SENSOR LAYER SYSTEM PRECURSOR, SENSOR LAYER SYSTEM WHICH CAN BE PRODUCED THEREFROM, HYDROGEN SENSOR ELEMENT WHICH USES SAID SENSOR LAYER SYSTEM, AND CORRESPONDING PRODUCTION METHOD

Abstract

A sensor layer system precursor (48) configured for forming a sensor layer system (26), the sensor layer system (26) being configured for absorbing hydrogen, includes a sensing layer precursor (42) made from a sensing layer precursor material that consists of: 20% by weight to 90% by weight palladium or palladium alloy, the palladium alloy consisting of palladium and at least one palladium alloy partner chosen from group VIIIB, wherein the amount-of-substance fraction of palladium is at least 85% and the sum of the amount-of-substance fractions of all palladium alloy partners contained in the palladium alloy is at most 15% with respect to the whole amount of substance of the palladium alloy, respectively; 10% by weight to 80% by weight sacrificial metal, the sacrificial metal being at least as electropositive as palladium and each palladium alloy partner and/or the sacrificial metal being selectively transformable by a chemical process into a soluble and/or ionic form; remainder unavoidable impurities; and optionally up to and including 30% by weight pore filler precursor metal that is transformable into a pore filler by means of a pore filler reaction component.

Claims

1. A sensor layer system precursor (48) configured for forming a sensor layer system (26), the sensor layer system (26) being configured for absorbing hydrogen, the sensor layer system precursor (48) including a sensing layer precursor (42) made from a sensing layer precursor material that consists of: 20% by weight to 90% by weight palladium or palladium alloy, preferably a single phase palladium alloy, the palladium alloy consisting of palladium and at least one palladium alloy partner chosen from group VIIIB, wherein the amount-of-substance fraction of palladium is at least 85% and the sum of the amount-of-substance fractions of all palladium alloy partners contained in the palladium alloy is at most 15% with respect to the whole amount of substance of the palladium alloy, respectively; 10% by weight to 80% by weight sacrificial metal, the sacrificial metal being at least as electropositive as palladium and each palladium alloy partner and/or the sacrificial metal being selectively transformable by a chemical process into a soluble and/or ionic form; remainder unavoidable impurities; and optionally up to and including 30% by weight pore filler precursor metal that is transformable into a pore filler by means of a pore filler reaction component.

2. The sensor layer system precursor (48) according to claim 1, wherein each palladium alloy partner is chosen from a group comprising gold, iridium, copper, nickel, platinum, rhodium, ruthenium and silver.

3. The sensor layer system precursor (48) according to claim 1 or 2, wherein the sacrificial metal of the sensing layer precursor material (42) is chosen from a group comprising aluminum, cobalt, iron, lithium, zinc and alkaline earth metals, preferably calcium or magnesium or mixtures thereof, as well as copper, nickel and silver, wherein copper, nickel and silver are only chosen, if they are not chosen as a palladium alloy partner.

4. The sensor layer system precursor (48) according to any of the claims 1 to 3, wherein the pore filler precursor metal is chosen from a group comprising zinc and copper.

5. The sensor layer system precursor (48) according to any of the claims 1 to 4, further comprising a cover metal layer precursor (38, 44) that is applied to at least one side of the sensing layer precursor (10) and that is made from a cover metal layer precursor material that consists of: at least 40% by weight silver, gold, or silver-gold-alloy consisting of silver, gold and unavoidable impurities; 10% by weight to 60% by weight sacrificial metal, the sacrificial metal being at least as electropositive as each other constituent of the cover metal layer precursor material and/or the sacrificial metal being selectively transformable by a chemical process into a soluble and/or ionic form; remainder unavoidable impurities; and optionally up to and including 50% by weight palladium; optionally up to and including 27% pore filler precursor metal, that is transformable into a pore filler by means of a pore filler reaction component.

6. A sensor layer system (26) for a hydrogen sensor element (20) configured for sensing a hydrogen concentration of, preferably non-bound, hydrogen in a fluid, the sensor layer system (26) being configured for absorbing hydrogen, the sensor layer system (26) being manufacturable from a sensor layer system precursor (48) according to any of the preceding claims by selectively removing sacrificial metal, preferably from the sensing layer precursor, in such a way that the sensor layer system (26) includes a porous sensing layer (43) generated from the sensing layer precursor (42).

