the continuous palladium thin film hydrogen sensor, an important advantage of the palladium nanometer structure is that the severe lattice expansion caused by high-concentration hydrogen does not cause adverse effects on the performance of the sensor, that is, the sensor will not be brittle, cracked or peeled off due to the substrate limitation and strong lattice stress, resulting in rapid aging and failure of the sensor.

[0019] 2. The method for preparing the palladium nanometer film hydrogen sensor, by using the natural highly ordered nanopore structure of the porous anodic alumina film, the uniform arrangement and consistent size of the palladium nanometer column can be realized, so that the prepared hydrogen sensor has a highly consistent performance response, the electron beam evaporation technology can accurately control the deposition amount of the palladium material, greatly reduces the waste of the material, and improves the utilization rate of the material, unlike the traditional template assisted method or the use of a complex demolding step, the anodic alumina film can be used as a permanent support structure of the palladium nanometer film, without the demolding step, the whole preparation process is simplified, the production cost is reduced, the step of using chemical reagents for structure stabilization treatment is saved, the electron beam evaporation process itself does not need additional chemicals, and the potential pollution to the environment is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The comparison TEM images of the method for preparing the palladium nanometer film hydrogen sensor before (left) and after (right) the hole expansion experiment; Figure 2A preparation flow chart of the palladium nanometer membrane hydrogen sensor. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application.

[0022] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0023] Embodiment one: reference Figures 1-2 A method for preparing a palladium nanometer membrane hydrogen sensor, comprising the following steps: Step one, surface pretreatment of aluminum sheet; First, cut the aluminum sheet into the required size, then wash the surface with detergent, wash off the relatively large oil and dust impurities, rinse with tap water, then rinse several times with Milli-Q water, then sequentially place in Milli-Q water, alcohol and acetone solutions for ultrasonic treatment for 15 minutes each, then rinse with Milli-Q water and dry with nitrogen.

[0024] In this application, by washing with detergent, the surfactant component in the detergent can be used to emulsify and disperse oil in water, and at the same time, the scouring action of water flow can remove dust and the like, thereby providing a relatively clean surface basis for further fine processing.

[0025] Milli-Q water is ultrapure water prepared by a Milli-Q ultrapure water system, and Milli-Q water flushing can completely remove residual trace impurities, ensuring that the surface of the aluminum sheet is in a high-purity, non-polluted state, and preparing for subsequent more precise processing and handling steps. Ultrasonic treatment is to further enhance the cleaning effect, remove stubborn stains, remove surface organic matter, and improve surface activity. After ultrasonic treatment, the surface of the aluminum sheet will be left with Milli-Q water, alcohol, acetone and other solutions. The aluminum sheet is dried with nitrogen. On the one hand, it can quickly remove the water on the surface of the aluminum sheet, avoiding the possibility of re-adsorbing impurities during the natural air-drying process due to impurities left in the water or long-term contact with air. On the other hand, compared with using hot air to dry, nitrogen drying will not introduce active gases such as oxygen that can chemically react with the aluminum sheet, preventing unnecessary oxidation of the aluminum sheet surface during the drying process.

[0026] Step two, electrochemical polishing of the aluminum sheet; In order to obtain an aluminum sheet with a smoother surface, the pretreated aluminum sheet is ultrasonically cleaned with Milli-Q water, then flattened with a tablet press, and then placed in a 1M NaOH solution at room temperature for 14 minutes until the dense oxide layer on the surface is removed, and uniform bubbles appear. At this time, the aluminum sheet is removed, rinsed with a large amount of Milli-Q water and dried with nitrogen, and the aluminum sheet polishing work can be performed. The polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the temperature is controlled by cooling circulating water, the polishing cathode is a stainless steel plate, the plate spacing is about 5cm, the polishing voltage is 20v, and the polishing time is 35min.

