Resistance-type hydrogen sensor based on palladium-based amorphous alloy film

Abstract

The invention provides a resistance-type hydrogen sensor based on a palladium-based amorphous alloy film, and relates to the technical field of hydrogen sensors, the sensor comprises an anodic aluminum oxide substrate, a palladium-based amorphous alloy film layer arranged on the anodic aluminum oxide substrate, and electrodes arranged at two ends of the palladium-based amorphous alloy film layer, according to the method, the palladium-based amorphous alloy is combined with the anodic aluminum oxide substrate, efficient adsorption and rapid desorption of hydrogen are achieved through the synergistic effect of the porous structure of the substrate and the atom disorder of the amorphous alloy, the hydrogen permeability is enhanced, and the problems of hydrogen embrittlement, hysteresis, insufficient permeability and the like of a traditional palladium-based alloy are solved. Meanwhile, the sensor is prepared by an integrated process of a two-step anodic oxidation method, magnetron sputtering and electron beam evaporation, high consistency and repeatability of the sensor are realized by accurately controlling the aperture of the AAO substrate, the thickness of the film and electrode deposition parameters, the technological process is simple, the sensor is suitable for large-scale production, and the limitations of complex preparation and high cost of an optical fiber type sensor are broken through.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen sensors, and in particular to a resistive hydrogen sensor based on a palladium-based amorphous alloy film. Background Art

[0002] In the context of the global pursuit of sustainable development and energy transformation, hydrogen energy has become a highly promising new energy carrier with its significant advantages such as cleanliness, high efficiency and abundant reserves. From a chemical point of view, the combustion of hydrogen only produces water and almost no greenhouse gases and pollutants. This is in line with the urgent need to respond to global climate change and achieve carbon reduction targets, and provides a feasible path to alleviate the energy crisis and environmental pressure. However, hydrogen has the characteristics of low density (0.0899kg / m3), fast diffusion speed, and wide explosion limit range (4.0-75.6%). During the production, storage, transportation and application process, the slightest carelessness may cause leakage, leading to serious safety accidents such as fire and explosion. Therefore, the importance of hydrogen detection technology is self-evident, and it is necessary to develop hydrogen sensors with high sensitivity and fast response speed.

[0003] Existing hydrogen sensors include fiber optic sensors and resistive hydrogen sensors. Fiber optic sensors offer advantages such as strong resistance to electromagnetic interference, intrinsic safety, high sensitivity, and measurement accuracy. However, these sensors suffer from complex post-processing and lack a mature signal demodulation and detection system. Patent CN112325913A proposes a temperature-compensated fiber Bragg grating (FBG) hydrogen sensing system composed of two fiber Bragg gratings (FBGs) with different central wavelengths fused in series, using an amorphous palladium-based alloy thin film as the hydrogen-sensitive material. However, the system is complex and the preparation is tedious, making it unsuitable for large-scale production and commercial application.

[0004] Resistive hydrogen sensors, one of the most widely used types of hydrogen sensors, have attracted considerable attention from researchers due to their high sensitivity, fast response, low production cost, moderate power consumption and service life, and ease of integration and functionalization. Metallic palladium (Pd) is widely used in various hydrogen sensors due to its exceptional affinity for hydrogen and reversible absorption. However, the interconversion between the solid solution α phase and the hydride β phase during repeated adsorption and desorption of hydrogen on pure Pd makes pure Pd thin films susceptible to hydrogen embrittlement. Furthermore, these films suffer from hysteresis, poor selectivity, and susceptibility to interference from impurities such as CO and H2S. A common approach is to improve the performance of the sensing material by doping pure Pd with other elements such as gold, silver, nickel, and platinum to produce Pd-based alloys, including even ternary alloys such as Pd-Au-Cu. However, Pd-based alloy films still suffer from deficiencies in hydrogen permeability and resistance to poisoning. Amorphous alloys generally have stronger mechanical strength and corrosion resistance than traditional crystalline alloys. At the same time, palladium-based amorphous alloys are conducive to hydrogen penetration due to their amorphous structure and internal free volume. In addition, the use of non-precious metals greatly reduces the cost of raw materials and has commercial potential for practical applications. Summary of the Invention

[0005] The object of the present invention is to provide a resistive hydrogen sensor based on a palladium-based amorphous alloy film with fast response speed, high sensitivity, strong hydrogen permeability and suitable for large-scale production.

[0006] To achieve the above objectives, the present invention proposes a resistive hydrogen sensor based on a palladium-based amorphous alloy film, comprising: an anodized aluminum substrate, a palladium-based amorphous alloy film layer provided on the anodized aluminum substrate, and electrodes provided at both ends of the palladium-based amorphous alloy film layer.

