BekkTech s Procedures For Performing In Plane Membrane Conductivity Testing

Transcription

1 BekkTech s Procedures For Performing In Plane Membrane Conductivity Testing Important Equipment and Software Considerations in Conductivity Testing Work Performed Under US DOE Contract # DE FC36 06GO16028 February 2008

2 Contents Reproducing BekkTech Conductivity Test Results... 3 Gas, Equipment & Software Requirements... 3 Gas Flow & System Pressure... 3 Equipment Requirements (BekkTech Recommendations)... 3 Software... 4 Preparing a Membrane Sample for Testing... 5 Equilibrate Sample to Room Conditions... 5 Cut Sample... 5 Verify Sample Width... 5 Sample Length... 5 Measure Sample Thickness... 6 Assemble Sample in the Conductivity Cell... 6 Insert Thermocouple... 7 Assemble Conductivity Cell with Cell Hardware... 7 Connect to Heated Gas Lines & Back Pressure Regulator... 8 Connect to Keithley SourceMeter... 9 Measuring Resistance... 9 Connect Cell Hardware to Heater Power and Heater Thermocouple Test Protocol for Samples Submitted to BekkTech Under the DOE Program Prepare Equipment & Software for 30C Test C Test Prepare Equipment & Software for 80C Test C Test C Test Data Analysis Calculating Conductivity Sample Graphs Generated by the Reporting Template Files Nafion 212 at 30C Nafion 212 at 80C Nafion 212 at 120C BekkTech Product Listing Contact Information: Page 2

3 Reproducing BekkTech Conductivity Test Results Because various types of equipment may be used to perform membrane conductivity testing, BekkTech does not offer a detailed procedure that is equipment specific, except for procedures specific to the equipment we sell. However, if you understand your equipment and your equipment can operate at the conditions we discuss, the following information includes all the parameters you will need to reproduce our tests. Please remember that the equipment used to perform conductivity testing may have a significant impact on the time it takes you to perform a test. It may also have a significant impact on your test results. We have tried to point out the areas where your choice of equipment will have the greatest impact on your test results. Of course, if you want to ensure that you can reproduce our test results, use BekkTech s BT 512 Membrane Conductivity Test System. If the option of purchasing this system is not available to you, use this information to set the parameters of your equipment to perform tests as similar to the following as possible. Gas, Equipment & Software Requirements BekkTech uses the BT 512 Membrane Conductivity Test System which includes all the capabilities, equipment, and software listed below. Gas Flow & System Pressure Gas Hydrogen 30 C Tests o Gas Flow Control Two Mass Flow Controllers are required for gas mixing to achieve dew points for 30 C testing SCCM flow controllers with accuracy of + / 1% of set point. o System Pressure 100 kpa absolute. This is approximate 15 kpa gauge (2 psig) in Colorado. 80 C Tests o Gas Flow Control One 1000 SCCM Mass Flow Controller with accuracy of + / 10% of set point. o System Pressure 100 kpa absolute. This is approximate 15 kpa gauge (2 psig) in Colorado. 120 C Tests o Gas Flow Control One 500 SCCM Mass Flow Controller with accuracy of + / 10% of set point. o System Pressure 230 kpa absolute. This is approximate 145 kpa gauge (21 psig) in Colorado. Equipment Requirements (BekkTech Recommendations) Fuel cell hardware capable of testing at 120C (Product #ACC 920 Fuel Cell Technologies 5cm 2 fuel cell test hardware) BekkTech Conductivity Cell for testing up to 120C (Product #BT 112 BekkTech Conductivity Cell) Saturator capable of controlling dew points to + / 1 degree absolute accuracy. Requires prompt reaction to temperature changes to reproduce relative humidity steps every 15 minutes. (Product #BT 104 BekkTech Saturator) Page 3