[0027] Through electrochemical polishing, the protruding parts on the surface of the aluminum sheet can be dissolved faster than the flat and recessed parts, thereby effectively removing the small scratches, processing marks and some uneven places on the surface, and obtaining an aluminum sheet with extremely high surface finish Step three, primary oxidation of the aluminum sheet; The acid electrolyte used is 0.3M oxalic acid solution, which is prepared on site. The oxidation voltage is 40V, and the oxidation temperature is also controlled at 15±2℃ by cooling circulating water. Before primary oxidation, 3min of pre-oxidation is required to make the later applied masking layer stick more firmly. Then a thick masking layer is applied to the back of the aluminum sheet and the part of the aluminum sheet in contact with air, and is placed in a 60℃ oven for drying for 15min. The primary oxidation time is 12h.

[0028] Step four, secondary oxidation of the aluminum sheet to form a regular porous aluminum oxide layer on the surface; After the first oxidation for 12h, a porous alumina layer with a thickness of tens of microns is formed. The porous alumina layer is removed as a sacrificial layer, and at this time, the surface of the aluminum sheet leaves regular grooves, and on this basis, the second oxidation is carried out, that is, a relatively regular porous alumina layer is obtained. The specific method for removing the first oxidation layer is to put the oxidized aluminum sheet into a mixed solution of 12% phosphoric acid and 3.6% chromic acid, and the volume ratio of the two is 1:1, the reaction temperature is 65°C, and the reaction time is 10h, until a bright aluminum sheet layer is obtained. The steps and parameters of the second oxidation are the same as those of the first oxidation. The second oxidation is carried out after the first oxidation.

[0029] Step five, hole expansion experiment is carried out on the porous alumina layer; The pore size of the film just after the second oxidation often cannot meet the experimental needs, so it needs to be expanded. The solution selected for hole expansion is a 5% phosphoric acid solution, and the hole expansion temperature is 33.6°C. The comparison before and after hole expansion is shown in Figure 1

[0030] Step six, remove the aluminum substrate layer and the barrier layer and fish the film, and the specific steps are as follows, The expanded porous alumina is repeatedly washed with a large amount of acetone and Milli-Q water and dried with nitrogen. Then a relatively thick shielding layer is applied to the side with the porous alumina, and it is placed in a 60°C oven for 15min. Then, according to the size of the film-coated glass substrate, the appropriate size is cut with an art knife, and the side with the porous alumina layer is floated upwards in a CuCl2 and HCl mixed solution, and the self-made film fishing device is used to stir the copper metal that has been displaced and adsorbed on the bottom of the aluminum sheet, to ensure that the bottom of the aluminum sheet is relatively clean, and to ensure that the aluminum layer is completely removed. After the aluminum layer is completely removed, the porous alumina layer can be fished out. At this time, the porous alumina layer is a porous alumina film, which is placed in Milli-Q water for floating. After the aluminum substrate is removed, there is often an alumina barrier layer at the bottom of the porous alumina film. The porous alumina film with the shielding layer protection is floated in a 5% phosphoric acid solution at a temperature of 30°C, and then the residual phosphoric acid solution is taken out and rinsed in Milli-Q water. Then it is placed in an acetone solution to remove the shielding layer. At this time, a complete porous alumina film is obtained Among them, the mixed solution of CuCl2 and HCl is used, specifically 0.2M CuCl2 solution and 19% HCl solution with a volume ratio of 1:1.

