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EECS – Prof. A. Casalegno – 13th September 2019 1 Basic Part (3 points per questions, minimum score 12) 1. Write the Nernstian equilibrium potentials for both electrodes of a PEM electrolyser as a function of chemical activities 2. Write the Nernst-Plank equation for mass transport in a liquid electrolyte 3. Define the efficiency for a battery following a complex operation profile 4. Write Faraday’s law applied to reactants in a Vanadium flow battery Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 13th September 2019 2 Exercise 1 A PEM electrolyser stack consumes at full load 300 A at 360 V with an efficiency equal to 67.5% (LHV=120 MJ/kg). Assuming that 2% of H 2 is wasted and its performance follows the reported polarization curve, estimate the number of cell, cell area and efficiency at 20% current load. 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=3. 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 3.3 V, estimate the achieved SoC. ∆𝑉 0 𝑗 1.45 V 1.8 V 0.4 A cm -2 2 A cm -2 EECS – Prof. A. Casalegno – 13th September 2019 3 Intermediate Part (2.5 points per questions) 1. Is the overpotential positive when LiCoO2 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…