Electrochemical and thermodynamic studies of nickel electrodes in alkaline electrolytes

The nickel electrode is widely used as a positive electrode in rechargeable alkaline batteries. The electrochemical behaviour of nickel hydroxide powders in several kinds of electrolyte is investigated. The open-circuit voltage (OCV) of the nickel oxide electrode in 3 M KOH displays an S-shaped curve in the reduction process. On the other hand, the nickel oxide electrode in 3 M NaOH and 3 M LiOH shows two-step reduction OCV curves. In the first stage, the OCV curves are S-shaped, while in the second stage, the OCV curves are L-shaped. The S-shaped stage of the OCV curve is examined by using thermodynamic considerations. The thermodynamic simulation and experimental results are in fairly good agreement with one fitting parameter φ/RT; φ is an interaction energy parameter (J mol−1) and RT has the usual significance. The interaction energy parameter (φ) is found to increase in the order 3 M LiOH < 3 M NaOH < 3 M KOH. This concluded that the alkaline cation intercalated into the nickel oxide lattice decreases the interaction energy parameter (φ).