Electrochemical Impedance Spectroscopy – Just One of Many Tools to Study Batteries and Power Sources

Abstract

Electrochemical Impedance Spectroscopy (EIS) is one of the many methods available to the researcher in electrochemistry. To take full advantage of its capabilities, one should understand the method and the underlying principles. In this work voltammetry on a stationary electrode, as well as with a rotated disk electrode (RDE) are presented together with EIS results, exemplified by reduction and oxidation of vanadium salts in 3 mol/l sulfuric acid. This contribution summarizes highlights, but also pitfalls of impedance measurements and their interpretation, as they are relevant to the practice and theory of electrochemical work. The most significant component in the equivalent circuit is the change transfer resistance, which matches well the voltammetric curves of the RDE experiment. A high-frequency artifact can be eliminated by formally fitting it to an inductor and resistor of series; both of these components have, however, negative value. The Oxidation States of VanadiumVanadium has extremely rich chemistry and from electrochemical point of view it is interesting because it exists in a number of different oxidation states. Most of the soluble species exist in acidic solutions so the work is usually done in sulfuric acid. The reduction from dioxovanadium(V) to vanadyl cation VO 2 + + 2 H + + e -→ VO 2+ + H 2 O E o = + 1.0 V Reduction of vanadyl to vanadium +3 VO 2+ + 2 H + + e -→ V 3+ + H 2 O E o = + 0.34 V and reduction of vanadium +3 to +2 V 3+ + e -→ V 2+ E o = -0.26 V The colors are also interesting and can guide during the experiment: VO 2 + yellow, VO 2+ blue, V 3+ green, V 2+ purple. Based on the standard potential values, it is possible to predict existence of three consecutive peaks on a cyclic voltammogram, as demonstrated in this simulation (Fig. ECS Transactions, 48 (1) 33-42 (2014) 33 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 142.103.160.110 Downloaded on 2015-07-06 to IP