Redox mediated gas evolution

A system comprising:

• first and second reaction chambers, an electrochemical cell comprising first and second half-cells each comprising an electrode, first and second pumps, connections between the first pump, the first reaction chamber and the first half-cell providing a first flow circuit for the first pump to circulate a first liquid through the first reaction chamber, from the first reaction chamber to the first half-cell, through the first half-cell and back to the first reaction chamber, and connections between the second pump, the second reaction chamber and the second half-cell providing a second flow circuit for the second pump to circulate a second liquid through the second reaction chamber, from the second reaction chamber to the second half-cell, through the second half-cell and back to the second reaction chamber;
• wherein in each flow circuit, the half-cell defines a flow path to carry through flow of the liquid into contact with the electrode therein;
• the reaction chamber comprises a reaction catalyst, and the reaction chamber defines a flow path to carry through flow of liquid into contact with the catalyst;
• the liquid flowing through each reaction chamber is able to undergo reaction at the catalyst therein to form a gas;
• an electrochemically reactive mediator substance is dissolved in the liquid, the mediator substance being able to undergo an electrochemical conversion between a first state and a second state at the electrode;
• wherein the mediator substance and the liquid are such that when electric current is supplied to the electrode while the pump is circulating the liquid, the mediator substance is converted from its first state to its second state at the electrode;
• reaction at the catalyst in the reaction chamber forms gas from the liquid and returns the mediator substance to its first state;
• and further wherein the first and second liquids each contain a solute enabling the liquid to display elastic turbulence, and the flow path in the reaction chamber of each flow circuit is configured to compel changes in the direction of liquid flow, to cause elastic turbulence within flow of the liquid in contact with the catalyst.