Cycling regimes
used to analyze the various phenomena occurring
in the DHAQ flow battery. The regions of interest are highlighted
by dotted lines or solid arrows, and the voltage profiles are labeled
with the subsequent figures that provide a more detailed analysis
of the various processes. (a) Voltage of a 10 mM DHAQ versus 15 mM
K4[Fe(CN)6] and 3.75 mM K3[Fe(CN)6] full cell as a function of time. During charge, a constant
current of 10 mA was applied, followed by a voltage hold at 1.6 V.
During discharge, a constant current of −10 mA (where the sign
indicates the polarity of the electrodes) was applied, followed by
a potential hold at 0.6 V. The charge–discharge cycles were
repeated four times, then potential holds of 10 h each were applied
at 1.6 and 1.7 V. (b) Voltage of a 100 mM DHAQ versus 150 mM K4[Fe(CN)6] and 50 mM K3[Fe(CN)6] full cell. During charge, a constant current of 150 mA was applied
to a cutoff voltage of 1.7 V. During discharge, a constant current
of −150 mA was applied to a cutoff voltage of 0.6 V. The 7th
charge was followed by a voltage hold at 1.7 V for 20 h and another
20 charge/discharge cycles.