The utilization of clean energy, such as solar and wind energy, is a field of great prospect since it not only facilitates more sustainable energy consumption, but also a effective solution for providing electricity to millions of people of the world. One of the issues of the utilizing cleaning energy is the storage of the energy generated form clean power sources. Solution for the storage of clean electricity includes the utilization of solid oxide electrolysis cells(SOEC), which is an energy storage device that can turn electrical energy to more stable chemical energy through exploiting electrochemical reactions. The design of an effective SOEC however, faces a challenge, which is maintaining the efficiency of power generation throughout extended periods of usage.(8) Extensive research has been carried out on reaching higher current density as well as achieving high durability of the SOEC. (2) The objective of this project is to use input data from a well-vetted accelerated testing approach that combines electrochemical accelerated life testing, which means testing the material under conditions in excess to it’s normal service condition, with quantitative microstructural and chemical evaluation to eventually develop mechanistic degradation models that can realistically predict long-term Solid Oxide Electrolysis Cell durability.
A typical SOEC consists of three components: the cathode, where the water takes in free electrons and is decomposed into hydrogen gas and oxygen ion; the anode, both where the oxidation reaction happens and where the two oxygen ions generate four free electrons and turns into one oxygen gas particle; as well as the electrolyte, which acts as bridge between the anode and the cathode and allows the oxygen ion to travel through from the cathode to the anode. (4,6)
The most commonly used SOEC cathode material is a two phase nickel and yttria-stabilized zirconia (YSZ) composite of YSZ particles and nickel atoms. (7) Yttria–stabilized zirconia is a ceramic fabricated by adding yttrium oxide at a normal temperature to zirconium oxide crystal in order to stabilize it. Both the YSZ particles and the Nickel atom serve as catalysts in the anode oxidation reaction, facilitating the generation of electrons. Therefore, the efficiency of the SOFC is dependent on the area where the surface of the YSZ particles, the surface of the Nickel particles, as well as the porous gas areas of the anode intersects. The more area where the three phases intersect in the anode material, the more efficient the fuel cell is.
Maintaining a low degradation rate of the SOECs is a key challenge in achieving long term SOEC durability. Fundamental studies of degradation mechanisms are ongoing, including electrode degradation via particle coarsening. (Call et al. 2016) After extended periods of usage, nickel atoms may experience coarsening, where multiple separate Nickel atoms form thicker and rougher clusters of nickel. Because of coarsening, the micro-structure of the anode material is changed and the area where the three phases of material intersects is diminished, thereby decreasing the efficiency and performance of power density of the SOEC. It is crucial for the degradation rate for the SOEC to be low so that it can be applied in a real-life setting for considerably extended periods of time (> 40,000 hours).(1)
The Barnett group at Northwestern University his worked extensively on understanding degradation mechanisms in SOECs for many years and have developed new cell designs for SOEC cathode material structure. One of the new materials is called the LSM-YSZ composite oxygen electrode. The LSM-YSZ composite is a composite consists of the same YSZ that is used in the two phase nickel and yttria-stabilized zirconia (YSZ) composite, combined with LSM, which is (La0.80Sr0.20)0.95MnO3-X. Performance testing for this kind of new material has already started. For example, experiments concerning the quantification of the degradation rate versus current density have already been conducted. However, more experiments needs to be carried out to further identify and characterize the electrochemical mechanisms of this new material, including how it compares to the former cathode material Ni/YSZ.
The procedure that I will use in this experiment includes three parts: 1) Fabrication of fuel cell samples. 2) Performing electrochemical life testing on cell samples. 3) Carrying out microstructural evaluation comparing pre-test and post-test cells.
The process of fabricating cells includes using purchased LSM-YSZ composite and Ni/YSZ samples, and utilizing skills such as tape casting, as well as screen printing, to making different fuel cell samples. I need to use tape casting to make the electrolytes by mixing the given materials and compress them into tapes. For screen printing, I would use a mesh to transfer conducting materials on the anode and cathode cells. Two kinds to samples will be fabricated: regular full cells with anode-electrolyte-cathode configuration; as well as the symmetric cell with an anode-electrolyte-anode configuration to test specific degradations in the electrolyte. I will fabricate the cell according to the recipe of materials given and use the tape casting machine to fabricate thin layers of electrolyte and electrode. Then I will use screen printing to stick the electrolyte and electrode together to from cell samples.
