JP2019113423A - Contact combustion type hydrogen gas sensor and vehicle equipped with the same - Google Patents

Abstract

To provide a contact combustion type hydrogen gas sensor with desired start-up time, response time and resistance to silicone poisoning.SOLUTION: A contact combustion type hydrogen gas sensor 100 for detecting hydrogen gas, includes: a detection element 1 that has a precious metal wire 11 having a coil shape, a predetermined coil diameter Dc, coil length and wire diameter; and a carrier part 12 having a generally spherical shape covering the precious metal wire 11 and a predetermined element diameter Ds. The carrier part 12 is constituted of catalyst carrier supporting a noble metal catalyst and has a predetermined element diameter Ds of 0.2-0.6 mm. Predetermined element diameter Ds of the carrier part 12/coil diameter Dc of the precious metal wire 11 is 1.4 to 2.0.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a catalytic combustion type hydrogen gas sensor for detecting hydrogen gas and a vehicle provided with the same.

  Conventionally, as a gas sensor having a gas sensitive portion of a sintered body, a contact combustion type gas sensor, a semiconductor type gas sensor, a solid electrolyte type gas sensor, and the like are known.

  For example, as a catalytic combustion type gas sensor, one having two elements of a detection element that reacts with combustion to a detection target combustible gas and a compensation element that does not react with combustion is known (for example, Patent Document 1) reference).

  Next, the general principle of detecting the concentration of combustible gas by the catalytic combustion type gas sensor will be described. The detection element of the catalytic combustion type gas sensor includes: a noble metal wire such as platinum; and a gas sensitive portion (a combustion catalyst portion) made of a sintered metal oxide such as alumina supporting a noble metal catalyst such as platinum covering the noble metal wire. It consists of This sensing element is heated to a predetermined temperature, and the combustible gas to be detected is brought into contact with the noble metal catalyst in the gas sensitive part and burned to change the temperature change occurring during combustion as the change in the resistance value of the noble metal wire. To detect. On the other hand, the compensation element does not support the precious metal catalyst like the detection element, but the other configuration is configured in the same manner as the detection element. That is, the compensation element is configured of a noble metal wire such as platinum, and a sintered body of a metal oxide such as alumina covering the noble metal wire and not carrying a noble metal catalyst. Since the noble metal catalyst is not supported on the compensating element, combustion of the combustible gas does not occur, and the resistance value of the noble metal wire does not change. The heat of combustion of the flammable gas is proportional to the concentration of the flammable gas, and the resistance of the noble metal wire is proportional to the heat of combustion. Therefore, the combustible gas is measured by measuring the change in resistance of the noble metal wire due to the combustion of the flammable gas. It is possible to measure the concentration of Therefore, a voltage difference occurs in the bridge circuit in which the sensing element and the compensation element are on two sides. The voltage difference is detected as an output proportional to the gas concentration up to the lower limit of the explosion of the flammable gas.

  Such a contact combustion type gas sensor is mounted on, for example, a fuel cell automobile (hereinafter referred to as FCV) using compressed hydrogen gas as a hydrogen gas sensor (hydrogen detector) for detecting leakage of hydrogen gas from a fuel cell system. ing. There are several methods (sensors) for detecting hydrogen gas, but as a vehicle-mounted hydrogen gas sensor that is required to detect 0 to 4 vol% of hydrogen gas in order to meet FCV safety standards, a catalytic combustion type Gas sensors are suitable.

  When the user operates the fuel cell system to start up, the FCV first starts up the hydrogen gas sensor to detect the concentration of hydrogen, and after confirming that there is no leakage of hydrogen, the fuel cell system starts up. For this reason, when the catalytic combustion type gas sensor is mounted on the FCV, the hydrogen gas sensor is required to have performance for which the time from start to detection of hydrogen can be detected, that is, the start time and response time are less than predetermined values. In addition, it is known that cyclic siloxanes, which are environmental substances released from asphalt and silicone products used for road pavement, to environmental atmosphere, affect the sensitivity of the hydrogen gas sensor. Specifically, since the catalytic combustion type hydrogen gas sensor operates at high temperature, cyclic siloxanes are oxidized on the catalyst surface. As a result, silicon oxide adheres to the surface to cover the active site of the catalyst for hydrogen, and a mechanism is considered in which the catalyst action for hydrogen is lost. Therefore, a contact combustion type hydrogen gas sensor having desired silicone poisoning resistance is required. Specifically, there is a need for a catalytic combustion type gas sensor in which the rate of change in sensitivity of the sensor can be kept low even when siloxane is exposed in the presence of hydrogen gas.

