ECCS Exam 17 6 22

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EECS – Prof. A. Casalegno – 17th June 2022 1 Standard EECS exam [duration 1 h 40 min] Students who passed TiP reduced number of questions marked with (TiP) [duration 1 h 10 min] To upload https://forms.office.com/r/548eLjrfzX (maximum 5 single-side A4 pages – PDF file name MUST BEGIN with person code) Basic Part (4.5 points per question, 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 in a generic electrolyte 3. (TiP) Depict the charge curve of a Lithium-ion battery with reasonable values Exercise (TiP) A PEMFC stack with 500 cells supplies at full load 120 kW at 335 V (LHV=120 MJ/kg). Assuming that 3% of H2 is wasted and its performance follows the reported polarization curve, estimate the efficiencies at full power (335 V) and low power (390 V). Intermediate Part (3 points for each question) 1. Is the electrode overpotential positive or negative when ORR occurs? Demonstrate analyzing 𝐺̃ 2. (TiP) Show how voltage limits in batteries could reduce the available capacity during both discharge and charge at high C-rate ∆𝑉 0 𝑗 0.78 V 0.67 V 0.3 A cm -2 1.8 A cm -2 EECS – Prof. A. Casalegno – 17th June 2022 2 Exercise (TiP) A Li -ion battery with nominal capacity of 5 Ah operates at ambient pressure and temperature, supplying 3.6 V during discharge at SoC=80% and C -rate=2 and requiring 4.05 V during charge at SoC=30% and C-rate=1. 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 close to the value of SoC 4. electrolyte resistance is equal to 0.02 Ω 5. transfer coefficients of both electrodes during discharge are…