Hydrothermal synthesis of iron oxides in the presence of catecholate capping agent for supercapacitor electrodes

Caffeic acid (CA) is used as a capping agent for hydrothermal synthesis of iron oxides from FeCl2 and FeCl3 solutions. Iron oxide nanoparticles are utilized for the fabrication of supercapacitor anodes with mass loading of 40 mgcm−2 for operation in 0.5 M Na2SO4 electrolyte. Nanoparticles of γ-Fe2O3, prepared from FeCl2 solutions show ferrimagnetic properties and highest electrochemical capacitance of 4.49 Fcm−2. The synthesis from FeCl3 solutions results in the formation of antiferromagnetic α-Fe2O3 phase at low CA concentrations, its transformation to the metastable γ-Fe2O3 with increasing CA concentration and highest electrochemical capacitance of 4.35 Fcm−2. The increase in CA concentration in solutions results in increasing capacitance and decreasing resistance. The obtained γ-Fe2O3 nanoparticles exhibit valuable magnetic and electrical charge storage properties that are significantly superior to those of other magnetoelectric materials.