Effect of phase transformation on the electrochemical supercapacitive behavior of thermally exfoliated zirconia

Amorphous and crystalline zirconia (ZrO2) are successfully synthesized through a rapid thermal exfoliation process. The crystal structure and phase purity of exfoliated materials are examined using XRD. Crystalline ZrO2 reveals the formation of a tetragonal phase. Amorphous zirconia possesses a specific surface area of 45 m2/g. As synthesized, amorphous zirconia provides a specific capacity of 1406C/g at 2 A/g (3-electrode measurements). A two-electrode asymmetric supercapacitor of activated carbon, amorphous zirconia (ZrO2//AC), exhibits a better electrochemical performance than its crystalline phase. The amorphous ZrO2-based asymmetric supercapacitor gives a specific capacitance of 160 F/g at 3 A/g. The device delivered an energy density of 47.6 Wh/kg at a power density of 2.2 kW/kg. These high energy and power density values of asymmetric amorphous ZrO2 supercapacitors outperform most of the reported ZrO2-based electrode materials. Amorphous ZrO2 is a promising electrode material in terms of its capacitance retention of ∼75 % over 10,000 cycles. The as-developed device has a rate capability of 35 % at a current density of 25 A/g and a self-discharge current of 2.6 mA.