JP2009002813A - Catalyst activity evaluating device and catalyst activity evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst activity evaluating device and a catalyst activity evaluation method capable of accurately evaluating catalyst activity to gas and with superior reproducibility. <P>SOLUTION: A pressure-adjusting back pressure valve 16 as a pressure control means is provided near the electrolyte solution outlet 11b of a channel 11. The pressure-adjusting back pressure valve 16 has a function for controlling the pressure of electrolyte solution near a working electrode 2 and a counter electrode 3 in the channel 11, to be a higher prescribed pressure than the atmospheric pressure. Since aggregation effect of gas is suppressed and reproducibility with the passage of time of a gas concentration distribution state is improved, the catalyst activity can be evaluated properly accurately, with proper reproducibility. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a catalyst activity evaluation apparatus and a catalyst activity evaluation method for evaluating the activity of a catalyst with respect to a gas by an electrochemical measurement method.

Many chemical cells use a redox reaction via a catalyst. A polymer electrolyte fuel cell is also a type of chemical cell, and includes a membrane electrode assembly in which a catalyst electrode and an electrolyte are integrally formed, a gas diffusion layer, a gas flow path, a separator, and the like. One factor that determines the power generation performance of the fuel cell is the catalytic activity of the membrane electrode assembly. Catalytic activity is expressed by physical property values such as effective surface area and electrochemical property values such as limiting current. These physical property values can be measured by linear sweep voltammetry (LSV) or cyclic voltammetry (cyclic voltammetry; The electrochemical measurement method represented by CV) is applied. In a three-electrode electrochemical cell used in an electrochemical measurement method, an open glass flask having a plurality of ports containing a catalyst electrode, a counter electrode, a reference electrode, an electrolyte solution, and the like that function as a working electrode is generally used. Since the electrochemical cell is normally used in an atmospheric pressure open system, even if the purge gas or the target gas in which the catalyst is active is introduced into the electrolyte solution by bubbling, it is volatilized into the atmosphere.
JP 2004-076084 A

  By the way, the platinum-supported carbon catalyst electrode used in the polymer electrolyte fuel cell is a kind of electrode called a gas diffusion electrode. A gas diffusion electrode is composed of three different phases: a gas phase such as hydrogen or oxygen which is a reactive gas, a catalyst electrode phase in which electrons move, and an electrolyte phase in which ions move. Progress at the interface. Therefore, when performing catalytic activity evaluation, in addition to the necessity of considering the chemical state of the platinum-supported carbon catalyst itself, it is necessary to consider the state of the entire three-phase interface including the gas phase and the electrolyte phase. In general, a platinum-supported carbon electrode is generally prepared by mixing a platinum-supported carbon material and an ion exchange resin such as Nafion as an electrolyte phase. However, when the catalyst characteristics are evaluated using a gas diffusion electrode produced by such a production method, the influence of gas diffusion and ion diffusion in the electrolyte is greatly manifested. It is difficult to obtain. In addition, since the electrochemical cell is used in an open system, it has been pointed out that the gas concentration varies with time.

  On the other hand, a rotating electrode method is known as a method capable of accurately evaluating the catalytic activity value of a gas diffusion electrode by an electrochemical measurement method. In the rotating electrode method, the thickness of the diffusion phase can be controlled by rotating the catalyst electrode in the electrolyte solution. By extrapolating the point when the rotational speed is infinite, the diffusion phase thickness is infinitely small and the diffusion effect is affected. It is possible to measure the catalytic activity assuming the excluded state. In this method, the so-called activation dominant current is measured. However, in the rotating electrode method, the operating temperature range of the cell is from room temperature to 50 ° C. due to structural limitations such as the durability of the structure constituting the electrode rotation driving unit and the electrochemical cell having an open structure. Limited to a degree. Since the polymer electrolyte fuel cell is usually used at 80 ° C. or higher, the rotating electrode method cannot evaluate the catalytic activity of the fuel cell in the temperature environment during power generation.

  A channel flow double electrode (CFDE) method is known as a method for evaluating catalytic activity at a use temperature (about 100 ° C.) of a polymer electrolyte fuel cell. In this structure, a catalyst electrode, a counter electrode, and a reference electrode are disposed in contact with the channel inside a temperature resistant resin block having a channel through which the electrolyte solution flows. By flowing the electrolyte solution through the channel in a laminar flow, it is possible to control the reactant concentration and the diffusion phase thickness in the vicinity of the electrode. Since a more stable diffusion phase can be formed as compared with the rotating electrode method, a steady state can be reached in a short time and reproducibility is high. However, even in this method, when the catalytically active target substance is a gas, it is difficult to stably maintain the target gas concentration in the vicinity of the electrode.

