Controllable Syntheses Of Graphene Based2D Composites For Energy Storage And Conversion

The unique structural features and synergistic physical andelectrochemical properties have made2D functional nanohybridscomprising metal oxide or metal hydroxide nanoparticles (MO/MH NPs)on graphene attract numerous attentions. Nevertheless, there are still a lotof problems waiting for the solutions, such as the general incompatibilitybetween graphene and inorganic NPs under synthetic conditions, thegrowth of MO/MH NPs on a graphene substrate with uniform morphology,controllable size of nanoparticles of MO/MH and the enhanced couplingeffects. The biggest problem for the application of the graphene based2DMO/MH NPs composites in lithium battery or supercapacitor is the poorstability of this kind of materials. In this study, an efficient and universalstrategy was proposed for the controllable growth of MO/MH NPs ongraphene to construct unique2D nanohybrids by employing polymer asboth coupling linker and protection layer for MO/MH NPs. The details ofsynthesis and the application tests for each kind of composites aredescribed as follows:(1) The synthesis of carbon coated2D core-shell graphene-metaloxides composites and its application in Li-ion batteries. The2Dgraphen-metal oxides (G@MO) nanosheets were synthesized via anin-situ hydrolysis of corresponding metal salt on the poly(dimethyldiallylammonium) chloride (PDDA) functionalized graphene oxide (GO). Then,polymer coatings were produced by in-situ polymerization or hydrothermal treatment in the presence of G@MO nanosheets to obtainthe polymer coated2D graphen-metal oxides (G@MO) nanosheets(G@MO@Polymer). Later, the thermal treatment of G@MO@Polymerled to the formation of carbon shell coated grapheme-metal oxidecomposites as G@MO@C. The newly synthesized2D core-shell hybridsinherited the features of graphene which possesses a high electricalconductivity, a large aspect ratio and the negligible thickness. As aconsequence, the obtained G@MO@C manifests the superior reversiblecapacity, cycle performance and rate performance compared with the bareG@MO in the tests as anode material in Li-ion batteries. Moreover, theextremely efficient protection of the carbon shells to the active MOsparticles on graphene nanosheets was observed. G@MO@C evenexhibited much higher cycling stability than the other recently reportedgraphene based MOs composites, which generally suffered from theexfoliation of MOs particles and the rapid capacity fading after firstdecades of cycles.(2) The synthesis of polyaniline-coupled multifunctional2Dgraphene-metal oxides/hydroxide nanohybrids and its applications insupercapacitor and oxygen reduction reactions (ORR). An efficient anduniversal strategy was proposed for the controllable growth of MO/MH(such as Co3O4, Fe2O3, and Ni(OH)2) nanoparticles on graphene toconstruct the unique2D nanohybrids by employing polyaniline (PANI) asthe coupling linker between nanoparticles and graphene. Thesenanohybrids indicated a well-defined2D morphology, confined MO/MHNPs within the PANI nanostructures, controllable particle size and highspecific surface areas. The excellent rate capability and cycle performancewere measured when the fabricated ternary hybrids of graphene, PANI andCo3O4(G-PANI-Co3O4) was used as electrode materials in supercapacitors(The specific capacitances of G-PANI-Co3O4(1:10) were calculated to beapproximately1063,1028,952,900, and844F/g at current densities of1, 2,5,10, and20Ag-1, respectively.). Furthermore, the sequent thermaltreatment of G-PANI-MOs/MHs in inert gas atmosphere produced thenitrogen-doped carbon nanosheets integrated with size-controllable metalnanoparticles (GNC-M). For example, GNC-Co was synthesized bypyrolysis of G-PANI-Co3O4and exhibited outstanding catalytic behaviorin the oxygen reduction reaction (ORR).(3) The synthesis of the metal-nitrogen doped2D mesoporouscarbon materials and the applications in advanced electrochemical energystorage and conversion devices. The unique structural features of theG-PANI-MOs composites which was mentioned above provided numerousopportunities for a large-scale production of two-dimensional functionalmetal-N doped mesoporous carbon materials. In this part, the successfulfabrication of2D Fe/Co-N doped mesoporous carbon was demonstrated.The typical synthetic strategy involved the employment of G-PANI-MOsnanosheets as self-template precursors, followed by the sequent thermaltreatment in nitrogen atmosphere and etching by acid. The resultedGNC-M nanosheets possessed not only2D nature, a high content ofmetal-N active sites but also large amount of micro/mesopores, whichbrought a crucial element for the enhanced performance of catalysts inORR. Such unique features provided numerous open channels to theactive sites. As a consequence, the GNC-M mesoporouse nanosheetsexhibited a high activity and a good stability as catalysts in ORR.