Fabrication Of Graphene-Based Inorganic Nanocomposites In Supercritical Fluid And Preliminary Study Of Their Applications In Fuel Cells

Graphene has attracted intense interest due to its outstanding physical and chemical properties, such as extremely high specific surface area (2600m2/g), superior electronic conductivity, large surface to volume ratio and high stability. Especially for fuel cell, the combination of graphene sheets and metal nano-particles may open up a new avenue for designing the next generation catalysts. In this thesis, the new preparation methods of reduced graphite oxide (rGO) and low defect graphene based composites were presented and applications in the field of fuel cells were discussed. The main content concludes:1. By supercritical CO2and methanol mixed fluid, H2produced by DMAB were used to reduce graphene oxide. Because of the thin layers of graphene oxide and the strong penetration ability of supercritical fluids, it is not only beneficial to the reduction of graphene oxide and metal precursors, but also to the formation of ultrafine metal nanoparticles on the surface of graphene. Therefore, electrochemical catalysts with high performance were obtained. By using XRD, TEM, EDS, XPS, the morphorlogy and composition of Chemical concerted graphene/PtRuNi (CCG/PtRuNi) composites were obtained. Moreover, the catalytic activity and stability of CCG/PtRuNi for the oxidation of methanol and ethanol are also investigated and compared with the CCG/PtRu and XC-72/PtRuNi catalysts through cyclic voltameter (CV) and chronoamperometry (CA) tests at room temperature. Compared with CCG/PtRu and XC-72(carbon black)/PtRuNi catalysts, the CCG/PtRuNi nano-composites exhibit significantly enhanced electro-catalytic activity and stability for methanol and ethanol oxidation. 2. We developed a soft chemistry method to oxidation of graphene with weak acid at reflux to directly fabricate low defect graphene (LDG). The soft synthetic conditions of LDG introduce an adequate, but not excessive, amount of oxygen-containing groups on the graphene surface. These oxygen functionalities can stabilize the dispersion of the LDG sheets in solvents, and facilitate the deposition of Pd nanoparticles onto the LDG surface. With the aid of supercritical CO2and co-solvent methanol, ultrafine Pd nanoparticles are homogeneously deposited on the surfaces of LDG. By using XRD, TEM, EDS, XPS, Raman and other methods, the morphology and composition of the LDG/Pd composites were analyzed. Additionally the electrocatalytic activity and stability of LDG/Pd for the oxidation of formic acid and methanol were also investigated and compared with the CCG/Pd, peel graphene/Pd (PG/Pd) and XC-72(carbon black)/Pd catalysts prepared under the same condition. The results reveal the LDG/Pd nanocomposites exhibit significantly improved electrocatalytic activity and stability for formic acid and methanol oxidation.3. We developed a soft chemistry method to oxidation of graphene with weak acid at reflux to directly fabricate low defect graphene (LDG). By utilizing LDG as carriers and acetylacetonate platinum, acetylacetonate ruthenium, and acetylacetonate nickel as metal precursor, LDG/PtRuNi nanocompsites were synthesized successfully with the aid of supercritical CO2. By using XRD, TEM, EDS, XPS, the morphology and composition of LDG/PtRuNi composites were obtained. Moreover, the catalytic activity and stability of LDG/PtRuNi for the oxidation of methanol and ethanol are also investigated and compared with the LDG/PtRu, LDG/Pt, CCG/PtRuNi and XC-72/PtRuNi catalysts through cyclic voltameter (CV) and chronoamperometry (CA) tests at room temperature. Compared with LDG/PtRu, LDG/Pt, CCG/PtRuNi and XC-72/PtRuNi catalysts, the LDG/PtRuNi nanocomposites exhibit considerably enhanced electro-catalytic activity and stability for methanol and ethanol oxidation.