Testing Method and System for Gas Surface Adsorption Amount and Bulk Dissolution Amount

Abstract

The present invention provides a method and system for testing gas surface adsorption and bulk dissolution, relating to the field of fuel cell technology. The method comprises: step S1: preparing ionomer films of varying thicknesses on a quartz crystal microbalance wafer; step S2: measuring changes in the wafer vibration frequency and, based on the Sauerbrey equation, determining changes in the gas equilibrium within the film; and step S3: determining the surface adsorption and bulk dissolution per unit thickness based on the measured equilibrium. The method utilizes the quartz crystal microbalance's sensitivity to minute masses to determine changes in the gas equilibrium of the film under varying gas pressures or concentrations. Furthermore, the method utilizes the relationship between varying film thicknesses and gas equilibrium to determine surface adsorption and bulk dissolution, enabling offline testing of interfacial gas adsorption patterns.

Description

Technical Field

[0001] The present invention relates to the field of fuel cell technology, and in particular to a method for testing the surface adsorption and bulk solubility of gases in ultra-thin ionomer films, and more particularly to a method for offline measurement of the surface adsorption and bulk solubility of gases in ultra-thin ionomer films in fuel cell catalyst layers, and in particular to a method and system for testing the surface adsorption and bulk solubility of gases. Background Art

[0002] As proton exchange membrane fuel cells (PEMFCs) progress toward lower platinum content, the localized mass transfer resistance within the catalyst layer increases dramatically, primarily due to restricted oxygen transport within the ionomer. The ionomer film within the catalyst layer is only a few nanometers thick. Due to confinement and matrix effects, its structure changes, and oxygen transport across the interface gradually becomes the rate-determining step. The ability to measure and separate the adsorption and dissolution processes of oxygen within the film is highly valuable for studying the mass transfer mechanisms and improving the performance of membrane electrode systems.

[0003] At present, the study of oxygen transport in the ionomer film of the catalytic layer generally adopts the online limiting current test method. However, due to the small thickness of the film, it is impossible to effectively separate the oxygen adsorption and dissolution process on the ionomer surface, and it is difficult to analyze the transport law of gas at the ionomer interface. Therefore, it is very meaningful to study the gas transport phenomenon at the interface of the ionomer through offline testing methods. Summary of the Invention

[0004] In view of the defects in the prior art, the present invention provides a method and system for testing the surface adsorption and bulk dissolution of gases.

[0005] According to a method and system for testing gas surface adsorption and bulk dissolution, the present invention provides the following scheme:

[0006] In a first aspect, a method for testing gas surface adsorption and bulk dissolution is provided, the method comprising:

[0007] Step S1: preparing ionomer films of different thicknesses on a quartz crystal microbalance wafer;

[0008] Step S2: measuring the change in the wafer vibration frequency and obtaining the change in the equilibrium amount of gas in the film according to the Sauerbrey equation;

[0009] Step S3: according to the measured equilibrium amounts of ionomer films of different thicknesses, the surface adsorption amount and the bulk dissolution amount per unit thickness are obtained.

[0010] Preferably, the step S1 comprises: forming a thin film by titrating an ionomer solution, wherein the area of the titrated thin film is 4.5 times the test area of the quartz crystal microbalance wafer.

[0011] Preferably, the films of different thicknesses in step S1 are all less than 100 nm in thickness.

[0012] Preferably, step S2 includes: measuring the change in the vibration frequency of the wafer, and obtaining the change in the equilibrium amount of the gas in the film according to the Sauerbrey equation of formula (1):

[0013] (1)

[0014] in, is the equilibrium amount of gas in the film; is the molar mass of the gas; is the elastic-viscosity modulus; is the density of the chip; is the resonant frequency; is the frequency variation of the chip.

[0015] Preferably, in step S2, the test temperature is 30-50° C., the test total pressure range is less than 0.1 MPa, and the relative humidity is 100%.

[0016] Preferably, step S3 comprises: substituting the measured equilibrium amount of the ionomer films of different thicknesses into formula (2) to obtain the surface adsorption amount and the bulk dissolution amount per unit thickness:

[0017] (2)

[0018] in, is the equilibrium amount of gas in the film, is the surface adsorption amount, is the amount of bulk dissolved per unit thickness, is the film thickness, measured by atomic force microscopy.