[0031] Step seven, film plating by electron beam evaporation equipment; ​Ensure that the porous alumina film is ready and clean, fix the porous alumina film on the sample holder of the electron beam evaporation equipment, make sure it is stable and perpendicular to the evaporation source, put the palladium alloy material target into the evaporation source position of the electron beam evaporation equipment, start the electron beam evaporation equipment, and adjust the energy and focusing position of the electron beam to directly irradiate the palladium alloy material target, start the evaporation of the palladium alloy material; During the evaporation process, monitor the deposition rate of the palladium alloy material and the thickness of the film to ensure uniform palladium alloy material coating, adjust the evaporation time and evaporation rate according to the film thickness set by the experiment, until the predetermined thickness is reached, the predetermined thickness is set to 80 nm, and the temperature should be controlled during the evaporation process to avoid the structure of the porous alumina film being affected by high temperature, when the palladium alloy material coating reaches the predetermined thickness, the predetermined thickness is set to 80 nm, stop the evaporation, and wait for the porous alumina film to cool down to ensure that the coating is solidified and stable; Among them, the palladium alloy material selects one or more combinations of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, and palladium-silver alloy, and the mass fraction of nickel in the palladium-nickel alloy is 4%-20%, and in this embodiment, the mass fraction of palladium-nickel alloy is 20%.

[0032] Step eight, prepare the microelectrode, then complete the electrical connection and packaging; First, on a suitable silicon substrate, prepare the microelectrode using photolithography technology, and use platinum material for the electrode material because platinum material has good chemical stability and electrical conductivity, design the layout of the electrode to optimize the hydrogen response characteristics of the palladium alloy material film, generally staggered microelectrode structure to increase the contact area of the gas and the sensing film; Use cold welding technology to transfer the prepared palladium alloy material nanofilm to the substrate with microelectrode, this step needs to ensure good electrical contact between the palladium alloy material film and the microelectrode; Use fine platinum wire and micro-welding technology to connect the microelectrode with the external circuit, complete the electrical connection, and use epoxy resin to package the microelectrode and the wire connection part to protect them from external influences, but make sure that the sensitive area of the palladium alloy material nanofilm is exposed to fully contact hydrogen.

[0033] Example two: refer to Figures 1-2 A method for preparing a palladium nanofilm hydrogen sensor, comprising the following steps: Step one, surface pretreatment of aluminum sheet; Step two, electrochemical polishing of the aluminum sheet; Step three, primary oxidation of the aluminum sheet; Step four, secondary oxidation of the aluminum sheet to form a regular porous alumina layer on its surface; Step five, reaming experiment on the porous alumina layer; Step six, remove the aluminum substrate layer and barrier layer and fish the film, the specific steps are, A, pretreatment of porous alumina layer; B, after the pretreatment of the porous alumina layer on one side of the coating, dry after the mask layer; C, according to the size of the glass substrate, cut the porous alumina layer containing the aluminum substrate layer to float in the CuCl2 and HC1 mixed solution, ensure that the aluminum substrate layer is completely removed, then take out the porous alumina layer, and then put it in the Milli-Q water; D, the porous alumina layer containing the aluminum substrate layer protected by the mask layer is floated in the phosphoric acid solution, and the barrier layer existing at the bottom of the alumina layer is removed; E, take out the residual phosphoric acid solution floating in the Milli-Q water, and then put it into the acetone solution to remove the mask layer, and then the porous alumina film is obtained; Step seven, coating by electron beam evaporation equipment; Step eight, prepare the microelectrode, then complete the electrical connection and packaging.

[0034] In step one, during the pretreatment, the aluminum sheet is cut into the required size, then the surface is cleaned with washing agent, then it is washed with tap water, then it is washed with Milli-Q water several times, then it is sequentially placed in Milli-Q water, alcohol and acetone solutions for ultrasonic treatment for 10 minutes, then it is washed with Milli-Q water and dried with nitrogen.

[0035] In step two, after the pretreated aluminum sheet is cleaned with Milli-Q water, it is flattened with a tablet press, then it is placed in 1M NaOH solution at room temperature for 10 minutes until the surface dense oxide layer is removed, at this time the aluminum sheet is taken out, washed with Milli-Q water and dried with nitrogen, then the aluminum sheet polishing work is performed; the polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate, the plate spacing is 4cm, the polishing voltage is 20v, and the polishing time is 30 minutes.

