State of charge indicators for alkaline zinc-air redox flow batteries

Christian Zelger, Michael Süßenbacher, Andreas Laskos, Bernhard Gollas*

*Corresponding author for this work

Research output: Contribution to journalArticle


Physico-chemical properties of NaOH and KOH electrolytes are studied as possible state of charge indicators for the alkaline zinc-air redox flow battery. In order to predict the available energy of the battery and to prevent degradation as the result of unsuitable operating conditions, its state of charge has to be known. The state of charge is directly related to the composition of the negative electrolyte. A battery charging operation is simulated by electrodepositing zinc on a rotating cylinder electrode from NaOH electrolyte, while the simulation of a discharging operation is accomplished by dissolving ZnO in KOH electrolyte. The refractive index, conductivity, and density of NaOH- and KOH-electrolytes as well as the rest potential of the zinc electrode in these media are measured for different zincate and alkali concentrations at several temperatures. The electrolyte density and electrolyte conductivity are both linearly correlated with the zincate concentration. A linear correlation is found also between the rest potential and the logarithmic concentration term in the Nernst equation for the zinc half-cell reaction. These indicators permit a simple and straightforward monitoring of the state of charge of alkaline zinc-air redox flow batteries.

Original languageEnglish
Pages (from-to)76-81
Number of pages6
JournalJournal of Power Sources
Publication statusPublished - 1 Jun 2019


  • Conductivity
  • Density
  • Redox flow battery
  • Rest potential
  • State of charge
  • Zincate electrolyte

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Physical and Theoretical Chemistry
  • Electrical and Electronic Engineering

Fields of Expertise

  • Advanced Materials Science

Treatment code (Nähere Zuordnung)

  • Experimental


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