[0019] In a second aspect, a system for measuring gas surface adsorption and bulk dissolution is provided, the system comprising:

[0020] Module M1: Preparation of ionomer films of different thicknesses on a quartz crystal microbalance wafer;

[0021] Module M2: Tests the change in wafer vibration frequency and obtains the change in the equilibrium amount of gas in the film based on the Sauerbrey equation;

[0022] Module M3: Based on the equilibrium amount of the measured ionomer films of different thicknesses, the surface adsorption amount and the bulk dissolution amount per unit thickness are obtained.

[0023] Preferably, the module M1 comprises: forming a thin film by titrating an ionomer solution, wherein the area of the titrated film is 4.5 times the test area of the quartz crystal microbalance wafer;

[0024] Among them, the thickness of films of different thicknesses is less than 100 nm.

[0025] Preferably, the module M2 tests the change in the vibration frequency of the wafer and obtains the change in the equilibrium amount of the gas in the film according to the Sauerbrey equation (1):

[0026] (1)

[0027] in, is the equilibrium amount of gas in the film; is the molar mass of the gas; is the elastic-viscosity modulus; is the density of the chip; is the resonant frequency; is the frequency variation of the chip.

[0028] The test temperature in the module M2 is 30-50°C, the test total pressure range is less than 0.1 MPa, and the relative humidity is approximately 100%.

[0029] Preferably, the module M3 comprises: substituting the measured equilibrium amount of the ionomer film of different thicknesses into formula (2) to obtain the surface adsorption amount and the bulk dissolution amount per unit thickness:

[0030] (2)

[0031] in, is the equilibrium amount of gas in the film, is the surface adsorption amount, is the amount of bulk dissolved per unit thickness, is the film thickness, measured by atomic force microscopy;

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention eliminates the influence of electrochemical reaction on the oxygen adsorption and dissolution of ionomer films, and realizes the adsorption and dissolution test of gases on ultra-thin ionomer films;

[0034] 2. The present invention uses equilibrium test on ionomer films of different thicknesses. The thickness is less than 100 nm, so it does not affect the internal structure of the ionomer and can distinguish the surface adsorption and bulk dissolution of gases in the ionomer film.

[0035] 3. The present invention designs an offline test method for gas adsorption for the first time, realizing the test of the isothermal adsorption law of the interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0037] Figure 1 Schematic diagram of the quartz wafer and film used for testing;

[0038] Figure 2 Testing film thickness and roughness for atomic force microscopy;

[0039] Figure 3 is the fitting relationship between the equilibrium amount and film thickness obtained according to formula (1);

[0040] Figure 4 is the relationship between the surface adsorption amount and the oxygen partial pressure obtained according to formula (2);

[0041] Figure 5 is the relationship between the dissolved volume per unit thickness and the oxygen partial pressure obtained according to formula (2). DETAILED DESCRIPTION

[0042] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0043] Embodiments of the present invention provide a method for measuring gas surface adsorption and bulk dissolution, including a quartz crystal microbalance (QCM)-based gas equilibrium measurement system in an ionomer film. The system comprises a gas chamber, a control system, and a QCM. The gas chamber provides a gas atmosphere and includes a pressure gauge, a vacuum pump, and a temperature control and feedback system. The control system controls temperature, humidity, and pressure. The QCM includes a temperature-controlled electrolytic cell (QCM cell), a QCM analyzer (QCM cell flow module), and associated software.

[0044] Thin films with nanometer thickness and uniform morphology were prepared on a quartz crystal microbalance chip by titrating an ionomer solution.

[0045] The present invention provides a method for testing the surface adsorption and bulk dissolution of a gas, which specifically includes:

[0046] Step S1: preparing ionomer films of different thicknesses on a quartz crystal microbalance chip; forming the prepared films by titrating an ionomer solution, and the test area of the quartz crystal microbalance chip is much smaller than the titration film area.

[0047] The thin films were prepared by titrating ionomer solutions. Because the titrated film area is approximately 4.5 times the test area of the quartz crystal microbalance wafer, uneven thickness and roughness caused by uneven stress at the film edges can be avoided. The films of varying thickness were all less than 100 nm, so the effect of thickness on the internal structure of the ionomers can be ignored.

[0048] Step S2: Test the change in the wafer vibration frequency and obtain the change in the equilibrium amount of gas in the film according to the Sauerbrey equation (1):

[0049] (1)

[0050] in, is the equilibrium amount of gas in the film; is the molar mass of the gas; is the elastic-viscosity modulus; is the density of the chip; is the resonant frequency; is the frequency variation of the chip.

