Fuel cells represent a key technology for the decarbonization of the energy sector as they allow efficient conversion of molecular fuels into electrical energy. Among the fuel cell technologies, Proton Exchange Membrane Fuel Cells (PEMFCs) are already deployed in the mobility sector due to the high gravimetric and volumetric power density that can be developed by such devices. However, state-of-the-art solutions for PEMFCs make a widespread use of perfluorinated compounds also known as per- and polyfluoroalkyl substances (PFAS) such as perfluorosulfonic acids (PFSA) and polytetrafluorethylene (PTFE) posing a limitation to the upscaling of this technology due to environmental, health and production cost concerns. Additionally, a ban of PFAS by political regulations within the European Union is more than likely in the near future. In this work, a fluorine-free proton exchange membrane has been studied with respect to the compatibility with state-of-the-art catalyst layers. The membranes consist of a PE-reinforced blend of sulfonated poly-phenylene sulfones (S-240, EW = 240 g mol−1) and polybenzimidazole (sPPS:PBI-OO). Scope of the study is to assess the compatibility of solid electrolyte and catalysts for Membrane- Electrodes Assemblies (MEAs) with reduced content of perfluorinated compounds. Extremely thin sPPS:PBI-OO membranes (5−10μm) are used to prepare MEAs by means of high-throughput processing technologies. In situ characterizations are performed through polarization curves, galvanostatic EIS, Cyclic Voltammetry (CV) and limiting current measurements. Afterwards, samples have been characterized by means of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) to determine aging trends. It was found that S-240 is mobilized under fuel cell operating conditions, causing ionomer wash out and poisoning of the catalyst layer, leading to a 62 % reduction of Electrochemical Surface Area (ECSA) within the cathode catalyst layer and a 55 %increase in limiting current losses related to oxygen diffusion through ionomer layers. Moreover, direct contact of catalyst layer and membrane leads to premature soaking of the fuel cells. However, these membranes displayed advanced performance with respect to the ionic conductivity, with a minimum value of 24.8 mΩcm2. Additionally, a preparation route involving the addition of a Nafion layer between sPPS:PBI-OO membranes and catalyst layers was optimized. This route allows to stabilize performance during conditioning procedures, prevent catalyst poisoning and reduce water induced gas transport resistance by up to 50 % at 40 °C and 100 % RH. Amaximum power output of 2.46 W cm−2 was achieved while operating in H2/O2 at 80 °C and 100 % RH with 2.2 bar of backpressure on both electrodes and a gas flow of 2 and 5 Nl min−1 for anode and cathode, respectively. This indicates that once fluorine-free mitigation strategies will be developed to prevent sPPS from leaching, good performance will be accessible.

Fuel cells represent a key technology for the decarbonization of the energy sector as they allow efficient conversion of molecular fuels into electrical energy. Among the fuel cell technologies, Proton Exchange Membrane Fuel Cells (PEMFCs) are already deployed in the mobility sector due to the high gravimetric and volumetric power density that can be developed by such devices. However, state-of-the-art solutions for PEMFCs make a widespread use of perfluorinated compounds also known as per- and polyfluoroalkyl substances (PFAS) such as perfluorosulfonic acids (PFSA) and polytetrafluorethylene (PTFE) posing a limitation to the upscaling of this technology due to environmental, health and production cost concerns. Additionally, a ban of PFAS by political regulations within the European Union is more than likely in the near future. In this work, a fluorine-free proton exchange membrane has been studied with respect to the compatibility with state-of-the-art catalyst layers. The membranes consist of a PE-reinforced blend of sulfonated poly-phenylene sulfones (S-240, EW = 240 g mol−1) and polybenzimidazole (sPPS:PBI-OO). Scope of the study is to assess the compatibility of solid electrolyte and catalysts for Membrane- Electrodes Assemblies (MEAs) with reduced content of perfluorinated compounds. Extremely thin sPPS:PBI-OO membranes (5−10μm) are used to prepare MEAs by means of high-throughput processing technologies. In situ characterizations are performed through polarization curves, galvanostatic EIS, Cyclic Voltammetry (CV) and limiting current measurements. Afterwards, samples have been characterized by means of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) to determine aging trends. It was found that S-240 is mobilized under fuel cell operating conditions, causing ionomer wash out and poisoning of the catalyst layer, leading to a 62 % reduction of Electrochemical Surface Area (ECSA) within the cathode catalyst layer and a 55 %increase in limiting current losses related to oxygen diffusion through ionomer layers. Moreover, direct contact of catalyst layer and membrane leads to premature soaking of the fuel cells. However, these membranes displayed advanced performance with respect to the ionic conductivity, with a minimum value of 24.8 mΩcm2. Additionally, a preparation route involving the addition of a Nafion layer between sPPS:PBI-OO membranes and catalyst layers was optimized. This route allows to stabilize performance during conditioning procedures, prevent catalyst poisoning and reduce water induced gas transport resistance by up to 50 % at 40 °C and 100 % RH. Amaximum power output of 2.46 W cm−2 was achieved while operating in H2/O2 at 80 °C and 100 % RH with 2.2 bar of backpressure on both electrodes and a gas flow of 2 and 5 Nl min−1 for anode and cathode, respectively. This indicates that once fluorine-free mitigation strategies will be developed to prevent sPPS from leaching, good performance will be accessible.

Study of the interfacial stability between Proton Exchange Membranes with reduced perfluorinated content and PFSA based catalyst electrodes.

