A fuel cell catalyst layer evaporation drying monitoring system and method

Abstract

The present application relates to a kind of fuel cell catalytic layer evaporation drying monitoring system and method, by simultaneously measuring the mass change of catalytic layer coating and the loss of evaporation surface heat flux to calculate the evaporation rate of each solvent component in coating, realize in-situ monitoring of solvent evaporation behavior in the drying process of fuel cell catalytic layer coating.The present application is based on quasi-steady heat conduction model, by high-precision electronic balance monitoring coating mass change, by setting thermocouple matrix on the upper and lower surface of custom silica gel piece and applying Fourier heat conduction law to realize real-time monitoring of surface evaporation heat flux.Compared with prior art, the present application can decouple the evaporation behavior of double-component solvent, obtain the partial evaporation rate of each solvent component, and further monitor the real-time composition change of catalytic layer coating in drying process.

Description

Technical Field

[0001] This invention relates to the field of fuel cell catalyst drying, and in particular to a fuel cell catalyst evaporation drying monitoring system and method. Background Technology

[0002] The catalyst layer (CL) is the site of electrochemical reactions inside a proton exchange membrane fuel cell (PEMFC), and largely determines the performance and cost of the fuel cell. The catalyst layer preparation process mainly includes three stages: (1) Catalyst slurry preparation: As a precursor of the catalyst layer, the properties of the catalyst slurry are determined by its formulation and mixing method, which ultimately largely determines the structure and performance of the resulting catalyst layer; (2) Catalyst slurry coating: The catalyst layer is coated and deposited by coating a slurry film of a set thickness and size onto a decal transfer substrate, gas diffusion layer, or proton exchange membrane; (3) Catalyst slurry drying: The slurry coating is dried and cured under set drying conditions to allow the solvent components in the coating to evaporate, ultimately obtaining a completely dried porous catalyst layer. In the above process, the drying film formation stage is just as important as the slurry preparation stage, because the microstructure of the coating evolves continuously during the drying process, resulting in a certain difference between the final morphology of the catalyst layer structure and the observed structure in the slurry stage, thus affecting the final formation and electrochemical performance of the catalyst layer structure.

[0003] Solvent evaporation behavior in the coating is a key factor driving the evolution of the catalyst layer's microstructure, as it induces the recombination and arrangement of solid components and promotes the evolution of the coating's internal pore structure. However, monitoring and analyzing solvent evaporation behavior during coating drying is challenging because the catalyst slurry typically contains two solvent components: water and alcohol. During solvent evaporation, the evaporation of water and alcohol occurs simultaneously and is coupled, making real-time monitoring and analysis of the coating's composition a difficult task and hindering in-depth research into the mechanism of the catalyst layer drying process.

[0004] Current technologies primarily measure the change in coating weight loss per unit area over time using traditional weighing methods. This approach is only suitable for monitoring changes in the slurry composition of single-component solvents and cannot decouple the evaporation behavior of two-component solvents. Some studies have calculated the remaining composition of the coating by collecting and examining the composition of the convective gas after drying; however, this method requires a complex structural system and is susceptible to inaccuracies due to uneven gas mixing and delayed detection results. Therefore, based on the current research status, developing a precise drying monitoring method that can decouple the evaporation behavior of two-component solvents in the catalyst layer is of significant practical importance for understanding the drying process and mechanism of catalyst layer coatings. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a catalytic layer drying process monitoring system and method that can decouple the evaporation behavior of two-component solvents.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A fuel cell catalyst layer evaporation and drying monitoring system includes:

[0008] A drying device includes a heating element, a heat transfer pad, and a slurry coating forming tank connected in sequence from bottom to top; wherein, heat transfer temperature sensors are respectively provided on the upper and lower surfaces of the heat transfer pad; the slurry coating to be tested is disposed in the slurry coating forming tank;

[0009] Weighing components are used to weigh the weight change of the slurry coating during the drying process;

[0010] Surface thermometer, used to detect the surface temperature of evaporating slurry coating;

[0011] An ambient temperature thermometer is used to detect ambient temperature.

