The standard cell potential ( E cell ) of a fuel cell based on the oxidation of methanol in air that has been used to power television relay station is measured as 1.21 V. The standard half cell reduction potential for O2 ( E O2/H2O ) is 1.229 V. Choose the correct statement :
- Reactants are fed at one go to each electrode.
- Oxygen is formed at the anode.
- The standard half cell reduction potential for the reduction of CO2 ( E CO2/CH3OH ) is 19 mV
- Reduction of methanol takes place at the cathode.
Answer
(3) The standard half cell reduction potential for the reduction of CO2 ( E CO2/CH3OH ) is 19 mV
Solution
Anode (oxidation): CH3OH + H2O CO2 + 6H+ + 6e-
Cathode (reduction): 32O2 + 6H+ + 6e- 3H2O
E cell = E O2/H2O - E CO2/CH3OH
1.21 = 1.229 - E CO2/CH3OH
E CO2/CH3OH = 0.019 V = 19 mV (3) is correct.
(1) In a fuel cell, reactants are fed continuously to the electrodes. Incorrect.
(2) Oxygen is consumed (reduced) at the cathode, not formed at the anode. Incorrect.
(4) Methanol is oxidised at the anode. Incorrect.
Answer: (3)