# US 10,374,248 B2 · High solubility iron hexacyanides

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- Number: US 10,374,248 B2
- Document ID: US10374248B2
- Status: Granted
- Kind: B2
- Application number: 15/647,190
- Filed: 2017-07-11
- Published: 2017-10-26
- Granted: 2019-08-06
- Earliest claimed: 2013-05-06
- Assignees: Lockheed Martin Energy, LLC
- Applicants: Lockheed Martin Advanced Energy Storage, LLC
- Inventors: Arthur J. Esswein; John Goeltz; Desiree Amadeo
- Web page: https://patentgrep.com/patent/US10374248B2

## CPC

- H01M 8/222: {Fuel cells in which the fuel is based on compounds containing nitrogen, e.g. hydrazine, ammonia}
- H01M 8/08: Fuel cells with aqueous electrolytes
- H01M 8/188: {by recharging of redox couples containing fluids; Redox flow type batteries}
- H01M 8/20: Indirect fuel cells, e.g. fuel cells with redox couple being irreversible (H01M8/18 takes precedence)
- H01M 2300/0002: Aqueous electrolytes
- Y02E 60/36: Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
- Y02E 60/50: Fuel cells
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

Stable solutions comprising high concentrations of charged coordination complexes, including iron hexacyanides are described, as are methods of preparing and using same in chemical energy storage systems, including flow battery systems. The use of these compositions allows energy storage densities at levels unavailable by other iron hexacyanide systems.

## Claims

### Claim 1

A method comprising:
dissolving Ca2[Fe(CN)6], NaOH and KOH in water, to produce an aqueous solution having a concentration of Fe(CN)64− in the aqueous solution that exceeds a concentration of Fe(CN)64− in either a saturated aqueous solution of Na4[Fe(CN)6] or a saturated aqueous solution of K4[Fe(CN)6] in water at a same temperature as that of the aqueous solution,
wherein the aqueous solution is interconvertible between a ferricyanide state and a ferrocyanide state without forming a precipitate in either state.

### Claim 2 (depends on 1)

The method of claim 1, further comprising removing precipitated Ca(OH)2 from the aqueous solution.

### Claim 3 (depends on 1)

The method of claim 1, wherein the aqueous solution is substantially free of a co-solvent.

### Claim 4 (depends on 1)

The method of claim 1, wherein the Fe(CN)64− is present in the aqueous solution at a concentration ranging in a range of from 1 M to 3 M.

### Claim 5 (depends on 1)

The method of claim 1, wherein a molar ratio of sodium ions to potassium ions in the aqueous solution is in a range of from 1:10 to 10:1.

### Claim 6 (depends on 5)

The method of claim 5, wherein the molar ratio of sodium ions to potassium ions is in a range of from 0.9:1 to 1.1:1.

### Claim 7 (depends on 1)

The method of claim 1, further comprising adding one or more of a buffering agent, a supporting electrolyte, a viscosity modifier, or a wetting agent to the aqueous solution.