旋转圆盘电极研究氧还原PPT,PDF
合集下载
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
RDE Set-up @ NREL Activity & ECA @ 0.90 V, 100 kPa, 25oC
m2/gPt µA/cm2Pt mA/mgPt
Using poly-Pt disk & obtaining specific activity values of Is > 2.0 mA/cm2Pt can be considered a measure of acceptable cell cleanliness.
Innovation for Our Energy Future
Testing Oxygen Reduction Reaction Activity with the Rotating Disc Electrode Technique
Shyam S. Kocha: NREL Yannick Garsany: EXCET/NRL Deborah Myers: ANL
Measurement and active compensation of solution resistance
Solution resistance is caused by a combination of low electrolyte concentration and temperature as well as the distance of the Luggin capillary or Reference electrode to the surface of the working electrode. Expected value for resistance in 0.1 M perchloric acid is ~20 ohms.
V. Stamenkovic et al., “On the importance of correcting for the uncompensated ohmic resistance in model experiments of the Oxygen Reduction Reaction”, J. Electroanal. Chem. 647 (2010) 29-34.
1) 2) 3) 4) 5) Impact of Film Deposition & Drying Techniques Impact of Ink Formulation Impact of Nafion Incorporation Impact of particle size effects Correlation wsk
Trends of activity and durability in Rotating Disc Electrode (RDE) studies can be used to predict trends in Proton Exchange Membrane Fuel Cells (PEMFCs).
Besides its usefulness as a tool to predict electrocatalyst activity and durability in fuel cells, the RDE technique allows us to carry out the following diagnostics. • Cyclic Voltammograms under N2
The atmospheric pressure decreases with altitude and so labs such as those at NREL, Golden, CO (~6000 ft, ~83 kPa) have to apply a correction for limiting current as well as kinetics so that the data is normalized to 100 kPa O2. Limiting currents are expected to be ~5.7 mA/cm2 @ 1600 rpm when corrected to 100 kPa O2.
0.05–1.2 V, 100 mV/s, ~50 cycles, Pt/C, 25oC, N2
Conditioning protocol may have to be varied with electrocatalyst material. Conditioning is complete when the CV becomes invariant with time, cycles. 8
Date: Tuesday, March 12, 2013
https:///hydrogenandfuelcells/webinars.html
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Thin-film RDE
Dissolved O2 Pt/C | Nafion | Acid Acid Flooded pores Electrode (< 0.1 µm) Perchloric Acid: H+ Ionomer: Binder, Disp. Liquid Electrolyte Scan Rate: ~20 mV/s 10’s of mg Cat L = 4–36 µgPt/cm2
Kocha, S. S., et al., "Influence of Nafion on the Electrochemical Activity of Pt-based Electrocatalysts." ECS Trans. 2012, 50.
3
Information Obtainable from RDE Measurements
RDE Analysis
Ring held at 1.2 V
IL = 5.7 mA/cm2
9
RDE Test Protocol
Voltage Profile Protocol 0.90V 1.0 V
0.0 V I@ 0.90 V Protocol parameters such as: Scan Direction, Scan Rate, and Voltage Range will affect the measured catalyst activity.
5) Electrocatalyst Durability using RDE Measurements 6) Summary
2
Background
PEMFC MEA
O2 Flow Pt/C | Nafion Gas & H2O, pores Electrode (5–15 µm) Nafion Ionomer Ionomer: H+ 100 % RH 15 min/point 100’s of mg Cat L = 0.2–0.4 mgPt/cm2
0.90 V, 20 mV/s, 0–1.0 V, 1600 rpm, cathodic scan, 25oC, 0.1M HClO4, iR corrected, background current corrrected & corrected to 100 kPa reaction order w.r.t O2 of 0.85.
• • • • • • • • • • • •
HUPD ECA (m2/g) CO Chemisorption ECA (m2/g) Cu UPD ECA (m2/g) Double Layer Capacitance Pseudo-Capacitance (oxide coverage) Onset potential of support corrosion Short term durability for thousands of cycles Electrocatalyst specific and mass Activity • Poly-Pt, Pt/C, Pt-alloy/C, Pt core-shell/C, Extended thin films, NPGM Reaction Order w.r.t. PO2 Tafel slopes Effect of contaminants in electrolyte or reactant gases Electrolyte anion adsorption
10
µA/cm2Pt m2/gPt mA/mgPt
Corrections Applied to ORR I-V Curves
Background current correction
At lower potential scan rates, the effect of impurities and the formation of surface oxides suppress the measured ORR activity; at scan rates above 20mV s-1, capacitive current effects are higher. The background current is measured by running the ORR sweep profile (e.g., 1.03 V→0.05 V→1.03 V at 5 and 20 mV s-1 and 1600 rpm) in N2–purged 0.1 M HClO4 either before or after the ORR measurements to account for capacitive current contributions. This background current is subtracted from the experimental ORR current to eliminate any contributions of capacitive current.
• I–V Curves under O2
• Peroxide Generation using Ring disc (RRDE) • Complementary Techniques
• EIS, EQCN, etc.,
4
Experimental Aspects of RDE Testing
5
Electrochemical Set-up/Glassware Cleaning
Concentrated Acid/Oxidant
Boiling in DI Water
Contamination of cell/electrolyte poisons the catalyst and is one of the primary reasons for low and scattered activity data.
6
Ink Formulation, Electrode Preparation
Bath Sonicator Nanobalance
Horn Sonicator
Ink Deposition
Kocha, S. S., et al., ECS Trans. 2012, 50.