  For example, in the case of the contact combustion type gas sensor described in Patent Document 1, heat generation by the platinum wire (heater coil) is conducted to the entire catalyst layer and heat is released where the catalyst layer is in contact with the outside air. When the balance between the heat generation and the heat release of such a contact combustion type gas sensor is balanced, the gas can be detected in a stable state. Therefore, in order to satisfy the required performances such as start-up time, response time and silicone poisoning resistance, for example, when the detection gas is hydrogen, heat of combustion due to combustion of hydrogen, heat generation of the catalytic combustion type gas sensor and It is necessary to consider various parameters that contribute to heat dissipation. That is, there is a need for a catalytic combustion type hydrogen gas sensor configured to satisfy required performances such as desired start-up time, response time and silicone poisoning resistance by examining the relationship between the parameters and the performance of the sensor.

Patent No. 4559894

  Then, this invention is made in view of the said subject, and it aims at providing the contact combustion type hydrogen gas sensor which has desired start-up time, response time, and silicone poisoning resistance.

  The problem to be solved by the present invention is as described above, and next, means for solving the problem will be described.

  That is, the catalytic combustion type hydrogen gas sensor according to the present invention is a catalytic combustion type hydrogen gas sensor for detecting hydrogen gas, which has a coil shape and a substantially spherical shape covering a noble metal wire of a predetermined coil diameter, coil length and wire diameter and the noble metal wire. A carrier having a spherical diameter, and the carrier comprises a noble metal catalyst supported on the catalyst carrier, and the predetermined spherical diameter of the carrier is 0.2 to 0.6 mm, The predetermined sphere diameter of the carrier portion / the coil diameter of the noble metal wire is 1.4 to 2.0.

  In the catalytic combustion type hydrogen gas sensor of the present invention, the coil diameter of the noble metal wire / the coil length of the noble metal wire is 0.8 to 1.1.

  Further, in the catalytic combustion type hydrogen gas sensor of the present invention, the coil diameter of the noble metal wire / the wire diameter of the noble metal wire is 12 to 30.

  In the catalytic combustion type hydrogen gas sensor of the present invention, the element temperature at the time of operation is set to 280 to 350 ° C.

  Further, in the catalytic combustion type hydrogen gas sensor of the present invention, the carrier portion is formed by sintering alumina and has an average particle diameter of 300 to 800 nm.

  Further, in the catalytic combustion type hydrogen gas sensor of the present invention, the carried amount of the noble metal catalyst in the carrier portion is 10 to 30 wt%.

  A vehicle according to the present invention is a vehicle equipped with a fuel cell, and includes the above-described contact combustion type hydrogen gas sensor.

  According to the present invention, it is possible to realize a catalytic combustion type hydrogen gas sensor having desired start-up time, response time and resistance to silicone poisoning.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic which shows the contact combustion type hydrogen gas sensor which has a bridged circuit which concerns on one Embodiment of this invention. The schematic diagram which shows the structure of a detection element. The schematic diagram which shows the structure of a compensation element. The partial cross section side view which shows the structure of a detection element. It is a figure for comparing the sensing element which is the same in element diameter and wire diameter, and differs in other preparation conditions, (a) is a partial cross section side view, (b) is a partial cross section top view. It is a figure which shows the conditions which the noble metal wire protruded outside from the holding | maintenance part of a detection element, (a) is a partial cross section side view, (b) is a partial cross section top view. The graph which compared the starting time of the catalytic-combustion-type hydrogen gas sensor produced on the conditions of each Ds / Dc. The graph which compared the response time of the catalytic-combustion-type hydrogen gas sensor produced on each Ds / Dc conditions. The graph which compared the starting time of the catalytic-combustion-type hydrogen gas sensor produced on the conditions of each Ds / Dc. The graph which compared the response time of the catalytic-combustion-type hydrogen gas sensor produced on each Ds / Dc conditions. The graph which compared the starting time of the catalytic-combustion-type hydrogen gas sensor produced on the conditions of each Ds / Dc. The graph which compared the response time of the catalytic-combustion-type hydrogen gas sensor produced on each Ds / Dc conditions. The graph which compared the silicone poisoning tolerance of the catalytic-combustion-type hydrogen gas sensor produced on various conditions. The graph which shows the relationship between the sensor output with respect to hydrogen of a catalytic combustion type hydrogen gas sensor, and an alumina specific surface area. It is a photograph which shows the alumina particle from which calcination conditions differ, and each calcination condition is (1) 1100 ° C-10 h, (b) 1200 ° C-10 h, (c) 1300 ° C-10 h, (d) 1500 ° C- 10h.