[0012] A data acquisition unit is used to collect data from the surface thermometer and the heat transfer temperature sensor.

[0013] Furthermore, the monitoring system also includes a data processor for processing data from the weighing components and the data acquisition unit.

[0014] Furthermore, the weighing component is an electronic balance.

[0015] Furthermore, the heat transfer temperature sensor includes one thermocouple located at the center of the heat transfer pad and four thermocouples located around the central thermocouple.

[0016] Furthermore, the surface temperature measuring device is an infrared thermometer, which is located above the slurry coating evaporation tank to monitor the real-time changes in the surface temperature of the slurry coating.

[0017] Furthermore, the slurry coating evaporation tank is made of circular PTFE material.

[0018] Furthermore, the system also includes a temperature controller, which is wired to the heating element.

[0019] Furthermore, the data acquisition device is connected to the data processor via a wire.

[0020] A method for monitoring the evaporation and drying of a fuel cell catalyst layer based on the aforementioned fuel cell catalyst layer evaporation and drying monitoring system includes:

[0021] The drying rates r of solvent A and solvent B during the drying and molding process of the catalyst slurry in the dual-solvent system are obtained according to equations (1) and (2), respectively. A and r B :

[0022]

[0023]

[0024] Where, ΔH A and ΔH B q represents the latent heat of vaporization of solvents A and B, respectively; t h represents the heat flux of the slurry coating. sol T is the heat transfer coefficient of the evaporation surface; t and T a These are the evaporation surface temperature and the ambient temperature, respectively; r total r represents the total evaporation rate of the two solvents. total =r A +r B It is obtained by calculating the change in mass weighed by the electronic balance per unit time.

[0025] Furthermore, the q t The methods for obtaining it include:

[0026] Based on the one-dimensional thermal conductivity quasi-steady-state approximation, the heat flux of the slurry coating is approximately equal to the thermal conductivity of the heat transfer pad; the average temperatures T1 and T2 of the upper and lower surfaces of the heat transfer pad are collected during the drying process and calculated according to equation (3):

[0027]

[0028] Wherein, the average temperatures T1 and T2 are the average temperatures of the upper and lower surface thermocouples, respectively, and λ c δ is the thermal conductivity of the heat transfer pad; c The thickness of the heat transfer pad (13) is given.

[0029] Furthermore, h is obtained according to equation (4). sol :

[0030]

[0031] Where, λ s and λ a These are the thermal conductivity coefficients of the solvent and air, respectively. and These are the Prandtl numbers for the solvent and air, respectively; H air The heat transfer coefficient of air can be obtained through methods including:

[0032] Using the same q tThe method for obtaining the heat flux q of the heat transfer pad when no slurry coating is placed in the slurry coating molding tank is described. t0 And obtain h according to equation (5) air :

[0033]

[0034] Where T0 is the bottom surface temperature of the slurry coating forming tank.

[0035] Furthermore, the drying process is set to a temperature range of 50-120°C.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] (1) It can decouple the evaporation behavior of the two-component solvent in the slurry: The traditional weighing method can only obtain the total solvent evaporation rate of the slurry coating during the drying process, but cannot monitor each solvent component individually. Compared with the traditional method, the present invention can decouple the evaporation behavior of the two-component solvent in the slurry, obtain the evaporation rate of each solvent component, and then monitor the real-time composition change of the slurry coating during the drying process, which is of great significance for the study of the mechanism of the drying film formation process of the catalytic layer.

[0038] (2) By controlling the temperature controller, the present invention can set different constant temperature heating temperatures, thereby realizing the drying control of the coating under different drying conditions, which has important guiding value for the preparation and production of catalyst layer. Attached Figure Description

[0039] Figure 1 This is a structural diagram of a fuel cell catalyst layer evaporation and drying monitoring system according to the present invention;

[0040] Figure 2 This is a diagram showing the arrangement of thermocouple matrix on the upper and lower surfaces of a silica gel sheet in a fuel cell catalyst layer evaporation and drying monitoring system according to the present invention.

