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EECS – Prof. A. Casalegno – 14th June 2019 1 Basic Part (3 points per questions, minimum score 12) 1. Write the Nernstian equilibrium potentials for both electrodes of a PEMFC as a function of chemical activities 2. Write the Nernst-Plank equation for mass transport in a solid electrolyte with fixed charges 3. Define the efficiency for a fuel cell system including auxiliaries 4. Write Faraday’s law applied to reactants in a Vanadium flow battery Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 14th June 2019 2 Exercise 1 Associate the three PEMFC i /V curves to the following cathode operating conditions (assume T=65°C). 1. O2 feeding at 100%RH 2. Air feeding at λ=1.5, P=2.5 atm and 30%RH 3. Air feeding at λ=4, P=1.5 atm and 30%RH Exercise 2 A Li-ion battery with nominal capacity of 25 Ah operates at ambient pressure and temperature , supplying 3.6 V during discharge at SoC=90% and C-rate=4. 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 are close to the value of SoC 4. electrolyte resistance is equal to 4 mΩ 5. transfer coefficients of both electrodes during discharge are equal to 0.5 Discharging at C-rate=4, the voltage reaches the value 3.4 V, estimate the achieved SoC. EECS – Prof. A. Casalegno – 14th June 2019 3 Intermediate Part (2.5 points per questions) 1. Is the overpotential positive when Li/C oxidation occurs? Demonstrate analyzing 𝐺̃ 2. Show how voltage limits could reduce the available capacity at high C-rate in batteries 3. Depict the polarization curves of 3 different PEMFC: 1) ECSA=150 m2/m2; 2) ECSA=50 m2/m2; 3) ECSA=150 m2/m2 and double thickness membrane Name…