4 Potentiostat / Voltage Current Supply Must be capable of making a true 4 electrode measurement of a resistor in the 1 to 15 kohm range and allow at least 2 Volts between the current source and voltage sense leads. (Product #ACC 980 Keithley 2400 Sourcemeter with BekkTech Scanning DC Software) Temperature Controllers & Thermocouples Combined unit must have absolute accuracy of + / 1.5C with 0.2C reproducibility. (Product #BT 201 BekkTech Temperature Control System, includes Love Temperature Controllers and Type T Thermocouples) Heated Gas Inlet Line from the Saturator to the Cell Hardware which maintains the gas at a temperature above the dew point temperature. Care must be taken to avoid over heating the gas. (Product #BT 125 BekkTech Heated Gas Line) Water Management on the Gas Exit For accurate pressure control, the gas must be either heated to above the dew point through the back pressure regulator or water must be removed from the gas stream so that it does not interfere with the accurate control of back pressure. (Product #BT 130 BekkTech Heated Gas Exit Line and Back Pressure Regulator) Back Pressure Regulator sized appropriately for the gas and water flow associated with these tests. (Product #BT 130 BekkTech Heated Gas Exit Line and Back Pressure Regulator) Software To reproduce the graphs generated by the BekkTech procedures, you will need to know conductivity and relative humidity as a function of time. BekkTech s Conductivity Testing Software controls and records the following parameters, as a function of time: Gas Flow (includes wet & dry gas flow in gas mixing) Cell Temperature Saturator Temperature (Dew Point) Heated Gas Inlet Temperature Heated Gas Exit Temperature Voltage Current Pairs to Calculate Resistance Values BekkTech s Data Analysis Software takes the thousands of data points recorded in the Conductivity Testing Software, reduces the data, and generates the following graphs: Conductivity as a function of time Conductivity as a function of relative humidity Temperature of each component as a function of time Gas flow as a function of time Analysis of these graphs allows the researcher to determine the various factors affecting the conductivity of the sample under test. Important factors to consider if you are developing software for Conductivity Testing: 1) Cell temperature and dew point must be recorded as a function of time so that accurate relative humidity values can be calculated and trends can be observed. Page 4

5 2) Conductivity measurements must be recorded as a function of time and plotted with the temperature data so that trends can be observed. Preparing a Membrane Sample for Testing Equilibrate Sample to Room Conditions Place sample on clean counter surface for 24 hours to allow equilibration to room temperature and room humidity. BekkTech Facility Room Conditions: Room temperature of approximately 21C and average room relative humidity of 15% 25%. Cut Sample Use the Sample Punch to cut a piece from the membrane for testing. Sample to be tested measures approximately 5mm x 25 mm. Figure 1: Sample Punch BekkTech Product #ACC 960 Alternative Cutting Method: Use an Exacto knife and a straight edge to cut the sample. The advantage of using the Sample Punch is more consistent sample sizes with less trauma to the entire sample. Verify Sample Width Use the Width Measurement Tool to verify the width of the sample you will be testing. The Width Measurement Tool has magnification of 11x and a reticule with 0.1mm gradients. Figure 2: Width Measurement Tool BekkTech Product #ACC 940 Alternative Width Measurement: Using the Width Measurement Tool or loupe will provide accurate measurements. Other loupes may provide accurate results. Rulers may also be used. But, are much less accurate. Sample Length Sample length is set by the BekkTech Conductivity Cell. We use a length of 4.2mm for all conductivity calculations. Page 5

6 Measure Sample Thickness The dimensional measurement with the greatest chance of error is sample thickness. The challenge of this measurement is in the accuracy of the gauge which is significantly affected by the skill of the operator. Operator error is dramatically reduced by using a gauge with a non rotating stem and consistently applied force. We use a Mitutoyo Gauge which applies a constant pressure of 3.5 Newtons to the sample using a non rotating stem. Rated accuracy is + / 3 microns. Even by the ratings of this high quality gauge, there is an error of + / 6% on a 50 micron sample. Careful training and use will allow users to achieve gauge accuracy. Figure 3: Mitutoyo Gauge BekkTech Product #ACC 950 Assemble Sample in the Conductivity Cell Remove the top clamp of the Conductivity Cell. Use tweezers to gently lift the platinum wires up from the bottom clamp. Insert the membrane sample under the platinum wires. Place the sample under the platinum wires of the Conductivity Cell. Replace the top clamp. Figure 5: Assemble Sample Under Pt Wires Figure 4: Place Sample in Conductivity Cell Conductivity Cell is BekkTech Product #BT 112 Figure 6: Replace Top Clamp Page 6

7 Insert Thermocouple The thermocouple (TC) should be placed so that the TC Junction (location where temperature is measured) is directly below the membrane. The TC Junction is generally 0.5 mm to 1.0 mm from the end of the TC. Figure 7: Internal Thermocouple Placement Equipment Recommendations: BekkTech uses Type T thermocouples. For accurate measurement, do not use a TC with a floating junction. Use a TC with a grounded junction. Assemble Conductivity Cell with Cell Hardware The Conductivity Cell shown is designed to be used with Fuel Cell Technologies 5cm 2 fuel cell test hardware. Place the Conductivity Cell in the Fuel Cell Technologies cell hardware. Re assemble the cell hardware. You will need longer bolts than the standard set that is included with the cell hardware. BekkTech provides the longer bolts with the Conductivity Cell. You will use only 4 bolts to secure the assembly. The Conductivity Cell makes a good seal with the 4 bolts. Figure 8: Assemble Conductivity Cell Into Cell Hardware Cell Hardware is BekkTech Product #ACC 920 Figure 9: Assembled Page 7

