Three-dimensional ZnO tetrapods for high-performance supercapacitors: experimental and theoretical insights

The advancement of high-performance electrode materials is essential for improving the performance of electrochemical supercapacitors. In the present study, ZnO tetrapods (ZT) were successfully synthesized via a flame transport synthesis (FTS) technique and investigated as electrode materials for energy storage applications. The structural and physicochemical properties of the synthesized ZT were systematically characterized using XRD, FTIR, Raman spectroscopy, DRS, electron microscopy, and XPS, verifying the formation of highly crystalline wurtzite ZnO with a well-defined tetrapodal morphology. The electrochemical behavior of the ZT electrode was assessed using a three-electrode setup in 1 M KOH electrolyte, exhibiting a high specific capacitance of 263.7 F g^-1 at 1 A g^-1, with a pronounced decrease in the specific capacitance at higher current densities, indicating limited rate capability. To further examine its practical implementation, an asymmetric supercapacitor device was developed using ZnO tetrapods as the positive with activated carbon as the negative electrode in a CR-2032 coin-cell configuration. The fabricated ASC device operated within an extended potential window of 1.6 V and exhibited a maximum energy density of 35.5 Wh kg^-1 at a power density of 159 W kg^-1. Moreover, the device demonstrated excellent long-term stability with 88% capacitance retention after 10 000 charge-discharge cycles. Density functional theory calculations were further used to examine the ZnO structure, phonon properties, and quantum capacitance behavior of ZnO, providing theoretical insight into its charge storage mechanism. The combined experimental and theoretical findings demonstrate that the unique three-dimensional tetrapodal architecture facilitates efficient ion diffusion and electron transport, highlighting its potential for high-performance supercapacitor applications.