Impact of ZnO on structural and electrochemical properties of silver spinel ferrites for asymmetric supercapacitors

Supercapacitors are receiving great scientific attention as energy storage devices due to their rapid charge/dis-charge rates, high power densities, and high stability. Silver spinel ferrite (AgFe2O4) and its composites AgFe2O4@ZnO (5 & 10 %) have been synthesized by using the hydrothermal method. XRD showed that the prepared samples have a cubic spinel structure. The crystallite sizes of the samples vary from 20 to 27 nm. TEM results showed that all ferrite particles had a spherical morphology. In the UV-vis absorption spectrum, the estimated Eg was 4.9 eV for AgFe2O4 and Eg increased with higher ZnO concentration. The specific capac-ity for AgFe2O4@10 %ZnO is 585.4 C/g which is higher than 497 C/g for AgFe2O4@5%ZnO and 394.2 C/g for AgFe2O4. For making an asymmetric device AgFe2O4@10 %ZnO//AC, activated carbon was chosen as the neg-ative electrode and AgFe2O4@10 %ZnO as the positive electrode. With this device, a specific capacity of 171.3 C/g was attained. AgFe2O4@10 %ZnO was found to have a power density of 720 W/kg and an energy density of 28 Wh/kg. This work indicates that a mixture of silver spinel ferrite composite (AgFe2O4@10 %ZnO) may be a more suitable electrode material for supercapacitor applications.