  Next, a catalytic combustion type hydrogen gas sensor 100 according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the catalytic combustion type hydrogen gas sensor 100 detects a detection element 1 which burns and detects hydrogen gas as a detection gas, and changes based on temperature changes other than combustion of hydrogen gas, such as environmental changes. A compensation element 2 that compensates for the change in the resistance value of the element 1 and fixed resistors R1 and R2 are included to constitute a bridge circuit. The resistance value of the detection element 1 changes in accordance with the heat of combustion of the hydrogen gas. The sensing element 1 and the compensating element 2 are connected in parallel to the power supply E via fixed resistors R1 and R2 which are two resistors. The bridge circuit always supplies a current of about 90 to 120 mA by the power supply E, and holds the detection element 1 at a predetermined temperature at which hydrogen gas is easily combusted by contact.

  The sensing element 1 and the compensating element 2 are set to have the same resistance value. Therefore, when hydrogen gas is not present, the bridge circuit is in equilibrium and no sensor output V is generated. On the other hand, if hydrogen gas is present, the combustion causes the temperature of the sensing element 1 to rise and the resistance value to increase, so that the balance of the bridge circuit is lost and the sensor output V is generated. Since the sensor output V is proportional to the concentration of hydrogen gas, the concentration of hydrogen gas in air can be measured by the catalytic combustion type hydrogen gas sensor 100.

As shown in FIG. 2, the detection element 1 has a coil-shaped noble metal wire 11 and a substantially spherical carrier portion 12 which is a gas sensitive portion covering the noble metal wire 11 and being burned in contact with hydrogen gas. In addition, the noble metal wire 11 serves as a heating means for heating the carrier portion 12.
As a material of the noble metal wire 11, platinum etc. are applicable, for example. The carrier unit 12 is configured by supporting a noble metal catalyst on a catalyst carrier. The noble metal catalyst may be any noble metal having hydrogen gas catalytic activity, for example, platinum (Pt), palladium (Pd), platinum and palladium can be used without particular limitation. The catalyst carrier is not particularly limited as long as it supports a noble metal catalyst. For example, sintered bodies of metal oxides such as alumina and silica alumina can be applied.

  Such a detection element 1 is formed, for example, by mixing a metal oxide such as alumina constituting a catalyst carrier, a noble metal catalyst such as platinum, and an organic solvent (binder) such as ethylene glycol to form a paste. The paste is attached to the coil portion 11a which is a coiled portion of the noble metal wire 11 so as to have a predetermined spherical diameter, and then the noble metal wire 11 is sintered by self-heating to sinter the carrier portion 12 It can be produced by forming as a body.

  When the detection element 1 is placed in hydrogen gas, the noble metal catalyst provided in itself is heated by generating heat by energization to heat it and react with the hydrogen gas, depending on the heat of reaction (according to the concentration of the hydrogen gas) The output value changes.

As shown in FIG. 3, the compensation element 2 is basically the same as the sensing element 1 shown in FIG. 2 except that the different constitution does not include a precious metal catalyst. More specifically, the compensation element 2 is a substantially identical catalyst carrier as the sensing element 1 that does not include the precious metal catalyst, and covers the precious metal wire 11 in the same coil shape as the sensing element 1 and the precious metal wire 11. And a spherical carrier portion 13. The noble metal wire 11 also serves as a heating means for heating the carrier portion 13.
As a material of the noble metal wire 11, platinum etc. are applicable, for example. As the catalyst support, for example, a sintered body of a metal oxide such as alumina or silica alumina can be applied.

