236
5 – Applications
6. The technological development of the Na-S battery allows us to obtain a
specific energy W p of nearly 80 W h kg
−1
. Explain this difference between
W th and W p .
7. Propose a simplified scheme for an elementary Na-S battery.
8. Taking x = 1 in the polysufide that appears in the second state of the cathodic
reaction, evaluate the theoretical capacity Q of charge in a Na-S battery that
initially contains 230 g of sodium and 800 g of sulfur. Express Q in A h.
Exercise 5.15 – General information on fuel cells
1. What is a solid-electrolyte fuel cell?
2. Give three examples of a fuel cell that involves a solid oxide electrolyte.
Specify in particular the operating temperature.
3. Gaseous hydrogen H 2 is the simplest fuel to use in fuel cells. Give three
examples of processes for manufacturing this fuel.
4. a. Describe the shape of the curve for the potential difference and the power
density of a fuel cell as a function of the current density that it delivers.
b. Specify the phenomena that determine the operation of the fuel cell as
a function of current density.
c. At what points (P max ,I P max ,∆E P max ) is the optimum operation of a fuel
cell?
Exercise 5.16 – Solid oxide fuel cell (SOFC)
The following electrochemical chain describes a SOFC:
H 2 + H 2 O,Ni-YSZ / YSZ / LSM,air
where P H 2 = 0.98 bar, P H 2 O = 0.02 bar, Ni-YSZ is a ceramic-nickel composite,
called “cermet,” based on nickel and YSZ, where YSZ is yttria-stabilized zirconia with the formula (ZrO 2 ) 0.92 (Y 2 O 3 ) 0.08 , and the cathode LSM is a ceramic
with the composition La 0.8 Sr 0.2 MnO 3−δ .
1. Express the emf ∆E of the cell as a function of the partial pressures of the
gases in contact with the electrode.
5 – Applications
6. The technological development of the Na-S battery allows us to obtain a
specific energy W p of nearly 80 W h kg
−1
. Explain this difference between
W th and W p .
7. Propose a simplified scheme for an elementary Na-S battery.
8. Taking x = 1 in the polysufide that appears in the second state of the cathodic
reaction, evaluate the theoretical capacity Q of charge in a Na-S battery that
initially contains 230 g of sodium and 800 g of sulfur. Express Q in A h.
Exercise 5.15 – General information on fuel cells
1. What is a solid-electrolyte fuel cell?
2. Give three examples of a fuel cell that involves a solid oxide electrolyte.
Specify in particular the operating temperature.
3. Gaseous hydrogen H 2 is the simplest fuel to use in fuel cells. Give three
examples of processes for manufacturing this fuel.
4. a. Describe the shape of the curve for the potential difference and the power
density of a fuel cell as a function of the current density that it delivers.
b. Specify the phenomena that determine the operation of the fuel cell as
a function of current density.
c. At what points (P max ,I P max ,∆E P max ) is the optimum operation of a fuel
cell?
Exercise 5.16 – Solid oxide fuel cell (SOFC)
The following electrochemical chain describes a SOFC:
H 2 + H 2 O,Ni-YSZ / YSZ / LSM,air
where P H 2 = 0.98 bar, P H 2 O = 0.02 bar, Ni-YSZ is a ceramic-nickel composite,
called “cermet,” based on nickel and YSZ, where YSZ is yttria-stabilized zirconia with the formula (ZrO 2 ) 0.92 (Y 2 O 3 ) 0.08 , and the cathode LSM is a ceramic
with the composition La 0.8 Sr 0.2 MnO 3−δ .
1. Express the emf ∆E of the cell as a function of the partial pressures of the
gases in contact with the electrode.