8 Connect to Heated Gas Lines & Back Pressure Regulator Connect the heated gas line from your Saturator to the gas inlet port on your cell hardware. You will use only one of the two gas inlet ports on your cell hardware. Plug the 2 nd gas inlet port with a ¼ stainless steel cap. Gas Inlet Port Plugged Gas Inlet Port Open Figure 10: Connect to Gas Inlet Line Heated Gas Inlet Lines: BekkTech Product #BT 125 Connect the gas line from the cell hardware to your Back Pressure Regulator. We heat the gas exit line as added precaution against condensation. Gas Exit Port Plugged Gas Exit Port Open Figure 11: Connect to Gas Exit Line Heated Gas Exit Line & Back Pressure Regulator: Product #BT 130 You must pressurize your system for conductivity tests at dew points above approximately 100 C to prevent the water in your Saturator from boiling. The exact boiling point will vary depending on the atmospheric pressure of your location. Page 8

9 Connect to Keithley SourceMeter Connect cable with 4 connections to the front of the Keithley Sourcemeter in the ports labeled 4 Wire Sense and Input/Output. The clips on the end of this cable will connect to the platinum wires in the Conductivity Cell, from left to right, as follows: Large Red Clip Current Small Red Clip Voltage Small Black Clip Voltage Large Black Clip Current Figure 12: Keithley SourceMeter Cables Connected to Conductivity Cell Platinum Leads Keithley SourceMeter with Scanning DC Software: BekkTech Product #ACC 980 Measuring Resistance BekkTech uses a Keithley SourceMeter to set a voltage and measure the resulting current for conductivity tests. We perform a Scanning DC Sweep from 0.1V to 0.1V. The linear Voltage Current data is fit for resistance. Alternative Equipment: A potentiostat may also be used to perform a linear sweep. The sweep must be linear even as current flow changes polarity in order for the data to be valid. Or, a potentiostat and frequency response analyzer (FRA) may be used to measure AC Impedance. Impedance should remain constant from the mhz to khz range. And, the phase angle should be very small. Page 9

10 Connect Cell Hardware to Heater Power and Heater Thermocouple Plug the Internal Cell Thermocouple (TC) into the Thermocouple Outlet. Plug the power cable from the Cell Hardware Heaters into the Power Outlet on the test stand. CAUTION: We recommend that you always wait to connect the Cell Hardware Heaters to Power until after you have verified that the Cell Hardware Internal TC is properly placed in the Cell Hardware. If this TC is accidentally left out of the Cell Hardware or improperly installed, the TC will communicate an incorrect temperature to the Cell Hardware Temperature Controller. Irreparable damage to the Cell Hardware and Conductivity Cell may result. Test Protocol for Samples Submitted to BekkTech Under the DOE Program Each sample is tested for approximately 24 hours first at 30C, then 80C, then 120C. We use the BekkTech Conductivity Testing Software to automatically control each 8 hour test. Other methods of controlling the test and acquiring data are available. We will only be describing the procedures we use. A membrane sample is assembled into the Conductivity Cell/Cell Hardware fixture and tested at 30C, 80C, and 120C without removal from the Cell Hardware. Prepare Equipment & Software for 30C Test Ensure that the valve on the dry gas line which connects into the wet gas line is open. Open the BekkTech Conductivity Test Software. Click on the arrow in the upper left corner of the page. This will change the arrow from white to black. The black arrow indicates that the software is running. Ensure that the system is under operator control. The System Control button will read System Under Operator Control. If it does not, click on it to toggle to System Under Operator Control. Go to the Voltage Current tab. Click on Activate Keithley. Confirm that linear voltage current data is being collected. Go to the DataFile tab. Enter a new file name for the test to be performed. Click on Open Data File. Data is now being recorded. Go to the ScriptMode tab. Click on Upload Script File. From the drop down menu, select 30C Conductivity. The 30C script will upload. Review the script to ensure that you have uploaded the correct file. The script file includes gas flow rate, temperatures, dew points, and time for each step. Click on the System Control button so that it toggles to System Under Script Control. Set the back pressure of the system to 100kPa absolute. This is approximate 15 kpa gauge (2 psig) in Colorado. The system will now automatically run the 30C Conductivity Test. Page 10

