Suppose that the electric wall boundary conditions for a 1D PEMFC model impose a 0.6 V difference...

Suppose that the electric wall boundary conditions for a 1D PEMFC model impose a 0.6 V difference between the anode and the cathode. The solution of this model indicates that the ohmic overvoltage is 0.1 V. The entire fuel cell is at an isothermal temperature of 25∘C. The fuel cell is supplied with pure hydrogen and oxygen, both at 1 atm. Electronic resistance is ignored (= 0) in the catalyst layers and in the electrodes. Assuming that the over potentials at the interface of the anode catalyst/anode electrode and cathode catalyst/cathode electrode are zero, answer the following questions:

(a) Sketch the electronic potential profile across the anode, electrolyte, and the cathode.

(b) Derive an equation for the exchange current density profile across the catalyst layers assuming constant gas concentration profiles across the catalyst layers and electrodes. (Hint: Use the equations from Example 13.1, ignoring the backward reaction term.)

(c) Calculate the anodic and cathodic overpotentials. What is the current density? Both catalyst layers are 10 μm thick. Use parameter values from Table 13.2b if necessary.

(d) Sketch the ionic potential profile across the anode, electrolyte, and cathode.

Example 13.1

Based on Equation 13.12, establish the electrochemical reaction governing equations for a hydrogen/oxygen fuel cell model.