Capitalizing on the Iodometric Reaction for Energetic Aqueous Energy Storage.

Iodometric and iodimetric titrations represent a prevailing technique to determine the concentration of Cu ions in aqueous solutions; However, their utilization in electrochemical energy storage has been overlooked due to the poor reversibility between CuI and Cu related to the shuttling effect of I species. In this work, we developed a 4A zeolite separator capable of suppressing the free shuttling of I ions, thus achieving a record-high capacity retention of 95.7% upon 600 cycles. Theoretical and experimental studies reveal that the negatively charged zeolite can effectively impede the approach and penetration of I ions, as a result of electrostatic interaction between them. To explore the practical potential, a hybrid cell of Zn∥I consisting of Cu redox agent has been assembled with a discharge capacity of 356 mA h g. The cell affords a specific energy of 443 W h kg based on I, or 193 W h kg based on both electrodes. This work offers insight on the energy utilization of the iodometric reactions and advocates a Cu-mediated cell design that could potentially double the capacity and energy of conventional aqueous battery systems.