[0051] The test temperature is 30-50°C, the total test pressure range is less than 0.1 MPa, and the relative humidity is approximately 100%. The temperature control and feedback system within the oven is utilized, and the pressure is controlled by a vacuum pump and air valve. The pressure is displayed by a pressure gauge within the vacuum oven. The relative humidity is controlled by saturated water vapor within the enclosed space.

[0052] Step S3: Substitute the measured equilibrium amount into formula (2) to obtain the surface adsorption amount and the bulk dissolution amount per unit thickness:

[0053] (2)

[0054] in, is the equilibrium amount of gas in the film, is the surface adsorption amount, is the amount of bulk dissolved per unit thickness, is the film thickness, which can be measured by atomic force microscopy (AFM).

[0055] The present invention also provides a system for testing gas surface adsorption and bulk dissolution, which specifically includes:

[0056] Step M1: Prepare ionomer films of different thicknesses on a quartz crystal microbalance chip; the prepared film is formed by titrating the ionomer solution. The test area of the quartz crystal microbalance chip is much smaller than the titration film area, which can avoid uneven thickness and roughness caused by uneven stress at the edge of the film.

[0057] The thin films were prepared by titrating ionomer solutions. Because the titrated film area is approximately 4.5 times the test area of the quartz crystal microbalance wafer, uneven thickness and roughness caused by uneven stress at the film edges can be avoided. The films of varying thickness were all less than 100 nm, so the effect of thickness on the internal structure of the ionomers can be ignored.

[0058] Step M2: Test the change in the wafer vibration frequency and obtain the change in the equilibrium amount of gas in the film according to the Sauerbrey equation (1):

[0059] (1)

[0060] in, is the equilibrium amount of gas in the film; is the molar mass of the gas; is the elastic-viscosity modulus; is the density of the chip; is the resonant frequency; is the frequency variation of the chip.

[0061] The test temperature is 30-50°C, the total test pressure range is less than 0.1 MPa, and the relative humidity is approximately 100%. The temperature is controlled and fed back by the oven's internal temperature control and feedback system, while the pressure is controlled by a vacuum pump and air valve. The pressure is displayed by a pressure gauge within the vacuum oven, and the relative humidity is controlled by saturated water vapor within the enclosed space.

[0062] Step M3: Substitute the measured equilibrium amount into formula (2) to obtain the surface adsorption amount and the bulk dissolution amount per unit thickness:

[0063] (2)

[0064] in, is the equilibrium amount of gas in the film, is the surface adsorption amount, is the amount of bulk dissolved per unit thickness, is the film thickness, which can be measured by atomic force microscopy (AFM).

[0065] Next, the present invention will be described in more detail.

[0066] The present invention prepares a thin film on a gold-coated quartz wafer by titration. First, a 0.5 wt% ionomer Nafion solution is prepared, and the dispersing solvent is ethanol. The prepared solution is ultrasonicated for 5 minutes and allowed to stand for 24 hours. Different volumes of 0.5 wt% ionomer solution are dropped onto the test wafer using a pipette to prepare ultra-thin ionomer films of different thicknesses. The film is then placed in an oven and dried at 30°C. The wafer structure after being covered with the ionomer film is as shown below. Figure 1As shown, Figure 1 In the figure, ① is the ultra-thin ionomer film being titrated, ② is the coverage area of the ionomer film, ③ is the actual test area, ④ and ⑤ are gold-plated electrodes, and ⑥ is a quartz wafer.

[0067] The thickness of the ionomer film can be observed using an atomic force microscope (AFM). In this experiment, the ionomer film covered an area of 1.1 cm 2 Larger than the test area 0.24 cm 2 , in order to eliminate the influence of uneven film thickness and roughness caused by uneven stress at the edge of the film. Figure 2 As shown in the figure, atomic force microscopy (AEM) tests of thickness and roughness revealed that all three films were less than 100 nm thick and less than 2 nm roughness. Prior to the experiment, the films were placed in a test chamber at approximately 100% relative humidity for 24 hours to stabilize them at saturated moisture content.

[0068] The operating temperature of this embodiment is 30°C. The relative humidity is approximately 100%. O2 is selected as the experimental gas. By controlling the pressure in the gas chamber, the total pressure range is 0.0045-0.1 MPa. Based on the saturated vapor pressure of water at 30°C, the oxygen partial pressure P(O2) is calculated to be 0-0.0955 MPa.