  The compensation element 2 is an element for performing temperature compensation of the detection element 1 by being placed in air containing hydrogen gas as in the case of the detection element 1, and is made of a noble metal catalyst of the detection element 1. It is used to take out only the change of the output value according to the heat of combustion. The noble metal catalyst is not supported in the carrier portion 13 of the compensation element 2, and combustion of hydrogen gas does not occur due to the catalytic reaction of the noble metal catalyst as in the detection element 1. The compensation element 2 generates heat when it is energized, and heats the carrier portion 13 covering the periphery thereof, and its resistance value changes due to the heat.

  Such a compensation element 2 is prepared, for example, by mixing a metal oxide such as alumina constituting a catalyst support and an organic solvent (binder) such as ethylene glycol to form a paste, and making this paste into a noble metal The coil portion 11a, which is a coiled portion of the wire 11, is attached so as to have a predetermined spherical diameter, and then sintered by self-heating of the noble metal wire 11 to form the carrier portion 13 as a sintered body can do.

Here, the start-up time is the time from when the power E of the catalytic combustion type hydrogen gas sensor 100 is turned on to when the detection element 1 stabilizes, and the Joule heat of the coil portion 11a of the noble metal wire 11 is the catalyst carrier It is the time until the temperature is stabilized by conducting and radiating heat to etc.
The response time is the time until heat generation during hydrogen combustion on the sensing element 1 is transmitted to the coil portion 11 a of the noble metal wire 11 and heat generation and heat dissipation of the sensing element 1 reach equilibrium.
Further, as shown in FIG. 4, the element diameter of the sensing element 1 is Ds, the coil diameter of the coil portion 11a of the noble metal wire 11 is Dc, the coil length of the coil portion 11a is Lc, and the wire diameter of the noble metal wire 11 is Dw. .

  For example, if the calorific value of the coil portion 11a of the noble metal wire 11 is the same, the smaller the element size (for example, the element diameter Ds), the shorter the heat conduction time to the entire carrier portion 12 of the sensing element 1 becomes. That is, the time to reach thermal equilibrium is short, and the element temperature is quickly stabilized.

  The heat release rate of the sensing element 1 depends on the thermal conductivity of the support 12 which is a catalyst support. For example, when the support 12 is made of alumina, the thermal conductivity is determined by the porosity of alumina and the particle size of alumina. If the porosity is low, the support portion 12 is in a dense alumina state, and the support portion 12 easily conducts heat. On the other hand, if the porosity is high, the carrier portion 12 will be in a sparse alumina state, and the carrier portion 12 will be difficult to conduct heat. On the other hand, when the porosity is low, hydrogen gas is difficult to diffuse to the inside of the element, and catalytic combustion of hydrogen gas mainly occurs on the element surface, and when the porosity is high, hydrogen gas diffuses to the inside of the element quickly. The entire element can burn hydrogen.

The detection element 1 of the catalytic combustion type hydrogen gas sensor 100 has high sensitivity when hydrogen combustion occurs in the entire element. That is, in order to satisfy the predetermined required performance, the calorific value of the coil portion 11a of the noble metal wire 11, the element size, and the porosity of the catalyst need to be balanced.
Although the details will be described later, the constituent requirements satisfying the required performance derived from the above findings are summarized in Table 1.

The element temperature Ts in Table 1 is the set temperature of the detection element 1 at the time of the operation of the contact combustion type hydrogen gas sensor 100.

  Each item in Table 1 will be described in detail below with reference to the drawings.

  In the contact combustion type hydrogen gas sensor 100 configured as described above, the element diameter Ds which is the ball diameter of the carrier portion 12 of the detection element 1 is 0.2 to 0.6 mm, that is, 0.2 mm or more, 0 The thickness is preferably in the range of not more than 6 mm, and more preferably in the range of not less than 0.3 mm and not more than 0.6 mm. That is, when the element diameter Ds is 0.2 mm or more, it is possible to maintain silicone poisoning resistance described later which is an example of the durability of the detection element 1. Further, by setting the element diameter Ds to 0.6 mm or less, sufficient silicone poisoning resistance can be maintained, and a small contact combustion type hydrogen gas sensor is configured to suppress the sensor output to further reduce power consumption. It can be suppressed.

  The element diameter Ds / coil diameter Dc, which is the ratio of the element diameter Ds to the coil diameter Dc of the coil portion 11a, is 1.4 to 2.0, that is, in the range of 1.4 to 2.0. Is preferably, and more preferably in the range of 1.5 or more and 1.9 or less. The details will be described in the examples described later.

