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Abstract A three-electrolyte cell configuration, in which an additional compartment filled with salt solution is created between the cation-exchange membrane and the anion-exchange membrane to separate the respective opposite charged ionic species, can be used to realize novel electrochemical systems using promising redox couples. Using lead-acid metal hydride hybrid redox couple as a typical three-electrolyte prototype, we monitored the potential change of individual components during operation to obtain better understanding on the factors affecting the electrochemical performance (including types of salt solution, electrolyte concentration, inter-electrode gap). Key issues (i.e., salting-out) and proposed solutions are discussed. This work offers new solutions to develop promising energy storage techniques. Highlights • Effect of salt solution, concentration and inter-electrode gap of the three-electrolyte battery system was studied. • Salt solution with higher ionic conductivity in the buffer chamber, lowers the change voltage across the membranes. • The inter-electrode gap is optimised to reduce the internal resistance of the system. [ABSTRACT FROM AUTHOR]

Abstract: Performance characteristics of a three electrolyte rechargeable acid–alkaline hybrid battery using a PbO2 positive plate and a nickel metal hydride (NiMH x ) negative electrode in separate electrolyte of H2SO4 and KOH were studied. This hybrid battery has three electrolytes in a single cell. A neutral K2SO4 salt solution was placed between the acid and alkaline compartments of the cell, in which a cation exchange membrane and an anion exchange membrane, were employed to separate these three electrolytes. The open circuit voltage of this hybrid cell was found to be 2.64V in an electrolyte configuration of 1M H2SO4|0.2MK2SO4|2M KOH electrolyte configuration, compared to 1.92V in the conventional lead-acid cell in 1M H2SO4 and 1.40V in a NiMH x cell in 2M KOH. This hybrid acid–alkaline PbO2/NiMH x battery was shown to operate with a voltage 20% higher than the conventional lead acid battery and 110% higher than nickel–metal hydride battery at 1/3C discharging rate. The concentrations of the three electrolytes, the dimension of the electrolyte chamber, and other cell/operation parameters with impacts on the hybrid cell performance were investigated. [Copyright &y& Elsevier]