Protic ammonium salts containing the anthraquinone moiety as redox-active species for non-aqueous energy storage

Increasing electrical energy demands and transitions to renewable energy sources has driven
expanding interest in the development of solutions for large-scale energy storage. For this
role of energy storage, redox flow batteries are a promising technology due to their scalability
and flexibility in electrolyte materials. Organic redox-active species have seen much interest
for their greater tunability over metal systems and quinones are a highly desirable group of
compounds under investigation for their two-electron redox behaviour. Due to accessibility
of certain quinones and their generally poor organic solubilities, the field of research has
been largely limited to aqueous systems. This thesis investigates the preparation of ionic
compounds containing the redox-active anthraquinone moiety as candidates for use in non�aqueous energy storage applications to utilise the greater potential window of common
organic solvents compared to water. Five anthraquinone ammonium cations were
synthesised each as triflate, trifluoroacetate and bis(trifluoromethylsulfonyl)azanide salts for
a total of 15 novel compounds. These were characterised structurally, physically (including
quantitative solubility in acetonitrile) and electrochemically through cyclic voltammetric
analysis. Highly alkylated salts were found to have solubilities competitive with other
quinone-derived compounds found in the literature. The salts displayed two sequential one�electron redox processes in acetonitrile with reduction potentials of -0.63 V (vs SHE) for the
first and -1.13 to -1.22 V (vs SHE) for the second reduction. The salts exhibited strong
hydrogen bonding under cyclic voltammetry causing an exceeding sensitivity to water
content and driving a reversible adduct formation following reduction. Synthesis procedures
were also presented for several naphthoquinone and benzoquinone ammonium salts. These
compound classes were more reactive requiring protection of the quinone moiety for
syntheses to progress effectively.