1. Consider a fuel cell stack that can operate at either 300kPa or 170kPa (inlet pressure) with oxygen stoichiometric ratio of 5. The stack performance (polarization curve) is shown in Fig., below. Calculate the net power output and the net efficiency at both pressures. Assume current density of 600 mA/cm. Note: operation at higher pressure (300kPa) would yield 0.66V per cell. Calculate: i) The net power density ii) System efficiency of the unit (Take Molar mass of dry air = 29, Cp = 1, Operating temperature = 18C) 60C 30 psig (308 kPa) average cell potential (V) 0.9 20 psig (239 kPa) H2/Air 1.5/2.0 10 psig (170 kPa) 0.8 0.7 0.6 0.5 0.4 0 0.2 0.6 0.4 current density (A/cm) 0.8 1 1.2 1.4