  The coil diameter Dc / coil length Lc, which is the ratio of the coil diameter Dc of the coil portion 11a to the coil length Lc, is 0.8 to 1.1, that is, in the range of 0.8 to 1.1. Is preferred.

  The coil diameter Dc / Dw, which is the ratio of the coil diameter Dc of the coil portion 11a to the wire diameter Dw of the noble metal wire 11, is preferably 12 to 30, that is, 12 or more and 30 or less. And more preferably in the range of 13 or more and 29 or less.

  The amount of the catalyst supported on the carrier portion 12 is preferably 10 to 30 w%, that is, 10 to 30 wt%. By setting the amount of the catalyst carried within such a range, it is possible to maintain a heat balance between heat generation and heat release in the carrier portion 12.

  Further, the number of turns of the coil portion 11a may be appropriately set according to the coil diameter Dc and the wire diameter Dw. For example, in the configuration requirements shown in Table 1, the number of turns is preferably 5 to 20. . If the number of turns is less than 5, the mechanical strength of the detection element is insufficient. On the other hand, when the number of turns is greater than 20, the gap between the adjacent noble metal wires 11 in the coil portion 11a is narrowed, which may cause an excessive temperature rise.

  The other configurations and functions of the catalytic combustion type hydrogen gas sensor 100 including the detection element 1 and the compensation element 2 are the same as those of the conventionally known catalytic combustion type hydrogen gas sensor.

  Below, the Example of the contact combustion type hydrogen gas sensor 100 using the sensing element 1 and the compensation element 2 is shown, and this invention is demonstrated in more detail. However, the present invention is not limited to these examples.

As an example satisfying the constituent requirements of the sensing element shown in Table 1, sensing elements 1A, 1B and 1C were produced as shown in FIG. Specifically, a platinum wire (wire diameter Dw = 0.02 mm) having a coil portion 11a processed into a coil shape as the noble metal wire 11 by the above-described method of manufacturing a detection element, platinum relative to alumina which is a catalyst carrier Alternatively, the carrier portion 12 carrying platinum and palladium at a predetermined concentration (10 to 30 wt% in the present embodiment) is formed to be substantially spherical, and fired at 1300 ° C. for 10 hours for an element diameter Ds of 0. The sensing elements 1A, 1B, and 1C were manufactured so as to have an average particle size of about 5 mm and an average particle diameter of 300 to 800 nm. The main preparation conditions of each of the detection elements 1A, 1B, and 1C are as follows.
(Preparation conditions)
Detection element 1A: Ds / Lc = 2.0, Ds / Dc = 2.0 (element diameter Ds = 0.5 mm, coil diameter Dc = 0.25 mm, coil length Lc = 0.25 mm)
Detection element 1B: Ds / Lc = 1.6, Ds / Dc = 1.6 (element diameter Ds = 0.5 mm, coil diameter Dc = 0.31 mm, coil length Lc = 0.31 mm)
Detection element 1C: Ds / Lc = 1.4, Ds / Dc = 1.4 (element diameter Ds = 0.5 mm, coil diameter Dc = 0.36 mm, coil length Lc = 0.36 mm)

In addition, according to the method of manufacturing a compensation element described above, a platinum element having a coil portion 11a processed into a coil shape as the noble metal wire 11 is provided with a substantially spherically shaped carrier element 13 manufactured using alumina. did. The compensation element 2 is formed to have the same size (dimension) as each part of the corresponding detection element.
The sensing element 1 and the compensating element 2 produced in this manner were incorporated into the bridge circuit shown in FIG. 1 to produce a contact combustion type hydrogen gas sensor 100.