11 30C Test The 30C script will control the system to the following parameters. Gas Flow 1000 SCCM Hydrogen Gas Mixing The dew points are set using a mixture of dry gas ( 50C) with gas saturated to a dew point of 45C. System Pressure 100 kpa absolute. This is approximate 15 kpa gauge (2 psig) in Colorado. Sample Conditioning Wet up at 30C, 70% RH for 2 hours. After 2 Hours of Conditioning Operating conditions are adjusted every 15 minutes. Note that 2 Mass Flow Controllers are required for this temperature. One flows gas through the Saturator (Wet Gas). The second mixes with the saturated gas after the Saturator (Dry Gas). Relative Humidity ( %RH) Wet Gas Flow Rate (45 C dew point) (SCCM) Dry Gas Flow Rate (-50 C dew point) (SCCM) 70% % % % % % % % % % % % % % % % % When the test has completed the script, take the system out of Script Mode. Then, go to the DataFile tab and click on Close Data File. Page 11

12 Prepare Equipment & Software for 80C Test Ensure that the valve on the dry gas line which connects into the wet gas line is closed. Gas mixing is not needed for controlling dew points at 80C. Go to the DataFile tab and enter a new data file name for the 80C test. Click on Open Data File. Go to the ScriptMode tab. Click on Upload Script. Select the 80C Conductivity Script. The 80C script will upload. Review the script to ensure that you have uploaded the correct file. Click on the System Control button so that it toggles to System Under Script Control. Set the back pressure of the system to 100kPa absolute. This is approximate 15 kpa gauge (2 psig) in Colorado. 80C Test The system will now run the 80C test at the following parameters: Gas Flow 1000 SCCM Hydrogen Gas Mixing None System Pressure 100 kpa absolute. This is approximate 15 kpa gauge (2 psig) in Colorado. Sample Conditioning Wet up at 80C, 70% RH for 2 hours. After 2 Hours of Conditioning Operating conditions are adjusted every 15 minutes, as follows: Dew Point of 67.9 C for 60% RH Dew Point of 63.8 C for 50% RH Dew Point of 58.9 C for 40% RH Dew Point of 52.9 C for 30% RH Dew Point of 49.2 C for 25% RH Dew Point of 44.8 C for 20% RH Dew Point of 49.2 C for 25% RH Dew Point of 52.9 C for 30% RH Dew Point of 58.9 C for 40% RH Dew Point of 63.8 C for 50% RH Dew Point of 67.9 C for 60% RH Dew Point of 71.4 C for 70% RH Dew Point of 74.6 C for 80% RH Dew Point of 77.4 C for 90% RH Dew Point of 78.7 C for 95% RH Dew Point of 80.0 C for 100% RH When the system has run through the end of this script, take the system out of script control. Then, go to the DataFile tab and click on Close Data File. Page 12

13 120C Test Go to the Data File field and enter a new data file name for the 120C test. Click on Open Data File. Go to the ScriptMode tab. Click on Upload Script. Select the 120C Conductivity Script. The 120C script will upload. Review the script to ensure that you have uploaded the correct file. Click on the System Control button so that it toggles to System Under Script Control. Set the back pressure to 230 kpa absolute. This is approximate 145 kpa gauge (21 psig) in Colorado. The system will now run the 120C test at the following parameters: Gas Flow 500 SCCM Hydrogen Gas Mixing None System Pressure 230 kpa absolute. This is approximate 145 kpa gauge (21 psig) in Colorado. Sample Conditioning Wet up at 80C, 70% RH for 2 hours. After 2 Hours of Conditioning Operating conditions are adjusted every 15 minutes, as follows: Dew Point of C for 60% RH Dew Point of 99.2 C for 50% RH Dew Point of 93.0 C for 40% RH Dew Point of 85.4 C for 30% RH Dew Point of 81.1 for 25% RH Dew Point of 75.2 C for 20% RH Dew Point of 81.1 for 25% RH Dew Point of 85.4 C for 30% RH Dew Point of 93.0 C for 40% RH Dew Point of 99.2 C for 50% RH Dew Point of C for 60 % RH Dew Point of C for 70% RH Dew Point of C for 80% RH Dew Point of C for 90 % RH Dew Point of C for 95% RH Dew Point of C for 100% RH When the test has completed running through the script, take the system out of script control. Go to the DataFile tab and close the data file. Purge the system with Nitrogen. Cool the system by reducing the temperatures on the temperature controllers. De activate the Keithley SourceMeter. End the Program. Close the Conductivity Testing Software. Turn the Temperature Control Box power to Off. Turn the Keithley Sourcemeter power to Off. Page 13

