Temperature- and thickness-dependent electrical conductivity of few-layer graphene and graphene nanosheets

Composites synthesized through the deposition of Mn3O4 on graphene, carbon nanotube and other carbon based materials have attracted much attention recently as potential electrode materials for different electrochemical applications such as pseudocapacitor; Lithium-ion battery; and catalysis. The primary reason Mn3O4 is grown on these substrates in spite of having high charge storage capacity as pseudocapacitor or Lithium-ion battery electrodes on its own is to enhance its electrical conductivity and/or to impart flexibility to the electrode, which is difficult for a fully metallic electrode. Higher electrical conductivity prolongs the cycle life of an electrode. In addition, the substrate contributes capacity and thus, enhances the overall energy density of an electrode. Mn3O4 acts as a spacer and keeps graphene nanosheets separated when used as the substrate for capacitor electrode fabrication. This helps retain the high surface area of graphene nanosheets in the electrode which contributes additional capacitance. Mn3O4 supported on graphene and other carbon substrates have recently been investigated as catalyst for methanol electro-oxidation in alkaline media; CO oxidation; and Oxygen reduction reaction (ORR). High surface area substrate uniformly distributes metal particles and prevents their agglomeration and dissolution during catalytic process. In addition, high electrical conductivity of graphene and carbon substrates enhances the electronic conductivity of Mn3O4 which is of importance for superior catalytic activity. Composite of Mn3O4 combined with carbon based substrate has also found non-electrochemical application such as the removal of Pb and Cu ions from aqueous solution because of their adsorptive behaviour. A myriad of procedures have been adopted for the synthesis of Mn3O4 on graphene or other carbonaceous substrates. All of these methods involve one or more of the following factors that complicate the process, such as: long synthesis time; high synthesis temperature; use of hazardous/toxic chemicals; multistep process and the requirement for sophisticated device or highly controlled environment. In fact, the complicacies associated with the synthesis of Mn3O4 have already been acknowledged and investigations have been directed at finding relatively simpler route such as the use of microwave technique. In this research, we report the synthesis of clusters of nearly octahedral shapedn Mn3O4 nanoparticles on few-layer graphene nanoplatalet (GnP) surface through a simple, wet-chemical, polyethyleneimine (PEI) mediated route. Few-layer graphene nanoplatelets are ultrathin particles of graphite prepared through proprietary intercalation and exfoliation method (XG Sciences, Inc., Lansing, MI, USA). The components involved in this synthesis method are manganese salts (KMnO4 and MnSO4.H2O); water; PEI; and GnP as the substrate. The synthesis is carried out at a temperature of 80°C only and in open air. Highly crystallized Mn3O4 particles, as observed by X-Ray Diffraction (XRD), can be synthesized on GnP surface. It has also been observed that PEI acts as a reducing agent and as a capping agent on a continuous network of ribbon-like Birnessite-MnO2 (IV) to produce a nearly octahedral shaped nanoparticles of Mn3O4 (II, III). It has already been mentioned that composites of Mn3O4 on graphene or other carbonaceous substrates find a myriad of applications. Thus, our research findings to synthesize GnP-Mn3O4 composite through a simple method should be of interest to a broad group of researchers. In this research, we have investigated the performance of this composite system as a Lithium-ion battery anode only. Our preliminary investigations reveal that the Mn3O4 composite synthesized through this method has just as much potential as the ones prepared through other alternative methods.

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Synthesis of Clustered Mn3O4 Nanoparticles through a Polymer Surfactant Mediated Route on Few-Layer Graphene Nanoplatelet Surface and its Application for Electrochemical Energy Storage: Lithium-ion Battery Anode

10.26434/chemrxiv.12086493.v1 ◽

2020 ◽

Author(s):

Debkumar Saha ◽

Lawrence T. Drzal

Keyword(s):

