ALL-VANADIUM REDOX FLOW BATTERY SYSTEM EMPLOYING A V+4/V+5 REDOX COUPLE AND AN ANCILLARY Ce+3/Ce+4 REDOX COUPLE IN THE POSITIVE ELECTROLYTE SOLUTION

摘要

An ancillary Ce+3/Ce+4 redox couple is added to the positive electrolyte solution containing the V+4/V+5 redox couple of an RFB energy storage system in a mole content sufficient to support charge current in case of localized depletion of oxidable V+4V ions in the anode double layer on a wetted carbon electrode surface at a polarization voltage approaching 1.5 V, thus restraining any further increase that would lead to massive OH- discharge on the carbon electrode. Such a "buffering" function of the fraction of oxidable of C+3 ions, substitutes of no longer present oxidable V+4 ions, may eventually continue after a substantially complete oxidation to V+5 of the vanadium of the main redox couple V+4/V+5 in the positive electrolyte solution and to this end a balancing mole amount of a reducible redox couple is also added to the negative electrolyte solution. Of course, the added fractions (concentrations) of ancillary redox couple element or elements in the two electrolyte solutions will be determined in function of the minimum time interval after full oxidation of the vanadium load the system may remain operating before stopping an inadvertent run out charging process (maximum tolerable overcharge).