13 09 18

Pagina 1

EECS – Prof. A. Casalegno – 13th September 2018 1 Basic Part (3 points per questions, minimum score 12) 1. Draw the electrical potential in the double layer for a ORR in equilibrium 2. Write the Nernst-Plank equation for mass transport of an ion in a generic electrolyte 3. Depict the charge curve of a Lithium-ion battery with reasonable values 4. Write the Nernst equilibrium potential for a PEM electrolyser as a function of chemical activities Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 13th September 2018 2 Exercise 1 An automotive PEMFC stack, composed of 400 cells, supplies at full load 400 A at 260 V. 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 25,6 kW for 700 Km at an average vehicle speed of 100 km/h. Exercise 2 A 3 Ah Li-ion battery operates at ambient pressure and temperature, following the operation reported in figure. 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 equal to the state of charge 4. electrolyte resistance is equal to 0.02 Ω 5. transfer coefficients of both electrodes during charge are equal to 0.5 Define a meaningful efficiency and estimate its value. 𝑡𝑖𝑚𝑒 0 min (SoC=80%) 20 𝑚𝑖𝑛 ∆𝑉 50 𝑚𝑖𝑛 discharge at C-rate 1.5 3.6𝑉 3.4𝑉 3.8𝑉 80 𝑚𝑖𝑛 charge at C-rate 1 ∆𝑉 0 𝑗 0.8 V 0.65 V 0.4 A cm-2 2 A cm-2 EECS – Prof. A. Casalegno – 13th September 2018 3 Intermediate Part (3 points per questions) 1. Is the electrode overpotential positive or negative when HOR occurs? Demonstrate analyzing 𝐺 2. Define and depict the thermodynamic efficiency with and without…