[0041] Figure 3 This is a schematic diagram of a fuel cell catalyst layer evaporation and drying monitoring system according to the present invention;

[0042] Figure 4 The graph shows the evaporation rate of the two-component solvent and the change in coating composition at 50°C in Example 2.

[0043] Figure 5 The diagram shows the evaporation rate of the two-component solvent at 70°C and the changes in coating composition in Example 3.

[0044] Figure reference numerals:

[0045] Slurry coating-11, slurry coating forming tank-12, heat transfer pad-13, upper center thermocouple-130, lower center thermocouple-135, upper peripheral thermocouples-131~134, lower peripheral thermocouples-136~139, heating element-14, weighing assembly-2, temperature controller-3, data processor-4, data acquisition unit-5, surface thermometer-6. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0047] Example 1

[0048] This embodiment provides a fuel cell catalyst layer evaporation and drying monitoring system, such as... Figure 1 As shown,

[0049] In this embodiment, the fuel cell catalyst layer evaporation and drying monitoring system includes:

[0050] The drying device includes a heating element 14, a heat transfer pad 13, and a slurry coating forming tank 12 connected in sequence from bottom to top; wherein, the upper and lower surfaces of the heat transfer pad 13 are respectively provided with heat transfer temperature sensors; the slurry coating 11 to be tested is disposed in the slurry coating forming tank 12;

[0051] Weighing component 2 is used to weigh the weight change of the slurry coating 11 during the drying process;

[0052] Surface thermometer 6 is used to monitor the evaporation surface temperature of the slurry coating 11;

[0053] Data acquisition unit 5 is used to acquire data from surface thermometer 6 and the heat transfer temperature sensor; and

[0054] Data processor 4 is used to process data from weighing component 2 and data acquisition unit 5;

[0055] Temperature controller 3 is connected to heating element 14 to achieve constant control of heating temperature.

[0056] In this embodiment, the slurry coating 11 is uniformly coated in the slurry coating forming tank 12. A heat transfer pad 13 with customized size and thermal conductivity is provided at the bottom of the slurry coating forming tank 12. The heat transfer pad 13 is continuously heated by the bottom heating plate 14.

[0057] In this embodiment, the slurry coating 11, the slurry coating molding tank 12, the heat transfer pad 13, and the heating element 14 are placed on the weighing assembly 2. A 5×5 thermocouple matrix (e.g., ...) is respectively arranged on the upper and lower surfaces of the heat transfer pad 13. Figure 2As shown), the upper (lower) surface thermocouple matrix consists of a central thermocouple 130 (135) and four peripheral thermocouples 131-134 (136-139). The average temperature of the upper and lower surfaces of the heat transfer pad 13 is measured through the thermocouple matrix. Thermocouples 130-139 are connected to the data acquisition unit 5 to collect real-time temperature.

[0058] In this embodiment, the weighing component 2 is a high-precision electronic balance with wireless data transmission function, which can transmit data to the data processor 4;

[0059] In this embodiment, the slurry coating forming tank 12 is made of circular PTFE material to reproduce the real coating conditions of the slurry coating in the PTFE substrate decal transfer process commonly used in engineering.

[0060] In this embodiment, the surface temperature sensor 6 is an infrared thermometer, which is located above the slurry coating forming tank 12 to detect the real-time changes in the surface temperature of the slurry coating 11.

[0061] In this embodiment, the heating element 14 is connected to the temperature controller 3 to control a constant drying temperature, and the surface thermometer 6 is used to monitor the temperature change of the evaporation surface of the slurry coating 11. The measurement data of the surface thermometer 6 is transmitted to the data acquisition unit 5 for real-time recording.