During the life-testing process, I will place the fabricated cells in an environment similar to the cell’s working environment. Symmetric cell tests will be used to isolate degradation a specific electrode, whereas full cells will show electrolyte and overall cell degradation.(Appendix 1) Both kinds of electrode materials will go through the same simulation environment for accelerated-life-testing. In our experiment setting I will be using an 800 °C operating temperature, a 0.8 A/cm2 current density and a 3% humidified hydrogen gas (3% of the gas is water) for symmetric cells, and a 1A/cm2 current density and a 50% humidified hydrogen gas for the full button cells.
Microstructural evaluation will be conducted both before and after the electrochemical life testing. The main procedure of the evaluation utilizes the electrochemical impedance spectroscopy (EIS). The EIS utilizes the trajectory of a moving electron in an electric field to detect the inner structure of a given material. Through using EIS, I hope to collect data that can shows the pattern of structural changes within the SOEC material. An example of EIS is given in appendix one. The different shapes of the plots reflect different micro-structures inside the electrode. A larger the curve means that there is larger resistance, and that implies that more material is condensed. If the new LSM-YSZ material shows a lower rate of resistance increase compared to that of the old Ni/YSZ material, I may conclude the new material as superior to the old one in terms of durability. (see appendix 2)
I joined the Barnett lab in late January, and I have been working with postdoctoral fellow Dr. Beom-Kyeong Park. Under the guidance of Dr. Park, I am currently learning the key procedures of experiments that we will be conducting in the summer. In regards to schoolwork, I am dedicated to further my studies in the material science field and I am planning to take MAT_SCI 301 in the spring quarter to gain greater familiarity. Furthermore, I have previous experiences in chemistry labs and have done experiments dealing with instruments such as the infrared spectroscopy. I have worked in the Chinese Academy of Sciences: Research Center for Eco-Environmental Sciences during my high school career as part of a group that research the photo catalyst effect of silver chloride enwrapped silver grafted on nitrogen-doped reduced graphene oxide. I believe my past experiences, as well as my in-class and extracurriculars can continue help me develop problem-solving abilities as well as scientific analytic skill, and help me step into the energy industry which has been my major goal.
Characterization and Accelerated Life Testing of a New Solid Oxide Electrolysis Cell
The utilization of clean energy, such as solar and wind energy, is a field of great prospect since it not only facilitates more sustainable energy consumption, but also a effective solution for providing electricity to millions of people of the world. One of the issues of the utilizing cleaning energy is the storage of the energy generated form clean power sources. Solution for the storage of clean electricity includes the utilization of solid oxide electrolysis cells(SOEC), which is an energy storage device that can turn electrical energy to more stable chemical energy through exploiting electrochemical reactions. The design of an effective SOEC however, faces a challenge, which is maintaining the efficiency of power generation throughout extended periods of usage.(8) Extensive research has been carried out on reaching higher current density as well as achieving high durability of the SOEC. (2) The objective of this project is to use input data from a well-vetted accelerated testing approach that combines electrochemical accelerated life testing, which means testing the material under conditions in excess to it’s normal service condition, with quantitative microstructural and chemical evaluation to eventually develop mechanistic degradation models that can realistically predict long-term Solid Oxide Electrolysis Cell durability.
A typical SOEC consists of three components: the cathode, where the water takes in free electrons and is decomposed into hydrogen gas and oxygen ion; the anode, both where the oxidation reaction happens and where the two oxygen ions generate four free electrons and turns into one oxygen gas particle; as well as the electrolyte, which acts as bridge between the anode and the cathode and allows the oxygen ion to travel through from the cathode to the anode. (4,6)
The most commonly used SOEC cathode material is a two phase nickel and yttria-stabilized zirconia (YSZ) composite of YSZ particles and nickel atoms. (7) Yttria–stabilized zirconia is a ceramic fabricated by adding yttrium oxide at a normal temperature to zirconium oxide crystal in order to stabilize it. Both the YSZ particles and the Nickel atom serve as catalysts in the anode oxidation reaction, facilitating the generation of electrons. Therefore, the efficiency of the SOFC is dependent on the area where the surface of the YSZ particles, the surface of the Nickel particles, as well as the porous gas areas of the anode intersects. The more area where the three phases intersect in the anode material, the more efficient the fuel cell is.
