Effects of additives and surface treatment on electrochemical performance for bafeo4 electrode/ Comparison of different additives effect

# Springer-Verlag 2008

Abstract BaFeO₄ was prepared by using the raw material K₂FeO₄. The structure of the product was characterized by X-ray diffraction and infrared radiation. Particle size and morphology were analyzed by SEM. BaFeO₄, the mixture of BaFeO₄, and additives were used as cathode, zinc used as anode, with which discharge performance test was carried out in the KOH electrolyte with a concentration of 14 mol/L. The results show that the discharge performance of BaFeO₄ is obviously enhanced, the discharge platform is increased by 0.3 V, and the capacity reached up to 240 mAh/ g, increased by 40 mAh/g after 5% of K₂S₂O₈ was added. In addition, the discharge capacity is increased by 65 mAh/g via treating the electrode surface with TiO₂ sol, reached up to 265 mAh/g, and electrochemical performance is obviously improved. The reason of improving property is discussed in the work too.

Keywords Cathodes . Charging/discharging . Electrochemical characterizations . Electrodes

Introduction

Since Israel scientist Lich [1] discovered that ferrate can be used as cathode materials for electrochemical storage

batteries in 1999, more and more researchers focused much attention to the electrochemical performance of ferrate due to its high intrinsic energy, the flat discharge platform, and the environmentally friendly discharge product compared with traditional Zn/MnO₂ battery which used MnO₂ as cathode [2–5]. K₂FeO₄ and BaFeO₄ are two ferrates that have been studied and applied the most at present and BaFeO₄ attracts more attention. The development of ferrate batteries was restricted by its instability, because sexavalentiron of the ferrates is reduced quite easily to trivalent ions in solution, causing attenuation in capacity. The key point of enhancing electrochemical properties of BaFeO₄ batteries lies in how to hold a stable and continuous discharging reaction. In order to solve this problem, namely, to enhance the electrochemical performance of BaFeO₄ batteries, some additives with different mechanisms were added into the ferrate electrode, for example, MnO₂, KMnO₄ [6–11], and nano-SrTiO₃ [12] etc., by the literature reports. In this study, the electrochemical performance of BaFeO₄ was researched, a new additive K₂S₂O₈ was added, and the property was compared with other additives. In addition, surface of the electrode including additive K₂S₂O₈ was treated by TiO₂ sol, as a result discharge capability of the electrode was increased and the discharge platform of the electrode was also obviously enhanced. To our knowledge, so far it is not reported to use additive K₂S₂O₈ in BaFeO₄ electrode and treat surface of BaFeO₄ electrode with TiO₂ sol.

Experimental

Reagents

Deionized water, KOH, Ti(OC₄H₉)₄, K₂S₂O₈, KMnO₄, and Fe(NO₃)₃ are analytical reagents.

DO00241; No of Pages

Preparation of samples

SrTiO₃ and K₂FeO₄ were prepared by literatures [12]

Preparation of TiO₂ sol Absolute alcohol, 12 mL, and 12 mL acetic acid were added into 3.6374 g butyl titanate, 8 mL deionized water was also slowly added into it by stirring for 2 h at room temperature. Then, the transparent TiO₂ sol was prepared.

Preparation of BaFeO₄ Ba(OH)₂·8H₂O, 6.30 g, was dissolved in 150 mL deionized water without CO₂, the solution A was filtrated by Whatman GF/A filter paper at 0 ° C. The solution B was obtained by adding 2.40 g K₂FeO₄ into 48 mL 2% KOH at 0 °C, then put B into A to produce solid–liquid mixture solution under Ar atmosphere protection. The mixture solution was stirred for 15 min and centrifugated for 5 min to obtain BaFeO₄, which was washed several times till pH=7. The pink powders were dried under vacuum for 24 h at ambient temperature. Figure 1 shows the prepared process.