As shown in FIG. 5, when Ds / Dc and Ds / Lc gradually become smaller than 2.0 (when going to the right in FIGS. 5A and 5B), the coil portion 11a of the noble metal wire 11 Since the curvature of the surface becomes large and the stress in the noble metal wire 11 becomes high, the electric resistance value of the coil portion 11a tends to be gradually unstable. On the other hand, when Ds / Dc and Ds / Lc are larger than 2.0, the coil portion 11a of the noble metal wire 11 which is a heat generating portion is concentrated at the center of the carrier portion 12 (element sphere). There is a temperature distribution in which the temperature is high and the temperature is low toward the outside. Heat generated by hydrogen gas combustion on the surface of the carrier portion 12 can not be efficiently transferred to the coil portion 11a due to the heat conduction loss due to the bulky alumina outside the coil portion 11a in the radial direction.
Further, as shown in FIG. 6, in the case of the sensing element 20 (Ds / Dc = 1.2, and Ds / Lc = 1.2) in which Ds / Dc and Ds / Lc are smaller than 1.4 as a comparative example, As shown in 6 (a), both end portions 11b in the longitudinal direction of the coil portion 11a protrude from the carrier portion 12 and protrude to the outside. On the other hand, as shown in FIG. 5A, as Ds / Dc is 1.4 or more, the coil portion 11a of the noble metal wire 11 is accommodated in the inside of the carrier portion 12 without sticking out, as in the sensing element 1C. It can be done. Further, under the preparation conditions of the above-mentioned comparative example, the influence of the decrease in the activity of the surface of the carrier portion 12 due to the siloxane exposure tends to appear as a decrease in the sensitivity of the hydrogen gas. Therefore, Ds / Dc is preferably 1.4 to 2.0.

Next, using the catalytic combustion type hydrogen gas sensor manufactured under the same manufacturing conditions as in Example 1, the start-up time and response time of the detection element with respect to the concentration (ppm) of hydrogen gas were examined (FIG. 7 to FIG. 12).
(Conditions of producing sensing element according to FIGS. 7 and 8)
Ds = 0.25 mm, Dw = 0.01 mm are common, and Ds / Dc is the following conditions.
Condition 1) Ds / Dc = 1.4
Condition 2) Ds / Dc = 2.0
Condition 3) Ds / Dc = 2.5
(Fabrication conditions of sensing element according to FIGS. 9 and 10)
Ds = 0.5 mm and Dw = 0.02 mm are common, and Ds / Dc is the following conditions.
Condition 1) Ds / Dc = 1.4
Condition 2) Ds / Dc = 2.0
Condition 3) Ds / Dc = 2.5
(Conditions of producing sensing element according to FIGS. 11 and 12)
Ds = 0.75 mm and Dw = 0.03 mm are common, and Ds / Dc is the following conditions.
Condition 1) Ds / Dc = 1.4
Condition 2) Ds / Dc = 2.0
Condition 3) Ds / Dc = 2.5

  FIG. 7, FIG. 9, and FIG. 11 are graphs comparing the activation time of the sensing element fabricated under the conditions of each of the above Ds / Dc. In each graph of FIG. 7, FIG. 9 and FIG. 11, the vertical axis is the sensor output / hydrogen concentration converted value (ppm) of the contact combustion type gas sensor, and the horizontal axis is the activation time (seconds).

FIG. 8, FIG. 10, and FIG. 12 are graphs comparing the response times of the sensing elements fabricated under the conditions of each of the above Ds / Dc. In each graph of FIG. 8, FIG. 10, and FIG. 12, the vertical axis is the sensor output / hydrogen concentration converted value (ppm) of the contact combustion type gas sensor, and the horizontal axis is the response time (seconds).
Here, the target achievement value of the startup time is within 2 seconds, and the target achievement value of the response time is within 3 seconds. By satisfying these target achievement values, the required performance as a catalytic combustion type hydrogen gas sensor mounted on FCV can be satisfied.
Note that "the target achieved value of the startup time is within 2 seconds" means that the sensor output and hydrogen concentration converted value (ppm) becomes 1000 ppm or less within 2 seconds in FIGS. 7, 9, and 11. . In addition, “the target achieved value of response time is within 3 seconds” means that the sensor output and hydrogen concentration conversion value (ppm) becomes 18000 ppm or more within 3 seconds in FIGS. 8, 10, and 12 is there.

  As shown in FIGS. 7 to 12, Ds / Dc = 1.4 and 2.0 satisfy the required performance of the startup time and response time, but Ds / Dc = 2.5 does not. That is, when Ds / Dc is in the range of 1.4 to 2.0, both the required performance of the startup time and the response time can be satisfied.