Maintaining a low degradation rate of the SOECs is a key challenge in achieving long term SOEC durability. Fundamental studies of degradation mechanisms are ongoing, including electrode degradation via particle coarsening. (Call et al. 2016) After extended periods of usage, nickel atoms may experience coarsening, where multiple separate Nickel atoms form thicker and rougher clusters of nickel. Because of coarsening, the micro-structure of the anode material is changed and the area where the three phases of material intersects is diminished, thereby decreasing the efficiency and performance of power density of the SOEC. It is crucial for the degradation rate for the SOEC to be low so that it can be applied in a real-life setting for considerably extended periods of time (> 40,000 hours).(1)
The Barnett group at Northwestern University his worked extensively on understanding degradation mechanisms in SOECs for many years and have developed new cell designs for SOEC cathode material structure. One of the new materials is called the LSM-YSZ composite oxygen electrode. The LSM-YSZ composite is a composite consists of the same YSZ that is used in the two phase nickel and yttria-stabilized zirconia (YSZ) composite, combined with LSM, which is (La0.80Sr0.20)0.95MnO3-X. Performance testing for this kind of new material has already started. For example, experiments concerning the quantification of the degradation rate versus current density have already been conducted. However, more experiments needs to be carried out to further identify and characterize the electrochemical mechanisms of this new material, including how it compares to the former cathode material Ni/YSZ.
The procedure that I will use in this experiment includes three parts: 1) Fabrication of fuel cell samples. 2) Performing electrochemical life testing on cell samples. 3) Carrying out microstructural evaluation comparing pre-test and post-test cells.
The process of fabricating cells includes using purchased LSM-YSZ composite and Ni/YSZ samples, and utilizing skills such as tape casting, as well as screen printing, to making different fuel cell samples. I need to use tape casting to make the electrolytes by mixing the given materials and compress them into tapes. For screen printing, I would use a mesh to transfer conducting materials on the anode and cathode cells. Two kinds to samples will be fabricated: regular full cells with anode-electrolyte-cathode configuration; as well as the symmetric cell with an anode-electrolyte-anode configuration to test specific degradations in the electrolyte. I will fabricate the cell according to the recipe of materials given and use the tape casting machine to fabricate thin layers of electrolyte and electrode. Then I will use screen printing to stick the electrolyte and electrode together to from cell samples.
During the life-testing process, I will place the fabricated cells in an environment similar to the cell’s working environment. Symmetric cell tests will be used to isolate degradation a specific electrode, whereas full cells will show electrolyte and overall cell degradation.(Appendix 1) Both kinds of electrode materials will go through the same simulation environment for accelerated-life-testing. In our experiment setting I will be using an 800 °C operating temperature, a 0.8 A/cm2 current density and a 3% humidified hydrogen gas (3% of the gas is water) for symmetric cells, and a 1A/cm2 current density and a 50% humidified hydrogen gas for the full button cells.
Microstructural evaluation will be conducted both before and after the electrochemical life testing. The main procedure of the evaluation utilizes the electrochemical impedance spectroscopy (EIS). The EIS utilizes the trajectory of a moving electron in an electric field to detect the inner structure of a given material. Through using EIS, I hope to collect data that can shows the pattern of structural changes within the SOEC material. An example of EIS is given in appendix one. The different shapes of the plots reflect different micro-structures inside the electrode. A larger the curve means that there is larger resistance, and that implies that more material is condensed. If the new LSM-YSZ material shows a lower rate of resistance increase compared to that of the old Ni/YSZ material, I may conclude the new material as superior to the old one in terms of durability. (see appendix 2)
I joined the Barnett lab in late January, and I have been working with postdoctoral fellow Dr. Beom-Kyeong Park. Under the guidance of Dr. Park, I am currently learning the key procedures of experiments that we will be conducting in the summer. In regards to schoolwork, I am dedicated to further my studies in the material science field and I am planning to take MAT_SCI 301 in the spring quarter to gain greater familiarity. Furthermore, I have previous experiences in chemistry labs and have done experiments dealing with instruments such as the infrared spectroscopy. I have worked in the Chinese Academy of Sciences: Research Center for Eco-Environmental Sciences during my high school career as part of a group that research the photo catalyst effect of silver chloride enwrapped silver grafted on nitrogen-doped reduced graphene oxide. I believe my past experiences, as well as my in-class and extracurriculars can continue help me develop problem-solving abilities as well as scientific analytic skill, and help me step into the energy industry which has been my major goal.
Appendix 1:
This graph shows the change of total resistance of a La0.6Sr0.4Fe0.8Co0.2O3-δ Oxygen Electrodes in respect to time under different current densities. The change in resistance is a result of the coreasening of the electrode material. In the context of this graph, as the current density increases, the rate of change of the total resistance in respect time increases, which means that the material is degrading at a faster rate. (5)
Appendix 2:
This figure shows Impedance plots of the LSM-ESB electrode (a type of solid oxide fuel cell electrode material) under different ambient temperatures: a) 600°C, b)650°C, c) 700°C, d) 750°C, and e) 800°C. The different shapes of the plots reflect different micro-structures inside the electrode. A larger the curve means that there is larger resistance, and that implies that more material is condensed. In this case (3)
Reference Page:
1. Call, A. V., Railsback, J. G., Wang, H., & Barnett, S. A. (2016). Degradation of nano-scale cathodes: a new paradigm for selecting low-temperature solid oxide cell materials. Physical Chemistry Chemical Physics, 18(19), 13216-13222.
