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EECS – Prof. A. Casalegno – 29th June 2018 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 an equation for electroneutrality 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 – 29th June 2018 2 Exercise 1 An automotive PEMFC stack, composed of 300 cells, supplies at full load 400 A at 208 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 20.5 kW for 720 Km at an average vehicle speed of 120 km/h. Exercise 2 A Li-ion battery with nominal capacity of 50 Ah operates at ambient pressure and temperature, supplying 3.5 V during discharge at SoC=90% and C-rate=5. Assuming that: 1. Tafel kinetics is valid for both electrodes 2. ion and mass transport effects in electrodes are negligible 3. activities of reactants in discharge/charge are close to the value of SoC/(1-SoC) 4. electrolyte resistance is equal to 2 mΩ 5. transfer coefficients of both electrodes during discharge are equal to 0.5 Discharging at C-rate=5, the voltage reaches the value 3.35 V, estimate the achieved SoC. ∆𝑉 0 𝑗 0.8 V 0.65 V 0.4 A cm-2 2 A cm-2 EECS – Prof. A. Casalegno – 29th June 2018 3 Intermediate Part (3 points per questions) 1. Is the overpotential positive or negative when ORR occurs? Demonstrate analyzing 𝐺 2. Show how voltage limits could reduce the available capacity at high…