[On silicone poisoning resistance]
Regarding silicone poisoning resistance, the rate of change of sensor sensitivity is specified even if the catalytic combustion type hydrogen gas sensor is operated for 100 hours under the following environment assuming the worst condition of the actual environment when the catalytic combustion type hydrogen gas sensor is mounted on a vehicle It is required to be within the value.
Environmental conditions (concentration): cyclic siloxane 1000 ppm + hydrogen 2000 ppm
Sensitivity change rate: within ± 15%

The cyclic siloxane is adsorbed and ring-opened on a noble metal catalyst, and is finally oxidized to SiO ₂ through several elementary reactions. The following findings have been obtained from the observation results of the catalyst surface state using TOF-SIMS etc. up to now.
1) When hydrogen and siloxane coexist, hydrogen consumes the dissociatively adsorbed oxygen on the noble metal catalyst, so that an oxygen adsorption site on the catalyst is vacated, and the siloxane is easily adsorbed there.
2) Since siloxane takes time to oxidize to SiO ₂ , as the adsorption amount increases, undecomposed products accumulate and the activity of the noble metal temporarily decreases (the combustion of hydrogen gas is inhibited).
3) siloxane crystals SiO ₂ in the aggregation reaction is oxidized grown to SiO _2, the active sites on the catalyst which had been coated with undecomposed product of the siloxane is in contact with the atmosphere before, the active Will recover. That is, in order to accelerate the oxidation reaction of siloxane, it is advantageous that the device temperature is high.
4) Since siloxane has a large molecular size, diffusion into the inside of the device is limited, and undecomposed products are more likely to be deposited on the device surface. When the element size is extremely small, the ratio of the surface to the volume of the entire element is high, and thus the deterioration of the activity on the element surface tends to appear in the sensitivity of hydrogen gas.

[Silicone Poisoning Resistance Test]
Next, using three catalytic combustion type hydrogen gas sensors manufactured under the same manufacturing conditions (Ds = 0.5 mm, Dw = 0.02 mm, Ds / Dc = 2.0), each temperature (Ts = 250, 280) The silicone poisoning resistances when exposed to cyclic siloxane (1000 ppm) in the presence of hydrogen gas in a state where the sensor was operated at 310 ° C. were compared (see FIG. 13). In the graph shown in FIG. 13, the vertical axis represents the sensor output / hydrogen concentration conversion value (ppm) of the catalytic combustion type hydrogen gas sensor, and the horizontal axis represents the exposure time of the cyclic siloxane (time: hr). The results of the silicone poisoning resistance test shown in FIG. 13 show that the rate of change in sensitivity of 20000 ppm of hydrogen immediately before, during, and after 100 hours of exposure to a catalytic combustion type hydrogen gas sensor in a mixed gas of 1000 ppm of siloxane and 2000 ppm of hydrogen for 100 hours. Was evaluated.
Here, as the required performance of the silicone poisoning resistance, as described above, in the silicone poisoning resistance, the sensitivity change rate of the sensor at 100 hours is within 15%. By satisfying this target achievement value, the required performance of the catalytic combustion type hydrogen gas sensor mounted on FCV can be satisfied.

  According to the results shown in FIG. 13, when measurement is performed in a hydrogen gas concentration of, for example, about 20000 ppm, the catalytic combustion type hydrogen gas sensor whose operating temperature is 250 ° C. decreases the detected hydrogen gas concentration in about 65 hours Therefore, the rate of change in sensitivity exceeds -15% (17000 ppm indicated by a dotted line in the figure). This is considered to be due to the deterioration of the activity of the catalytic combustion type hydrogen gas sensor for hydrogen gas due to the exposure of the cyclic siloxane. On the other hand, catalytic combustion type hydrogen gas sensors with operating temperatures of 280 ° C and 310 ° C keep the sensitivity change rate within 15% even at 100 hours exposure time, and can meet the required performance of silicone poisoning resistance . Thus, in the catalytic combustion type hydrogen gas sensor based on the preparation conditions, it is preferable that the element temperature at the time of sensor operation be 280 ° C. or higher in order to satisfy the silicone poisoning resistance. On the other hand, the element temperature during sensor operation is preferably 350 ° C. or less. This is because, if the operating temperature of the sensor is high, the resistance value tends to increase with time due to a decrease in active points due to sintering (aggregation) of catalyst particles and heat load on the coil portion of platinum (Pt) wire. It is because it becomes easy to produce a bad effect. Therefore, it is preferable that the element temperature at the time of sensor operation is set to 280 to 350 ° C., that is, set in the range of 280 ° C. or more and 350 ° C. or less.

