ESTIMATION OF THE STATE OF CHARGE OF A POSITIVE ELECTROLYTE SOLUTION OF A WORKING REDOX FLOW BATTERY CELL WITHOUT USING ANY REFERENCE ELECTRODE

摘要

A measure of the state of charge of the positive electrolyte solution of a working redox flow battery without using a reference electrode is obtained by using an undivided cell assembly comprising a stable electro catalytic metal electrode and a porous carbon base counter-electrode, immersed in the positive electrolyte solution of an all vanadium battery. In the interval between about 0.35V and 0.45V, a spread out of the voltage- current characteristic curves is at maximum of amplitude and allows an excellent discrimination of the state of oxidation of vanadium by locating the point on the voltage-current plane, on which the characteristic curves at different known degrees of oxidation have been recorded during a calibration work carried out on the specific undivided cell sensor to be used thereafter for monitoring the state of charge of the positive electrolyte solution. In operation, the undivided cell sensor immersed at any desirable point of the positive electrolyte circuit is constantly supplied at a controlled fixed DC bias voltage between the positive metal electrode and the porous carbon counter-electrode by an appropriate voltage regulator of adequate power capability, or cyclically at two or more different voltages, all within a range that includes the region between 0.35V and 0.45V, measuring simultaneously the current flowing across the undivided cell sensor at the fixed voltage or voltages bias. By correlating the paired voltage and current values, using a look up table compiled at calibration, estimated values of the degree of oxidation or state of charge of the redox ion couple of the positive electrolyte solution are produced.