7. The sensor layer system (26) according to claim 6, further comprising a cover metal layer (39, 45) that is manufacturable by selectively removing sacrificial metal, preferably from the cover metal layer precursor (38, 44), such that the cover metal layer (39, 45) is generated on at least one side of the sensing layer (43).

8. The sensor layer system (26) according to claim 6 or 7, wherein the sensing layer (43) has pores (52) that at least partially include a pore filler material (56) that is chosen from a group comprising zinc, copper, nano porous material, MOF, copper oxide, copper doped calcium phosphate hydroxyapatite, cerium oxide, praseodymium oxide, iron, gold nano-particles, transitional metals, transitional metal oxides, rare earth metal oxides, manganese, cerium oxide, praseodymium oxide ore copper doped apatite and phosphates, silicates, carbonates, preferably of transitional metals or rare earth metals.

9. The sensor layer system (26) according to any of the claims 6 to 8, wherein the sensing layer (43) has a layer thickness from 50 nm to 500 nm, preferably from 50 nm to 400 nm, preferably from 200 nm to 400 nm, preferably from 200 nm to 300 nm.

10. The sensor layer system (26) according to any of the claims 6 to 9, wherein the porosity of the sensing layer (43) and/or the cover metal layer (39, 45) and/or the metal base layer (41) and/or the terminal metal layer (47) is more than 30% by volume and less than 100% by volume of the respective layer.

11. The sensor layer system (26) according to any of the claims 6 to 10, wherein the average pore diameter of the sensing layer (43) and/or the cover metal layer (39, 45) and/or the metal base layer (41) and/or the terminal metal layer (47) is from 5 nm to 30 nm, preferably from 10 nm to 20 nm.

12. A hydrogen sensor element (20) for a hydrogen sensor device (10) for sensing a concentration of, preferably non-bound, hydrogen in a fluid, the hydrogen sensor element (20) comprising at least one oscillating member (24) and a sensor layer system (26) according to any of the claims 6 to 11 arranged on a portion of the oscillating member (24).

13. A manufacturing method for manufacturing a sensor layer system (26) for a hydrogen sensor element (20) that is configured for a hydrogen sensing device (10) for sensing a concentration of, preferably non-bound, hydrogen in a fluid, the method comprising: providing a sensor layer system precursor (48) according to any of the claims 1 to 5; and selectively removing sacrificial metal from the sensor layer system precursor (48) in order to form pores (52).

14. A manufacturing method for manufacturing a hydrogen sensor element (20) for a hydrogen sensor device (10) for sensing a concentration of, preferably non-bound, hydrogen in a fluid, the method comprising: providing an oscillating member (24); applying a sensor layer system precursor (48) according to any of the claims 1 to 5 to the oscillating member (26); and selectively removing sacrificial metal from the sensor layer system precursor (48) in order to form pores (52), preferably such that a sensor layer system (26) according to any of the claims 6 to 11 is obtained.

15. A method of using a sensor layer system (26) according to any of the claims 6 to 11 on an oscillating member (24) or a bending oscillating member so as to detect a hydrogen concentration of a fluid.

Description

[0172] Embodiments of the invention are described in more detail with reference to the accompanying schematic drawings. Therein:

[0173] FIG. 1 depicts an embodiment of a hydrogen sensor device;

[0174] FIG. 2 depicts an embodiment of a hydrogen sensor element;

[0175] FIG. 3 a further embodiment of a hydrogen sensor element;

[0176] FIG. 4 to FIG. 9 an embodiment of a manufacturing method for a hydrogen sensor element;

[0177] FIG. 10 an embodiment of a hydrogen sensor element;

[0178] FIG. 11 an embodiment of a hydrogen sensor element;

[0179] FIG. 12 a section of the sensor layer system of FIG. 9;

[0180] FIG. 13 a section of the sensor layer system of FIG. 10; and

[0181] FIG. 14 a section of the sensor layer system of FIG. 11.

[0182] Initial reference is made to FIG. 1 showing an embodiment of a hydrogen sensor device 10 that is configured for sensing hydrogen concentration. The hydrogen sensor device 10 comprises a housing device 12. The housing device 12 is provided with a housing opening 14. The housing opening 14 can be closed by a membrane 16 that is configured such that hydrogen may diffuse through the membrane 16. Furthermore, a heating device 18 can be arranged within the housing device 12.

[0183] In addition, a hydrogen sensor element 20 is arranged within the housing device 12. The hydrogen sensor element 20 can be heated by the heating device 18.

