Toward Efficient Electrochemical Synthesis of Fe(VI) Ferrate and Super-Iron Battery Compounds

Abstract

Electrochemical synthetic pathways for Fe͑VI͒ salts from an iron anode in alkaline electrolyte were compared, including a novel in situ direct synthesis of solid BaFeO 4 , or an ex situ two-step solution-phase electrochemical synthesis followed by chemical precipitation. A variety of electrolysis conditions including cell configuration, applied current density, temperature, synthesis duration, electrolyte composition and concentration, and the molar ratio between the reactants were probed and optimized. The in situ methodology decreases the complexity and time of synthesis, generating up to 95.9% BaFeO 4 purity, prepared at high current density from anodically biased iron in an aqueous co-electrolyte containing both Ba(OH) 2 and NaOH. In situ electrochemically synthesized BaFeO 4 exhibits near-identical IR absorption spectrum, and powder X-ray diffraction determined crystalline structure, as the chemically synthesized material, and exhibits enhanced stability towards prolonged thermal decomposition. It also supports facile charge transfer when incorporated as a cathode and discharged in nonaqueous lithium anode and aqueous alkaline zinc anode super-iron batteries.

Usage of mother liquor recycling for the obtaining of Fe(VI) compounds

“…It has been established that the main impurities in the liquid phase are manganese and chromium oxoanions (MnO 4 2-, CrO 4 2-) ( Table 2). Table 2 The content of manganese and chromium oxoanions in the mother liquor after electrosynthesis These results do not go against the works [6,10,13], which inform about the inclusions of manganese and chromium in the crystalline ferrates prepared by electrochemical and chemical methods.…”

“…Ferrates(VI) are new "green" oxidants, which due to their unique properties are used in many spheres, such as industrial ecology [1][2][3][4], organic and inorganic synthesis [5,6], batteries production [7], etc. The widespread use of ferrates and their large-scale production are largely cut down by the high price that has currently developed in the market of iron(VI) compounds.…”

Effect of manganese compounds on synthesis of ferrates(VI)

“…Так, по данным [9], при растворении чугунного анода (0,50 % Mn), марганец в раствор не переходит. Напротив, дру гие авторы после синтеза зафиксировали: оксоанионы MnO 4 2-и MnO 4 -в растворе [10], карбонат марганца в кристаллическом K 2 FeO 4 [11] и неидентифицирован ные формы марганца в BaFeO 4 [4].…”

“…[1][2][3][4][5]. Однако, производство со единений Fe(VI) все еще остается малотоннажным, что в определенной степени связано с высокой скоростью разложения ферратных растворов и достаточно низ кой устойчивостью кристаллических ферратов, полу чаемых по традиционным технологиям [6].…”

“…Однако, производство со единений Fe(VI) все еще остается малотоннажным, что в определенной степени связано с высокой скоростью разложения ферратных растворов и достаточно низ кой устойчивостью кристаллических ферратов, полу чаемых по традиционным технологиям [6]. Склонность растворов ферратов к разложению вполне объяснима, ведь анион FeO 4 2--это один из самых сильных окислителей, легко разлагающий воду с выделением кислорода: 4FeO 4 2-+ 6H 2 O → 4FeОOH + 3O 2 + 8OH -.…”