[0069] According to formula (1), the balance quantity of the quartz crystal microbalance (QCM) test is obtained as follows: Figure 3 As shown in formula (2), the equilibrium amount is proportional to the thickness. A linear fit is performed between the film thickness and the equilibrium amount. The intercept of the fitting curve in the figure is obtained according to formula (2) to obtain the surface adsorption amount (such as Figure 4 As shown in the figure), the slope of the fitting curve is used to obtain the volume dissolution per unit thickness according to formula (2) (as shown in the figure). Figure 5 shown).

[0070] An embodiment of the present invention provides a method and system for testing the surface adsorption and bulk dissolution of gas. First, by utilizing the sensitivity of a quartz crystal microbalance to tiny masses, the changes in the gas balance of a thin film under different gas pressures or concentrations are obtained. Second, by utilizing the relationship between different film thicknesses and the gas balance, the surface adsorption and bulk dissolution are respectively obtained, thereby realizing offline testing of the interfacial gas adsorption law.

[0071] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0072] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for testing gas surface adsorption and bulk dissolution, characterized in that: include: Step S1: preparing ionomer films of different thicknesses on a quartz crystal microbalance wafer; Step S2: measuring the change in the wafer vibration frequency and obtaining the change in the equilibrium amount of gas in the film according to the Sauerbrey equation; Step S3: obtaining the surface adsorption amount and the bulk dissolution amount per unit thickness according to the measured equilibrium amounts of ionomer films of different thicknesses; The step S2 includes: testing the change of the wafer vibration frequency, and obtaining the change of the equilibrium amount of the gas in the film according to the Sauerbrey equation of formula (1): (1) in, is the equilibrium amount of gas in the film; is the molar mass of the gas; is the elastic-viscosity modulus; is the density of the chip; is the resonant frequency; is the frequency variation of the chip.

2. The method for testing gas surface adsorption and bulk dissolution according to claim 1, characterized in that: The step S1 comprises: forming a thin film by titrating an ionomer solution, wherein the area of the titrated thin film is 4.5 times the test area of the quartz crystal microbalance wafer.

3. The method for testing gas surface adsorption and bulk dissolution according to claim 1, characterized in that: The thickness of the films of different thicknesses in step S1 is all less than 100 nm.

4. The method for testing gas surface adsorption and bulk dissolution according to claim 1, characterized in that: In step S2, the test temperature is 30-50° C., the test total pressure range is less than 0.1 MPa, and the relative humidity is 100%.

5. The method for testing gas surface adsorption and bulk dissolution according to claim 1, characterized in that: The step S3 comprises: substituting the measured equilibrium amount of the ionomer films of different thicknesses into formula (2) to obtain the surface adsorption amount and the bulk dissolution amount per unit thickness: (2) in, is the equilibrium amount of gas in the film, is the surface adsorption amount, is the amount of bulk dissolved per unit thickness, is the film thickness, measured by atomic force microscopy.

6. A system for testing gas surface adsorption and bulk dissolution, characterized in that: include: Module M1: Preparation of ionomer films of different thicknesses on a quartz crystal microbalance wafer; Module M2: Tests the change in wafer vibration frequency and obtains the change in the equilibrium amount of gas in the film based on the Sauerbrey equation; Module M3: Calculate the surface adsorption amount and the bulk dissolution amount per unit thickness based on the measured equilibrium amount of ionomer films of different thicknesses; The module M2 tests the change in the wafer vibration frequency and obtains the change in the equilibrium amount of gas in the film according to the Sauerbrey equation (1): (1) in, is the equilibrium amount of gas in the film; is the molar mass of the gas; is the elastic-viscosity modulus; is the density of the chip; is the resonant frequency; is the frequency variation of the chip.

7. The gas surface adsorption and bulk dissolution testing system according to claim 6, characterized in that: The module M1 includes: forming a thin film by titrating an ionomer solution, wherein the area of the titrated film is 4.5 times the test area of the quartz crystal microbalance wafer; Among them, the thickness of films of different thicknesses is less than 100 nm.

8. The gas surface adsorption and bulk dissolution testing system according to claim 6, characterized in that: The test temperature in the module M2 is 30-50°C, the test total pressure range is less than 0.1 MPa, and the relative humidity is 100%.

9. The gas surface adsorption and bulk dissolution testing system according to claim 6, characterized in that: The module M3 includes: substituting the measured equilibrium amount of the ionomer film of different thicknesses into formula (2) to obtain the surface adsorption amount and the bulk dissolution amount per unit thickness: (2) in, is the equilibrium amount of gas in the film, is the surface adsorption amount, is the amount of bulk dissolved per unit thickness, is the film thickness, measured by atomic force microscopy.

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