Gold inverse opal (Au--IO) thin films are active for CO 2 reduction to CO with high efficiency at modest over--potentials and high selectivity relative to hydrogen evolution. The specific activity for hydrogen evolution diminishes by ten fold with increasing porous film thickness while CO evo--lution activity is largely unchanged. We demonstrate that the origin of hydrogen suppression in Au--IO films stems from the generation of diffusional gradients within the pores of the mesostructured electrode rather than changes in surface faceting or Au grain size. For electrodes with optimal meso--porosity, 99% selectivity for CO evolution can be obtained at overpotentials as low as 0.4 V. These results establish elec--trode mesostructuring as a complementary method for tun--ing selectivity in CO 2 --to--fuels catalysis.The electroreduction of carbon dioxide is a promising meth--od for storing intermittent renewable electricity in energy dense carbonaceous fuels. 1--4 However, the high cost and low efficiency of electrochemical CO 2 reduction (CDR) has pre--vented this technology from reaching economic viability. 4 CDR is most practically achieved in aqueous electrolytes, in which the more kinetically facile reduction of protons to H 2 often outcompetes CO 2 reduction, eroding reaction selectivi--ty. Indeed, the paucity of general materials design principles for selectively inhibiting the hydrogen evolution reaction (HER) impedes the systematic development of improved CDR catalysts. 1 Recently, numerous nanostructured metals have been shown to catalyze CO 2 reduction with improved selectivity relative to planar polycrystalline foils. For example gold, copper, and lead films prepared by electrochemical reduction of copper, gold, and lead oxides, respectively, display high CDR selectiv--ity at low overpotentials. 5--7Likewise, de--alloyed porous Ag films 8 and carbon--supported Au nanoparticle 9 --11 and nan--owire electrodes 12 have been shown to catalyze the reduction of CO 2 to CO with high selectivity. This enhanced selectivity may arise from increases in the specific (surface area normal--ized) activity for CDR and/or from a decrease in specific ac--tivity for HER. For oxide--derived gold, evidence points to both effects, 13 whereas for oxide--derived Cu and Pb, specific HER activity have been shown to diminish more dramatically than CDR activity, giving rise to enhanced selectivity for the latter. 5,7 In general, selectivity differences have been attribut--ed to the intrinsic selectivity of the active sites in the materi--al. However, observations of thickness--dependent product selectivity for electrodeposited porous copper thin films 14 suggest that mass transport effects may also play a role in determining product selectivity. For example, when consid--ering CO 2 reduction catalyzed by Au, which generates CO and H 2 predominantly, both the desired reaction (eq. 1) and H 2 evolution (eq. 2) consume protons,necessitating the formation of a pH gradient at the electrode surface irrespective of the product...

Graphene/Mn3O4 composites were prepared by a simple hydrothermal process from KMnO4 using ethylene glycol as a reducing agent. Mn3O4 nanorods of 100 nm to 1 μm length were observed to be well-dispersed on graphene sheets. To assess the properties of these materials for use in supercapacitors, cyclic voltammetry and galvanostatic charging–discharging measurements were performed. Graphene/Mn3O4 composites could be charged and discharged faster and had higher capacitance than free Mn3O4 nanorods. The capacitance of the composites was 100% retained after 10 000 cycles at a charging rate of 5 A/g.

Refluxing graphene oxide (GO) in N-methyl-2-pyrrolidinone (NMP) results in deoxygenation and reduction to yield a stable colloidal dispersion. The solvothermal reduction is accompanied by a color change from light brown to black. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images of the product confirm the presence of single sheets of the solvothermally reduced graphene oxide (SRGO). X-ray photoelectron spectroscopy (XPS) of SRGO indicates a significant increase in intensity of the C=C bond character, while the oxygen content decreases markedly after the reduction is complete. X-ray diffraction analysis of SRGO shows a single broad peak at 26.24° 2θ (3.4 Å), confirming the presence of graphitic stacking of reduced sheets. SRGO sheets are redispersible in a variety of organic solvents, which may hold promise as an acceptor material for bulk heterojunction photovoltaic cells, or electromagnetic interference shielding applications.

An electrode's performance for catalytic CO conversion to fuels is a complex convolution of surface structure and transport effects. Using well-defined mesostructured silver inverse opal (Ag-IO) electrodes, it is demonstrated that mesostructure-induced transport limitations alone serve to increase the turnover frequency for CO activation per unit area, while simultaneously improving reaction selectivity. The specific activity for catalyzed CO evolution systematically rises by three-fold and the specific activity for catalyzed H evolution systematically declines by ten-fold with increasing mesostructural roughness of Ag-IOs. By exploiting the compounding influence of both of these effects, we demonstrate that mesostructure, rather than surface structure, can be used to tune CO evolution selectivity from less than 5 % to more than 80 %. These results establish electrode mesostructuring as a powerful complementary tool for tuning both catalyst selectivity and efficiency for CO conversion into fuels.