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EECS – Prof. A. Casalegno – 25th January 2019 1 Basic Part (3 points per questions, minimum score 12) 1. Write the Nernstian equilibrium potential for an electrochemical cell based on H2/O2 as a function of chemical activities 2. Write the Nernst-Plank equation for mass transport of an ion in a generic electrolyte 3. Define the efficiency for a battery during cycling operation, indicating SoC variation 4. Write Faraday’s law applied to electrolyte and both products in an alkaline electrolyzer Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 25th January 2019 2 Exercise 1 An automotive PEMFC stack, composed of 300 cells, supplies at full load 400 A at 195 V. Assuming that 3% of H2 is wasted and its performance follows the reported polarization curve, estimate the mass of H2 that is necessary to operate the stack at an average power of 19.2 kW for 720 Km at an average vehicle speed of 120 km/h. 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 0.8 V 0.65 V 0.4 A cm-2 2 A cm-2 𝑡𝑖𝑚𝑒 0 min (SoC=80%) 20 𝑚𝑖𝑛 ∆𝑉 50 𝑚𝑖𝑛 discharge at C-rate 1.5 3.5𝑉 3.3𝑉 3.8𝑉 80 𝑚𝑖𝑛 charge at C-rate 1 EECS – Prof. A. Casalegno – 25th January 2019 3 Intermediate Part (3 points per questions) 1. Is the overpotential positive or negative when HOR occurs? Demonstrate analyzing 𝐺 2. Show how voltage limits…