Question

Write electrode reaction and net cell reaction for fuel cell. Calculate e.m.f. of the following cell at 25 °C.

Standard reduction potential (SRP) of Zn and Cu are − 0.76 V and 0.334 V respectively

Answer 1

Cell reactions for fuel cell:

1) Oxidation at anode (−):

At anode, hydrogen gas is oxidized to H₂O.

2H_2(g) + `4OH_(aq)^-` → 4H₂O_(l) + 4e⁻

2) Reduction at cathode (+):

The electrons released at anode travel to cathode through the external circuit.
Here O2 gas is reduced to OH⁻

O_2(g) + 2H₂O_(l) + 4e⁻ → `4OH_((aq))^-`

3) Net cell reaction

The overall cell reaction is the sum of oxidation at anode and reduction at cathode.
Thus,

4) Calculation of e.m.f.:

`E_(Cu)^0` = 0.334 V

`E_(Zn)^0` = −0.76 V

The overall cell reaction is the redox reaction which is the sum of oxidation half reaction at anode and reduction half reaction at cathode.