A flow battery system comprising: a first half-cell containing a first electrolyte solution; and a second half-cell containing a second electrolyte solution; wherein both the first half-cell and the second half-cell are in fluid communication with an electrochemical balancing cell for balancing the pH-value in an electrolyte solution comprising: a first chamber containing a first electrode; a second chamber containing a second electrode; a third chamber disposed between the first chamber and the second chamber; an ion-selective membrane comprising a cation-exchange material or an anion-exchange material forming a first interface between the first chamber and the third chamber, wherein the ion-selective membrane comprising a cation-exchange material allows the passage of positively charged ions across the interface between the first chamber and the third chamber and substantially excludes the passage of negatively charged ions such that migration of positively charged ions can occur in both directions across the ion-selective membrane, and wherein the ion-selective membrane comprising an anion- exchange material allows the passage of negatively charged ions across the interface between the first chamber and the third chamber and substantially excludes the passage of positive charged ions such that migration of the negatively charged ions can occur in both directions at ion-selective membrane; and a bipolar membrane comprising both a cation-exchange material and an anion exchange material, thus excluding the passage of positively charged materials and negatively charged materials, respectively, in both directions, and forming a second interface between the second chamber and the third chamber; wherein at least one of the first electrolyte solution and the second electrolyte solution comprises an aqueous electrolyte solution. a first half-cell containing a first electrolyte solution; and a second half-cell containing a second electrolyte solution; wherein both the first half-cell and the second half-cell are in fluid communication with an electrochemical balancing cell for balancing the pH-value in an electrolyte solution comprising: a first chamber containing a first electrode; a second chamber containing a second electrode; a third chamber disposed between the first chamber and the second chamber; an ion-selective membrane comprising a cation-exchange material or an anion-exchange material forming a first interface between the first chamber and the third chamber, wherein the ion-selective membrane comprising a cation-exchange material allows the passage of positively charged ions across the interface between the first chamber and the third chamber and substantially excludes the passage of negatively charged ions such that migration of positively charged ions can occur in both directions across the ion-selective membrane, and wherein the ion-selective membrane comprising an anion- exchange material allows the passage of negatively charged ions across the interface between the first chamber and the third chamber and substantially excludes the passage of positive charged ions such that migration of the negatively charged ions can occur in both directions at ion-selective membrane; and a bipolar membrane comprising both a cation-exchange material and an anion exchange material, thus excluding the passage of positively charged materials and negatively charged materials, respectively, in both directions, and forming a second interface between the second chamber and the third chamber; wherein at least one of the first electrolyte solution and the second electrolyte solution comprises an aqueous electrolyte solution. a first chamber containing a first electrode; a second chamber containing a second electrode; a third chamber disposed between the first chamber and the second chamber; an ion-selective membrane comprising a cation-exchange material or an anion-exchange material forming a first interface between the first chamber and the third chamber, wherein the ion-selective membrane comprising a cation-exchange material allows the passage of positively charged ions across the interface between the first chamber and the third chamber and substantially excludes the passage of negatively charged ions such that migration of positively charged ions can occur in both directions across the ion-selective membrane, and wherein the ion-selective membrane comprising an anion- exchange material allows the passage of negatively charged ions across the interface between the first chamber and the third chamber and substantially excludes the passage of positive charged ions such that migration of the negatively charged ions can occur in both directions at ion-selective membrane; and a bipolar membrane comprising both a cation-exchange material and an anion exchange material, thus excluding the passage of positively charged materials and negatively charged materials, respectively, in both directions, and forming a second interface between the second chamber and the third chamber; wherein at least one of the first electrolyte solution and the second electrolyte solution comprises an aqueous electrolyte solution.