Electrochemical synthesis of Au-MnO2 on electrophoretically prepared graphene nanocomposite for high performance supercapacitor and biosensor applications

Herein, we report a facile electrochemical synthesis of an Au-MnO2 nanocomposite highly dispersed on an electrophoretically prepared graphene surface for the first time. Fascinatingly, we obtained a nanowires-like morphology for the MnO2 by using a simple in situ electrochemical deposition method. The as-synthesized Au-MnO2-graphene nanocomposite is characterized by various analytical and spectroscopic techniques viz. SEM, EDX, TEM, XRD, Raman spectroscopy and XPS. The as-prepared nanocomposite is employed in an electrochemical supercapacitor and for the sensitive detection of epinephrine. The supercapacitor performance is evaluated in 0.5 M NaOH by both cyclic voltammetry (CV) and galvanostatic charge discharge (GCD) methods. The MnO2 : Au ratio during deposition plays a vital role to influence the capacitance properties. The highest specific capacitance of 575 F g(-1) for 1 : 0.01 (MnO2 : Au) at a current density of 2.5 A g(-1) has been obtained. The effect of current density, MnO2 : Au ratio, scan rate, mass loading and electrolyte concentration were also optimized and good cycle stability was demonstrated. The comparison of specific capacitance over MnO2-graphene and Au-MnO2-graphene nanocomposites suggests that the incorporation of Au nanoparticles on MnO2-graphene surfaces has a highly substantial effect for enhancement of capacitive behaviour. Furthermore, the epinephrine sensor performance of an Au-MnO2-graphene nanocomposite modified glassy carbon electrode is evaluated by CV and differential pulse voltammetry (DPV) techniques. Interestingly, the DPV sensor exhibited a very low detection limit of 24 nM and an excellent current sensitivity value of 35.6 mu A mu M-1 cm(-2), surpassing several related modified electrodes and demonstrating several practical industrial applications.