Electrode response of NaFeTiO4 in aqueous supercapacitor cells

Abstract

We report electrochemical performance of a calcium ferrite type NaFeTiO4 electrode for capacitor cell applications. High-resolution transmission electron microscopy results confirmed single-phase polycrystalline surface property comprising non-uniform grain distribution. X-ray photoelectron spectrum (XPS) analysis results confirmed presence of Fe3+ and Ti4+ oxidation states. The electrochemical performance of NaFeTiO4 in a three-electrode capacitor cell using different aqueous electrolytes: 1 M H2SO4, 1 M Na2SO4, and 1 M Li2SO4 confirmed superior performance only for capacitor cell with 1 M H2SO4 exhibiting typical pseudo-capacitive response in cyclic voltammetry. In contrast, the cell response of NaFeTiO4 with 1 M Na2SO4 and 1 M Li2SO4 electrolytes was electric double-layer charge (EDLC) accumulation induced capacitive effect predominantly. The electrolyte-driven distinct charge storage mechanism has been attributed to surface adsorption-induced redox action in the former whereas the EDLC response in the latter is attributed to larger size of the hydrated Na+ and Li+ ions causing charge accumulation at the interface. An excellent cyclic stability up to 10000 cycle with capacity retention up to 91% and coulombic efficiency ~ 100% has been noted @ 1 Ag−1 in 1 M H2SO4. Two electrode symmetric cell results exhibit similar pseudo-capacitive response as in three electrode cell configuration. The material delivered maximum power density ~ 18 kW/kg @ 10 Ag−1 and energy density ~ 2.55 Wh/kg @ 0.1 Ag−1 in a three-electrode-cell configuration whereas for a two-electrode cell, corresponding values are ~ 3.13 kW/kg @ 0.43Ag−1 and ~ 2.26 Wh/kg @ 0.04 Ag−1.