Characterization Methods in Flow Batteries: A General Overview

Successful development of efficient and robust systems for the conversion and storage of energy requires systematic materials characterization. Oftentimes, this is only accomplished by the smart combination of multiple complementary techniques carried out ex situ (i.e. before and after operation), in situ (i.e. at relevant temperatures pressures, pH), and in operando (i.e. in most realistic conditions). Considering the very different nature of the individual components of redox-flow batteries, e.g. porous carbonaceous electrodes, polymer membranes, liquid aqueous and organic electrolytes, and bipolar plates, a multitude of analytical techniques can provide valuable insights into the physicochemical properties of the system at hand. In this chapter, fundamental and sophisticated spectroscopic, microscopic, and diffraction techniques will be summarized. Emphasizing the vanadium redox flow system (VRFB) the most commonly used analytical methods are introduced that provide the reader with the necessary background knowledge and an overview on physicochemical and electroanalytical tools for addressing specific research questions and arriving at confident conclusions.