Upcycling waste plastics into rGO-Yb@NiFe₂O₄ hybrid electrodes for high-performance supercapacitors and hydrogen evolution

It is essential to reduce and upcycle the waste for energy conversion and storage for sustainability. Plastic milk pouches have been converted into a value-added carbon source for the facile synthesis of reduced graphene oxide (rGO). The obtained rGO was anchored with Yb-doped spinel NiFe₂O₄ and Yb@NiFe₂O₄/rGO nanocomposite was obtained. The morphological and structural characterization shows the uniform dispersion of spherical Yb@NiFe₂O₄ over rGO sheets and mixed valence states of metals with oxygen defects. The synthesized materials were used as electrode materials for supercapacitors and the calculated specific capacitances are 151, 413, and 926 F/g at a scan rate of 2 mV/s, respectively, for Yb@NiFe₂O, rGO and Yb@NiFe₂O₄/rGO. The Yb@NiFe₂O₄/rGO electrode showed a maximum power density of 109.3 W/kg at an energy density of 750 Wh/Kg. Asymmetric supercapacitor device was fabricated using Yb@NiFe₂O₄/rGO nanocomposite as the positive electrode and activated carbon as the negative electrode and the observed specific capacitance was found to be of 345.1 F/g at a current density of 1 mA/g. Electrochemical hydrogen evolution reaction (HER) was examined using linear sweep voltammetry (LSV) studies and the observed overpotentials of Yb@NiFe₂O₄ and Yb@NiFe₂O₄/rGO nanocomposite at 10 mA/cm² current density are 136 and 107 mV, respectively. The Tafel slopes for the platinum electrode, Yb@NiFe₂O₄/rGO, and Yb@NiFe₂O₄ composites were calculated to be 101, 182, and 225 mV/dec, respectively. The higher conductivity, surface area, diverse oxidation states, and quick electron mobility in Yb@NiFeO₄/rGO could be the reasons for the superior activity as compared to pristine materials. The robust stability of Yb@NiFe₂O₄/rGO in various electrochemical applications for energy conversion and storage presents an opportunity for further investigation into ferrite-based carbon materials.