Electrochemistry

Photochemistry

Materials science

Ferrocene

Viologen

Molecule

Inorganic chemistry

Intermolecular force

Physical chemistry

Redox

Organic chemistry

Aqueous solution

Radical

Chemistry

Electrode

Electrolyte

Nano Energy

Aqueous organic redox flow battery (AORFB) using viologens suffers from poor cycling life especially at high concentrations due to the dimerization of viologen radical cations. Here, we report a molecular spectator approach, exploiting α-cyclodextrin (α-CD) with suitable cavity size as the spectator, to weaken the intermolecular interaction of viologen radicals and suppress dimerization in AORFBs. UV–vis spectroscopy reveals that α-CD effectively suppresses the dimerization of viologen radicals. Applying α-CD as the spectator, a symmetric static cell (0.1 M EV-0.01 M α-CD) demonstrated a significantly lower capacity decay rate of 0.075% per day (20 days, 100% capacity utilization) compared to the sole EV electrolyte (0.31% per day). Asymmetric flow cells (1.0 M EV-0.1 M α-CD) coupling with a ferrocene derivative demonstrated stable cycling over 500 cycles during 26 days at 80% capacity utilization. This work provides a facile and effective strategy to stabilize the viologen radicals for AORFBs applications.

Viologen radical stabilization by molecular spectators for aqueous organic redox flow batteries