A combination of redox active compounds is useful in connection with a rechargeable battery and includes a first redox active compound having a first solubility, and a second redox active compound having a second solubility, wherein the combination has a third solubility that is greater than one or both of the first solubility and the second solubility.

A combination of redox active compounds is useful in connection with a rechargeable battery and includes a first redox active compound having a first solubility, and a second redox active compound having a second solubility, wherein the combination has a third solubility that is greater than one or both of the first solubility and the second solubility.

A desalination method that may be used to reduce limescale buildup in desalination electrodes. The desalination method includes providing an electrode including a first material having at least one compound of a formula before a desalination step. The formula is A.sub.xFe.sub.yCu.sub.z(CN).sub.6, where A is Na, Li or K, 0.1≤x≤2, 1≤y, and z≤2. The desalination method further includes exchanging A in A.sub.xFe.sub.yCu.sub.z(CN).sub.6 with Ca to form a second material from the first material during the desalination step.

A desalination method that may be used to reduce limescale buildup in desalination electrodes. The desalination method includes providing an electrode including a first material having at least one compound of a formula before a desalination step. The formula is A.sub.xFe.sub.yCu.sub.z(CN).sub.6, where A is Na, Li or K, 0.1≤x≤2, 1≤y, and z≤2. The desalination method further includes exchanging A in A.sub.xFe.sub.yCu.sub.z(CN).sub.6 with Ca to form a second material from the first material during the desalination step.

The present invention discloses a method for rapidly preparing a Prussian blue analogue with a monoclinic crystal structure. The Prussian blue analogue with a monoclinic crystal structure has a chemical formula of Na.sub.xM[Fe(CN).sub.6].sub.y.Math.zH.sub.2O, where M=Mn or Fe, 1.5<×<2, and 0.5<y<1. In this method, a mixture of sodium ferrocyanide and sodium chloride is adopted as a solution A, and a solution of manganese salt or iron salt in water is adopted as a solution B; the solutions A and B are continuously and rapidly mixed by a micromixer, and the precipitation reaction is conducted to obtain a nano-precursor slurry; and the nano-precursor slurry is aged at 80° C. to 160° C. for 3 min to 2 h to obtain a Prussian blue analogue with a monoclinic crystal structure that has a particle diameter of 200 nm to 2,000 nm.

The present invention discloses a method for rapidly preparing a Prussian blue analogue with a monoclinic crystal structure. The Prussian blue analogue with a monoclinic crystal structure has a chemical formula of Na.sub.xM[Fe(CN).sub.6].sub.y.Math.zH.sub.2O, where M=Mn or Fe, 1.5<×<2, and 0.5<y<1. In this method, a mixture of sodium ferrocyanide and sodium chloride is adopted as a solution A, and a solution of manganese salt or iron salt in water is adopted as a solution B; the solutions A and B are continuously and rapidly mixed by a micromixer, and the precipitation reaction is conducted to obtain a nano-precursor slurry; and the nano-precursor slurry is aged at 80° C. to 160° C. for 3 min to 2 h to obtain a Prussian blue analogue with a monoclinic crystal structure that has a particle diameter of 200 nm to 2,000 nm.

The present disclosure provides a prussian blue analogue positive electrode material, a preparation method therefor and an electrochemical energy storage device. A molecular formula of the prussian blue analogue positive electrode material is A.sub.xM.sub.c[M′(CN).sub.6].sub.1-y(b-H.sub.2O).sub.6y-dL.sub.d.□.sub.y.(i-H.sub.2O).sub.z, where, A is one or more selected from a group consisting of alkali metal cation, alkaline-earth metal cation, Zn.sup.2+ and Al.sup.3+; M is a metal with the valence of 2+ or 3+; M′ is a metal with the valence of 2+ or 3+; b-H.sub.2O is a coordinated water; □ is a M′(CN).sub.6 cavity; L is a neutral ligand, the neutral ligand is one or more selected from a group consisting of CH.sub.3CN, NH.sub.3, CO and C.sub.5H.sub.5N; i-H.sub.2O is an interstitial water; 0<x≤2; 0<c≤1; 0<y<1; 0<d≤6y; 0≤z≤16. In the prussian blue analogue positive electrode material of the present disclosure, the neutral ligand L participates in the coordination with a transition metal and substitutes the coordinated water partly or wholly, so that a content of the coordinated water is decreased or even eliminated, therefore, the water absorption performance of the prussian blue analogue positive electrode material will be decreased significantly, in turn the performance of the electrochemical energy storage device is significantly improved.

The present disclosure provides a prussian blue analogue positive electrode material, a preparation method therefor and an electrochemical energy storage device. A molecular formula of the prussian blue analogue positive electrode material is A.sub.xM.sub.c[M′(CN).sub.6].sub.1-y(b-H.sub.2O).sub.6y-dL.sub.d.□.sub.y.(i-H.sub.2O).sub.z, where, A is one or more selected from a group consisting of alkali metal cation, alkaline-earth metal cation, Zn.sup.2+ and Al.sup.3+; M is a metal with the valence of 2+ or 3+; M′ is a metal with the valence of 2+ or 3+; b-H.sub.2O is a coordinated water; □ is a M′(CN).sub.6 cavity; L is a neutral ligand, the neutral ligand is one or more selected from a group consisting of CH.sub.3CN, NH.sub.3, CO and C.sub.5H.sub.5N; i-H.sub.2O is an interstitial water; 0<x≤2; 0<c≤1; 0<y<1; 0<d≤6y; 0≤z≤16. In the prussian blue analogue positive electrode material of the present disclosure, the neutral ligand L participates in the coordination with a transition metal and substitutes the coordinated water partly or wholly, so that a content of the coordinated water is decreased or even eliminated, therefore, the water absorption performance of the prussian blue analogue positive electrode material will be decreased significantly, in turn the performance of the electrochemical energy storage device is significantly improved.

A method of testing the composition or quality of water includes dissolving about two parts by weight of a 2-hydroxybenzyl alcohol and about one part by weight of a sodium nitroprusside in about seventy-five parts by weight of a polyethylene glycol; adding the sodium nitroprusside solution to a water sample to catalyze an indophenol monochloramine reaction; and detecting the concentration of monochloramine in the water sample. The polyethylene glycol may be a polyethylene glycol 300, a PEG-400 or a PEG-1000. The method may also be accomplished with a solution made by dissolving a 2-hydroxybenzyl alcohol and a sodium nitroprusside in a mixture of propane-1,2-diol and water.

The present invention provides a method of preparing a graphene-wrapped cobalt Prussian blue nano-crystalline composite material, and a method of preparing a working electrode using the same and an application thereof. The preparation method of the composite material includes: dispersing a ligand solution containing cobalt and a graphene oxide solution in an aqueous solution fully by stirring and ultrasonication, next, adding a cobalt metal salt solution and fully stirring, and then calcining the mixture in an inert atmosphere after centrifugation and lyophilization to obtain the above composite material. The preparation method of the present invention is simple in operation, low in energy consumption and low in material costs and the like. The composite material is obtained by uniformly and closely wrapping cobalt Prussian blue nano-crystals in graphene with excellent conductivity, thereby significantly improving electron transfer efficiency and active site utilization rate of the composite material.