Chapter 21.1, Problem 6LC

Interpretation Introduction

Interpretation: The overall reaction in a hydrogen-oxygen fuel cell needs to be determined. The product formed needs to be identified. Also, the half-reactions in the cell need to be described.

Concept Introduction: In an electrochemical process, a redox reaction takes place. Here, two half-reactions occur where in one reaction oxidation takes place and in the other reaction, reduction takes place. The sum of these two-half reactions gives the overall reaction for the process.

In oxidation, the loss of electrons takes place by an element and its oxidation state increases Similarly in reduction, the gain of electrons takes place by an element. Here, the oxidation state of the element decreases.

Explanation of Solution

The overall reaction in a hydrogen-oxygen fuel cell is as follows:

  ${\text{2H}}_{\text{2}}+{\text{O}}_2\to 2{\text{H}}_{\text{2}}\text{O}$

Here, the product formed is water.

In the hydrogen-oxidation fuel cell, hydroxide ions from KOH are used to carry current. Here, hydroxide ions contain oxygen and water is formed at the anode. The dissociation of KOH electrolyte is represented as follows:

  $\text{KOH}\rightleftharpoons {\text{K}}^{+}+{\text{OH}}^{-}$

Here, hydrogen (neutral) at the anode reacts with hydroxide ions to form water. The reaction is represented as follows:

  $2{\text{H}}_{\text{2}}+4{\text{OH}}^{-}\to 4{\text{H}}_{\text{2}}\text{O}+4e$

Similarly, at the cathode, hydroxide ions are regenerated by the electrons.

  ${\text{O}}_2+2{\text{H}}_{\text{2}}\text{O}+4e\to 4{\text{OH}}^{-}$

The overall cell reaction will be:

  ${\text{2H}}_{\text{2}}+{\text{O}}_2\to 2{\text{H}}_{\text{2}}\text{O}$