CAPACITIVE HYDROGEN SENSOR

Abstract

The invention relates to a capacitive sensing material and a method of manufacturing thereof, a capacitive sensing coating formulation, a capacitive chip, a capacitive sensor, a method for manufacturing a coated chip, a method for analysing the composition of a gaseous mixture, a use of particles comprising titanium oxide and platinum for sensing hydrogen, and a use of capacitive sensing material for detecting a gas leak. The capacitive sensing material comprises composite particles wherein porous titanium dioxide is at least in part coated with platinum particles.

Claims

1. A capacitive sensing material, comprising composite particles wherein porous titanium dioxide is at least in part coated with platinum particles.

2. The capacitive sensing material of claim 1, wherein the composite particles have an average particle size of 50-500 nm, as measured with transmission electron microscopy, the platinum particles are at least in part present in the pores of the porous titanium dioxide, and the platinum particles having an average particle size of 1-20 nm, as measured with transmission electron microscopy.

3. The capacitive sensing material of claim 1, wherein the amount of platinum is 10-45% by total weight of the composite particles.

4. The capacitive sensing material of claim 1, having selectivity for adsorption and/or absorption of hydrogen.

5. A capacitive sensing coating formulation, comprising the capacitive sensing material of claim 1.

6. A capacitive chip, comprising the capacitive sensing material of claim 1 or a capacitive sensing coating formulation comprising the capacitive sensing material.

7. A capacitive sensor, comprising the capacitive sensing material of claim 1 and/or a capacitive chip; wherein the capacitive chip comprises (1) the capacitive sensing material or (2) a capacitive sensing coating formulation comprising the capacitive sensing material.

8. The capacitive sensor of claim 7, being a capacitive gas sensor.

9. The capacitive sensor of claim 7, further comprising one or more additional (capacitive) chips comprising one or more coatings.

10. The capacitive sensor of claim 7, further comprising one or more additional sensing elements for measuring (physical) gas properties.

11. The capacitive sensor of claim 10, wherein the (physical) gas properties are selected from the group consisting of pressure, temperature, thermal conductivity, viscosity, speed of sound, density, and heat capacity.

12. The capacitive sensor of claim 10, comprising a thermal conductivity sensing element.

13. The capacitive sensor of claim 7, suitable for measurement of hydrogen concentrations between 0.01-100 vol. % by total gas volume measured.

14. A method for manufacturing the capacitive sensing material of claim 1, the method comprising: i) preparing a dispersion comprising porous titanium dioxide particles, and ii) coating the porous titanium dioxide particles with platinum particles, thereby forming the capacitive sensing material.

15. The method of claim 14, wherein step ii) is performed at a temperature of 20-150° C.

16. A method for manufacturing a capacitive chip of claim 6, comprising: i) applying the capacitive sensing material and/or a capacitive sensing coating formulation which comprises the capacitive sensing material, onto a chip, thereby forming a coated chip.

17. A method for sensing a gas in a gaseous mixture, the method comprising: i) contacting the gaseous mixture with the capacitive sensing material as described in claim 1, and ii) measuring a change in capacitance of the capacitive sensing material.

18. The method of claim 17, further comprising: iii) providing an energy input to a chip, for example, a capacitive sensing chip, whereon the capacitive sensing material is present, that is converted to output signals based on at least one property, which at least one property is responsive to at least part of the gaseous mixture when exposed thereto.

19. The method of claim 17, wherein the gaseous mixture is a gaseous stream of natural gas, syngas, biogas, expanded liquefied natural gas, or a mixture thereof.

20. The method of claim 17, wherein the gaseous mixture comprises at least hydrogen.

21. The method of claim 17, further comprising: iv) providing output signals and/or data signals to a computer processor which is in communication with a computer memory device in which instructions are stored for conversion of the data signals to an estimated composition parameter, and v) calculating in the computer processor the estimated composition parameter using the instructions and the output signals and/or data signals, and wherein the estimated composition parameter is preferably the hydrogen concentration.

22. The method of claim 17, wherein the method is performed in an oxygen-free atmosphere.

23. The method of claim 17, wherein the method is performed at room temperature.

24.-25. (canceled)

Description

EXAMPLES

Example 1

Synthesis of Porous Titanium Dioxide Particles

[0107] 8 ml 0.1 M KCl was added to 1580 g ethanol and the solution was stirred for 10 min in a 2 l reactor. After 10 min 30.6 ml of titanium isopropoxide was added at a stirring speed of 300 rpm, after addition the stirring speed was set to 200 rpm. The dispersion was stirred overnight.

[0108] After overnight stirring a white dispersion was obtained which was centrifuged at 6000 rpm. After removal of the supernatant to the obtained sedimented material was added ethanol again a centrifuge step was used, this was repeated twice with water and after the last centrifuge step the sedimented material was dispersed in 200 ml demineralised water. The obtained dispersion was given an ultrasonic treatment in an ultrasonic bath. The average particle size was 300 nm (FIG. 1).

