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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]

Three-electrolyte configuration with two oppositely charged ion-exchange membranes can be used to yield various promising pH differential power sources. pH change, ion transport and potential profiles across the membranes and electrode/electrolyte interfaces of a three-electrolyte pH differential lead dioxide-metal hydride system are therefore systematically investigated for the first time. We find that i) pH changes of the acid and alkaline chambers are dependent on the combined effect of the electrode reaction and the ion transport. In addition, the pH change of the middle chamber is also affected by the crossover of protons from acid chamber if the anion-exchange membrane has a low permselectivity; ii) the electrical potential gradient mainly controls the ion transport with current flows; iii) the high overall cell voltage is attributed to the large pH acid-alkaline , while the potential across the membranes and electrode/electrolyte interfaces is affected by both pH and the concentration gradient. Key issues and proposed solutions are discussed to improve the electrochemical performance of this three-electrolyte pH differential electrochemical system. This work offers new opportunities to develop promising energy storage technologies. Ionic interfaces of a three-electrolyte pH differential system are studied, and feasible solutions are put forward to further improve the electrochemical performance of such a system. Image 1 • Ionic interfaces of a three-electrolyte pH differential system were studied. • Adding salts into electrolyte solutions was put forward to improve the cell performance. • This work offers new opportunities to develop promising energy technologies. [ABSTRACT FROM AUTHOR]