  An object of the present invention is to provide a catalyst activity evaluation apparatus and a catalyst activity evaluation method capable of accurately and reproducibly evaluating the activity of a catalyst with respect to a gas.

The catalytic activity evaluation apparatus of the present invention is a catalytic activity evaluation apparatus that evaluates the activity of a catalyst with respect to a gas by an electrochemical measurement method. Pressure control means for controlling the pressure of the electrolyte solution stored in the storage means to a predetermined pressure higher than atmospheric pressure.
According to this catalytic activity evaluation apparatus, the pressure of the electrolyte solution is controlled to a predetermined pressure higher than the atmospheric pressure, so that the gas aggregation effect is suppressed and the reproducibility of the gas concentration distribution state over time is improved. The catalytic activity can be evaluated accurately and with good reproducibility.

  The housing means may be configured as a channel through which the electrolyte solution flows.

  The pressure control means may be disposed downstream of the catalyst electrode and the counter electrode of the channel.

  The pressure control means may be constituted by a pressure regulating valve outside the channel.

  The pressure control means may be constituted by a filler inside the channel.

  The pressure control means may be configured as a narrowed portion of the channel.

  You may arrange | position the filler for suppressing a pressure fluctuation before and behind the said catalyst electrode and counter electrode in the said channel.

  You may evaluate the activity of the catalyst used for a polymer electrolyte fuel cell.

The catalyst activity evaluation method of the present invention is a catalyst activity evaluation method for evaluating the activity of a catalyst with respect to a gas by an electrochemical measurement method. And a step of controlling the pressure of the electrolyte solution thus made to be a predetermined pressure higher than the atmospheric pressure.
According to this catalytic activity evaluation method, the pressure of the electrolyte solution is controlled to a predetermined pressure higher than the atmospheric pressure, so that the gas aggregation effect is suppressed and the reproducibility with time of the gas concentration distribution state is also improved. The catalytic activity can be evaluated accurately and with good reproducibility.

  According to the catalytic activity evaluation apparatus of the present invention, since the pressure of the electrolyte solution is controlled to a predetermined pressure higher than the atmospheric pressure, the gas aggregation effect is suppressed and the reproducibility of the gas concentration distribution state with time is improved. Therefore, the catalytic activity can be evaluated accurately and with good reproducibility.

  According to the catalytic activity evaluation method of the present invention, the pressure of the electrolyte solution is controlled to a predetermined pressure higher than the atmospheric pressure, so that the gas aggregation effect is suppressed and the reproducibility of the gas concentration distribution state with time is improved. Therefore, the catalytic activity can be evaluated accurately and with good reproducibility.

  Hereinafter, with reference to FIGS. 1-3, embodiment of the catalyst activity evaluation apparatus by this invention is described.

  Fig.1 (a) is sectional drawing which shows the structure of the channel flow cell used for the catalyst activity evaluation apparatus of this embodiment. This catalytic activity evaluation apparatus evaluates catalytic activity by the channel flow double electrode (CFDE) method. The catalytic activity is evaluated by measuring the potential and current between the electrodes while flowing the electrolyte solution in the channel flow cell shown in FIG.

  As shown in FIG. 1A, the channel flow cell is composed of a cell matrix 1 formed of a temperature-resistant polymer or an inorganic material such as glass or ceramics, and an electrolytic solution is accommodated inside the cell matrix 1. The channel 11 as a means penetrates. The channel 11 is formed from the electrolyte solution inlet 11a toward the electrolyte solution outlet 11b from the upstream to the downstream of the electrolyte solution, and has a liquid passage 11c that branches in the middle and guides the electrolyte solution to a reference electrode (not shown). Constitute.

  In the vicinity of the electrolyte solution inlet 11a of the channel 11, a gas introduction part 15 for introducing gas into the electrolyte solution is provided. A working electrode (catalyst electrode) 2 and a counter electrode 3 are provided near the branch point of the channel 11. The working electrode 2 and the counter electrode 3 are exposed in the channel 11 and are in direct contact with the electrolyte solution.

  As shown in FIG. 1A, a pressure adjusting back pressure valve 16 as a pressure control means is provided in the vicinity of the electrolyte solution outlet 11b of the channel 11. The pressure adjusting back pressure valve 16 has a function of controlling the pressure of the electrolyte solution in the vicinity of the working electrode 2 and the counter electrode 3 in the channel 11 to a predetermined pressure higher than the atmospheric pressure.

  Next, the operation of the catalyst activity evaluation apparatus of this embodiment will be described.

