New electrochemical power source: Lead-iodine hybrid redox flow battery

Energy storage system is an important element of energy grids that facilitates transition of energy sector from fossil fuels towards renewable energy sources. Redox flow batteries are developed targeting the high energy end of the storage systems. A concept of Lead-Iodine hybrid redox flow battery is proposed. The battery is based on the following processes: At the negative electrode metal lead is transformed into iodoplumbous acid HPbI3 in 2-electron process. At the positive electrode 1-electron transformation HI–poly-hydroiodic acid takes place. Both electrolytes contain concentrated HI. Cations in both electrolytes of the flow cell are mostly hydrated protons. Compartments of the cell are separated by cation-exchange membrane. Current flow through the cell results mostly in transport of protons through the membrane. Experiments with rotating disk electrode and with small unoptimized redox flow battery proved the concept. The battery survived 30 deep charge-discharge cycles with the loss of 50 % of its discharge capacity. The capacity loss is ascribed, at least partially, to removal of powdered lead from the negative electrode compartment by the electrolyte flow. Current efficiency averaged over 30 cycles was 94 %. Hydrogen evolution competing with lead deposition on the negative electrode was found to be the cause of relatively low current efficiency.