An electrode for electrochemical applications is coated with a layer of a-C, wherein the layer of a-C comprises at least 10 each of first and second sub-layers, being(i) first sub-layers having high conductivity with a sp2 content of 60-95%, alternating with(ii) second sub-layers having high corrosion resistance with a sp2 content of 50-90%, wherein the sp2 content of the first sub-layers is at least 3% greater than the sp2 content of the second sub-layers. A method of making such electrodes comprises: a) depositing a first sub-layer comprising a-C, b) depositing a second sub-layer comprising a-C wherein the sp2 content of the first sub-layer is at least 3% greater than the sp2 content of the second sub-layer, andc) repeating the steps above to deposit at least 10 first sub-layers alternating with 10 second sub-layers, so as to produce the electrodes.

One embodiment is a redox flow battery system that includes an anolyte; a catholyte; an anolyte tank configured for holding at least a portion of the anolyte; a catholyte tank configured for holding at least a portion of the catholyte; a primary redox flow battery arrangement, and a second redox flow battery arrangement. The primary and secondary redox flow battery arrangements share the anolyte and catholyte tanks and each includes a first half-cell including a first electrode in contact with the anolyte, a second half-cell including a second electrode in contact with the catholyte, a separator separating the first half-cell from the second half-cell, an anolyte pump, and a catholyte pump. The peak power delivery capacity of the secondary redox flow battery arrangement is less than the peak power delivery capacity of the primary redox flow battery arrangement.

Flow batteries can be constructed by combining multiple electrochemical unit cells together with one another in a cell stack. High-throughput processes for fabricating electrochemical unit cells can include providing materials from rolled sources for forming a soft goods assembly and a hard goods assembly, supplying the materials to a production line, and forming an electrochemical unit cell having a bipolar plate disposed on opposite sides of a separator. The electrochemical unit cells can have configurations such that bipolar plates are shared between adjacent electrochemical unit cells in a cell stack, or such that bipolar plates between adjacent electrochemical unit cells are abutted together with one another in a cell stack.

A gas diffusion electrode substrate that is used in a fuel cell and is constituted by an electrode substrate and microporous parts, in which a microporous part (A) is formed on one surface of the electrode substrate, and a microporous part (B) is formed in a part of the inside of the electrode substrate, the gas diffusion electrode substrate having a part in which the microporous part (B) is continuously present from the electrode substrate surface on the side on which the microporous part (A) is formed to a position near the electrode substrate surface on the opposite side, and a part in which pores are continuously distributed from the electrode substrate surface on the side on which the microporous part A is formed to the electrode substrate surface on the opposite side.

An electrode for redox flow batteries, the electrode being formed of a carbon fiber aggregate including a plurality of carbon fibers. Each of the carbon fibers has a plurality of pleats formed in the surface thereof. The ratio of L.sub.1 to L.sub.2, that is, L.sub.1/L.sub.2, is more than 1, where L.sub.1 is the peripheral length of a cross section of the carbon fibers and L.sub.2 is the peripheral length of a virtual rectangle circumscribing the cross section of the carbon fibers.

A method for preparation of electrolyte for a redox flow battery includes reducing chromium ore using a carbon source to convert the chromium ore to an iron/chromium alloy with carbon particles; dissolving the iron/chromium alloy with carbon particles in sulfuric acid to form a first solution; adding calcium chloride or barium chloride to the first solution to produce a second solution including FeCl.sub.3 and CrCl.sub.3; and adding an acid to the second solution to form the electrolyte. Other methods can be used for preparing an electrolyte from chromium waste material.

Flow batteries can be constructed by combining multiple electrochemical unit cells together with one another in a cell stack. High-throughput processes for fabricating electrochemical unit cells can include providing materials from rolled sources for forming a soft goods assembly and a hard goods assembly, supplying the materials to a production line, and forming an electrochemical unit cell having a bipolar plate disposed on opposite sides of a separator. The electrochemical unit cells can have configurations such that bipolar plates are shared between adjacent electrochemical unit cells in a cell stack, or such that bipolar plates between adjacent electrochemical unit cells are abutted together with one another in a cell stack.

A bipolar plate for a fuel cell stack or for an electrolyzer stack, having an anode plate and a cathode plate which are joined to face-to-face. Wherein the face of the anode plate that faces the face of the cathode plate delimits an internal space that forms a circuit for the distribution of a first fluid, thereby forming a bipolar plate. Wherein the first opening and the second opening facing one another thereby forming a collector configured to enable the passage of the first fluid or a second fluid through the bipolar plate. Wherein the first opening and the second opening have distinct dimensions such the peripheral end of the first opening and the peripheral end of the second opening are offset in relation to one another in the plane of the bipolar plate, forming a shoulder at the peripheral end of the collector.

There is provided a frame body used for a cell of a redox flow battery, that can improve heat dissipation of an electrolyte in a slit and can suppress rise of the temperature of the electrolyte. It is a frame body used for a cell of a redox flow battery, comprising: an opening formed inside the frame body; a manifold allowing an electrolyte to pass therethrough; and a slit which connects the manifold and the opening and forms a channel of the electrolyte between the manifold and the opening, the slit having a pair of sidewalls facing each other in a cross section orthogonal to a direction in which the electrolyte flows, the slit having, at at least a portion thereof in the slit's depthwise direction, a width narrowing portion allowing the sidewalls to have a spacing narrowed in the depthwise direction.

There is provided a frame body used for a cell of a redox flow battery, that can improve heat dissipation of an electrolyte in a slit and can suppress rise of the temperature of the electrolyte. It is a frame body used for a cell of a redox flow battery, comprising: an opening formed inside the frame body; a manifold allowing an electrolyte to pass therethrough; and a slit which connects the manifold and the opening and forms a channel of the electrolyte between the manifold and the opening, the slit having a pair of sidewalls facing each other in a cross section orthogonal to a direction in which the electrolyte flows, the slit having, at at least a portion thereof in the slit's depthwise direction, a width narrowing portion allowing the sidewalls to have a spacing narrowed in the depthwise direction.