26 06 17

Pagina 1

EECS – Prof. A. Casalegno – 26th June 2017 1 Basic Part (3 points per questions, 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 an equation for electroneutrality in a generic electrolyte 3. Define the efficiency for a battery, indicating how SoC varies 4. Write Faraday’s law applied to electrolyte and both products in a PEM electrolyzer Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 26th June 2017 2 Exercise 1 A PEM fuel cell operates at 70°C with high excess of pure H2 and O2, supplying at 0.8 V a current density equal to 1 A/cm2. Assuming that: 1. anode behaves as an ideal H2 electrode (𝐸"+𝜂"=0) 2. ion and mass transport effects in catalyst and diffusion layers are negligible 3. chemical activities of H2 and O2 are close to 1 4. membrane ion conductivity and thickness are respectively 0.05 S/cm and 50 μm 5. transfer coefficient of ORR is equal to 0.45 Estimate the voltage at 2 A/cm2. Exercise 2 A Li-ion battery with nominal capacity of 7 Ah operates at ambient pressure and temperature, supplying 3.4 V during discharge at SoC=50% and C-rate=2. 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 equal to 0.5 Estimate the voltage at SoC=25% and C-rate=1. EECS – Prof. A. Casalegno – 26th June 2017 3 Intermediate Part (3 points per questions) 1. Write the Butler-Volmer and Tafel equations and depict them as 𝑖=𝑓(𝐸+𝜂) 2. Show how voltage limits could reduce the available…