The hydrogen fuel cell offers a method of generating energy electrochemically. T
ID: 514581 • Letter: T
Question
The hydrogen fuel cell offers a method of generating energy electrochemically. The cell is: Pt | H_2(g)(1 bar) | H_2O, pH2.00 | O_2(g) (1 bar) | Pt a) Calculate the open circuit potentials (E_or's) E_R and E_l. at 373 K. b) In a hydrogen oxygen fuel cell at 373 K the exchange current densities (j_o's) for the oxygen reduction and hydrogen oxidation are 3.0 m/lm and 100 mA m respectively. Using a Butler Volmer equation for each half reaction, and assuming alpha = 0.5 for both reactions, calculate the overvoltage (n) at each half cell required to maintain a current density (U) of 300 mA/m^2 c) What is the output voltage (EMF) of the hydrogen oxygen fuel cell in 30b above when it is producing 300 mA/m^2?Explanation / Answer
Nernst equation of a half cell: a nF RT Eeq E ln 0
The standard potential E0 is listed in literature. By convention, the redox-reaction is written in the following way:
O + ze- R and its standard potential is the standard reduction potential.
Therefore the above written Nernstequation gives us equilibrium “reduction” potentials. If those potentials are negative, the oxidation reaction is preferred.
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