The present invention relates to electrolyte compositions comprising distinct redox-active compounds, namely, a redox-active compound, which is phenazine or a phenazine derivative, and a distinct redox-active compound, which is not phenazine or a phenazine derivative. The present invention also relates to the use of such electrolyte compositions as redox flow battery electrolytes. Accordingly, the invention further provides a redox flow battery comprising said compositions.

The present invention provides methods for producing hydrogen using a mediator that is capable of reversibly donating and accepting four or more electrons. A method of the invention comprises the steps of reducing a mediator by four or more electrons to yield a reduced mediator, and oxidising a reduced mediator to yield a mediator, and reducing protons to yield hydrogen.

At a position between a fuel offgas inlet portion and a fuel gas inlet portion in a main body portion in the facing direction where a first end faces a second end, a fluid confluence joint is provided with at least either one of (i) at least one step formed over a whole circumference of an inner wall of the main body portion by reducing the passage sectional area on a fuel gas passage portion side to be smaller than the passage sectional area on a confluence passage portion side, and (ii) at least one partition wall formed over the whole circumference so as to project inwardly from the inner wall of the main body portion.

An ion conducting polymer comprising a modified poly(phenylene oxide) is described. In an exemplary modified polymer, a portion of the monomeric units are attached to a sulfonate-substituted arylamino moiety, such as a monovalent derivative of phenoxy aniline trisulfonate (BOATS), to form a monomeric unit with a charged side chain. Ion conducting polymers can also be prepared with polyether-containing side chains. The ion conducting polymer can be used to prepare ion exchange membranes which can be used in a variety of applications, such as in non-aqueous redox flow batteries and related energy storage systems.

At least some embodiments herein disclose a vanadium-based solution formed by a combination of a vanadium compound, vanadium in metallic form and an appropriate reducing agent. A manufacturing process of the combination foregoes a need of using at least one among a relatively strong reducing agent that subsequently requires removal thereof and using an electrochemical reaction to achieve sufficient chemical reduction of vanadium that is needed for the vanadium-electrolyte solution to act as the liquid electrode in the vanadium-based battery. The liquid electrode, accommodated in a battery case, has an average oxidation state of within a range of +3.3 to +3.7, which is suitable for a catholyte and an anolyte in the battery.

A flow battery system with a cathode cell including a first electrode, an anode cell includes a second electrode, and a membrane between the two cells. A first electrolyte tank includes a catholyte. A second electrolyte tank includes an anolyte. The system includes two rebalancing cells. A first rebalancing cell is in fluid communication between the cathode cell and the first electrolyte tank and is configured to reduce active species from the catholyte. The second rebalancing cell is in fluid communication with the first electrolyte tank and the second electrolyte tank such that the first electrolyte tank and the second electrolyte tank are in direct fluid communication. The second rebalancing cell is configured to reduce active species from the catholyte and the reduced catholyte may be combined directly with the anolyte. The second rebalancing cell may be a chemical reactor, a catalytic reactor, or an electrochemical reactor.

A method and systems are provided for utilizing black powder to form an electrolyte for a flow battery. In an exemplary method the black powder is heated under an inert atmosphere to form Fe.sub.3O.sub.4. The Fe.sub.3O.sub.4 is dissolved in an acid solution to form an electrolyte solution. A ratio of iron (II) to iron (III) is adjusted by a redox process.

An uninterruptible power supply unit for subsea applications includes a flow battery including: at least one flow battery module including at least a negative electrode cell and a positive electrode cell, a first electrolyte storage tank connected to the negative electrode cell to provide the negative electrode cell with a first electrolyte, and a second electrolyte storage tank connected to the positive electrode cell to provide the positive electrode cell with a second electrolyte. The unit further includes at least one electrolyte pressure compensator, connected to the first electrolyte storage tank and connected to the second electrolyte storage tank, respectively, to provide pressure balancing between an ambient medium surrounding the at least one electrolyte pressure compensator and first electrolytes and second electrolytes inside the first electrolyte storage tank and inside the second electrolyte storage tank, respectively.

The invention is directed to a mediated metal-sulfur flow battery. This battery format that is readily scalable to grid-scale levels at low cost, while maintaining battery safety by physically separating the anode and cathode. As an example, the marriage of a redox-targeting scheme to an engineered Li solid electrolyte interphase (SEI) enables a scalable, high efficiency, membrane-less Li—S redox flow battery. Redox mediators can be sued to kick-start the initial reduction of solid S into soluble polysulfides on the cathode side and final reduction of polysulfides into solid Li.sub.2S, precluding the need for conductive carbons. On the anode side, a LiI and LiNO.sub.3 pretreatment and additive strategy encourages a stable SEI and lessens capacity fade, avoiding the need for ion-selective separators.

Disclosed is a unitized regenerative fuel cell system, comprised of a unitized regenerative fuel cell able to operate in a fuel cell mode for electric power generation and in a water electrolysis mode for hydrogen and oxygen production, and a plurality of fire-detecting sensors for detecting fire in each zone of a tunnel, and configured to supply oxygen to zones wherein fire has not occurred if occurrence of fire has been detected in a tunnel, and a method for controlling the same.