[0036] In step three, before the first oxidation, a thick mask layer is coated on the back of the aluminum sheet and the part of the aluminum sheet in contact with the air, then the pre-oxidation is performed for 3 minutes, the acid electrolyte for the first oxidation is 0.3M oxalic acid solution, the oxidation voltage is 40V, the oxidation temperature is 15±2℃, and the first oxidation time is 11h, after the first oxidation, a preliminary porous alumina layer is formed on the surface of the aluminum sheet.

[0037] In step four, the primary porous alumina layer obtained after the first oxidation is removed as a sacrificial layer, leaving regular grooves on the surface of the aluminum sheet, and based on this, the second oxidation is carried out, the steps and parameters of the second oxidation are the same as those of the first oxidation, and then a relatively regular porous alumina layer is obtained. The method for removing the primary porous alumina layer is: The aluminum sheet after the first oxidation is placed in a mixed solution of 12% by mass phosphoric acid and 3.6% by mass chromic acid, the volume ratio of phosphoric acid to chromic acid is 1:1, the reaction temperature is 60°C, and the reaction time is 6h, until a shiny aluminum sheet layer is obtained.

[0038] In step five, the solution selected for hole expansion is a 5% by mass phosphoric acid solution, and the hole expansion temperature is 33.6°C.

[0039] In step six, the pretreatment operation is to repeatedly rinse the porous alumina sheet after hole expansion with a large amount of acetone and Milli-Q water and dry it with nitrogen; the drying operation uses a 60°C oven for 12min; the temperature of the phosphoric acid solution is 30°C, and the mass fraction is 5%.

[0040] In step seven, the clean porous alumina film is fixed on the electron beam evaporation device, ensuring that it is stable and perpendicular to the evaporation source, then the palladium alloy material target is placed in the evaporation source position of the electron beam evaporation device, the electron beam evaporation device is started, and the energy and focusing position of the electron beam are adjusted to directly irradiate the palladium alloy material target, and the evaporation of the palladium alloy material begins. When the palladium alloy material coating reaches the predetermined thickness, the predetermined thickness is set to 100nm, the evaporation is stopped, and the porous alumina film is cooled to ensure that the coating is solidified and stable. Among them, the palladium alloy material selects one or more combinations of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, and palladium-silver alloy, and the mass fraction of nickel in the palladium-nickel alloy is 4%-20%, and in this embodiment, a palladium-nickel alloy with a mass fraction of 5% is selected.

[0041] In step eight, a microelectrode is prepared on a silicon substrate using photolithography technology, the electrode material is any one of platinum or gold, and the electrode structure is an interlaced microelectrode structure.

[0042] The prepared palladium alloy nanofilm is transferred to the substrate with microelectrodes using cold welding technology, the microelectrode is connected to the external circuit using a platinum wire and micro-welding technology, the electrical connection is completed, and the microelectrode and the wire connection part are encapsulated with epoxy resin.

[0043] Example three: refer to Figures 1-2 A method for preparing a palladium nanofilm hydrogen sensor, comprising the following steps: Step one, surface pretreatment of aluminum sheet; Step two, electrochemical polishing of the aluminum sheet; Step three, the aluminum sheet is oxidized once; Step four, the aluminum sheet is oxidized twice to form a regular porous alumina layer on its surface; Step five, the porous alumina layer is subjected to a pore expansion experiment; Step six, the aluminum base layer and the barrier layer are removed and the film is taken out, the specific steps are as follows, A. Pretreatment of the porous alumina layer; B. After the pretreatment of the porous alumina layer is completed, the side is coated with a shielding layer and then dried; C. According to the size of the glass substrate, cut it, let the porous alumina layer face up and float in the CuCl2 and HCl mixed solution, make sure that the aluminum base layer is completely removed, then take out the porous alumina layer and place it in Milli-Q water for floating; D. Float the porous alumina layer with the removed aluminum base protected by the shielding layer in a phosphoric acid solution to remove the barrier layer present at the bottom of the alumina layer; E. Take out the residual phosphoric acid solution floating in the Milli-Q water, and then put it into an acetone solution to remove the shielding layer, and at this time the porous alumina film is obtained; Step seven, film plating by electron beam evaporation equipment; Step eight, preparation of microelectrode, then electrical connection and packaging are completed.