[0062] Example 2

[0063] This embodiment provides a method for monitoring the evaporation and drying of a fuel cell catalyst layer, which is implemented according to the fuel cell catalyst layer evaporation and drying monitoring system provided in Embodiment 1. By real-time monitoring and conversion calculation of data, the real-time evaporation rate of each of the two solvent components is obtained, thereby obtaining the real-time compositional change of the coating. This monitoring method is based on the following principle to achieve decoupling of the evaporation rates of the two solvent components.

[0064] A catalytic layer drying monitoring system and method based on simultaneous measurement of coating quality and heat flux is characterized in that the monitoring system calculates the evaporation rate of each of the two solvent components by simultaneously measuring the quality change of the coating and the loss of heat flux on the evaporation surface, thereby realizing in-situ monitoring of solvent evaporation behavior during the drying process.

[0065] In this embodiment, the catalyst slurry to be tested includes: 5g Pt / catalyst, 11.25g Nafion solution, 28.8g deionized water, and 27.45g ethanol, with a solid content of 10%, an I / C ratio of 0.9, and a water-to-ethanol ratio of 1. The monitoring method is used to detect the evaporation rate of water and ethanol during the evaporation and drying process.

[0066] When using a bottom-heated, water- and ethanol-based two-component solvent slurry coating, the coating surface is exposed to ambient air, causing the solvent components to continuously evaporate into the environment until the solvent is completely evaporated, forming a completely dry porous catalytic layer. The total heat flux q on the coating surface during the evaporation process... t It is the sum of the latent heat flux of the evaporation of the two solvents and the convective heat transfer flux driven by the temperature difference between the liquid surface and the ambient air, and can be expressed as:

[0067] q t =r A ΔH A +r B ΔH B +h sol (T t -T a (6)

[0068] Therefore, the evaporation rates of the water and ethanol binary solvents can be calculated using the following expression.

[0069]

[0070]

[0071] Where, r A and r B ΔH represents the drying rate of solvents water and ethanol as a function of time, respectively. A and ΔH B represents the latent heat of vaporization of solvents water and ethanol, respectively, and is a readily available solvent property parameter; h sol T is the heat transfer coefficient of the evaporation surface; t and t a These are the evaporation surface temperature and the ambient temperature, respectively; r total r represents the total evaporation rate of the two solvents. total =r A +r B Therefore, in order to solve r A With r B The attribute parameters that the above expression needs to look up include ΔH. A ΔH B The parameters to be measured include q t h sol T t T a and r total .

[0072] For the parameter to be measured q t This is the sum of the latent heat of solvent evaporation and the convective heat flux, and its in-situ measurement is difficult. Therefore, a design such as Figure 3The model shown calculates heat flux conversion. In the model, a paste coating is applied to an impermeable transfer substrate. A silicone sheet with a customized thermal conductivity and thickness is placed at the bottom of the transfer substrate to calculate the heat flux. The bottom of the silicone sheet is heated by a heating element, and the heat transfer direction is vertically upward. Based on the quasi-steady-state approximation, the thickness is δ. c The thermal flux of the silicone sheet can be expressed as:

[0073]

[0074] According to the thermal equilibrium relationship q t =q c , convert to get q t The calculation expression:

[0075]

[0076] Where, λ c The thermal conductivity is customized for the silicone sheet, and T1 and T2 are the temperatures of its upper and lower surfaces.

[0077] For the parameter to be measured h sol Boundary layer theory shows that the convective heat transfer coefficient in most simple flow fields is related to P. r 1 / 3 Proportional, where Prandtl number Therefore, the correlation between the convective heat transfer coefficient of the evaporation surface before and after slurry deposition can be established by the following expression:

[0078]

[0079] Where, λ s and λ a These are the thermal conductivity coefficients of the solvent and air, respectively. and Prandtl numbers for solvent and air, respectively, and heat transfer coefficient h before evaporation. air It can be calculated using the following expression:

[0080]

[0081] Where, q t0 T0 represents the heat flux before the slurry is deposited, and T0 represents the surface temperature of the substrate before the slurry is deposited.