[0184] The hydrogen sensor device 10 further comprises a control device 22 that can control the sensing process. The control device 22 can also be partially accommodated within the housing device 12. The control device 22 is configured for controlling the heating device 18 and the hydrogen sensor element 20, particularly for activating the heating device 18 in order to heat the hydrogen sensor element 20 and/or for determining the hydrogen concentration sensed by the hydrogen sensor element 20.

[0185] As depicted in FIG. 2, the hydrogen sensor element 20 can comprise an oscillating member 24 on which a sensor layer device 26 is arranged. The sensor layer device 26 will be discussed in more detail later. The oscillating member 24 is, for example, a quartz oscillating member 28 an can be excited to oscillate by means of electrical (alternating) current. The oscillation frequency of the oscillating member 24 depends on the geometry (here: cylindrical) of the oscillating member 24 and the configuration of the sensor layer system 28. Other geometries are also usable, such as a tuning fork geometry.

[0186] The sensor layer system 28 is configured such that it can particularly absorb unbound hydrogen. Thereby the mass of the sensor layer system 26 is increased and the oscillating frequency of the oscillating member 24 changes depending on the mass change. This change of the oscillating frequency can be detected by the control device 22 and be translated into a value corresponding to the hydrogen concentration.

[0187] As depicted in FIG. 3, the hydrogen sensor element 20 may also have a bar like oscillating member 24. This oscillating member 24 can be made from stainless steel. Additionally, an actuator 30 can be provided that causes the oscillating member 24 to oscillate. The functional principle, however, is the same as in the embodiment of FIG. 2.

[0188] Referring now to FIG. 4 through FIG. 9, manufacture of the sensor layer system 26 is depicted schematically. The layers are preferably sputtered; although other depositing processes may be used.

[0189] Initially a bonding agent layer 34 made of a bonding agent is preferably deposited on a substrate layer 32 that particularly may be formed by the oscillating member 24. The bonding agent layer 34 has a layer thickness between 1 nm and 5 nm. Tantalum is preferably used as the bonding agent.

[0190] A connecting layer 36 made of connecting material having a layer thickness between 5 nm and 20 nm may be deposited on the bonding agent layer 34. Gold, silver or an alloy thereof may be preferably used as the connecting material.

[0191] A lower cover metal layer precursor 38 that is made from a cover metal layer precursor material having a layer thickness of 10 nm to 30 nm can be deposited on the connecting layer 36. The cover metal precursor material consists of at least 40 wt % silver, gold or silver gold alloy, wherein the silver gold alloy in turn consists of silver, gold and unavoidable impurities as well as 10 wt-% to 60 wt-% sacrificial metal that is at least as electropositive as each other component of the cover metal layer precursor material and/or wherein the sacrificial metal is selectively transformable by a chemical process into a soluble and/or ionic form, e.g. magnesium or calcium. The cover metal layer precursor material may also include up to and including 50 wt-% palladium.

[0192] The lower cover metal layer precursor 38 is also called metal base layer precursor 40. The cover metal layer precursor material is then called metal base layer precursor material.

[0193] Further, a sensing layer precursor 42 made from a sensing layer precursor material that has a layer thickness of 50 nm to 300 nm, preferably of 50 nm to 250 nm, preferably of 100 nm to 250 nm, preferably of 100 nm to 200 nm can be deposited on the lower cover metal layer precursor 38. The sensing layer precursor material consists of 20 wt-% to 90 wt-% palladium or palladium alloy, wherein the palladium alloy consists of palladium and at least one palladium alloy partner that is chosen from group VIIIB, wherein the mole fraction of palladium is at least 85% and the sum of the mole fractions of all palladium alloy partners included in the palladium alloy is at most 15% with respect to the total amount of substance of the palladium alloy as well as 10 wt-% to 80 wt-% sacrificial metal, wherein the sacrificial metal is at least as electropositive as palladium and each palladium alloy partner and/or wherein the sacrificial metal is selectively transformable by a chemical process into a soluble and/or ionic form.

[0194] An upper cover metal layer precursor 44 that is made from the cover metal precursor material with a layer thickness of 10 nm to 30 nm. The composition, however, may be different from the lower cover metal layer precursor 38. The upper cover metal layer precursor 44 is also called a terminal metal layer precursor 46. The cover metal layer precursor material is then called terminal metal layer precursor material.

