Preparation, Characterization Of Ferrate And Its Application For Novel Super-Iron (Ⅵ) Battery

The research of novel super-iron (VI) battery becomes a new hot spot in battery field since the end of last century, and attracts more and more attentions at home or aboard. In this thesis, the process of rapid preparation of ferrates, and their basic physical, chemical properties, structure characteristic, electrochemical performance was systematically investigated. Several kinds of ferrates could be obtained rapidly by improved and simplified hypochlorite oxidation method. XRD and SEM indicated that all ferrates constitute of uniform sub-micron to nano-sized particles. The effect of amount of ferrate(Ⅲ) raw material and concentration or temperature of alkali absorbs on the purity and productivity of ferrates was studied. When the ratio of ferrate(Ⅲ) salts in reaction was controlled at 85～95 %, alkali absorbs' concentration at 10.5 mol·L-1, temperature at 0～5℃, the purity and productivity of the products could be apparently improved. Potassium ferrate and barium ferrate have both certain solubility in alkaline solution, however, barium ferrate is more stable and has a smaller solubility than other ferrates, and these are obvious preponderance for the material applied in alkali super-iron battery. The stability of ferrates(VI) in alkaline solutions changes with the concentration of KOH solutions, it has a better stability in 10 mol·L-1 KOH which was also a turning point at solubility curve of potassium ferrate in KOH solutions.Two kinds of electrode were used to study the electrochemical performance of ferrates: one is powder microelectrode, the other is Pt electrode in certain concentration K2FeO4 solutions. There was only ferrate's reduction peak at 0.1～0.2Ｖ,but no the corresponding oxide peak in cyclic voltammogram of both powder microelectrode and Pt electrode. We believe that peak of oxidation of OH-` on platinum electrode overlaps the Fe3+ oxidation peak. As for cyclic voltammetric curves of K2FeO4 solutions on Pt electrode, the peak current changed linearly with the square root of scanning rate, that is , this shows that the electrode process was controlled by diffusion that FeO42- diffused to working electrode then was reduced to low valence. When the amount of conductivity was 10% in Zn-K2FeO4 battery, 20% in Zn-BaFeO4 battery, and 15% in Zn-SrFeO4 battery, discharge performance of batteries behave much better. Since barium ferrate has higher stability than other ferrates, Zn-BaFeO4 battery has better discharge performance. Nickel and cobalt can accelerate decomposition of ferrates (VI), so, the discharge capacity was obviously diminished when Ni(OH)2 or CoO was used as additives. KMnO4 is favorable to enhance the discharging platform of super-iron battery, and Ba(OH)2 is beneficial to enhance the concentration of Ba2+, then efficiently lowering the solubility of ferrate(VI) in the electrolyte, therefore the discharge performance of Zn-BaFeO4 battery was greatly improved when 3% KMnO4 and 2% Ba(OH)2 were used as additive in Zn-BaFeO4 battery.