[0007] Furthermore, the anodized aluminum substrate has a porous structure with a pore diameter of 25-75 nm.

[0008] Furthermore, the palladium-based amorphous alloy film has a composition of Pd-Cu-Si or Pd-Cu-Ni-P, a thickness of 25-50 nm, and a porous structure.

[0009] Furthermore, the electrode material is silver or gold, and has a thickness of 150-200 nm.

[0010] Furthermore, the preparation method of the sensor includes the following steps:

[0011] S1: Preparation of anodized aluminum substrate with uniform porous structure;

[0012] S2: depositing a palladium-based amorphous alloy thin film on the anodic aluminum oxide substrate by magnetron sputtering;

[0013] S3: Depositing silver or gold electrodes at both ends of the film by electron beam evaporation and connecting them to an external circuit through copper wires.

[0014] Furthermore, in step S1, the anodized aluminum substrate is prepared by a two-step anodizing method. Since the porous anodized aluminum prepared by one-step oxidation usually has a high pore disorder, the position of the pore nucleus formation during the oxidation process is random, resulting in irregular pore arrangement and a wide pore size distribution, while the porous anodized aluminum prepared by the two-step anodizing method has a highly controllable pore structure, improved pore structure orderliness, good pore size uniformity, high porosity and good penetration. At the same time, the pore position sequence obtained by the multi-stage anodizing method is similar to that of the two-step anodizing method. Therefore, the two-step anodizing method is a more suitable choice. The two-step anodizing method preparation method comprises the following steps:

[0015] 1) Annealing, mechanical polishing and electrochemical polishing of the aluminum sheet;

[0016] 2) The treated aluminum sheet is used as the anode and placed in an oxalic acid or sulfuric acid electrolyte for anodization in two steps.

[0017] Furthermore, in step 2), a sulfuric acid solution with a concentration of 15-20% is selected, and the voltage is set to 10-25V; an oxalic acid solution with a concentration of 3-5% is selected, and the voltage is set to 40-60V.

[0018] Furthermore, in step S2, the working gas pressure of the magnetron sputtering method is 0.4 Pa, the target material is a pure metal target of Pd, Cu and Si or Ni-P, and the proportion of film components is controlled by adjusting the sputtering power, wherein the Pd target power is set to 60W, the Si target power is set to 140W, and the Cu target power is set to 5W.

[0019] Furthermore, the palladium-based amorphous alloy film is deposited on an anodic aluminum oxide substrate by magnetron sputtering, wherein the atomic content of Pd is 70-80%, and the atomic content of Si or P is 15-20%.

[0020] Furthermore, in step S3, the background vacuum degree of the electron beam evaporation method is 10 -5 Pa, the electrode deposition thickness is 150-200nm.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1. This invention combines the advantages of palladium metal and amorphous alloys to prepare an amorphous palladium-based alloy film for use as a hydrogen sensing material. This material can inhibit the transition of the palladium film from the α to β phase, effectively improving hydrogen embrittlement and enhancing the stability and service life of the sensing film. Compared to traditional palladium-based alloys, the loose atomic clusters and free volume within the amorphous palladium-based alloy film give it greater hydrogen permeability, thereby reducing the response and recovery time of hydrogen sensing and lowering production costs. Furthermore, this material has enhanced corrosion resistance and mechanical strength, making it suitable for more complex environments.

[0023] 2. The present invention uses an anodic aluminum oxide (AAO) template as a substrate, which has unique advantages over conventional silicon / silicon dioxide substrates. It can provide a uniform nanoporous structure with controllable diameter and thickness, thereby further increasing the specific surface area of ​​the amorphous palladium-based alloy film, which is conducive to accelerating the hydrogen adsorption and desorption rate and shortening the response and recovery time. At the same time, the AAO template can further enhance the mechanical strength and thermal stability of the amorphous palladium-based alloy film, providing a good fixation effect for the amorphous palladium-based alloy film.

[0024] 3. The present invention creatively combines a palladium-based amorphous alloy with an anodic aluminum oxide (AAO) substrate. This combination achieves efficient adsorption and rapid desorption of hydrogen through the synergistic effect of the porous structure of the substrate and the atomic disorder of the amorphous alloy; hydrogen permeability is enhanced through the high hydrogen affinity of palladium and the loose atomic structure of the amorphous alloy, while the controllable nanoporous structure of the AAO substrate is used to greatly increase the specific surface area of ​​the film, significantly shortening the hydrogen response and recovery time (in seconds), and solving the problems of hydrogen embrittlement, hysteresis and insufficient permeability of traditional palladium-based alloys.

