Performance of an all quinone redox flow battery is enhanced via using electrolytes with

contrasting pH on both sides of the proton exchange membrane. This performance increase

includes elevation of the open circuit voltage by 300 mV to 1.5 V at SOC of 50% and augmentation

of energy density by a factor of three to 20.6 Wh/Kg in reference to the previous redox flow battery

developed earlier. The battery is able to operate at current densities up to 80 mA/cm2 and meeting

columbic efficiency of 99.9% and energy density of 70%. Moreover, the battery with contrasting

pH was able to operate for more than 140 hours continuously. Final system pH was similar to the

initial system pH. Furthermore, durability of the referenced flow battery is enhanced by using this

technique via maintaining a neutral pH on the cathode side of the flow battery comprising of

Dihydroxy Anthraquinone and ferricyanide ion.

Electrolyte pH might affect redox reaction of the analytes significantly. For example, redox

potential of quinone compounds that entail protonation step in their electrochemical reaction might

change by pH and some compounds such ferricyanide ion or TEMPO compounds might not be

able to demonstrate reversible reactions at a specific pH. Capability of manipulation of the pH of

each half cell independently from the other half cell can bring various advantages such as coupling

half reactions that operate at completely different pH and affect redox potential, durability or

energy density accordingly and such applications might even transcend the boundaries of the redox

flow batteries.

Half-cell characteristics of the catholyte such as redox potential, reversibility, stability and

kinetics have been analyzed in this work while the similar aspects of the anolyte have been

analyzed in literature. Single-cell tests for both systems have been performed and the results as

well as the test conditions and methods are displayed. The systems include the DHAQ (pH=14)

vs Ferricyanide ion (pH= 7) redox flow battery that is discussed in chapter 3 as well as DHAQ

(pH=14) vs HQDS (pH=0.3) (hydroquinone disulfonic acid) flow battery that is discussed in

chapter 4.