  The electrolyte solution is fed into the channel 11 at a constant flow rate by a liquid feed pump (not shown) through the electrolyte solution inlet 11a. Further, a predetermined gas is added to the electrolyte solution to be fed by continuous or intermittent bubbling in the gas introduction unit 15. In the catalyst activity evaluation apparatus of the present embodiment, the pressure of the electrolyte solution fed in the channel 11 by the pressure adjusting back pressure valve 16 is controlled to a predetermined pressure higher than the atmospheric pressure.

  In general, in a flow in a narrow tube such as a channel flow cell, in most cases, the flow of the electrolyte solution flowing in the channel is a laminar flow. Under laminar flow conditions, the flow characteristics in the channel have a Poiseuille flow path distribution represented by Equation (1) as a fluid sandwiched between two parallel flat plates. At this time, the maximum flow rate Umax, the flow rate Q, and the average flow rate Umean are calculated by Expression (2), Expression (3), and Expression (4), respectively.

Incidentally, when the distance from the entrance channel to the electrode is of the formula (5) or l _e value calculated by the following flow path distribution of Poiseuille flow is sufficiently grown after the electrolyte solution is within the channel, the electrode A stable flow is formed in the vicinity.

  When a gas having a sufficiently high solubility in the electrolyte solution is added by bubbling through the gas introduction part, the dissolved gas maintains a gas concentration distribution influenced by the channel distribution of the Poiseuille flow in the channel cross section near the electrode. However, in the case of gases with low solubility, such as oxygen, nitrogen, hydrogen, etc., the bubble agglomeration effect is not negligible. Therefore, compared to the original gas concentration distribution formed by the Poiseuille flow path distribution in the channel cross section near the electrode. Further, the degree of distribution becomes larger. In addition, since the reproducibility of distribution over time is deteriorated, a stable gas concentration cannot be maintained in the vicinity of the electrode. The conventional channel flow cell is configured on the basis of such a fluid state, and it cannot be expected to accurately and accurately measure the activity of the catalyst electrode with respect to the gas.

  On the other hand, when the electrolyte solution is placed under pressure by the pressure regulating back pressure valve 16 as in the catalyst activity evaluation apparatus according to the present invention, the gas solubility increases according to the pressure. Compared with the state close to, the gas aggregation effect is suppressed. As a result, when the electrolyte is flowed at the same linear velocity, the dissolved gas concentration distribution in the cross section of the flow path near the electrodes (working electrode 2 and counter electrode 3) is more Poiseuille flow than in the conventional non-pressurized state. The distribution state corresponding to the flow path distribution is shown. Furthermore, by placing the electrolyte solution, which is a fluid, under pressure, the reproducibility of the gas concentration distribution in the cross-section near the electrode over time is improved. As a result, it is possible to evaluate the catalytic activity of the working electrode (catalytic electrode) 2 with respect to the gas more accurately and with good reproducibility.

  FIG. 2A shows an example of a cyclic voltammogram obtained when the catalytic activity evaluation apparatus according to the present invention is used to evaluate the catalytic activity of a specific catalyst with respect to a specific gas. The scanning potential width is set within the range of the potential window of the catalyst electrode and within the range including the oxidation-reduction potential of the specific gas. As shown in FIG. 2 (a), according to the catalytic activity evaluation apparatus of the present invention, the gas concentration in the vicinity of the electrode can be kept sufficiently high, so that the oxidation peak and reduction peak due to the specific gas can be obtained with good reproducibility. Can do.

  On the other hand, FIG. 2B shows an example of a cyclic voltammogram when the same evaluation is performed using the rotating electrode method using a conventional three-electrode electrolytic cell. In the conventional three-electrode measurement method, the gas concentration in the vicinity of the electrode cannot be sufficiently ensured, so that the oxidation-reduction peak due to the specific gas cannot be obtained.

  As described above, according to the catalytic activity evaluation apparatus of the present invention, the pressure of the electrolyte solution is controlled to a predetermined pressure higher than the atmospheric pressure, so that the gas aggregation effect is suppressed and the gas concentration distribution state is changed over time. Therefore, the catalytic activity can be evaluated accurately and with good reproducibility.

  In the above embodiment, the pressure adjusting back pressure valve 16 is used as the pressure control means. However, as shown in FIG. 1B, instead of the pressure adjusting back pressure valve, the constricted portion 17 of the channel 11 is provided with an electrode (action). It may be provided downstream of the electrode 2 and the counter electrode 3). Thereby, the pressure of the electrolyte solution can be controlled to a predetermined pressure higher than the atmospheric pressure. Moreover, the same effect can also be acquired by fixing a filler in the inside of the channel 11.

