A flow battery comprising: a first aqueous electrolyte comprising a first redox active material; a second aqueous electrolyte comprising a second redox active material; a first carbon electrode in contact with said first aqueous electrolyte in a first chamber containing the first aqueous electrolyte; a second carbon electrode in contact with said second aqueous electrolyte in a second chamber containing the second aqueous electrolyte; and a separator comprising a ionomer disposed between said first aqueous electrolyte and said second aqueous electrolyte; wherein said flow battery has an open circuit potential of at least 1.4 V measured by using standard techniques when the current flow between the first and second electrode is equal to zero and referenced to their values at 50% SOC and is capable of operating at a current density ranging between 50 mA/cm 2 and 500 mA/cm 2 at discharge when charging to 60% SOC and discharging to 40% SOC indicated as the total current passed in an electrochemical cell divided by the geometric area of the electrodes of the cell for a given round trip voltage efficiency V EFF,RT of at least 50%; and wherein the first redox active material remains soluble in said first aqueous electrolyte in both a charged state and a discharged state thereof, said second redox active material remains soluble in said second aqueous electrolyte in both a charged state and a discharged state thereof, and at least one of said first and second redox active materials is a metal ligand coordination compound according to the formula M x y z m, wherein L1, L2, and L3 are each independently ascorbate, a catecholate, citrate, a glycolate or polyol (including ligands derived from ethylene glycol, propylene glycol, or glycerol), gluconate, glycinate, α-hydroxyalkanoate (e.g., α-hydroxyacetate, or from glycolic acid), β-hydroxyalkanoate, γ-hydroxyalkanoate, malate, maleate, a phthalate, a pyrogallate, sarcosinate, salicylate, or lactate; x, y, and z are independently 0, 1, 2, or 3, and x + y + z = 3; and m is +1, 0, -1, -2, -3, -4, or -5, and M is Al, Cr, Fe, or Ti, wherein at least one of said first aqueous electrolyte and said second aqueous electrolyte has a pH in a range from 8 to 13. a first aqueous electrolyte comprising a first redox active material; a second aqueous electrolyte comprising a second redox active material; a first carbon electrode in contact with said first aqueous electrolyte in a first chamber containing the first aqueous electrolyte; a second carbon electrode in contact with said second aqueous electrolyte in a second chamber containing the second aqueous electrolyte; and a separator comprising a ionomer disposed between said first aqueous electrolyte and said second aqueous electrolyte; wherein said flow battery has an open circuit potential of at least 1.4 V measured by using standard techniques when the current flow between the first and second electrode is equal to zero and referenced to their values at 50% SOC and is capable of operating at a current density ranging between 50 mA/cm 2 and 500 mA/cm 2 at discharge when charging to 60% SOC and discharging to 40% SOC indicated as the total current passed in an electrochemical cell divided by the geometric area of the electrodes of the cell for a given round trip voltage efficiency V EFF,RT of at least 50%; and wherein the first redox active material remains soluble in said first aqueous electrolyte in both a charged state and a discharged state thereof, said second redox active material remains soluble in said second aqueous electrolyte in both a charged state and a discharged state thereof, and at least one of said first and second redox active materials is a metal ligand coordination compound according to the formula M x y z m, wherein L1, L2, and L3 are each independently ascorbate, a catecholate, citrate, a glycolate or polyol (including ligands derived from ethylene glycol, propylene glycol, or glycerol), gluconate, glycinate, α-hydroxyalkanoate (e.g., α-hydroxyacetate, or from glycolic acid), β-hydroxyalkanoate, γ-hydroxyalkanoate, malate, maleate, a phthalate, a pyrogallate, sarcosinate, salicylate, or lactate; x, y, and z are independently 0, 1, 2, or 3, and x + y + z = 3; wherein L1, L2, and L3 are each independently ascorbate, a catecholate, citrate, a glycolate or polyol (including ligands derived from ethylene glycol, propylene glycol, or glycerol), gluconate, glycinate, α-hydroxyalkanoate (e.g., α-hydroxyacetate, or from glycolic acid), β-hydroxyalkanoate, γ-hydroxyalkanoate, malate, maleate, a phthalate, a pyrogallate, sarcosinate, salicylate, or lactate; x, y, and z are independently 0, 1, 2, or 3, and x + y + z = 3; and m is +1, 0, -1, -2, -3, -4, or -5, and M is Al, Cr, Fe, or Ti, wherein at least one of said first aqueous electrolyte and said second aqueous electrolyte has a pH in a range from 8 to 13.