[0082] For the parameter to be measured r total The total solvent evaporation rate was obtained by weighing the coating mass change using an electronic balance to calculate the weight difference.

[0083] For the parameter T to be measured t An infrared thermometer was used to monitor the real-time temperature of the coating surface. Ambient temperature T a The temperature of the drying chamber can be adjusted via a preset setting.

[0084] Specifically, the following steps are included:

[0085] (1) System setup: A fuel cell catalyst layer evaporation and drying monitoring system was built according to Example 1;

[0086] (2) Pre-operation: The temperature controller 3 controls the temperature of the heating element 14 to be kept constant at 50℃, and the ambient temperature T is set. a At 25℃, the data acquisition device 5 and the surface thermometer 6 are turned on to collect the temperature of the surface of the heat transfer pad 13.

[0087] (3) System preheating stage: The heat output from heating element 14 preheats the drying device to a stable temperature. When the temperature measured by data acquisition unit 5 and surface thermometer 6 remains relatively constant, it indicates that the system has reached thermal stability, and the system preheating is complete. At this time, q is solved according to equation 8. t0 :

[0088]

[0089] And based on the heat flux q t0 The surface temperature T0 of the slurry coating molding tank 12 is calculated using equation 5. air ;

[0090]

[0091] And solve h according to Equation 4 sol :

[0092]

[0093] Among them, T 1,0 T 2,0 λ represents the temperature of the upper and lower surfaces of the silicone sheet before the slurry is deposited. s and λ a The thermal conductivity of the solvent and air. and Here are the Prandtl numbers for the solvent and air:

[0094]

[0095]

[0096] Where μ represents the dynamic viscosity of the fluid, C p The specific heat capacity of the fluid is represented by , and the thermal conductivity of the fluid is represented by k. The property parameters of air can be found online. In this embodiment, the catalyst solvent is a dual-solvent system of water and ethanol. The thermal conductivity of each solvent can be found online, and the property parameters of the mixture can be calculated by arithmetic average based on their respective ratios (1:1 volume ratio in this embodiment).

[0097] (4) Drying test stage: The pre-prepared catalyst solvent slurry (the solvent in this embodiment is water and ethanol) is uniformly coated in the slurry coating forming tank 12. The weighing component 2, data acquisition device 5 and surface thermometer 6 measure the mass and temperature data in real time and store them in the data processor 4.

[0098] Temperatures T1 and T2 were collected, and the thermal conductivity λ of the silicone sheet was used as a reference. c =2.8W / m 2 Thickness δ c =5mm, and the thermal flux q of the silicone sheet is calculated using Equation 3. c That is, the heat flux q of the slurry coating. t :

[0099]

[0100] Based on the weight difference of the slurry coating 11 at a certain moment during the drying process obtained by weighing component 2 relative to the weight of the slurry when the catalyst was added, r is determined. total ;

[0101] Finally, the evaporation surface temperature T was measured in real time by the surface thermometer 6. t The ambient temperature T measured by the ambient temperature thermometer a The latent heat of vaporization of water and ethanol ΔH A =2258kJ / kg and ΔH B =879kJ / kg and Equations 1 and 2 are used to calculate the real-time evaporation rate of water and ethanol solvents.

[0102]

[0103]

[0104] (5) End of drying test stage: When the output value of weighing component 2 remains constant, it indicates that the solvent in slurry coating 11 has been completely evaporated, the coating becomes a completely dry catalytic layer, and the drying test ends.

