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EECS – Prof. A. Casalegno – 15th September 2017 1 Basic Part (3 points per questions, minimum score 12) 1. Compute the Nernstian equilibrium potential for a PEMFC fed with dry H2/air at ambient pressure 2. Depict the polarization curve of a PEM electrolyzer with reasonable values 3. Write an example of electrochemical reactions occurring in a Lithium-ion battery and the typical operating voltage range 4. Indicate the typical energy density (Wh/kg) of a Lithium-ion battery pack and power density of a PEMFC system (kW/dm3) for automotive application Name _____________________________ Person N. __________________________ EECS – Prof. A. Casalegno – 15th September 2017 2 Exercise 1 A PEM electrolyser stack consumes at full load 500 A at 400 V with an efficiency equal to 68% (LHV=120 MJ/kg). Assuming that 1.5% of H2 is wasted and its performance follows the reported polarization curve, estimate the number of cell, cell area and efficiency at 25% current load. Exercise 2 A PEM fuel cell operates at 80°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 0.5 Estimate the voltage feeding high excess of air with O2 chemical activity equal to 0.15. ∆𝑉 0 𝑗 1.5 V 1.8 V 0.4 A cm-2 2 A cm-2 EECS – Prof. A. Casalegno – 15th September 2017 3 Intermediate Part (3 points per questions) 1. Is the electrode overpotential positive or negative when ORR occurs? Demonstrate analyzing 𝐺 2. Depict the polarization curve of a PEMFC and…