Graphite oxide as an efficient and robust support for Pt nanoparticles in electrocatalytic methanol oxidation

Pt nanoparticles were encapsulated in graphite oxide (GTO) and used as electrocatalysts for methanol oxidation. When compared with Pt nanoparticles composited with graphene oxide (GO/Pt), Pt nanoparticles sandwiched between the graphene layers of a GTO framework (GTO/Pt) showed significantly improved electrocatalytic performance and stability for methanol oxidation. The simultaneous reduction of Pt4+ and oxygen moieties of GTO during the synthesis of GTO/Pt resulted in a composite with moderately stacked graphene layers. This structure enhanced the kinetic feasibility of methanol oxidation with no decrease in the active surface area of Pt nanoparticles, and also increased the tolerance for the adsorption of surface-adsorbed intermediates. In addition, in contrast to the GO/Pt composite, the Pt nanoparticles in GTO/Pt did not aggregate during the electrochemical reaction, which was responsible for the superior long-term stability of the GTO/Pt. Thermal reduction of GTO/Pt (rGTO/Pt) resulted in rather inferior electrocatalytic responses due to a decrease in the accessible surface area of Pt nanoparticles in the densely stacked graphene layers. Therefore, other than a synthetic convenience (GTO does not require a mechanical exfoliation step.), this work suggests that the use of GTO rather than GO as a support could be a more efficient tactic in preparing graphene composites when the electrochemical reaction on the surface of impregnated nanoparticles is important.close

Dense CoO/graphene stacks via self-assembly for improved reversibility as high performance anode in lithium ion batteries

(Graph Presented) Here, we propose a novel strategy to prepare dense stacks composed of alternating CoO and graphene layers for an anode in lithium ion batteries (LIBs), which contributes to enhanced stability and relatively large reversible capacity. This is accomplished by spontaneously pre-aligning negatively charged CoO-anchored graphene oxide (CG) and positively charged amine-functionalized graphene (GN) in an acidic medium, followed by thermal reduction. The performance of this product is contrasted with that of CG prepared under the identical conditions without the addition of GN, in which CoO nanoparticles are sandwiched between relatively loose and randomly oriented graphene stacks. For example, the composite delivers a capacity greater than 800 mAh g-1 with a fading rate of 0.04 mAh g-1 cycle-1 during 1000 charge/discharge (C/D) cycles at 1.0 A g-1, in contrast to ca. 400 mAh g-1 and 0.24 mAh g-1 cycle-1 for thermally reduced CG without the addition of GN. The origin of the superior electrochemical performance in the dense stacks is ascribed to the enhanced reversibility of a conversion reaction, which in turn contributes to a persistent formation/dissolution of gel-like polymer films (i.e., stable pseudo-capacitance). Experimental evidences that substantiate the aforementioned behaviors (improved reversibility for both processes) are presented.close1