Ba0.5Sr0.5CoxFe1-XO3-d As High Volumetric Capacitance Pseudocapacitive Electrode Materials

Abstract

The design and fabrication of high volumetric energy density supercapacitors lead to high density pseudocapacitive materials to be considered as electrode material. After our previous, and still on-going, work on FeWO4 [1], Ba0.5Sr0.5CoxFe1-xO3- δ phases, with 0.75<x<0.85, so-called BSCF, are currently under investigation. Our motivation towards these materials are (i) on the sub-stoechiometry in oxygen suggesting a flexible balance of either Fe and Co redox centers as well as (ii) on their attractive intrinsic electronic conductivity. These phases have been prepared by various synthetic methods, including Pechini and flash combustion syntheses, at various temperatures ranging from 850 to 950 °C. Despite the eventual presence of small amount of CoO and BaO impurities (depending on the synthesis type and temperature), resulting materials show the same perovskite structural arrangement and similar morphological characteristics.The electrochemical performances have been evaluated by cyclic voltamperometry at room temperature, at various scan rates from 5 to 200 mV.s-1 and in various aqueous electrolytes: KOH 0.5 M, H2SO4 0.5 M, K2SO4 0.5 M, Na2SO4 0.5 M, Li2SO4 0.5 M, and LiNO3 0.5, 1.0 and 5 M. The potential window was shown to vary depending on the electrolyte nature but, most of the time, prepared BSCFs showed promising pseudocapacitive behaviors as electrode material. A specific capacitance of 64 F.g-1 was measured at 5 mV.s-1 in LiNO3 5M for the electrode based on the material prepared by flash combustion at 850°C. This value corresponds to a volumetric capacitance of 377 F.cm-3. The electrode also exhibited fair capacitance retention over 2000 cycles.The electrochemical performances were shown to vary depending on the Co/Fe ratio and are discussed toward the involved charge storage mechanism. Reference [1] N. Goubard-Bretesché, O. Crosnier, C. Payen, F. Favier, T. Brousse, Electrochem. Com. 57, 61–64, 2015