Flow Batteries

In conventional secondary (rechargeable) batteries, energy is charged and discharged in the active masses of the electrodes. A flow battery is also a rechargeable battery, but the energy is stored in one or more electro active species which are dissolved in liquid electrolytes.

The electrolytes are stored externally in tanks and pumped through the electrochemical cell that converts chemical energy directly to electricity and vice versa. The power is defined by the size and design of the electrochemical cell whereas the energy depends on the size of the tanks.

A flow battery offers the inherent safety of storing the active materials separately from the reactive point source. Other advantages are quick response times, high electricity-to-electricity conversion efficiency, simple state-of-charge indication based on electro-active concentrations, low maintenance, tolerance to overcharge and over discharge, and the ability for deep discharges without affecting cycle life.

With this characteristic flow batteries can be fitted to a wide range of stationary applications.

Flow batteries are classified into red - ox flow batteries and hybrid flow batteries.

Red – ox flow batteries (RFB) have all the reactants and products of the electro-active chemicals stored external to the power conversion device.

In Hybrid flow battery (HFB) one of the active masses is internally stored within the electrochemical cell, whereas the other remains in the liquid electrolyte and is stored externally in a tank. Therefore, as for conventional secondary batteries, capacity depends on the size of the electrochemical cell.

Chemistries with higher electrodes potentials increase the effectiveness of the battery but also material requirements: conventional carbon electrodes are not stable above 1V SHE. In addition, higher surface areas allow an increase in the current flow through the battery. For these reasons, titanium-coated electrodes are often not a choice but the only technical solution for some Red - Ox couples.

In the last few years De Nora has developed a new electro-catalyst and cathode electrode for bromine / bromide conversion in Zn – bromine HFB.
Additionally, we can develop specific electrodes solutions for different RFB and HFB chemistries on request.