Week 4 Challenge

Question 1:

Define Nernst equation for fuel cell and then define what parameters affect the reaction in a fuel cell in what way.

E_cell = E_ner-E_act-E_ohm-E_mt

E_{ner =} E₀ + (RT/2F) ln [P_H2 P^1/2O₂/P_H2O]

Parameters affect the reaction in the fuel cell:

Parameters affect the reaction in the fuel cell:

1.Temperature

2.Partial pressure of the fuel and oxygen

3.Concentration of the fuel and oxygen

Question 2:

Consider the following operating points of a fuel cell during a short period of operation.

• 15 W/cm2
• 3 W/cm2
• 27 W/cm2

Where would these points go in the diagram below?

1. Ohmic losses will account 27 W/cm2. due to major losses in the fuel cell.

2. Open circuit losses will be minimal 3 W /cm2 due to fuel crossover.

3. mass transport losses will be 15W/cm2 at higher current.

Question 3:

Which among the three points is the best operating point and why?

we cannot avoid all the three losses due to operating condition and chemical reaction.

PEMFC efficiency point of operating at the 0.75 to 1 A/cm2

as per the graph better fuel cell operation region would be at the current density 0.6 to 0.9 A/Cm2

At low power densities, the cell potential drops as a result of the activation polarization.
• At moderate current densities, the cell potential decreases linearly with current due to ohmic losses.
• At high current densities, the cell potential drop departs from the linear relationship with current density as a result of a more pronounced concentration polarization.