Herein, we report new sustainable design strategies of aqueous electrolytes for redox flow batteries using redox-active organic materials. A green spontaneous grafting reaction occurred between a redox-active organic radical and an electrochemically activated structural modifier at room temperature through a simple mixing step. Then, by using a physical mixing method, we formulated a structured aqueous electrolyte and achieved aqueous solubilization of the organic solute from below 0.5 to 1.5 M beyond the conventional dissolution limit. The as-obtained concentrated mixture can be readily used as catholyte for a redox flow battery. Remarkably, a record high discharge cell voltage (1.6 V onset output voltage) in aqueous non-hybrid flow cell was achieved using the studied electrolytes.