FINCO, MATTEO
2022/2023

Abstract

Fuel cells represent a key technology for the decarbonization of the energy sector as they allow efficient conversion of molecular fuels into electrical energy. Among the fuel cell technologies, Proton Exchange Membrane Fuel Cells (PEMFCs) are already deployed in the mobility sector due to the high gravimetric and volumetric power density that can be developed by such devices. However, state-of-the-art solutions for PEMFCs make a widespread use of perfluorinated compounds also known as per- and polyfluoroalkyl substances (PFAS) such as perfluorosulfonic acids (PFSA) and polytetrafluorethylene (PTFE) posing a limitation to the upscaling of this technology due to environmental, health and production cost concerns. Additionally, a ban of PFAS by political regulations within the European Union is more than likely in the near future. In this work, a fluorine-free proton exchange membrane has been studied with respect to the compatibility with state-of-the-art catalyst layers. The membranes consist of a PE-reinforced blend of sulfonated poly-phenylene sulfones (S-240, EW = 240 g mol−1) and polybenzimidazole (sPPS:PBI-OO). Scope of the study is to assess the compatibility of solid electrolyte and catalysts for Membrane- Electrodes Assemblies (MEAs) with reduced content of perfluorinated compounds. Extremely thin sPPS:PBI-OO membranes (5−10μm) are used to prepare MEAs by means of high-throughput processing technologies. In situ characterizations are performed through polarization curves, galvanostatic EIS, Cyclic Voltammetry (CV) and limiting current measurements. Afterwards, samples have been characterized by means of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) to determine aging trends. It was found that S-240 is mobilized under fuel cell operating conditions, causing ionomer wash out and poisoning of the catalyst layer, leading to a 62 % reduction of Electrochemical Surface Area (ECSA) within the cathode catalyst layer and a 55 %increase in limiting current losses related to oxygen diffusion through ionomer layers. Moreover, direct contact of catalyst layer and membrane leads to premature soaking of the fuel cells. However, these membranes displayed advanced performance with respect to the ionic conductivity, with a minimum value of 24.8 mΩcm2. Additionally, a preparation route involving the addition of a Nafion layer between sPPS:PBI-OO membranes and catalyst layers was optimized. This route allows to stabilize performance during conditioning procedures, prevent catalyst poisoning and reduce water induced gas transport resistance by up to 50 % at 40 °C and 100 % RH. Amaximum power output of 2.46 W cm−2 was achieved while operating in H2/O2 at 80 °C and 100 % RH with 2.2 bar of backpressure on both electrodes and a gas flow of 2 and 5 Nl min−1 for anode and cathode, respectively. This indicates that once fluorine-free mitigation strategies will be developed to prevent sPPS from leaching, good performance will be accessible.
2022
Study of the interfacial stability between Proton Exchange Membranes with reduced perfluorinated content and PFSA based catalyst electrodes.
Fuel cells represent a key technology for the decarbonization of the energy sector as they allow efficient conversion of molecular fuels into electrical energy. Among the fuel cell technologies, Proton Exchange Membrane Fuel Cells (PEMFCs) are already deployed in the mobility sector due to the high gravimetric and volumetric power density that can be developed by such devices. However, state-of-the-art solutions for PEMFCs make a widespread use of perfluorinated compounds also known as per- and polyfluoroalkyl substances (PFAS) such as perfluorosulfonic acids (PFSA) and polytetrafluorethylene (PTFE) posing a limitation to the upscaling of this technology due to environmental, health and production cost concerns. Additionally, a ban of PFAS by political regulations within the European Union is more than likely in the near future. In this work, a fluorine-free proton exchange membrane has been studied with respect to the compatibility with state-of-the-art catalyst layers. The membranes consist of a PE-reinforced blend of sulfonated poly-phenylene sulfones (S-240, EW = 240 g mol−1) and polybenzimidazole (sPPS:PBI-OO). Scope of the study is to assess the compatibility of solid electrolyte and catalysts for Membrane- Electrodes Assemblies (MEAs) with reduced content of perfluorinated compounds. Extremely thin sPPS:PBI-OO membranes (5−10μm) are used to prepare MEAs by means of high-throughput processing technologies. In situ characterizations are performed through polarization curves, galvanostatic EIS, Cyclic Voltammetry (CV) and limiting current measurements. Afterwards, samples have been characterized by means of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) to determine aging trends. It was found that S-240 is mobilized under fuel cell operating conditions, causing ionomer wash out and poisoning of the catalyst layer, leading to a 62 % reduction of Electrochemical Surface Area (ECSA) within the cathode catalyst layer and a 55 %increase in limiting current losses related to oxygen diffusion through ionomer layers. Moreover, direct contact of catalyst layer and membrane leads to premature soaking of the fuel cells. However, these membranes displayed advanced performance with respect to the ionic conductivity, with a minimum value of 24.8 mΩcm2. Additionally, a preparation route involving the addition of a Nafion layer between sPPS:PBI-OO membranes and catalyst layers was optimized. This route allows to stabilize performance during conditioning procedures, prevent catalyst poisoning and reduce water induced gas transport resistance by up to 50 % at 40 °C and 100 % RH. Amaximum power output of 2.46 W cm−2 was achieved while operating in H2/O2 at 80 °C and 100 % RH with 2.2 bar of backpressure on both electrodes and a gas flow of 2 and 5 Nl min−1 for anode and cathode, respectively. This indicates that once fluorine-free mitigation strategies will be developed to prevent sPPS from leaching, good performance will be accessible.
fluorine-free PEM
PEMFC
polymer electrolyte
interface stability
membrane for PEMFC
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12608/45463