Electrical Conductivity ◽

Lithium Ion Battery ◽

Graphene Nanosheets ◽

High Surface ◽

High Surface Area ◽

Lithium Ion ◽

Layer Graphene ◽

Carbon Substrates ◽

Few Layer Graphene ◽

Battery Anode

Composites synthesized through the deposition of Mn3O4 on graphene, carbon nanotube and other carbon based materials have attracted much attention recently as potential electrode materials for different electrochemical applications such as pseudocapacitor; Lithium-ion battery; and catalysis. The primary reason Mn3O4 is grown on these substrates in spite of having high charge storage capacity as pseudocapacitor or Lithium-ion battery electrodes on its own is to enhance its electrical conductivity and/or to impart flexibility to the electrode, which is difficult for a fully metallic electrode. Higher electrical conductivity prolongs the cycle life of an electrode. In addition, the substrate contributes capacity and thus, enhances the overall energy density of an electrode. Mn3O4 acts as a spacer and keeps graphene nanosheets separated when used as the substrate for capacitor electrode fabrication. This helps retain the high surface area of graphene nanosheets in the electrode which contributes additional capacitance. Mn3O4 supported on graphene and other carbon substrates have recently been investigated as catalyst for methanol electro-oxidation in alkaline media; CO oxidation; and Oxygen reduction reaction (ORR). High surface area substrate uniformly distributes metal particles and prevents their agglomeration and dissolution during catalytic process. In addition, high electrical conductivity of graphene and carbon substrates enhances the electronic conductivity of Mn3O4 which is of importance for superior catalytic activity. Composite of Mn3O4 combined with carbon based substrate has also found non-electrochemical application such as the removal of Pb and Cu ions from aqueous solution because of their adsorptive behaviour. A myriad of procedures have been adopted for the synthesis of Mn3O4 on graphene or other carbonaceous substrates. All of these methods involve one or more of the following factors that complicate the process, such as: long synthesis time; high synthesis temperature; use of hazardous/toxic chemicals; multistep process and the requirement for sophisticated device or highly controlled environment. In fact, the complicacies associated with the synthesis of Mn3O4 have already been acknowledged and investigations have been directed at finding relatively simpler route such as the use of microwave technique. In this research, we report the synthesis of clusters of nearly octahedral shapedn Mn3O4 nanoparticles on few-layer graphene nanoplatalet (GnP) surface through a simple, wet-chemical, polyethyleneimine (PEI) mediated route. Few-layer graphene nanoplatelets are ultrathin particles of graphite prepared through proprietary intercalation and exfoliation method (XG Sciences, Inc., Lansing, MI, USA). The components involved in this synthesis method are manganese salts (KMnO4 and MnSO4.H2O); water; PEI; and GnP as the substrate. The synthesis is carried out at a temperature of 80°C only and in open air. Highly crystallized Mn3O4 particles, as observed by X-Ray Diffraction (XRD), can be synthesized on GnP surface. It has also been observed that PEI acts as a reducing agent and as a capping agent on a continuous network of ribbon-like Birnessite-MnO2 (IV) to produce a nearly octahedral shaped nanoparticles of Mn3O4 (II, III). It has already been mentioned that composites of Mn3O4 on graphene or other carbonaceous substrates find a myriad of applications. Thus, our research findings to synthesize GnP-Mn3O4 composite through a simple method should be of interest to a broad group of researchers. In this research, we have investigated the performance of this composite system as a Lithium-ion battery anode only. Our preliminary investigations reveal that the Mn3O4 composite synthesized through this method has just as much potential as the ones prepared through other alternative methods.

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Green Synthesis of Clean Edge Graphene Nanosheets Using Natural Precursor

Materiale Plastice ◽

10.37358/mp.21.3.5518 ◽

2021 ◽

Vol 58 (3) ◽

pp. 210-216

Author(s):

Balakrishnan Somasekaran ◽

Alwarsamy Thirunarayanaswamy ◽

Ilamathi Palanivel

Keyword(s):

Environmental Concern ◽

Graphene Nanosheets ◽

Agricultural Waste ◽

Chemical Activation ◽

Advantages And Disadvantages ◽

Layer Graphene ◽

Smooth Edge ◽

Novel Method ◽

Traditional Approaches ◽

Few Layer Graphene

Graphene, a two-dimensional crystalline allotrope of carbon, has received greater attention from numerous researchers due to its excellent properties. Graphene could be produced by various techniques, each method has its advantages and disadvantages. In this research article, a novel method using agricultural waste rice husk as a precursor and chemical activation to produce few-layer graphene nanosheets was developed. Traditional approaches significant shortcomings and the environmental concern of agricultural waste have been eliminated. The synthesized material was characterized using FESEM, Raman Spectroscopy, X-Ray diffractometer, UV-Vis absorbance and FTIR analysis. FESEM analysis of the surface morphology revealed smooth edge few-layer graphene. The formation of sp2 hybridized atoms can be seen in XRD spectra at 26.3 degrees. The C=C stretching bonds detected at 1612 cm-1 wavelength are responsible for the graphitic structure.

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