Operando UV/Vis spectra deconvolution for comprehensive electrolytes analysis of vanadium redox flow battery

Monitoring the state of charge (SoC) is one of the most important challenges of vanadium redox flow battery (VRFB) technology to solve. Among other methods, optical spectroscopy seems promising, however, existing approaches have their problems, primarily because of limited applicability for high vanadium concentrations, uncertainty in accounting for electrolyte imbalance during VRFB operation, and applicability limitations for mixed acid electrolytes. In this work, a method for determining SoC of VRFB based on the deconvolution of electrolyte absorption spectra is proposed. This method was successfully implemented for 0.5 M and 1 M vana-dium electrolytes with 0.05 M phosphoric acid additive and demonstrated good accuracy for determining vana-dium concentration and SoC in both half-cells, including analysis during VRFB galvanostatic cycling. Besides, this method allows us to obtain complex spectra: V2O33+ in posolyte and a previously never demonstrated com-plex in negolyte that presumably corresponds to the V3+ complex.