Aqueous Redox Flow Batteries Enhanced by Solid Boosters

One of the main challenges for certain electricity production technologies (e.g. renewables) is the capability to supply energy according to the demand. It follows that storing energy is a possible solution to the inadequacy between production and demand. Among various technologies, electrochemical energy storage is a particularly good solution. Redox flow batteries, as electrochemical energy storage technology are scalable, durable, robust and quite safe, but as compared to other technologies, they have a quite poor volumetric capacity (10-40 Wh/L) determined by the solubility limit of the redox-active species dissolved in the electrolytes. In this thesis, an approach to overcome the low storage capacity in aqueous redox flow batteries is presented. The approach consists of adding solid-phase materials (herein called solid boosters) into the liquid electrolytes contained in the battery reservoirs. These boosters can receive charge from the redox-active species reacting in the flow cell, if the respective Fermi levels are aligned to those of the liquid electrolyte materials. This concept is denoted as “redox-mediated” charge transfer, where solid boosters become the primary storage media, bypassing the solubility limit issue that restraints the storage capacity. This work opens a series of future studies to enable bulk-phase charge storage in the reservoirs of redox flow batteries and it looks promising for industrial demonstrators.