[0025] 4. The present invention realizes the preparation of hydrogen sensors through the integrated process of "two-step anodization + magnetron sputtering + electron beam evaporation". By precisely controlling the pore size of the AAO substrate, the film thickness (25-50nm) and the electrode deposition parameters, the high consistency and repeatability of the sensor are achieved. The process flow is simple and suitable for large-scale production, breaking through the limitations of the complex preparation and high cost of optical fiber sensors.

[0026] 5. The present invention introduces elements such as Cu, Si or Ni-P into the amorphous alloy, which not only suppresses the α→β phase transition of pure palladium (avoiding hydrogen embrittlement), but also increases the hydrogen diffusion rate through the free volume space of the amorphous state, while reducing the amount of precious metals used, taking into account both performance and cost.

[0027] 6. The resistive hydrogen sensor of the present invention uses a palladium-based amorphous alloy as its sensing layer. This material exhibits excellent hydrogen response, a short response time, and operates normally at room temperature, even in some harsh operating environments. It exhibits excellent stability and a long service life. Furthermore, compared to metallic palladium, this material effectively avoids hydrogen embrittlement.

[0028] 7. The sensor of this invention utilizes an anodic aluminum oxide template with a uniformly porous structure as its substrate, and a porous palladium-based amorphous alloy thin film as its sensing layer. By utilizing the principle that its resistivity changes during hydrogen adsorption and desorption, the sensor converts the hydrogen concentration in the environment into a change in the film's resistivity. The controllable pore size and thickness of the anodic aluminum oxide template enhance the mechanical properties and thermal stability of the palladium-based amorphous alloy thin film, providing excellent anchoring and a high specific surface area, thereby achieving a rapid hydrogen response. This material combines the remarkable affinity of palladium for hydrogen with the internal spaces of the amorphous alloy that facilitate hydrogen permeation, effectively improving the sensitivity and stability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of a method for preparing a resistive hydrogen sensor based on a palladium-based amorphous alloy film according to an embodiment of the present invention;

[0030] Figure 2 Schematic side view of a resistive hydrogen sensor based on a palladium-based amorphous alloy film according to an embodiment of the present invention;

[0031] Figure 3 Schematic top view of a resistive hydrogen sensor based on a palladium-based amorphous alloy film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be further described below.

[0033] The present invention proposes a resistive hydrogen sensor based on a palladium-based amorphous alloy film. Figure 2 and Figure 3 As shown, the sensor includes: an anodic aluminum oxide (AAO) substrate 1, a palladium-based amorphous alloy thin film layer 2 deposited on the anodic aluminum oxide substrate 1, and electrodes 3 provided at both ends of the palladium-based amorphous alloy thin film layer.

[0034] The anodized aluminum substrate 1 has a uniform porous structure with a pore size of 25-75 nm. The palladium-based amorphous alloy is Pd-Cu-Si or Pd-Cu-Ni-P, and the palladium-based amorphous alloy film has a thickness of 25-50 nm and a uniform porous structure. The electrode material 3 at each end can be silver or gold, with a thickness of 150-200 nm.

[0035] The preparation method of the resistive hydrogen sensor based on the palladium-based amorphous alloy film is as follows Figure 1 As shown, the following steps are included:

[0036] S1: preparing an anodic aluminum oxide (AAO) substrate 1 having a uniform porous structure;

[0037] The present invention prepares an anodic aluminum oxide (AAO) substrate 1 through a two-step anodization process. Anodization is a process that electrochemically generates an oxide film on a metal surface. Its core is to use the metal as an anode to generate an oxidation reaction in an electrolyte. The present invention uses a metal aluminum sheet as the anode, selects a suitable electrolyte, and, under specific process conditions and an applied current, forms an oxide film on the aluminum sheet surface. The oxide film structure can be divided into an outer porous layer and an inner barrier layer.

[0038] The preparation method of the anodic aluminum oxide (AAO) substrate 1 is as follows:

[0039] (1) Aluminum sheet annealing, mechanical polishing and cleaning

[0040] The purity and surface flatness of the aluminum sheet to be oxidized have a significant impact on the order of the final anodized aluminum morphology. Therefore, aluminum sheets with higher purity must be selected for electrolysis. The aluminum sheet is annealed in air, nitrogen or argon at a high temperature of 500℃–600℃ for 4-6 hours. The purpose of annealing is to eliminate the internal stress of the aluminum sheet. Subsequently, mechanical polishing is performed, and the surface of the aluminum sheet is polished with sandpaper (800#~2000#) to remove scratches and oxide layers and improve surface flatness. The annealed aluminum sheet is then ultrasonically cleaned with acetone, ethanol and ultrapure water in sequence. The purpose of this step is to remove organic matter such as oil stains on the surface of the aluminum sheet by using acetone and ethanol.