[0195] The previously described metal layers (bonding agent layer 34, connecting layer 36, lower cover metal layer precursor 38, metal base layer precursor 40, sensing layer precursor 42, upper cover metal layer precursor 44, terminal metal layer precursor 46) need not all be present. Depending on the application single layers except for the sensing layer precursor 42 may be omitted. The metal layers collectively form a sensor layer system precursor 48 that can be transformed into the sensor layer system 26 as subsequently described.

[0196] In a chemical process, the sensor layer system precursor 48 is contacted with a solution that includes 20 g/l disodium ethylenediaminetetraacetate (Na.sub.2EDTA) and 0.1 g to 5 g of a non-ionic surfactant, preferably based on ethylene glycol or a wetting agent or other surface active substance or more than 20 g of a monoalkyloligoethyleneglycol, such as diethyleneglycolmonobutylether. Preferably a solution bath formed from this solution is heated to a slightly increased temperature between 40 C. and 60 C., preferably 50 C.

[0197] With this the sacrificial metal is removed from the sensor layer system precursor 48, wherein the remaining components of the sensor layer system precursor 48 are deposited in a porous configuration. Subsequently this intermediate product may be rinsed multiple times with highly purified water and isopropyl alcohol and dried. Finally the result may be tempered under nitrogen at about 100 C. to 250 C.

[0198] Now the sensor layer system precursor 48 has become the sensor layer system 26. Therein the lower cover metal layer precursor 38 and the metal base layer precursor 40 were respectively transformed into a lower cover metal layer 39 and a metal base layer 41. The sensing layer precursor 42 has become the sensing layer 43 in which hydrogen can be well absorbed. The upper cover metal layer precursor 44 and the terminal metal layer precursor 46 have respectively become upper cover metal layer 45 and terminal metal layer 47.

[0199] The lower cover metal layer 39, the metal base layer 41, the sensing layer 43, the upper cover metal layer 45 and the terminal metal layer 47 are respectively porous due to removal of the sacrificial metal.

[0200] After cooling the sensor layer system 26 can be fixed to the oscillating member 24 so as to form the hydrogen sensor element 20. The hydrogen sensor element 20 can be calibrated and subsequently used as a sensor for hydrogen.

[0201] As depicted in a section in FIG. 12, the sensor layer system 26 has a porous configuration. The material is depicted in a cross-section, wherein there is a palladium rich portion 50 and a pore 52.

[0202] Subsequently further embodiments are explained insofar as they differ from the previous embodiments.

[0203] In addition to the metal layers explained so far, in this embodiment a pore filler precursor metal is deposited or sputtered. The pore filler precursor metal can be deposited onto the inner surface of the pores or at least partially be dissolved within the palladium containing layer.

[0204] In order to transform this sensor layer system precursor 48 into the sensor layer system 26, the already porous sensor layer system precursor is additionally brought into contact with a reaction component that is able to transform the pore filler precursor metal into a pore filler material or cause a migration of the pore filler precursor metal from the palladium containing layers into the pores 52 so as to form the pore filler material.

[0205] For the transformation into a porous form a solution of 50 g/l ethanoic acid and 0.1 g to 5 g of a non-ionic surfactant is used, preferably based on ethylene glycol or a wetting agent or other surface active substance or more than 20 g of a short chained monoalkyloligoethyleneglycol such as diethyleneglycolmonobutylether. After that the layers are rinsed with highly purified water and isopropyl alcohol multiple times and dried and tempered under nitrogen at 250 C.

[0206] For transforming or generating the pore filler material from the pore filler precursor metal the porous sensor layer system precursor 48 is brought into contact with a warm solution that includes 10 g to 80 g 2-methylimidazole per liter methanol and 5 g to 50 g sodium formate per liter methanol. Thus a sensor layer system 26 with pore filler material 56 is formed.

[0207] Subsequently, it is intensely rinsed with pure methanol, tempered under nitrogen at 120 C., and the hydrogen sensor element 20 is formed an used as a sensor after cooling.

[0208] Optionally, as depicted in FIG. 11, 5 nm to 25 nm gold may be deposited by means of a vacuum depositing method onto the sensor layer system 26. With this a second terminal layer 58 is formed that is not porous but massive. Yet there is no significant pore closure due to the gold not being able to close off the pores entirely due to the low occupancy. Consequently a good gas transport can still take place.

[0209] As depicted in a section of FIG. 13 in more detail, the sensor layer system 26 comprises a porous configuration with pore filler material 56. The material is depicted in a cross-section wherein palladium rich portions 50 and the pore 52 are present. The pore 52 is filled with pore filler material 56 that is in contact with the palladium rich portion 50 via contact surface 60.