14 Data Analysis The data you collected is saved in the files you created at the beginning of each test. Open the BekkTech Data Conversion file. Enter the file name of the 30C data file you created during the 30C test. This is the file name you entered on the DataFile tab. Open the Reporting Template file. Go to the Data Conversion file. Click on the Convert Data File button. The program will reduce the raw data based on the parameters set in the Data Conversion file and write the reduced data into the Reporting Template file. Review the resulting tables and graphs in the Reporting Template file for reasonableness. Save the Reporting Template file using an appropriate file name. You will perform the procedures listed above for the 80C and 120C data files also. The Reporting Template files you create will generate graphs such as the following. Calculating Conductivity The formula for calculating conductivity is included in the BekkTech Software. To manually calculate conductivity, use the following information. R is calculated using a Least Squares Fit of the voltage current data. I V ΔV R = ΔI W T σ = L = R* A L R* W * T L σms = 1cm Lmm* 10mm 1000mS * 1cm 1cm Rohms * Wmm * * Tmicrons * 1S 10mm 10,000microns Page 14

15 Sample Graphs Generated by the Reporting Template Files Nafion 212 at 30C Four Electrode Conductivity 30 C at 100 kpa Relative Humidity (%RH) 110% 100% 90% 80% 70% 60% 50% 40% 30% NRE212 at 30 C ( ) Relative Humidity Select Relative Humidities NRE212 at 30 C ( ) Conductivity Select 4 Electrode Conductivities Conductivity Calculated based on dry dimensions and no swelling Conductivity (ms / cm) 20% Time (Minutes) Figure 13: Nafion 212 at 30C Conductivity as a function of time Comparing Nafion Samples at 30 C 100 kpa 1000 NRE212 at 30 C ( ) N112 at 30 C ( ) Conductivity (ms/cm) Conductivity Calculated based on dry dimensions and no swelling 1 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% Relative Humidity (%RH) Figure 14: Nafion 212 at 30C Conductivity as a function of relative humidity Page 15

16 Nafion 212 at 80C 110% Four Electrode Conductivity 80 C at 100 kpa 180 Relative Humidity (%RH) 100% 90% 80% 70% 60% 50% NRE212 at 80 C ( ) Relative Humidity Select Relative Humidities NRE212 at 80 C ( ) Conductivity Select 4 Electrode Conductivities 40% 40 Conductivity Calculated 30% based on dry dimensions and no swelling 20 20% Time (Minutes) Conductivity (ms / cm) Figure 15: Nafion 212 at 80C Conductivity as a function of time Comparing Four Electrode Conductivity of N C 100 kpa 1000 NRE212 at 80 C ( ) N112 at 80 C ( ) Conductivity (ms/cm) Conductivity Calculated based on dry dimensions and no swelling 1 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% Relative Humidity (%RH) Figure 16: Nafion 212 at 80C Conductivity as a function of relative humidity Page 16

17 Nafion 212 at 120C Four Electrode Conductivity 120 C at 230 kpa Relative Humidity (%RH) 110% 100% 90% 80% 70% 60% 50% 40% NRE212 at 120 C ( ) Relative Humidity Select Relative Humidities NRE212 at 120 C ( ) Conductivity Select 4 Electrode Conductivities Conductivity Calculated based on dry dimensions and no swelling Conductivity (ms / cm) 30% 40 20% Time (Minutes) 0 Figure 17: Nafion 212 at 120C Conductivity as a function of time Comparing Four Electrode Conductivity of N C 230 kpa 1000 NRE212 at 120 C ( ) N112 at 120 C ( ) Conductivity (ms/cm) Conductivity Calculated based on dry dimensions and no swelling 1 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% Relative Humidity (%RH) Figure 18: Nafion 212 at 120C Conductivity as a function of relative humidity Page 17

18 BekkTech Products Referenced in this Document ACC 920 Fuel Cell Technologies 5cm 2 fuel cell hardware ACC 940 Width Measurement Tool ACC 950 Thickness Measurement Tool ACC 960 Sample Punch ACC 980 Keithley 2400 SourceMeter with BekkTech Scanning DC Software BT 104 BekkTech Saturator BT 112 BekkTech Conductivity Cell for Fuel Cell Technologies cell hardware BT 125 BekkTech Heated Gas Inlet Line (includes heating pad & Type T thermocouple) BT 130 BekkTech Heated Gas Exit Line & Back Pressure Regulator BT 201 BekkTech Temperature Control System (includes temperature controllers and thermocouples) BT 512 BekkTech Membrane Conductivity Test System BT 3000 BekkTech Data Analysis and Report Template Software Note: The BekkTech Conductivity Testing Software is available with the purchase of the BT 512 Membrane Conductivity Test System. Contact Information: BekkTech LLC tech@bekktech.com Phone: +1 (970) Fax: +1 (970) Page 18