Vrb Energy

The VRB Energy Storage System (VRB-ESS) is an electrical energy storage system based on the patented vanadium-based redox regenerative fuel cell that converts chemical energy into electrical energy. Energy is stored chemically in different ionic forms of vanadium in a dilute sulphuric acid electrolyte. The electrolyte is pumped from separate plastic storage tanks into flow cells across a proton exchange membrane (PEM) where one form of electrolyte is electrochemically oxidized and the other is electrochemically reduced. This creates a current that is collected by electrodes and made available to an external circuit. The reaction is reversible allowing the battery to be charged, discharged and recharged.

The principle of the VRB is shown in more detail in Figure 1 - it consists of two electrolyte tanks, containing active vanadium species in different oxidation states (catholyte: V(IV)/V(V) redox couple, anolyte: V(II)/(III) redox couple). These energy-bearing liquids are circulated through the cell stack by pumps. The stack consists of many cells, each of which contains two half-cells that are separated by a membrane. In the half-cells the electrochemical reactions take place on inert carbon felt polymer composite electrodes from which current may be used to charge or discharge the battery.

Concept of a Redox Flow Battery System

The VRB-ESS employs vanadium ions in both half-cell electrolytes. Therefore, cross-contamination of ions through the membrane separator has no detrimental influence on the battery capacity, as is the case in redox flow batteries employing different metal species in the positive and negative half-cells. The vanadium half-cell solutions can even be remixed bringing the system back to its original state.

The open circuit cell voltage at a concentration of 2 mole per liter for each vanadium species is 1.6 V when fully charged. The relatively fast kinetics of the vanadium redox couples allows high Coulombic and voltage efficiencies to be achieved without costly catalysts. The same current is passed through all of the cells as they are arranged in series. Such systems have many admirable properties including high efficiency, long cycle life, ease of scalability and negligible environmental impact.

A primary advantage of the VRB-ESS is in its modularity - the separation of the power component and the storage component