Enhancing The Electrochemcal Performances Of Graphene/Mn₃O₄ Composites Via Highly Conductive Nanoparticals

As electrode material, trimanganese tetroxide (Mn3O4) possesses poor electrical conductivity and low utilization ratio. Besides, nanoscale Mn3O4 always gets the problem of agglomeration during its storage and use. Therefore, Mn3O4 is often combined with carbon-based material with large specific surface area. Herein, graphene nanosheet (GNS) with high specific surface area and good electrical conductivity was used as conductive carrier, a facile and one-pot synthesis method was presented to fabricate binary GNS/Mn3O4 nanocomposites, and their electrochemical properties were studied in detail. Then two kinds of highly conductive nanoparticles including carbon nanotubes (CNTs) and polyaniline coated carbon nanotubes (PANI-CNT) were introduced into above-mentioned binary nanocomposites, respectively, and their effects on the electrochemical performances of GNS/Mn3O4 nanocomposites were discussed. Our main results are listed as follows:(1) Binary GNS/Mn3O4 nanocomposites:A facile, low-temperature and one-pot synthesis was presented to fabricate binary GNS/Mn3O4 nanocomposites. The X-ray diffraction (XRD) results indicated that all the diffraction peaks about manganese oxide could be indexed to tetragonal Mn3O4 for the GNS/Mn3O4 nanocomposites. Raman results demonstrated that the efficient chemical reduction of GO into GNS was achieved. Field emission scanning electron microscope (FESEM) showed that Mn3O4 nanoparticles uniformly dispersed on the surface of the GNS, exhibiting a sandwich-like structure. With the decrease of reaction ratio of manganese chloride to GO, the average diameter of the Mn3O4 nanoparticles decreased. Electrochemical tests indicated that GM-0.8 exhibited a maximum capacitance value of 282.9 F/g among all the binary composites, which would decrease by 10.2% after 500 cycles, showing good cycle stability.(2) Ternary GNS/Mn3O4/CNT nanocomposites:Tetragonal Mn3O4 nanoparticals were anchored on the surface of GNS, and CNTs as conductive bridge interspersed between the GNS and Mn3O4, forming a three-dimensional network structure. Electrochemical tests indicated that GMC-0.8 exhibited the highest specific capacitance of 347.9 F/g, in which the utilization ratio of Mn3O4 was improved to 80%. Electrochemical impedance spectroscopy (EIS) measurements showed that GMC-0.8 had a lower charge transfer resistance and smaller relaxation time. Excellent cycling stability with retaining 98.1%of the initial specific capacitance after 500 cycles could be observed for GMC-0.8.(3) GNS/Mn3O4/(PANI-CNT) nanocomposites:Tetragonal Mn3O4 nanoparticals were anchored on the surface of the GNS, PANI-CNT as a conductive bridge interspersed between the GNS and Mn3O4, forming a three-dimensional network structure. In acid electrolyte, GMPC-0.8 showed enhanced electrochemical performance due to the addition of PANT-CNT. While in neutral electrolyte, the specific capacitance of the GMPC system declined, however, better capacitance retention can be achieved at high scan rate. Due to the wastage of Mn3O4 and the swelling and shrinkage of PANI chains during the long-term cycle, the specific capacitance for GMPC-0.8 decreased by 16.4% after 500 cycles. However, the addition of PANI-CNT delayed the transformation of Mn3O4 to MnO2.