The equations show the standard electrode potentials of two half-cells used in a rechargeable sodium-ion cell:
Na++e−⇌NaE⊖=−2.71 V \text{Na}^+ + \text{e}^- \rightleftharpoons \text{Na} \quad E^{\ominus} = -2.71\text{ V} Na++e−⇌NaE⊖=−2.71 V CoO2+Na++e−⇌NaCoO2E⊖=+0.55 V \text{CoO}_2 + \text{Na}^+ + \text{e}^- \rightleftharpoons \text{NaCoO}_2 \quad E^{\ominus} = +0.55\text{ V} CoO2+Na++e−⇌NaCoO2E⊖=+0.55 VWhich statement is correct for this cell during discharge?
The standard cell potential is 3.26 V3.26\text{ V}3.26 V.
The reaction at the positive electrode is: NaCoO2→CoO2+Na++e−\text{NaCoO}_2 \rightarrow \text{CoO}_2 + \text{Na}^+ + \text{e}^-NaCoO2→CoO2+Na++e−.
The overall cell reaction is: NaCoO2→Na+CoO2\text{NaCoO}_2 \rightarrow \text{Na} + \text{CoO}_2NaCoO2→Na+CoO2.
The oxidation number of cobalt changes from +3 to +4.
