We developed concentrated hydrogen bonded electrolytes (CoHBEs) derived from a mixture of choline chloride (ChCl) and ethylene glycol (EG) containing ferrocene and viologen redox species for redox flow batteries. CoHBEs are similar to deep eutectic solvents (DESs) in terms of having distinct physical properties including wide electrochemical window, and low volatility. However, CoHBEs do not necessarily meet the requirement of “deep eutectic temperature” at a specific composition of the parent compounds that form the DES. CoHBEs formed with viologen and ferrocene species in ChCl:EG demonstrate reversible redox reactions. More importantly, 0.5 M of a viologen derivative coupled with 1 M of a ferrocene derivative was achieved owing to the good solvent strength of ChCl:EG at 1:4 and 1:6 compositions. The resulting electrolyte presents about 2M equivalent concentration of the redox couple since the viologen derivative is able to undergo two successive electron transfer. A theoretical cell voltage of 1.35V is possible with this electrolyte. This presentation will discuss the electrochemical and transport properties of this electrolyte system, and their applicability in redox flow batteries as studied by spectro-electrochemical and flow cell experiments.