Monitoring the State-of-Charge in All-Iron Aqueous Redox Flow Batteries

Abstract

Monitoring the state-of-charge (SOC) in redox flow batteries is indispensable as a diagnosis tool to detect changes in the electrolyte concn. that can deteriorate the battery performance. Existing methods, which measure elec. variables of the cell or are dependent on recalibration during battery operation, become time consuming for practical uses. Here we present a simple and abs. method for monitoring the SOC in iron aq. redox flow batteries. The method is based on the detn. of the Fe(II) concn. with photometry after forming the complex of Fe(II)-1,10-phenanthroline. It can be applied in both the neg. and pos. electrolytes, and it is independent of the pH, concn., and temp. of the electrolytes. The SOC values are compared with the redox potential of the neg. electrolyte during chronopotentiometry expts. using different cells in a ferro/ferricyanide (pos. electrolyte) and Fe(III)/(II)-triethanolamine (neg. electrolyte) system. The SOC values as a function of the redox potential measurements follow a Nernst equation, which demonstrates the validity of the method. [on SciFinder(R)]