In this invention disclose report, hydroxyl compound additives are disclosed as significantly improve the kinetics of the FL (fluorenone)-based aqueous redox flow battery (ARFB) (Selected examples of hydroxyl compounds and examples of molecular engineered FLs tested as illustrated in Supporting Figure 1). Application of FL derivatives in flow battery has been reported in nonaqueous systems and aqueous systems. Higher energy density and power density are always the pursuits during RFB redox-active material development. For a certain redox pair applied in RFB, capacity utilization usually decreases while current density increases due to the kinetics limit. It is of keen interest to maintaining battery discharge capacity at elevated current density, thus achieving long-time operation and high-power output at the same time. Here we disclose hydroxyl compound can serve as additives for FL-based ARFBs to significantly improve their rate capability and power output. To our best knowledge, this is a first-time demonstration of the utilization of additives to boost rate capability in RFBs. The development of this approach will have a revolutionary impact. In our examination, selected examples of molecular engineered FLs benefited from 0.1 M beta CD additive, demonstrating significant discharge capacity enhancement at higher current densities when comparing with a blank test. A case study using 27S4CFL extended the additive ranges to other hydroxyl-containing redox-inert compounds. Cyclic Voltammetry (CV) scans of these additives revealed no redox peak within the water window in alkaline conditions. Conductivity and viscosity both exhibited a negative effect on the battery performance while the overall current density was boosted by adding in these additives. An observation that is contrary to common understanding of those skilled in the field of energy storage and electrochemistry. The additive concentration effect was investigated using beta CD, the result showed a peak battery performance when 0.086 M beta CD was employed in the system. The long-term battery operation revealed a minimal effect on the battery cycling stability.