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EECS – Prof. A. Casalegno – 18th June 2021 1 Basic Part (4.5 points per question, minimum score 12) 1. Draw the electrical potential in the double layer for ORR in equilibrium 2. Write, for a generic electrolyte, the total current density equation, coming from the Nernst-Plank mass transport equation 3. Depict the polarization curve of an alkaline electrolyzer with reasonable values Exercise A Li-ion battery with nominal capacity of 50 Ah operates at ambient pressure and temperature , requiring 3.8 V for charging at SoC=20% and C-rate=1 h-1. 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 charge are close to the value of (1-SoC) 4. electrolyte resistance is equal to 1.8 mΩ 5. transfer coefficients of both electrodes during discharge are equal to 0.5 During charge at C-rate=1 h-1, the voltage reaches the value of 4 V, estimate the achieved SoC. Intermediate Part (3 points for each theory question and 3.5 for the exercise) 1. Write the Butler-Volmer and Tafel kinetic equations and represent them on the same graph 𝑖 = 𝑓(𝐸 + 𝜂) for positive and negative current density values 2. Show the effect on the discharge curve at Crate=1 h-1 of both capacity and power fading caused by battery aging EECS – Prof. A. Casalegno – 18th June 2021 2 Exercise 1 A PEM fuel cell operates at 90°C with pure H2 and air at 0.25 MPa pressure and supplies at 0.65 V a current density equal to 1.7 A/cm2 and related impedance is reported in the figure. Assuming that: 1. anode behaves as an ideal H 2 electrode [𝐸− + 𝜂−=0] 2. ion and mass transport effects in catalyst layers are negligible 3. the average O 2 molar fraction in the cathode channel is equal to 0.07 4. diffusion layer diffusivity Dref…