[0044] In step one, during pretreatment, the aluminum sheet is cut into the required size, then the surface is cleaned with washing agent, then rinsed with tap water, washed several times with Milli-Q water, then sequentially placed in Milli-Q water, alcohol and acetone solutions for ultrasonic treatment for 20 min each, then rinsed with Milli-Q water and dried with nitrogen.

[0045] In step two, after the pretreated aluminum sheet is ultrasonically cleaned with Milli-Q water, it is flattened with a tablet press, then placed in a 1M NaOH solution at room temperature for 20 min until the dense oxide layer on the surface is removed, at this time the aluminum sheet is taken out, rinsed with Milli-Q water and dried with nitrogen, then the aluminum sheet polishing work is performed; the polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate, the plate spacing is 6 cm, the polishing voltage is 20v, and the polishing time is 40 min.

[0046] In step three, before the first oxidation, a thick shielding layer is coated on the back of the aluminum sheet and the part of the aluminum sheet in contact with air, and then pre-oxidation is performed for 3 minutes, the acid electrolyte for the first oxidation is 0.3M oxalic acid solution, the oxidation voltage is 40V, the oxidation temperature is 15±2℃, and the first oxidation time is 13 hours. After the first oxidation, a preliminary porous aluminum oxide layer is formed on the surface of the aluminum sheet.

[0047] In step four, the preliminary porous aluminum oxide layer obtained after the first oxidation is removed as a sacrificial layer, at this time the aluminum sheet surface will leave regular grooves, and on this basis, the second oxidation is performed, the steps and parameters of the second oxidation are the same as those of the first oxidation, and then a relatively regular porous aluminum oxide layer is obtained. The way to remove the preliminary porous aluminum oxide layer is: The aluminum sheet after the first oxidation is placed in a mixed solution of 12% phosphoric acid and 3.6% chromic acid, the volume ratio of phosphoric acid to chromic acid is 1:1, the reaction temperature is 70℃, and the reaction time is 12 hours, until a bright aluminum sheet layer is obtained.

[0048] In step five, the solution selected for hole expansion is a 5% phosphoric acid solution, and the hole expansion temperature is 33.6℃.

[0049] In step six, the pretreatment operation is to repeatedly rinse the expanded porous aluminum oxide sheet with a large amount of acetone and Milli-Q water and dry it with nitrogen; the drying operation uses a 60℃ oven for 18 minutes; the temperature of the phosphoric acid solution is 30℃, and the mass fraction is 5%.

[0050] In step seven, the clean porous aluminum oxide film is fixed on the electron beam evaporation device, ensuring that it is stable and perpendicular to the evaporation source, then the palladium alloy material target is placed in the evaporation source position of the electron beam evaporation device, the electron beam evaporation device is started, and the energy and focusing position of the electron beam are adjusted to directly irradiate the palladium alloy material target, and the evaporation of the palladium alloy material is started. When the palladium alloy material plating film reaches the predetermined thickness, the predetermined thickness is set to 200nm, the evaporation is stopped, and the porous aluminum oxide film is cooled to ensure that the plating film is solidified and stable. Among them, the palladium alloy material selects one or more combinations of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, and palladium-silver alloy, the mass fraction of nickel in the palladium-nickel alloy is 4%-20%, and in this embodiment, the palladium-gold alloy is selected.

[0051] In step eight, a microelectrode is prepared on a silicon substrate using photolithography technology, the electrode material uses any one of platinum or gold, and the electrode structure uses an interlaced microelectrode structure.

