Electronic environments, optical and electrochemical properties of FeAlOx/reduced graphene oxide nanocomposites

Iron oxide-aluminium oxide/reduced graphene oxide (FeO_x-AlO_x/rGO) nanocomposites (NCs) were synthesized using a chemically reduced process. The grain and crystallite sizes varied from 65 to 195 nm and 2.48–17.44 nm, respectively, with an increase in Al wt%. The rGO sheets showed hexagonal symmetry, as confirmed by the SAED pattern of the rGO sheets appearing with three concentric circles. UV–Vis spectra revealed that optical absorption was a red shift from 367.09 to 273.76 nm with increased AlO_x concentration. The sp³ to sp² carbon ratio, I_D/I_G, increases from 1.16 to 1.36 from 0 to 50 wt% AlO_x decreased to 1.19 for the further increment of AlO_x. The degree of passivation, I_D1/I_G and degree of stacking fault, I_D3/I_G, decreased from 0.55 to 0.23 and 0.24 to 0.08 for FeO_x/rGO and (FeO_x)_0.25-(AlO_x)_0.75/rGO respectively, further increased to 0.33 and 0.32 for AlO_x/rGO NC, respectively. The degree of dislocation, I_D2/I_G, decreased from 0.55 to 0.07, reducing the defects in the graphene structure by increasing AlOx wt.% of (FeO_x)_0.5-(AlO_x)_0.5/rGO NC. The highest specific capacitance, C_sp is observed at 434 and 292.95 F g⁻¹ for (FeO_x)_0.75-(AlO_x)_0.25/rGO NC by cyclic voltammetry and galvanostatic charge-discharge measurements, respectively. Maximum C_dl and minimum R_ct of 3.04 × 10⁻⁹ Fg⁻¹ and 120.93 Ω were observed for 75 wt% of AlO_x content. The protective layer of FeO_x prevents corrosion by acting as an inhibitor in the 1 M H₂SO₄ electrolytic solution. Moreover, the semi-empirical electronic environment of elements was explained using core orbital spectra.