Investigation of chemical network, electronic environments and electrochemical performance of Fe3O4/ZnO/rGO nanocomposites

The present study synthesized reduced graphene oxide-reinforced iron oxide and zinc oxide (Fe₃O₄/ZnO/rGO) nanocomposites with varying ZnO content using a facile chemical reduction method for energy storage application. The scanning electron microscope reveals that the grain size of Fe₃O₄/ZnO/rGO varied between 8 and 17.09 µm on the surface of the graphene sheet. The (101) and (102) planes were at 36.42 and 47.03°, respectively, confirming the ZnO wurtzite hexagonal structure. The crystallite size and lattice strain varied from 14.18 to 19.37 nm and 0.0018 to 0.0093, respectively, estimated from the Williamson–Hall plot with 60, 70, and 80 wt.% ZnO content. X-ray photoelectron spectroscopy (XPS) confirmed that the Fe and Zn contents varied from 21.5 to 24.48 at.% and 37.93 to 40.65 at.%, respectively. The C1s core orbital binding energy indicated the presence of C-Zn, C-Fe, and C-O-/C=O functional groups. Dominance of s-orbital in the valence band is observed in all Fe₃O₄/ZnO/rGO nanocomposites, and p-orbital is dominant in the valence band of pure rGO. The structural defect study in Raman shows that the defect parameter (I_D/I_G) varied from 0.28 to 0.38 with 60, 70, and 80 wt.% ZnO content, indicating an increase in defects with increasing 60 to 80 wt.% ZnO content in Fe₃O₄/ZnO/rGO network. The cyclic voltammetry showed that the specific capacitances for 70 and 80 wt.% ZnO content is 550 and 645 F g⁻¹, respectively, and for ZnO/rGO is 641 F g⁻¹ at 10 mV s⁻¹ scan rate, which indicates that the specific capacitance increases with the increase in ZnO.