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EECS – Prof. A. Casalegno – 13th July 2017 1 Basic Part (3 points per questions, minimum score 12) 1. Draw the electrical potential in the double layer for a ORR in equilibrium 2. Write the Nernst-Plank equation for mass transport of an ion in a generic electrolyte 3. Depict the discharge curve of a Lithium-ion battery with reasonable values 4. Write the Nernst equilibrium potential for Lithium-ion battery as a function of chemical activities Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 13th July 2017 2 Exercise 1 A PEMFC stack supplies at full load 300 A at 180 V with an efficiency equal to 46% (LHV=120 MJ/kg). Assuming that 4% of H2 is wasted and its performance follows the reported polarization curve, estimate the number of cell, cell area and efficiency at 33% current load. Exercise 2 A 3 Ah Li-ion battery operates at ambient pressure and temperature, following the operation reported in figure. Assuming that: 1. Tafel kinetics is valid for both electrodes 2. ion and mass transport effects in electrodes are negligible 3. chemical activities of reactants are equal to the state of charge 4. electrolyte resistance is equal to 0.02 Ω 5. transfer coefficients of both electrodes during charge are equal to 0.5 Define a meaningful efficiency and estimate its value. ∆𝑉 0 𝑗 0.78 V 0.6 V 0.6 A cm-2 1.8 A cm-2 𝑡𝑖𝑚𝑒 0 (SoC=80%) 30 𝑚𝑖𝑛 ∆𝑉 60 𝑚𝑖𝑛 discharge at C-rate 1 4𝑉 3.9𝑉 4.2𝑉 90 𝑚𝑖𝑛 charge at C-rate 0.5 EECS – Prof. A. Casalegno – 13th July 2017 3 Intermediate Part (3 points per questions) 1. Is the electrode overpotential positive or negative when HER occurs? Demonstrate analyzing 𝐺 2. Define and depict the thermodynamic efficiency with and without auxiliary consumption and the electrochemical efficiency of a PEMFC as a…