Energy Engineering - Electrochemical Energy Conversion and Storage

Theoretical questions - 2018

Etc

ECCS – Examples of theory questions Basic (students must know to pass the exam) 1. Draw the electrical potential in the double layer for a HOR in equilibrium 2. Draw the electrical potential in the double layer for a ORR in equilibrium 3. Is !"#$−!#& positive or negative for HOR in equilibrium in a PEMFC? Why? 4. Is !"#$−!#& positive or negative for ORR in equilibrium in a PEMFC? Why? 5. Write the Nernstian equilibrium potential for an electrochemical cell based on H2/O2 as a function of chemical activities 6. Is the electrode overpotential positive or negative when HOR occurs? Why? 7. Is the electrode overpotential positive or negative when ORR occurs? Why? 8. Write the Butler-Volmer kinetics equation for HOR 9. Write the Tafel equation for ORR 10. Write an equation for electroneutrality in a generic electrolyte 11. Write the Nernst-Plank equation for mass transport in a generic electrolyte 12. Write the total current density equation in a generic electrolyte 13. Write Faraday’s law for electrolyte and reactants 14. Depict the polarization curve of a PEMFC with reasonable values 15. Depict the polarization curve of a PEM electrolyzer with reasonable values 16. Describe how the triple phase boundary is achieved in a catalyst layer of a PEMFC 17. List the more common materials adopted in the components of a MEA for PEMFC 18. List the more common materials adopted in the components of a MEA for PEM electrolyzer 19. Write the electrochemical reactions occurring in a PEMFC and the typical operating voltage range 20. Write the electrochemical reactions occurring in an alkaline electrolyzer and the typical operating voltage range 21. Write an example of electrochemical reactions occurring in a Lithium-ion battery and the typical operating voltage range 22. Depict the discharge curve of a Lithium-ion battery with reasonable values 23. Depict the charge curve of a Lithium-ion battery with reasonable values 24. Write the Nernstian equilibrium potential for Lithium-ion battery as a function of chemical activities 25. Define the efficiency for a battery, indicating how SoC varies 26. Indicate the typical energy density (Wh/kg) of a Lithium-ion battery pack and power density of a PEMFC system (kW/dm3) for automotive application 27. Indicate the typical cost targets for a Lithium-ion battery pack (€/kWh) and a PEMFC system (€/kW) for automotive application 28. Which chemical species are an adequate fuel for a SOFC? Intermediate (students must know to reach mark till 30, whether reports or projects criteria are satisfied) 1. Draw the electrical potential in the double layer when HOR occurs and compare with the equilibrium one 2. Draw the electrical potential in the double layer when ORR occurs and compare with the equilibrium one 3. Draw the electrical potential in the double layer when HER occurs and compare with the equilibrium one 4. Draw the electrical potential in the double layer when OER occurs and compare with the equilibrium one 5. Write !"#$−!#& as a function of reactants and products activities for a HOR in equilibrium 6. Write !"#$−!#& as a function of reactants and products activities for a ORR in equilibrium 7. Is the electrode overpotential positive or negative when HOR occurs? Demonstrate analyzing ' 8. Is the electrode overpotential positive or negative when ORR occurs? Demonstrate analyzing ' 9. Is the electrode overpotential positive or negative when HER occurs? Demonstrate analyzing ' 10. Is the electrode overpotential positive or negative when OER occurs? Demonstrate analyzing ' 11. Represent on the same graph (=*(,+.) the Butler-Volmer and Tafel equations 12. Show how current density equation simplifies in solid electrolyte with fixed charge 13. Represent impedance spectrum of a PEMFC in Nyquist plot and indicate at which frequencies information on membrane resistance can be obtained 14. Depict the polarization curve of a PEMFC and indicate the contributions of anode, cathode and membrane varying current density with reasonable values 15. Depict the polarization curve of a PEM electrolyzer and indicate the contributions of anode, cathode and membrane varying current density with reasonable values 16. Depict the polarization curve of an alkaline electrolyzer and indicate the contributions of anode, cathode and membrane varying current density with reasonable values 17. Depict two polarization curves of a PEMFC fed respectively with pure O2 and air and shortly comment 18. Define and depict the thermodynamic and electrochemical efficiencies of a PEMFC as a function of current density 19. List the major degradation mechanisms in a PEMFC 20. Depict two polarization curves of a PEMFC before and after a considerable cathode ECSA loss 21. Draw the electrolyte potential including the double layer domain in a PEMFC during both operation and open circuit 22. Draw the electrolyte potential including the double layer domain in a PEM electrolyzer during both operation and open circuit 23. Depict the discharge curves of a Lithium-ion battery at different C-rates, indicating the contribution of different losses 24. Depict the charge curves of a Lithium-ion battery at different C-rates, indicating the contribution of different losses 25. Show how operating voltage limits could reduce maximum available capacity at high C-rate 26. Depict the effect of degradation on the discharge curve and capacity of a battery 27. List the main advantages and issues of Vanadium Flow Battery compared to Lithium-ion battery 28. List the main advantages and issues of Solid Oxide fuel cell compared to PEM fuel cell 29. Write the electrochemical reactions occurring in a SOFC and the chemical reaction of internal reforming 30. Write the electrochemical reactions occurring in a Vanadium Flow Battery and shortly describe the cross-contamination 31. Demonstrate that an electrochemical cell can extract a work equal to −0'1#23$456 from a chemical disequilibrium 32. Show that Butler-Volmer equation is consistent at equilibrium with Nernst equation 33. Write an equation for charge conservation in the reactive domain including the double layer capacitance 34. Draw the electrical potential profile and the diffusive and migration contributions of positive and negative ions to current in a H2/O2 cell with sulfuric acid electrolyte 35. Derive the Nernst-Planck equation for mass transport in an electrolyte from a gradient of electrochemical potential 36. Represent impedance spectrum of a PEMFC in Nyquist plot and indicate qualitatively the information obtained at different frequencies 37. Represent impedance spectrum of a PEMFC in Nyquist plot and indicate the features related to proton and oxygen transport phenomena 38. Depict a Cyclic Voltammogram for a PEMFC cathode electrode and indicate where ECSA can be estimated 39. Depict in the Nyquist plot two impedance spectra of a PEMFC operating at the same current density fed respectively with pure O2 and air and shortly comment 40. Depict the variation of polarization curves and impedance spectra of a PEMFC after a considerable cathode ECSA loss and an increase of membrane resistance 41. Motivate why voltage limits are adopted in Lithium-ion battery 42. Explain what SEI is and its effect in Lithium-ion battery operation 43. Why OCV measurement is not a reliable method to determine SoC of a Lithium-ion battery during real operation? 44. What is the battery management system (BMS) devoted to? 45. What are the main aspects of operation that affect Lithium-ion battery degradation? Difficult (students must know to aim at 30 e lode) 1. Derive the forward reaction rate of HOR from ∆'89: (the electrochemical Gibbs free energy of the rate determining step) 2. Depict a scheme representing how C corrosion can occurs at the start-up of a PEMFC 3. Derive Nernst-Plank equation for electrolyte