Supplementary MaterialsSupplementary Information Supplementary information srep02300-s1. the look of highly effective ORR catalysts. The introduction of nanotechnology and the capability to synthesize a marvelous panoply of nanocrystals possess breathed a fresh existence to the catalysis technology1,2,3,4,5. The idea that catalysts are always nanomaterials can be rooted in the need for surface area in activating chemical substance bonds. Although there were numerous reviews on the catalytic actions of nanomaterials, complete knowledge of how surface area framework affects catalytic efficiency continues to be lacking. There can be therefore a have to systematically research the catalytic activity as a function of nanocrystalline morphology apart from the size because the surface framework can be tunable by varying the morphology. The prerequisite may be the selective synthesis of differently shaped nanocrystal catalysts with uniform crystal surfaces, preferably dispersed on a supporting substrate. The spinel type Co3O4, in which the Co2+ and Co3+ ions occupy the tetrahedral and octahedral sites, respectively6, is known to be a promising catalytic material7,8,9,10,11,12. It has been reported that different morphologies of Co3O4 nanocrystals have a direct bearing on their catalytic activities for SCH 54292 cost CO oxidation. For example, the 110 faces of Co3O4 nanocrystals have a higher catalytic activity for CO oxidation than 100 and 111, because of the more abundant catalytically active Co3+ sites on SCH 54292 cost the former12. For the CH4 combustion, however, the catalytic activity of the nanocrystalline surfaces was found to be in the order of 112 011 ? 001, depending instead on the surface energy13. In the main, the catalytic activity of a given catalyst is therefore determined by the nature of adsorption/activation/desorption of the reactants and products on the catalytically active sites12,13,14,15. The spinel-type Co3O4 nanocrystals are also a potential alternate for the high cost Pt and its alloys to catalyze the oxygen reduction reaction (ORR), a critical reaction which underlies Rabbit Polyclonal to CSGALNACT2 a battery of renewable-energy technologies such as fuel cell. To our knowledge, however, no study has been reported on the correlation between the shape and the ORR catalytic activities of Co3O4 nanocrystals. Such a study requires anchoring the Co3O4 nanocrystals onto a substrate, which is preferably conductive and thus can enhance the ORR activity and stabilize the catalyst system. As a relatively new class of carbon-based nanomaterials, graphene and carbon nanotube (CNT) have high electrical conductivity, large surface area, high mechanical SCH 54292 cost strength, and structural flexibility, making them ideal substrates for supporting SCH 54292 cost such nanocrystal catalysts. Indeed, graphene and CNT supported Co-based SCH 54292 cost electro-catalysts have already been used for ORR with improved catalytic activity and stability16,17,18,19. However, shape-controllable synthesis of Co3O4 nanocrystals on graphene and CNT as composites is still an unmet challenge. In this paper, we report the controllable synthesis of Co3O4 nanorods, nanocubes and nano-octahedrons with difference exposed surfaces uniformly immobilized in situ on graphene sheets. This series of nanocrystals showed much enhanced ORR catalytic activity when dispersed on graphene. More significantly, the quantitative catalytic activity depends on the detailed nanocrystalline morphology and thus the surface structure of the nanocrystals, namely, 111 100 110, pointing to the Co2+ ions as the ORR active sites. Results Shape-selective synthesis of Co3O4 nanocrystals Detailed procedures for the synthesis of Co3O4 nanoparticles (NP), nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) on the surface of reduced graphene oxides (RGO) have been given in the experimental section, and are here illustrated in Scheme 1. The crystalline phases of these nanocomposites were ascertained by XRD patterns (Figure SI-1), with the help of the standard crystal structure of Co3O4 (JCPDS 65-3103). Co3O4 NP around 10?nm across were formed by thermally decomposing the precursors nucleated from the supersaturated metal bicarbonate solution accompanied by the slow release of CO2 (Figure SI-2), as we reported previously20,21,22. Presumably, through the Ostwald ripening process, the initially nucleated precursors were transformed into.