[Evaluation test of specific surface area of catalyst support and hydrogen gas sensitivity]
FIG. 14 shows the results of evaluation of the relationship between the specific surface area of alumina, which is an example of the catalyst support, and the hydrogen gas sensitivity. In the graph of FIG. 14, the vertical axis on the left is the sensor output (mV) for hydrogen of 20000 ppm in the catalytic combustion type gas sensor, the vertical axis on the right is the average particle size (nm) of alumina, and the horizontal axis is the alumina specific surface area (m ²⁾ / G). The average particle size of alumina can be controlled by the firing conditions, and the higher the firing temperature, the larger the particle size and the smaller the specific surface area. Generally, the higher the specific surface area of the catalyst support (alumina), the higher the activity of the catalyst can be obtained. However, in the catalytic combustion type hydrogen gas sensor, in addition to the catalytic activity, the combustion efficiency of hydrogen in the entire element sphere is sensitive Affect For example, a sensing element using alumina having a specific surface area of 108 m ² / g (firing temperature-baking time: 1100 ° C.-10 h, see FIG. 15A) forms a dense sintered body, so hydrogen Gas does not diffuse to the inside of the element, and contact combustion of hydrogen gas mainly occurs on the element surface, and the sensitivity (sensor output) is lowered by the heat conduction loss to the coil portion 11a of the noble metal wire 11 such as platinum wire. On the other hand, in the sensing element using alumina having a specific surface area of 1.2 m ² / g (firing temperature-baking time: 1500 ° C.-10 h, see FIG. 15D), the porosity is high (gap between particles) Although the sintered body is formed and hydrogen gas diffuses easily to the inside of the device, the sensitivity is low because the activity as a catalyst is low. Therefore, by applying alumina having an average particle diameter of 300 to 800 nm (specific surface area: 4.2 to 6.3 m ² / g) in the carrier portion 12, the element having high activity and hydrogen gas can be obtained. It is possible to form a sintered body having a porous structure in which the diffusivity of the above is superior.

  As described above, according to the catalytic combustion type hydrogen gas sensor 100 according to the present embodiment, a catalytic combustion type hydrogen gas sensor having desired start-up time, response time and silicone poisoning resistance can be realized.

  In addition, the catalytic combustion type hydrogen gas sensor 100 according to the present embodiment can be mounted, for example, on a vehicle (car, truck, work vehicle, etc.) equipped with a fuel cell such as FCV, and detects hydrogen gas leaking from the fuel cell. be able to.

  The present invention can be used for a catalytic combustion type hydrogen gas sensor provided with a detection element whose resistance value changes according to the heat of combustion of hydrogen gas.

DESCRIPTION OF SYMBOLS 1 detection element 2 compensation element 11 noble metal wire 11a coil part 12 carrier part 100 contact combustion type hydrogen gas sensor Ds element diameter Dc coil diameter

Claims (7)

In a catalytic combustion type hydrogen gas sensor for detecting hydrogen gas,
A detection element having a coil shape and a noble metal wire of a predetermined coil diameter, coil length and wire diameter, and a substantially spherical carrier portion of a predetermined spherical diameter covering the noble metal wire;
The carrier portion is configured by supporting a noble metal catalyst on a catalyst carrier,
The predetermined sphere diameter of the carrier portion is 0.2 to 0.6 mm,
The contact combustion type hydrogen gas sensor whose predetermined ball diameter of the said support | carrier part / coil diameter of the said noble metal wire is 1.4-2.0.   The contact combustion type hydrogen gas sensor according to claim 1, wherein a coil diameter of the noble metal wire / a coil length of the noble metal wire is 0.8 to 1.1.   The contact combustion type hydrogen gas sensor according to claim 1 or 2, wherein a coil diameter of the noble metal wire / a wire diameter of the noble metal wire is 12 to 30.   The catalytic combustion type hydrogen gas sensor according to any one of claims 1 to 3, wherein an element temperature at the time of operation is set to 280 to 350 ° C.   The catalytic combustion type hydrogen gas sensor according to any one of claims 1 to 4, wherein the carrier portion is formed by sintering alumina and has an average particle diameter of 300 to 800 nm.   The contact combustion type hydrogen gas sensor according to any one of claims 1 to 5, wherein a loading amount of the noble metal catalyst in the carrier portion is 10 to 30 wt%. A vehicle equipped with a fuel cell,
A vehicle comprising the catalytic combustion type hydrogen gas sensor according to any one of claims 1 to 6.