## Abstract

The ultraviolet-visible spectra of catholytes for vanadium flow batteries (VFBs) were measured and analyzed for a range of V
^{IV}:V
^{V} ratios and vanadium concentrations. Using a model of V
_{2}O
_{3}
^{3+} in equilibrium with VO
^{2+} and VO
_{2}
^{+}, the spectra were characterized in terms of an excess absorbance parameter p and the molar extinction coefficients ε
_{4} and ε
_{5} of VO
^{2+} and VO
_{2}
^{+}, respectively. The results showed that p varies weakly with the vanadium concentration C and this variation was quantified relative to a reference concentration C
_{r} by means of a concentration coefficient φ
_{r}. Experimental data showed that plots of φ
_{r} versus Cφ
_{r} and plots of 1/φ
_{r} versus C are linear and, based on this linearity, φ
_{r} was expressed as a simple function of C in terms of its reference concentration C
_{r} and a single parameter M that is independent of the choice of C
_{r}. Standard spectra of p at a concentration C
_{0} = 1 mol dm
^{-3} and of ε
_{4} and ε
_{5} were generated from which the spectrum of any catholyte may be simulated using the measured value of M in a governing equation. This enables determination of the state of charge for any VFB catholyte using absorbance measurements at a small number of wavelengths.

Original language | English (Ireland) |
---|---|

Pages (from-to) | 5068-5083 |

Journal | Journal of the Electrochemical Society |

Volume | 163 |

Issue number | 1 |

DOIs | |

Publication status | Published - 2016 |