7
RDE Conditioning or Break-in
Outline
1) 2) 3) 4) Background Experimental Aspects of RDE Testing Basic Measurement Technique & Analysis Parameters Affecting RDE Activity Measurements
m2/gPt µA/cm2Pt mA/mgPt
Using poly-Pt disk & obtaining specific activity values of Is > 2.0 mA/cm2Pt can be considered a measure of acceptable cell cleanliness.
Innovation for Our Energy Future
Testing Oxygen Reduction Reaction Activity with the Rotating Disc Electrode Technique
Shyam S. Kocha: NREL Yannick Garsany: EXCET/NRL Deborah Myers: ANL
Measurement and active compensation of solution resistance
Solution resistance is caused by a combination of low electrolyte concentration and temperature as well as the distance of the Luggin capillary or Reference electrode to the surface of the working electrode. Expected value for resistance in 0.1 M perchloric acid is ~20 ohms.
V. Stamenkovic et al., “On the importance of correcting for the uncompensated ohmic resistance in model experiments of the Oxygen Reduction Reaction”, J. Electroanal. Chem. 647 (2010) 29-34.
1) 2) 3) 4) 5) Impact of Film Deposition & Drying Techniques Impact of Ink Formulation Impact of Nafion Incorporation Impact of particle size effects Correlation wsk
Trends of activity and durability in Rotating Disc Electrode (RDE) studies can be used to predict trends in Proton Exchange Membrane Fuel Cells (PEMFCs).
Besides its usefulness as a tool to predict electrocatalyst activity and durability in fuel cells, the RDE technique allows us to carry out the following diagnostics. • Cyclic Voltammograms under N2
The atmospheric pressure decreases with altitude and so labs such as those at NREL, Golden, CO (~6000 ft, ~83 kPa) have to apply a correction for limiting current as well as kinetics so that the data is normalized to 100 kPa O2. Limiting currents are expected to be ~5.7 mA/cm2 @ 1600 rpm when corrected to 100 kPa O2.
0.05–1.2 V, 100 mV/s, ~50 cycles, Pt/C, 25oC, N2
Conditioning protocol may have to be varied with electrocatalyst material. Conditioning is complete when the CV becomes invariant with time, cycles. 8
Date: Tuesday, March 12, 2013
https:///hydrogenandfuelcells/webinars.html
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Thin-film RDE
Dissolved O2 Pt/C | Nafion | Acid Acid Flooded pores Electrode (< 0.1 µm) Perchloric Acid: H+ Ionomer: Binder, Disp. Liquid Electrolyte Scan Rate: ~20 mV/s 10’s of mg Cat L = 4–36 µgPt/cm2
Kocha, S. S., et al., "Influence of Nafion on the Electrochemical Activity of Pt-based Electrocatalysts." ECS Trans. 2012, 50.
3
Information Obtainable from RDE Measurements
RDE Analysis
Ring held at 1.2 V
IL = 5.7 mA/cm2
9
RDE Test Protocol
Voltage Profile Protocol 0.90V 1.0 V
0.0 V I@ 0.90 V Protocol parameters such as: Scan Direction, Scan Rate, and Voltage Range will affect the measured catalyst activity.
5) Electrocatalyst Durability using RDE Measurements 6) Summary
2
Background
PEMFC MEA
O2 Flow Pt/C | Nafion Gas & H2O, pores Electrode (5–15 µm) Nafion Ionomer Ionomer: H+ 100 % RH 15 min/point 100’s of mg Cat L = 0.2–0.4 mgPt/cm2
0.90 V, 20 mV/s, 0–1.0 V, 1600 rpm, cathodic scan, 25oC, 0.1M HClO4, iR corrected, background current corrrected & corrected to 100 kPa reaction order w.r.t O2 of 0.85.
• • • • • • • • • • • •
HUPD ECA (m2/g) CO Chemisorption ECA (m2/g) Cu UPD ECA (m2/g) Double Layer Capacitance Pseudo-Capacitance (oxide coverage) Onset potential of support corrosion Short term durability for thousands of cycles Electrocatalyst specific and mass Activity • Poly-Pt, Pt/C, Pt-alloy/C, Pt core-shell/C, Extended thin films, NPGM Reaction Order w.r.t. PO2 Tafel slopes Effect of contaminants in electrolyte or reactant gases Electrolyte anion adsorption
10
µA/cm2Pt m2/gPt mA/mgPt
Corrections Applied to ORR I-V Curves
Background current correction
At lower potential scan rates, the effect of impurities and the formation of surface oxides suppress the measured ORR activity; at scan rates above 20mV s-1, capacitive current effects are higher. The background current is measured by running the ORR sweep profile (e.g., 1.03 V→0.05 V→1.03 V at 5 and 20 mV s-1 and 1600 rpm) in N2–purged 0.1 M HClO4 either before or after the ORR measurements to account for capacitive current contributions. This background current is subtracted from the experimental ORR current to eliminate any contributions of capacitive current.
• I–V Curves under O2
• Peroxide Generation using Ring disc (RRDE) • Complementary Techniques
• EIS, EQCN, etc.,
4
Experimental Aspects of RDE Testing
5
Electrochemical Set-up/Glassware Cleaning
Concentrated Acid/Oxidant
Boiling in DI Water
Contamination of cell/electrolyte poisons the catalyst and is one of the primary reasons for low and scattered activity data.
6
Ink Formulation, Electrode Preparation
Bath Sonicator Nanobalance
Horn Sonicator
Ink Deposition
Kocha, S. S., et al., ECS Trans. 2012, 50.
7
RDE Conditioning or Break-in
Outline
1) 2) 3) 4) Background Experimental Aspects of RDE Testing Basic Measurement Technique & Analysis Parameters Affecting RDE Activity Measurements