[0052] The prepared palladium alloy material nanometer film is transferred to the substrate with microelectrode by using cold welding technology, the microelectrode is connected with external circuit by using fine platinum wire and micro welding technology, the electrical connection is completed, and the microelectrode and the wire connecting part are packaged by using epoxy resin.

[0053] In the application, the porous alumina film of the prepared palladium nanometer film hydrogen sensor has a highly ordered nanometer pore structure, the size, spacing and depth of the pores can be accurately controlled by controlling the anodization conditions (such as temperature, voltage and time) in the preparation process, and it should be noted that the palladium alloy material plated film has a predetermined thickness of 10-200 nm, preferably 50-100 nm.

[0054] The pore size can be adjusted in the range of several nanometers to several hundred nanometers, which provides the possibility for precise nanometer processing, and is an ideal 'template' for preparing nanocomposites and nanostructures.

[0055] The porous alumina film has high uniformity and good repeatability under the same conditions, and is suitable for large-scale production; the porous structure provides a large specific surface area for the material, which significantly increases the contact area with the film, which is particularly important in catalysis, sensors or support materials, etc., and alumina is a corrosion-resistant material that can remain stable in harsh chemical environments, and is suitable as a substrate for many high-performance sensors and devices.

[0056] In the application, the ordered nanometer pore structure of the porous alumina is combined with the electron beam evaporation plating film technology to obtain a palladium film with a nanostructure, so that the response value and response speed of the palladium nanometer film hydrogen sensor prepared by the palladium nanometer film hydrogen sensor are significantly improved, the test range is increased, the sensitivity to hydrogen is higher, and the palladium nanometer film hydrogen sensor will not be brittle, cracked or peeled off due to substrate limitation and strong lattice stress, resulting in rapid aging and failure of the sensor.

[0057] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical solution and inventive concept of the application within the technical range disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. A method for preparing a palladium nanofilm hydrogen sensor, characterized in that, Includes the following steps: Step 1: Pre-treat the surface of the aluminum sheet; Step two: Electrochemical polishing of the aluminum sheet; Step 3: Perform a first oxidation on the aluminum sheet; Step four: Perform secondary oxidation on the aluminum sheet to form a regular porous aluminum oxide layer on its surface; Step 5: Perform a pore-expansion experiment on the porous alumina layer; Step six, remove the aluminum substrate layer and barrier layer and retrieve the film. The specific steps are as follows: A. Pretreatment of porous alumina layer; B. Apply a masking layer to one side of the pretreated porous alumina layer and then dry it. C. Cut the glass substrate according to its size, and float the porous alumina layer upward in the CuCl2 and HCl mixed solution. After ensuring that the aluminum substrate layer is completely removed, take out the porous alumina layer and then place it in Milli-Q water to float. D. Float the porous alumina layer containing the shielding layer protected by the aluminum substrate in a phosphoric acid solution to remove the barrier layer present at the bottom of the alumina layer. E. Remove the residual phosphoric acid solution that has been floating in Milli-Q water and rinse it. Then, put it into acetone solution to remove the masking layer. At this point, a porous alumina film is obtained. Step 7: Deposition film using an electron beam evaporation device; Step eight involves fabricating the microelectrodes, followed by electrical connection and encapsulation.

2. The method for preparing a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step one, during pretreatment, the aluminum sheet is first cut into the required size, then the surface is cleaned with detergent, then rinsed with tap water, and then rinsed several times with Milli-Q water. Then, it is placed in solutions of Milli-Q water, alcohol, and acetone, and sonicated for 10-20 minutes each. After that, it is rinsed with Milli-Q water and dried with nitrogen.

