A redox flow battery system, comprising: a. A redox flow battery, comprising: i. An electrochemical cell having a first compartment containing a positive electrolyte, comprising a redox couple selected from Ce 4+ /Ce 3+, V 5+ /V 4+, MnO 4 - /Mn 2+, Mn 3+ /Mn 2+, CO 3+ +/CO 2+, and Br - /BrO 3 -, with an electrode at least partially immersed in the positive electrolyte, a second compartment containing a negative electrolyte, comprising a redox couple selected from V /V, Ti 3+ /T 2+, Cr 3+ /C 2+, and Zn 2+ /Zn, with an electrode at least partially immersed in the negative electrolyte, and a membrane mutually separating the first and second compartments, ii. First and second storage tanks for the storage of the positive and negative electrolytes respectively, at different states of charge, iii. Pumps to pump the positive and negative electrolytes from the compartments to the storage tanks and from the storage tanks to the compartments; iv. A source and inlet of inert gas to deoxygenate the system and stabilise the charged electrolytes. b. A first catalytic bed, for oxidatively forming a chemical species from the positive electrolyte, and regeneration of the positive electrolyte for reuse in the redox flow battery; c. A second catalytic bed, for the reduction of protons from the negative electrolyte into molecular hydrogen gas, and regeneration of the negative electrolyte for reuse in the redox flow battery; and d. Valves for directing the electrolytes between different parts of the system. a. A redox flow battery, comprising: i. An electrochemical cell having a first compartment containing a positive electrolyte, comprising a redox couple selected from Ce 4+ /Ce 3+, V 5+ /V 4+, MnO 4 - /Mn 2+, Mn 3+ /Mn 2+, CO 3+ +/CO 2+, and Br - /BrO 3 -, with an electrode at least partially immersed in the positive electrolyte, a second compartment containing a negative electrolyte, comprising a redox couple selected from V /V, Ti 3+ /T 2+, Cr 3+ /C 2+, and Zn 2+ /Zn, with an electrode at least partially immersed in the negative electrolyte, and a membrane mutually separating the first and second compartments, ii. First and second storage tanks for the storage of the positive and negative electrolytes respectively, at different states of charge, iii. Pumps to pump the positive and negative electrolytes from the compartments to the storage tanks and from the storage tanks to the compartments; iv. A source and inlet of inert gas to deoxygenate the system and stabilise the charged electrolytes. i. An electrochemical cell having a first compartment containing a positive electrolyte, comprising a redox couple selected from Ce 4+ /Ce 3+, V 5+ /V 4+, MnO 4 - /Mn 2+, Mn 3+ /Mn 2+, CO 3+ +/CO 2+, and Br - /BrO 3 -, with an electrode at least partially immersed in the positive electrolyte, a second compartment containing a negative electrolyte, comprising a redox couple selected from V /V, Ti 3+ /T 2+, Cr 3+ /C 2+, and Zn 2+ /Zn, with an electrode at least partially immersed in the negative electrolyte, and a membrane mutually separating the first and second compartments, ii. First and second storage tanks for the storage of the positive and negative electrolytes respectively, at different states of charge, iii. Pumps to pump the positive and negative electrolytes from the compartments to the storage tanks and from the storage tanks to the compartments; iv. A source and inlet of inert gas to deoxygenate the system and stabilise the charged electrolytes. b. A first catalytic bed, for oxidatively forming a chemical species from the positive electrolyte, and regeneration of the positive electrolyte for reuse in the redox flow battery; c. A second catalytic bed, for the reduction of protons from the negative electrolyte into molecular hydrogen gas, and regeneration of the negative electrolyte for reuse in the redox flow battery; and d. Valves for directing the electrolytes between different parts of the system.