[0210] In a variant oxygen from the air, an oxidizer such as hydrogen peroxide or phosphorous buffers or other additives are used as reaction components in generating the pore filler material 56 from the pore filler precursor metal. The contact with the reaction components leads to a transformation of the pore filler precursor metal and formation of the pore filler material 56 that precipitates in the interior of the pores 52. Suitable pore filler materials can be materials that are able to oxidize hydrogen, such as copper oxide or copper doped calcium hydroxyapatite, or rare earth metal oxides such as cerium oxide praseodymium oxide.

[0211] In this variant a 10 g hydrogen peroxide solution (35% in water) per liter water is used as a reaction component.

[0212] As depicted in a section of FIG. 14 in more detail, the sensor layer system 26 can have a porous configuration in an embodiment. This again is a section of a cross-section. The palladium rich portion 50, a palladium poor or free portion 54 and the pore 52 are present, wherein the palladium rich portion 50 is a central portion 62 of the sensor layer system 26. Consequently in this embodiment the palladium concentration of the metal layers may continuously increase from the surface (FIG. 14, at the top) towards the bottom till the sensing layer 43.

[0213] Referring now to FIG. 1, the heating device 18 has at least one heating element 64. Suitable heating elements are sufficiently known and can produce heat via current or irradiation with light, specifically infrared light. The sensor layer system 26 is preferably attached to the oscillating member 24 such that it can be heated by applying a current, and thus absorbed and adsorbed gases may be removed from the layer. Applying current to the layer periodically can increase the sensitivity of the hydrogen sensor element 20.

[0214] In a variant of the hydrogen sensor element 20 an electrode or a part of the electrode required for operating the oscillating member 24 can be replaced by the sensor layer system 26. The hydrogen sensor element 20 may thus be manufactured in fewer steps and oscillation excitation as well as read out of the mass change of the oscillating member 24 can take place through the same material due to the sensing effect for hydrogen.

[0215] The hydrogen sensor device 10 is suitable to detect hydrogen in demanding environments, particularly in the presence of increased temperatures and other compounds, such as hydrocarbons, organic compounds, specific solvents, oils, foodstuff vapors, machine oils, fuels and electrolytes of fuel cells and batteries.

[0216] The membrane 16 can be a polymer membrane 66 through which hydrogen may diffuse. Suitable polymers are known as high performance polymers having high chemical and mechanical stability. Suitable polymers are among others polyimides, polyethers, polyetherketones and fluorous polymers such as polyvinylidenfluoride. In monitoring the hydrogen concentration in organic liquids the choice of membrane 16 with respect to stability is relevant. Suitable materials are sufficiently known.

[0217] With the measures described herein, porous metal layers are provided that are palladium rich in the center portion and are covered at least on one side with a thin hydrogen resistant and porous noble metal layer. The porous metal layers have a clearly defined geometry and can thus be employed in demanding environments, for example, on vibrating systems for detecting hydrogen. Furthermore, methods for manufacturing the abovementioned systems and composites including the abovementioned porous metals and pore fillers are provided.

LIST OF REFERENCE NUMERALS

[0218] 10 hydrogen sensor device [0219] 12 housing device [0220] 14 housing opening [0221] 16 membrane [0222] 18 heating device [0223] 20 hydrogen sensor element [0224] 22 control device [0225] 24 oscillating member [0226] 26 sensor layer device [0227] 28 quartz oscillating member [0228] 30 actuator [0229] 32 substrate layer [0230] 34 bonding agent layer [0231] 36 connecting layer [0232] 38 lower cover metal layer precursor (metal layer) [0233] 39 lower cover metal layer [0234] 40 metal base layer precursor (metal layer) [0235] 41 metal base layer [0236] 42 sensing layer precursor (metal layer) [0237] 43 sensing layer [0238] 44 upper cover metal layer precursor (metal layer) [0239] 45 upper cover metal layer [0240] 46 terminal metal layer precursor (metal layer) [0241] 47 terminal metal layer [0242] 48 sensor layer system precursor [0243] 50 palladium rich portion [0244] 52 pore [0245] 54 palladium poor/palladium free portion [0246] 56 pore filler material [0247] 58 second terminal layer [0248] 60 contact surface [0249] 62 central portion [0250] 64 heating member [0251] 66 polymer membrane