[0105] like Figure 4 The diagram shows the evaporation rate of the two-component solvent and the changes in coating composition measured at a bottom heating temperature of 50℃. Figure 4 (a) shows that the entire coating dries at a decreasing rate (dashed line), with ethanol showing a decreasing rate of drying throughout the process (solid black line), while water shows a trend of first increasing and then decreasing rate (solid gray line). Furthermore, the evaporation rate of ethanol is much greater than that of water in the early stage of drying, indicating that ethanol evaporates preferentially over water. Figure 4 (b) shows the real-time composition of the coating, where the mass of ethanol rapidly decreases and evaporates completely before the mid-drying stage due to the rapid evaporation of ethanol, after which only water remains in the coating until all the solvent has evaporated.

[0106] Example 3

[0107] This embodiment provides a method for monitoring the evaporation and drying of the catalyst layer of a fuel cell. The difference from Embodiment 2 is that in step (2), the temperature controller 3 controls the temperature of the heating element 14 to be kept constant at 70°C. Other steps are the same as in Embodiment 2.

[0108] like Figure 5 The figures shown are graphs illustrating the evaporation rate of the two-component solvent and the changes in coating composition measured at a bottom heating temperature of 70°C. The monitoring results are compared with those in Example 1 at 50°C. Figure 4 They exhibit the same trends and patterns; however, due to the increase in drying temperature, the evaporation rate of each solvent component increases significantly, and the coating drying time is significantly shortened.

[0109] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for monitoring the evaporation and drying of a fuel cell catalyst layer, characterized in that, A fuel cell catalyst layer evaporation drying monitoring system is adopted. The system includes: a drying device, including a heating plate (14), a heat transfer pad (13), and a slurry coating forming tank (12) connected from bottom to top; wherein, the upper and lower surfaces of the heat transfer pad (13) are respectively provided with heat transfer temperature sensors; the slurry coating (11) to be tested is placed in the slurry coating forming tank (12); a weighing component (2) is used to weigh the weight change of the slurry coating (11) during the drying process; a surface thermometer (6) is used to detect the evaporation surface temperature of the slurry coating (11); and a data acquisition device (5) is used to collect data from the surface thermometer (6) and the heat transfer temperature sensors. Methods for monitoring the evaporation and drying of fuel cell catalyst layers include: The drying rates of solvent A and solvent B during the drying and molding process of the catalyst slurry in the dual-solvent system were obtained according to equations (1) and (2), respectively. and : in, and Let A and B represent the latent heats of vaporization of solvents A and B, respectively. The heat flux of the slurry coating; The heat transfer coefficient of the evaporation surface; and These are the evaporation surface temperature and the ambient temperature, respectively. The total evaporation rate of the two solvents. .

2. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The weighing component (2) is an electronic balance.

3. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The heat transfer temperature sensor includes one thermocouple located at the center of the heat transfer pad (13) and four thermocouples located around the center thermocouple.

4. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The system also includes a temperature controller (3) connected to the heating element (14).

5. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The surface thermometer (6) is an infrared thermometer, which is located above the slurry coating forming tank (12) to detect the real-time changes in the surface temperature of the slurry coating (11).

6. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The slurry coating forming tank (12) is made of circular PTFE material.

7. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The The methods for obtaining it include: The average temperature of the upper and lower surfaces of the heat transfer pad (13) during the drying process was collected. and And calculated according to equation (3): Among them, average temperature and These are the average temperatures of the thermocouples on the upper and lower surfaces, respectively. δ is the thermal conductivity of the heat transfer pad (13); c The thickness of the heat transfer pad (13) is given.

8. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, According to equation (4), : in, and These are the thermal conductivity coefficients of the solvent and air, respectively. and These are the Prandtl numbers for the solvent and air, respectively; The heat transfer coefficient of air can be obtained through methods including: Using the same The method of obtaining the heat flux of the heat transfer pad (13) when no slurry coating (11) is provided in the slurry coating forming tank (12) is obtained. And obtain according to equation (5) : in, The bottom surface temperature of the slurry coating forming tank (12).

9. The method for monitoring the evaporation and drying of the fuel cell catalyst layer according to claim 1, characterized in that, The drying process is set to a temperature range of 50-120℃.

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