2. Hughes, G. A., Railsback, J. G., Yakal-Kremski, K. J., Butts, D. M., & Barnett, S. A. (2015). Degradation of (La0.8Sr0.2)0.98MnO3−δ–Zr0.84Y0.16O2−γ composite electrodes during reversing current operation. Faraday Discussions,182, 365-377.
3. Murray, E. P., Tsai, T., & Barnett, S. A. (1998). Oxygen transfer processes in (La,Sr)MnO3/Y2O3-stabilized ZrO2 cathodes: an impedance spectroscopy study. Solid State Ionics, 110(3-4), 235-243.
4. Haile, S. M. (2003). Fuel cell materials and components. Acta Materialia, 51(19), 5981 -6000.
5. Railsback, J. G., Wang, H., Liu, Q., Lu, M. Y., & Barnett, S. A. (2017). Degradation of La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3-δ Oxygen Electrodes on Ce 0.9 Gd 0.1 O 2-δ Electrolytes during Reversing Current Operation. Journal of The Electrochemical Society, 164(10).
6. Ni, M., Leung, M., & Leung, D. (2008). Technological development of hydrogen production by solid oxide electrolyzer cell (SOEC). International Journal of Hydrogen Energy, 33(9), 2337-2354. doi:10.1016/j.ijhydene.2008.02.048
7. Souza, S. D. (1997). Reduced-Temperature Solid Oxide Fuel Cell Based on YSZ Thin-Film Electrolyte. Journal of The Electrochemical Society, 144(3)
8. Laguna-Bercero, M. (2012). Recent advances in high temperature electrolysis using solid oxide fuel cells: A review. Journal of Power Sources, 203, 4-16.
Appendix 1:
This graph shows the change of total resistance of a La0.6Sr0.4Fe0.8Co0.2O3-δ Oxygen Electrodes in respect to time under different current densities. The change in resistance is a result of the coreasening of the electrode material. In the context of this graph, as the current density increases, the rate of change of the total resistance in respect time increases, which means that the material is degrading at a faster rate. (5)
Appendix 2:
This figure shows Impedance plots of the LSM-ESB electrode (a type of solid oxide fuel cell electrode material) under different ambient temperatures: a) 600°C, b)650°C, c) 700°C, d) 750°C, and e) 800°C. The different shapes of the plots reflect different micro-structures inside the electrode. A larger the curve means that there is larger resistance, and that implies that more material is condensed. In this case (3)
Reference Page:
1. Call, A. V., Railsback, J. G., Wang, H., & Barnett, S. A. (2016). Degradation of nano-scale cathodes: a new paradigm for selecting low-temperature solid oxide cell materials. Physical Chemistry Chemical Physics, 18(19), 13216-13222.
2. Hughes, G. A., Railsback, J. G., Yakal-Kremski, K. J., Butts, D. M., & Barnett, S. A. (2015). Degradation of (La0.8Sr0.2)0.98MnO3−δ–Zr0.84Y0.16O2−γ composite electrodes during reversing current operation. Faraday Discussions,182, 365-377.
3. Murray, E. P., Tsai, T., & Barnett, S. A. (1998). Oxygen transfer processes in (La,Sr)MnO3/Y2O3-stabilized ZrO2 cathodes: an impedance spectroscopy study. Solid State Ionics, 110(3-4), 235-243.
4. Haile, S. M. (2003). Fuel cell materials and components. Acta Materialia, 51(19), 5981 -6000.
5. Railsback, J. G., Wang, H., Liu, Q., Lu, M. Y., & Barnett, S. A. (2017). Degradation of La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3-δ Oxygen Electrodes on Ce 0.9 Gd 0.1 O 2-δ Electrolytes during Reversing Current Operation. Journal of The Electrochemical Society, 164(10).
6. Ni, M., Leung, M., & Leung, D. (2008). Technological development of hydrogen production by solid oxide electrolyzer cell (SOEC). International Journal of Hydrogen Energy, 33(9), 2337-2354. doi:10.1016/j.ijhydene.2008.02.048
7. Souza, S. D. (1997). Reduced-Temperature Solid Oxide Fuel Cell Based on YSZ Thin-Film Electrolyte. Journal of The Electrochemical Society, 144(3)
8. Laguna-Bercero, M. (2012). Recent advances in high temperature electrolysis using solid oxide fuel cells: A review. Journal of Power Sources, 203, 4-16.