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Dihydroxyphthalazines – new stable electrolyte substances for redox flow batteries

Ref-No: TA-TM 1010


The substances presented here are hydroquinone derivatives which are nitrogen-substituted in the carbon skeleton, so-called dihydroxyphthalazines. As a result of the nitrogen substitution, among other things, they have exceptionally good characteristics for use as redox-active electrolytes in flow batteries. A very favorable potential range of electrochemical activity (high redox potential) in connection with an extraordinarily good chemical long-term stability is to be emphasized here in particular. According to current knowledge, the reason for the favorable potential range is nitrogen substitution in the aromatic basic structure of phthalazines, while the increased stability results predominantly from the respective substitution pattern.


In order to shape the future sustainable energy supply, buffer storage facilities for electricity generated from renewable sources are required in a wide range of sizes, from a few kilowatt hours to dozens of megawatt hours of storage capacity.

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The most promising storage technology is the so-called redox flow battery. They are based on inorganic metal salt solutions (V2+/V3+) and on organic redox-active compounds such as hydroquinones. However, the organic systems known so far do not show sufficient long-term stability.


The combination of these structural characteristics result in the favorable properties for the use of dihydroxyphthalazines in redox flow batteries - in terms of stability and high redox potential. By suitable substitution, these properties can be further adapted and the solubility behavior can be optimized, which further enhances their suitability as a positive active material in the catholyte of redox flow batteries


  • Optimum potential range of electrochemical activity
  • High long-term chemical stability (only slight shifts in the cyclovoltamogram during repeated cyclovoltamogram measurements (laboratory tests) with up to n = 400 repetitions)

Due to their easy scalability in terms of withdrawal capacity and storage capacity, redox flow batteries can be used both as stationary large-scale systems to maintain grid stability and as mobile systems, for example in the field of electromobility.
Also in the field of building technology the first systems are already being used for the uninterruptible, regenerative power supply of private households.






Scope of application

Power supply:

  • Large storage tanks for grid stabilisation
  • Smaller stationary storage tanks for individual (self-)supply
  • Mobile storage systems for electric mobility

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Development status

Laboratory model

Patent situation

  • EP pending


Energy storage, electricity storage, organic electrolytes for redox flow batteries

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