3. The method for preparing a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step two, the pretreated aluminum sheet is ultrasonically cleaned with Milli-Q water, flattened using a tablet press, and then placed in a 1M NaOH solution at room temperature for 10-20 minutes until the dense oxide layer on the surface is removed. At this point, the aluminum sheet is taken out, rinsed with Milli-Q water, and dried with nitrogen gas before polishing. The polishing solution is a mixture of perchloric acid and ethanol, the polishing temperature is 15±2℃, the polishing cathode is a stainless steel plate with a plate spacing of 4-6cm, the polishing voltage is 15-25V, and the polishing time is 30-40 minutes.

4. The method for preparing a palladium nanofilm hydrogen sensor according to claim 3, characterized in that, In step three, before the first oxidation, a thicker masking layer is applied to the back of the aluminum sheet that does not need to be oxidized and the part of the aluminum sheet that is in contact with air. Then, a pre-oxidation is performed for 3 minutes. The acidic electrolyte for the first oxidation is a 0.3M oxalic acid solution, the oxidation voltage is 36-45V, the oxidation temperature is 15±2℃, and the first oxidation time is 11-13 hours. After the first oxidation, a preliminary porous aluminum oxide layer will be formed on the surface of the aluminum sheet.

5. The method for preparing a palladium nanofilm hydrogen sensor according to claim 4, characterized in that, In step four, the preliminary porous alumina layer obtained after the first oxidation is removed as a sacrificial layer. At this point, regular grooves will be left on the surface of the aluminum sheet. Based on this, a second oxidation is performed. The steps and parameters of the second oxidation are the same as those of the first oxidation, and then a more regular porous alumina layer can be obtained. The method for removing the preliminary porous alumina layer is as follows: The aluminum sheet after primary oxidation is placed in a mixture of 12% phosphoric acid and 3.6% chromic acid by mass, with a volume ratio of 1:

1. The reaction temperature is 60-70℃ and the reaction time is 6-12 hours until a bright aluminum sheet layer is obtained.

6. The method for preparing a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step five, the solution selected for pore enlargement is a 5% phosphoric acid solution, and the pore enlargement temperature is 30-35℃.

7. The method for preparing a palladium nanofilm hydrogen sensor according to claim 6, characterized in that, In step six, the pretreatment operation involves repeatedly rinsing the expanded porous alumina sheet with a large amount of acetone and Milli-Q water and then drying it with nitrogen gas; the drying operation involves drying it in a 60℃ oven for 12-18 minutes; the temperature of the phosphoric acid solution is 28-35℃ and the mass fraction is 5%.

8. The method for preparing a palladium nanofilm hydrogen sensor according to claim 1, characterized in that, In step seven, the cleaned porous alumina film is fixed on the electron beam evaporation equipment, ensuring that it is stable and perpendicular to the evaporation source. Then, the palladium alloy target is placed in the evaporation source position of the electron beam evaporation equipment, the electron beam evaporation equipment is started, and the energy and focusing position of the electron beam are adjusted so that it directly irradiates the palladium alloy target to begin evaporating the palladium alloy material. When the palladium alloy film reaches the predetermined thickness, evaporation is stopped, and the porous alumina film is allowed to cool to ensure that the film is solidified and stable. The palladium alloy material is selected from one or more combinations of palladium-nickel alloy, palladium-magnesium alloy, palladium-gold alloy, and palladium-silver alloy. The mass fraction of nickel in the palladium-nickel alloy is 4%-20%, and the predetermined thickness is preferably 50-100 nm.

9. The method for preparing a palladium nanofilm hydrogen sensor according to claim 8, characterized in that, In step eight, microelectrodes are fabricated on a silicon substrate using photolithography. The electrode material can be either platinum or gold, and the electrode structure is an interlaced microelectrode structure.

10. The method for preparing a palladium nanofilm hydrogen sensor according to claim 9, characterized in that, In step eight, the prepared palladium alloy nanofilm is transferred onto a substrate with microelectrodes using cold welding technology. The microelectrodes are then connected to an external circuit using fine platinum wires and micro-welding technology to complete the electrical connection. Finally, the microelectrodes and the wire connection parts are encapsulated with epoxy resin.

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