Deposition of Manganese Oxdies on Graphene Nanoplatelet (GnP) Surface for Energy Applications: Synthesis, Characterization and the Evaluation of Effect of Surfactant on the Synthesis Process

Effective synthesis methods are required to produce metal nanoparticles of controlled size and narrow size distribution as small particles tend to sinter together easily. This problem can be overcome by applying small particles on a support surface. Metal particles supported on carbon/graphitic substrate can find variety of applications in chemical industries; automobiles; energy and power generating devices; hydrogen economy and sensors. Graphene Nanoplatelet (GnP), a material with excellent mechanical properties; thermal and electrical conductivity; excellent corrosion and oxidation resistance; and low impurity levels has the potential to be an excellent substrate for nanoparticle deposition. Manganese Oxides (MnO_x) are interesting metal oxide structures with many crystal phases. Different crystal phases and structural arrangements can be obtained through various synthetic methods. In this work MnO_x has been deposited on the GnP surface through a redox reaction between KMnO₄ and MnSO₄.H₂O salts in the presence of GnP substrate in aqueous medium. Molar ratio and molar concentration of salts have been used as variable parameters keeping substrate amount; synthesis time and synthesis temperature as constant parameters. The MnO_x deposits are characterized in terms of several parameters such as particle morphology; particle size; distribution of particles; crystal phases and surface area. Polyethyleneimine (PEI) is a hydrophilic polymer with an overall positive charge in neutral aqueous solution that gets adsorbed on highly hydrophobic GnP surface and stabilizes the particles in water. It has been observed that MnO_x particle morphology and crystal phase changes drastically in the presence of PEI as surfactant. Highly uniform particle distribution can be obtained by controlling the molar concentration of reagent salts. Crystal structure analysis of MnO_x particles thus synthesized in this work indicates that the GnP-MnO_x composites may find application as Li-ion battery anode, Pseudocapacitor electrode and as catalyst for Li-air battery cathode.  Crystal structure and morphological analysis of the MnO_x has been performed with X-Ray Diffraction (XRD); Scanning Electron Microscopy (SEM); Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). Content of MnO_x and the net surface area of the composites have been measured with Thermo Gravimetric Analysis (TGA) and Brunauer Emmett Teller (BET) method respectively.