  Furthermore, as shown in FIG. 3, the filling material 21 and the filling material 22 may be fixed on the upstream side and the downstream side, respectively, so as to sandwich the electrodes (the working electrode 2 and the counter electrode 3). Thereby, while being able to raise the pressure of the electrolyte solution of the electrode (working electrode 2 and counter electrode 3) vicinity, the pressure fluctuation can be suppressed.

  Examples of fillers include those made of inorganic materials such as carbon, zirconia, alumina, silica, titania, glass, and ceramics in the form of fine particles, fibers, or an integral porous structure (monolithic structure), and polystyrene. Organic materials such as polystyrene-divinylbenzene, polypropylene, fluororesin, polyetherketone, etc., in the form of fine particles, fibers, or an integral porous structure can be used.

  The catalytic activity evaluation apparatus of the present invention includes cyclic voltammetry, linear sweep voltammetry, staircase voltammetry, chronocoulometry, normal pulse voltammetry, differential pulse voltammetry, chronopotentiometry, single pulse method, chronoamperometry, differential pulse amperometry, etc. When the fuel cell catalyst is evaluated by this electrochemical measurement method, the dissolved gas concentration in the vicinity of the electrode interface can be maintained at a desired value with good reproducibility, and the catalytic activity can be analyzed accurately. The catalyst activity evaluation apparatus according to the present invention contributes particularly to the improvement of fuel cell performance.

  In the above embodiment, application to the channel flow electrode method has been exemplified. However, the catalyst activity evaluation apparatus according to the present invention can be applied to methods other than the channel flow electrode method. Further, the catalyst activity evaluation apparatus according to the present invention is not limited to the case of evaluating a catalyst used in a fuel cell.

  The scope of application of the present invention is not limited to the above embodiment. The present invention can be widely applied to a catalyst activity evaluation apparatus and a catalyst activity evaluation method for evaluating the activity of a catalyst with respect to a gas by an electrochemical measurement method.

It is a figure which shows the structure of the channel flow cell used for a catalyst activity evaluation apparatus, (a) is sectional drawing which shows the structure of a channel flow cell, (b) is sectional drawing which shows the structure of the channel flow cell of another example. It is a figure which shows the example of a cyclic voltammogram, (a) shows the example at the time of using the catalyst activity evaluation apparatus by this invention, (b) shows the example at the time of using the conventional rotating electrode method, respectively. Figure. Sectional drawing which shows the structure which fixed the filling material 21 and the filling material to the upstream and downstream, respectively so that an electrode may be inserted | pinched.

Explanation of symbols

11 channels (accommodating means)
16 Back pressure valve for pressure adjustment (pressure control means)
17 Constriction (pressure control means)
21 Filling 22 Filling

Claims (9)

In a catalyst activity evaluation apparatus that evaluates the activity of a catalyst for gas by an electrochemical measurement method,
Storage means for storing the electrolyte solution in a state where the electrolyte solution is in contact with the catalyst electrode and the counter electrode;
Pressure control means for controlling the pressure of the electrolyte solution stored in the storage means to a predetermined pressure higher than atmospheric pressure;
A catalyst activity evaluation apparatus comprising: 2. The catalytic activity evaluation apparatus according to claim 1, wherein the accommodating means is configured as a channel through which the electrolyte solution flows. The catalyst activity evaluation apparatus according to claim 2, wherein the pressure control means is disposed downstream of the catalyst electrode and the counter electrode of the channel. The catalyst activity evaluation apparatus according to claim 3, wherein the pressure control means is configured by a pressure regulating valve inside the channel. 4. The catalyst activity evaluation apparatus according to claim 3, wherein the pressure control means is constituted by a filler inside the channel. 4. The catalytic activity evaluation apparatus according to claim 3, wherein the pressure control means is configured as a narrowed portion of the channel. The catalyst activity evaluation apparatus according to any one of claims 2 to 6, wherein a filler for suppressing pressure fluctuation is disposed before and after the catalyst electrode and the counter electrode in the channel. The catalyst activity evaluation apparatus according to any one of claims 1 to 7, which evaluates the activity of a catalyst used in a polymer electrolyte fuel cell. In a catalytic activity evaluation method for evaluating the activity of a catalyst for gas by an electrochemical measurement method,
Containing the electrolyte solution in a state where the electrolyte solution is in contact with the catalyst electrode and the counter electrode; and
Controlling the pressure of the stored electrolyte solution to a predetermined pressure higher than atmospheric pressure;
A catalyst activity evaluation method comprising:

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