Needle-like MnO₂/activated carbon nanocomposites derived from human hair as versatile electrode materials for supercapacitors

Bio-waste material, human hair, was used as a source to prepare activated carbon (ACs) by a simple NaOH activation method. MnO₂ with a needle like structure was successfully decorated on ACs by a wet impregnation method. TEM images confirmed the needle-like morphology of MnO₂ on ACs. The chemical state of Mn in MnO₂/ACs was found to be +4, as confirmed by XPS analysis. Other physicochemical properties of MnO₂/ACs were investigated by means of SEM-EDS, XRD, Raman and XPS analyses. After complete characterization, the resultant nanocomposites with different MnO₂-loading [MnO₂/ACs_(X:Y)] were employed as electrode materials for supercapacitors. Interestingly, the MnO₂/ACs nanocomposites showed an excellent capacitance in three different electrolytes (1.0 M H₂SO₄, 1.0 M KOH and 1.0 M Na₂SO₄). The MnO₂/ACs_(1:12) achieved a maximum capacitance of 410 F g^-1, 345 F g^-1 and 291 F g^-1 in 1.0 M H₂SO₄, 1.0 KOH and 1.0 Na₂SO₄, respectively. To the best of our knowledge, this is the first MnO₂-based carbon nanocomposite to show good capacitance performance in three different kinds of electrolytes. Moreover, the MnO₂/ACs showed a capacitance of ∼300 F g^-1 even after 500 cycles in 1.0 M H₂SO₄.