Question

The EMF of an $H_2$-$O_2$ fuel cell:

• A. is independent of partial pressures of $H_2$ and $O_2$
• B. decreases on increasing $P_{H_2}$ and $P_{O_2}$
• C. increases on increasing $P_{H_2}$ and $P_{O_2}$
• D. varies with the concentration of $O{H}^{-}$ ions in the cathodic and anodic compartments

Answer 1

Answer: (C)

increases on increasing $P_{H_2}$ and $P_{O_2}$

Below are the reactions that take place in $H_2-$ $O_2$ fuel cell.

Anode reaction: $H_2\to 2H^{+}+2e^{-}$

Cathode reaction: $\frac{1}{2}{O}_2+2e^{-}+2H^{+}\to H_{2}O$

Overall reaction: $H_2+\frac{1}{2}{O}_2\to H_{2}O$

The EMF of an $H_2-$ $O_2$ fuel cell is given by:

$E_{cell}=E_{cell}^{\circ }-\frac{0.059}{2}log\frac{1}{({P_{O_2}}^{\frac{1}{2}}\times P_{H_2})}$.
$⟹EMF=E_{cell}=E_{cell}^{\circ }+\frac{0.059}{2}log\left({P_{O_2}}^{\frac{1}{2}}\times P_{H_2}\right)$.

So, the EMF increases with increasing $P_{H_2}$ and $P_{O_2}$.