Example 2

Growing of Platinum Nanoparticles in the Porous Titanium dioxide particles

[0109] A 2 1 reactor was heated to 60° C. 1000 ml demineralised water was added to the reactor. 0.36 g chloroplatinic acid was added to 500 ml demineralised water. 4.53 g polyvinylpyrrolidone (PVP) was added while stirring/shaking. The mixture was stirred until all PVP is dissolved. This was added to 1000 ml demineralised water which was in the 2 l reactor. After 5 min of stirring, 150 ml of the 0.1 wt. % titanium dioxide dispersion was added under stirring. The mixture was heated until the temperature of the dispersion was 50° C. At 50° C., a solution of 1.8 g NaHB.sub.4 in 150 ml demineralised water was slowly added using a droplet addition system. The mixture was stirred for 2 hours at 50° C. and then centrifuged at 6000 rpm for 30 min. Then, the material was washed two times with 11 demineralised water. After the final centrifuge step in 200 ml total was dispersed. The concentration of platinum in the particles was 25 wt. % according to inductively coupled plasma (ICP) measurements. FIG. 2 displays TEM images of the titanium dioxide particles comprising impregnated platinum nanoparticles.

Example 3

Growing of Palladium Particles on the Porous Titanium Dioxide Particles

[0110] 0.1 g tetrachloropalladate (PdCl.sub.4) was added to 12 ml (50 mM) HCl. After 5 min, 540 ml demineralised water was added. After 10 min, 180 ml of 0.1 wt. % titanium dioxide dispersion was added to this 1 mM H.sub.2PdCl.sub.4 solution, under stirring. Then, 50 ml of 100 mM ascorbic acid solution was added under stirring. The dispersion was stirred for 60 min. After this the dispersion was given a centrifuge step, 6000 rpm for 20 min, to obtain the TiO.sub.2/Pd particles, the material was washed three times with demineralised water and centrifuged. The TiO.sub.2/Pd material was dispersed in 80 ml demineralised water. The amount of palladium on the particles was ca. 5 wt. % using ICP measurements. FIG. 3 displays TEM images of titanium dioxide particles having surface grown palladium particles.

Example 4

Hydrogen Sensing 2ith TiO.SUB.2./Pt Coating

[0111] The TiO.sub.2/Pt particles from example 2, were applied to a chip having interdigitated electrodes. The capacitance of the empty chip was 7 pF. The coating process was done one time, two times, three times and four times in order to assess the influence of the coating thickness on the response. This increased the capacitance of the chip to 10.4 pF, 13.4 pF, 14.1 pF and 13.9 pF, respectively. When this coated chip is exposed to 5 vol. % hydrogen in nitrogen, a significant response was measured. Even for the thickest coating, there was no short circuit of the capacitive electrodes. This was one of the risks identified, because the TiO.sub.2/Pt may give a conductive layer. The response to hydrogen increased between 1 and 2 times coating, but stayed constant for 2 to 4 times coating (FIG. 4).

Example 5

Comparison Between TiO.SUB.2./Pt Coating and Thermal Conductivity Sensor (TCD)

[0112] The new sensor, including the TCD and the chips coated with the titanium dioxide coating were inserted in the pressure vessel of the Gas Exposure System. Three sets of experiments were done: [0113] hydrogen mixtures in methane and methane/ethane/propane/nitrogen at 0, 1, 2, 5, 10 and 20 vol. % at 1 bara (FIG. 5); [0114] hydrogen mixtures in methane and methane/ethane/propane/nitrogen at 0, 1, 2, 5, 10 and 20 vol. % at 3 bara, and [0115] hydrogen mixtures in nitrogen at 0, 125, 250, 375 and 500 ppm at 1 bara.

[0116] The response of the coated chip to small changes in hydrogen concentrations was very high. Responses of 1.5 pF are very significant and open the possibilities of measuring hydrogen concentration at ppm levels. This was done using a gas mixture of 0.05 vol. % hydrogen in nitrogen. It was observed that the TCD registers a difference in signal when changing from methane to nitrogen, but the coated chip hardly measures a difference between nitrogen and hydrocarbons.

[0117] Both sensors (TiO.sub.2/Pt and TCD) are only slightly dependent on the flow rate of the gas. Furthermore, both sensors are also sensitive to changes in pressure. However, when no hydrogen is present, the coated chip shows no response, but the TCD does. Apparently, the coated chip is only sensitive for hydrogen partial pressure, but the TCD is sensitive for the total gas composition and hydrogen concentration. This is shown in more detail in FIG. 6.

Example 6

Comparison Between Platinum and Palladium Coated Titanium Dioxide Particles

[0118] Two capacitive sensor chips were prepared by coating the capacitive sensing material on the interdigitated electrodes. The two chips were exposed to the same variations in hydrogen concentration in methane and natural gas. FIG. 7 shows that the platinum chip shows a very high response, whereas the palladium chip does not respond at all.