ECCS Exam 4 2 22

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EECS – Prof. A. Casalegno – 4th February 2022 1 To upload: https://forms.office.com/r/brPrSW5qu8 (maximum 5 single-side A4 pages) Basic Part (4.5 points per question, minimum score 12) 1. Write the Nernstian equilibrium potential in generic form for an electrochemical electrode 2. Draw the electrical potential in the double layer of a PEMFC for the HOR in two cases: equilibrium and operation 3. Depict the discharge curve of a Lithium-ion battery at high current with reasonable values Exercise An automotive PEMFC stack, composed of 400 cells, supplies 100 kW at full load (1.8 A/cm2). 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 25 kW for 800 Km at an average vehicle speed of 100 km/h. Intermediate Part (3 points for each theory question and 3.5 for the exercise) 1. Depict the three losses related to electrodes and electrolyte as a function of current density during operation of an alkaline electrolyzer. 2. Depict three polarization curves of a PEMFC operating at 80°C: 1) O2 feeding at 1 atm and RH=100%; 2) air feeding at 3 atm and RH=20%; 3) air feeding at 3 atm and RH=80%. ∆𝑉 0 𝑗 0.86 V 0.65 V 0.34 A cm -2 1.8 A cm -2 EECS – Prof. A. Casalegno – 4th February 2022 2 Exercise A Li-ion battery with nominal capacity of 20 Ah operates at ambient pressure and temperature, supplying 3.8 V during discharge at SoC= 80% and C - rate=2; requiring 4 V during charge at SoC=20% and C-rate=2. Assuming that: 1. Tafel kinetics is valid for both electrodes 2. Tafel slope b for both electrodes during charge and discharge is equal to 0.12 V 3. ion and mass transport effects in electrodes are negligible 4. activities of reactants in discharge and charge are…