[0041] (2) Electrochemical polishing of aluminum sheets

[0042] After the treatment in step (1), the aluminum sheet needs to be placed in a polishing liquid for electrochemical polishing in order to improve the smoothness of the aluminum sheet surface. At the same time, it should be noted that the temperature should be controlled below 15°C, because the mixed solution is flammable and dangerous. Commonly used polishing liquid components include perchloric acid-ethanol system, phosphoric acid-sulfuric acid system, sodium hydroxide-sodium gluconate system or ammonia-ammonium chloride system, among which the most commonly used polishing liquid suitable for aluminum sheets is perchloric acid-ethanol system, i.e. 6-10 vol.% perchloric acid + 90-94 vol.% anhydrous ethanol. The voltage, polishing time and temperature conditions used in electrochemical polishing can be determined according to the polishing liquid composition used and the required pore size. For example, for the perchloric acid-ethanol system, the voltage can be controlled between 20 and 60 V, the temperature is below 10°C, and the polishing time is 5 minutes.

[0043] (3) Anodizing of aluminum sheets

[0044] The aluminum sheet treated in step (2) is placed as an anode in an electrolyte for anodization. Sulfuric acid, oxalic acid and phosphoric acid solutions are usually used as electrolytes for preparing porous anodized aluminum. Different electrolytes should be selected with different applied voltages and electrolyte concentrations. For example, a sulfuric acid solution with a concentration of 15-20% can be selected, and the voltage can be set to 10-25V, or an oxalic acid solution with a concentration of 3-5% can be selected, and the voltage can be set to 40-60V. However, it is not recommended to select a phosphoric acid solution with a concentration of 1-3%, because it is easy to cause excessive pore size, which is not conducive to hydrogen absorption by the palladium-based amorphous alloy film. The oxidation time depends on the specific situation. For example, a two-step oxidation method is used, and the first anodization time is set to 3 hours. Subsequently, 20 ml of a mixed solution of 6% H3PO4 and 1.8% H2CrO4 is used to remove the first layer of anodized aluminum. The purpose is to achieve an ordered surface morphology on the surface of the aluminum foil, which can serve as a growth template for the second anodization. The second anodization time is also set to 3 hours.

[0045] The pore size of the anodized aluminum substrate 1 can be 25 to 75 nm, and the pore size is relatively uniform. For example, the pore size of the anodized aluminum substrate 1 can be 50 nm.

[0046] S2: forming a palladium-based amorphous alloy thin film 2 on the anodized aluminum substrate 1;

[0047] The present invention forms a palladium-based amorphous alloy film 2 on an anodized aluminum substrate 1 using a suitable method such as magnetron sputtering. The palladium-based amorphous alloy film 2 can be composed of Pd-Cu-Si or Pd-Cu-Ni-P. Pd-Cu-Si is preferred, wherein the atomic content of Pd is 70-80% and the atomic content of Si or P is 15-20%. The palladium-based amorphous alloy film 2 has a porous structure and can be 25-50 nm thick.

[0048] In addition, the working gas pressure of the magnetron sputtering method is 0.4 Pa, and the target material is a pure metal target of Pd, Cu and Si or Ni-P. The ratio of the two components of the film is controlled by adjusting the sputtering power, where the Pd target power is set to 60W, the Si target power is set to 140W, and the Cu target power is set to 5W.

[0049] S3: depositing electrodes 3 at both ends of the palladium-based amorphous alloy film 2 .

[0050] The present invention uses electron beam evaporation to form electrodes 3 at both ends of a palladium-based amorphous alloy film 2, with a thickness of 150-200 nm. The material of the electrodes can be gold, silver, or other suitable materials. Specifically, a mask with two rectangular through holes in the shape of electrodes is formed on the palladium-based amorphous alloy film 2, and then the electrode material is deposited thereon using electron beam evaporation or other suitable methods. The mask is then removed, thereby forming electrodes 3 with predetermined shapes at both ends of the palladium-based amorphous alloy film 2. The background vacuum degree of the electron beam evaporation method is 10 -5 Pa, the electrode deposition thickness is 150-200nm.

[0051] Based on the above description, the embodiment proposes a resistive hydrogen sensor based on a palladium-based amorphous alloy thin film. The preparation method of the sensor is as follows:

[0052] Step 1: Prepare the anodized aluminum substrate using a two-step method

[0053] (1) Aluminum sheets (99.99%) were annealed at 500°C in air for 5 hours.

