The open circuit voltage of a hydrogen-oxygen fuel cell operating at RTP is 0.96

Question

The open circuit voltage of a hydrogen-oxygen fuel cell operating at RTP is 0.96 V and its internal resistance is 1.2 m Ohm. The activation voltage drop is given by V act =0.031 + 0.015 In I where I is in amperes. From thermodynamic data, the reversible voltage, V rev is known to be 1.20 V. Two hundred of the above cells are connected in series forming a battery that feeds a resistive load rated at 2.5 kW at 100 V. Determine the actual load voltage [V], and the thermal energy [W] generated internally.

Explanation / Answer

Activation voltage = 0.96 V

Internal Resistance = 1.2 mohm

V reversible = 1.2 V

200 of cells are connectes in series.

So Req= 200 * 1.2 * 10^-3 = 0.24 ohm

I at Vrev = 1.2 V = 1.2/0.24= 5 ampere.

(a) Actual load voltage = Vact = 0.031+0.015*ln5 = 0.055 V

(b) Thermal energy generated internally = Vact * I

W = 0.055*5 = 0.276 watt

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