Study of Redox and Pseudocapacitive Processes of K-Ion Storage Using New Transition Metal Oxides Derived from PBA Type-Materials

Abstract

The fast growing use of natural energy sources such as solar and wind to generate electricity, requires the development of reliable, affordable, and efficient electric energy storage systems [1]. Thus, electrochemical capacitor systems can offer excellent devices showing high power (>10 kW kg-1), high rate capability and long cycle life (>1 000 000 cycles) [2]. Many kind of materials have been widely investigated as supercapacitor electrodes, such as carbon materials, graphene-based composites of metal hydroxides and metal oxides. In this work, new pseudocapacitive materials were obtained by thermal descomposition of cyanometalates (PBAs) obtained by precipitation over different carbon structures (graphene oxide, carbon nanotubes and mesoporous carbon). The materials were characterized using XRD, Raman, ATR-FTIR, SEM, TEM and XPS. Furthermore, the electrochemical performance of the materials was tested by cyclic voltammetry, step potential electrochemical spectroscopy, electrochemical impedance spectroscopy and charge-discharge curves at different current rates in 1 M KOH. These techniques were applied in order to understand the double layer and pseudocapacitive mechanism of K ion storage. The material formed in presence of graphene oxide exhibited the best electrochemical behavior, maintaining almost constant its initial capacitance after 500 cycles at 1 A g-1.