[0054] (2) The surface of the aluminum sheet was polished with sandpaper, and then the annealed aluminum sheet was ultrasonically cleaned with acetone, ethanol and ultrapure water for 15 minutes in sequence; then the aluminum sheet was treated with 50 ml of 1 mol / L sodium hydroxide solution.

[0055] (3) The aluminum sheet was electrochemically polished using a perchloric acid-ethanol mixed solution, wherein the volume fractions of perchloric acid and ethanol were 10% and 90%, respectively. Constant voltage conditions were used, the voltage was set to 60 V, and the polishing time was 5 minutes.

[0056] (4) A two-step oxidation method was used, and 0.3 mol / L oxalic acid solution was used as the electrolyte for both steps. The oxidation voltage was set to 40 V. At the same time, the first-step oxidation time and the second-step oxidation time were both 3 hours. After the first-step oxidation, 20 ml of a mixed solution of 6% H3PO4 and 1.8% H2CrO4 was used to remove the first layer of anodized aluminum.

[0057] Step 2: Magnetron sputtering deposition of palladium-based amorphous alloy thin films

[0058] DC sputtering is adopted, and the target materials are Pd target, Cu target and Si target with a purity of 99.99%. The working pressure of the sputtering chamber is 0.4Pa. The film thickness and the proportion of each component of the palladium-based amorphous alloy are controlled by the size of the DC power supply current applied to a single target. The film thickness is about 40nm.

[0059] Step 3: Electron beam evaporation deposition of electrodes

[0060] In this embodiment, the electrode material is silver metal, and the silver electrode is prepared by electron beam evaporation and connected to the external circuit through a copper wire. -5 Pa, the electrode deposition thickness is 150nm.

[0061] The above description is merely a preferred embodiment of the present invention and does not limit the present invention in any way. Any person skilled in the art who, without departing from the scope of the present invention, makes any equivalent substitution, modification, or other changes to the technical solution and technical content disclosed in the present invention shall be deemed to be within the scope of the present invention and still fall within the scope of protection of the present invention.

Claims

1. A resistive hydrogen sensor based on a palladium-based amorphous alloy film, characterized in that: include: An anodic aluminum oxide substrate, a palladium-based amorphous alloy thin film layer arranged on the anodic aluminum oxide substrate, and electrodes arranged at both ends of the palladium-based amorphous alloy thin film layer.

2. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 1, characterized in that: The anodized aluminum substrate has a porous structure with a pore diameter of 25-75 nm.

3. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 1, characterized in that: The palladium-based amorphous alloy film has a composition of Pd-Cu-Si or Pd-Cu-Ni-P, a thickness of 25-50 nm, and a porous structure.

4. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 1, characterized in that: The electrode material is silver or gold, and the thickness is 150-200 nm.

5. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 1, characterized in that: The preparation method of the sensor includes the following steps: S1: Preparation of anodized aluminum substrate with uniform porous structure; S2: depositing a palladium-based amorphous alloy thin film on the anodic aluminum oxide substrate by magnetron sputtering; S3: Depositing silver or gold electrodes at both ends of the film by electron beam evaporation and connecting them to an external circuit through copper wires.

6. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 5, characterized in that: In step S1, the anodized aluminum substrate is prepared by a two-step anodizing method, which includes the following steps: 1) Annealing, mechanical polishing and electrochemical polishing of the aluminum sheet; 2) The treated aluminum sheet is used as the anode and placed in an oxalic acid or sulfuric acid electrolyte for anodization in two steps.

7. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 6, characterized in that: In step 2), a sulfuric acid solution with a concentration of 15-20% is selected, and the voltage is set to 10-25V; an oxalic acid solution with a concentration of 3-5% is selected, and the voltage is set to 40-60V.

8. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 1, characterized in that: In step S2, the working gas pressure of the magnetron sputtering method is 0.4 Pa, the target material is a pure metal target of Pd, Cu and Si or Ni-P, and the proportion of film components is controlled by adjusting the sputtering power.

9. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 8, characterized in that: The palladium-based amorphous alloy film is deposited on an anodic aluminum oxide substrate by magnetron sputtering, wherein the atomic content of Pd is 70-80%, and the atomic content of Si or P is 15-20%.

10. The resistive hydrogen sensor based on palladium-based amorphous alloy thin film according to claim 1, characterized in that: In step S3, the background vacuum degree of the electron beam evaporation method is 10 -5 Pa, the electrode deposition thickness is 150-200nm.

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