Boosting hot electron flux and catalytic activity at metal-oxide interfaces of PtCo bimetallic nanoparticles

Despite numerous studies, the origin of the enhanced catalytic performance of bimetallic nanoparticles (NPs) remains elusive because of the ever-changing surface structures, compositions, and oxidation states of NPs under reaction conditions. An effective strategy for obtaining critical clues for the phenomenon is real-time quantitative detection of hot electrons induced by a chemical reaction on the catalysts. Here, we investigate hot electrons excited on PtCo bimetallic NPs during H-2 oxidation by measuring the chemicurrent on a catalytic nanodiode while changing the Pt composition of the NPs. We reveal that the presence of a CoO/Pt interface enables efficient transport of electrons and higher catalytic activity for PtCo NPs. These results are consistent with theoretical calculations suggesting that lower activation energy and higher exothermicity are required for the reaction at the CoO/Pt interface

Associative desorption of hydrogen isotopologues from copper surfaces: Characterization of two reaction mechanisms.

We report quantum-state resolved measurements of angular and velocity distributions of the associative desorption of H-2, HD, and D-2 from Cu(111) and Cu(211) surfaces. The desorbing molecules have bimodal velocity distributions comprising a "fast" channel and a "slow" channel on both facets. The "fast channel" is promoted by both hydrogen incidence translational and vibrational energy, while the "slow channel" is promoted by vibrational energy but inhibited by translational energy. Using detailed balance, we determine state-specific reaction probabilities for dissociative adsorption and compare these to theoretical calculations. The results for the activation barrier for the " fast channel" on Cu(111) are in agreement with theory within "chemical accuracy" (1 kcal/mole). Results on the Cu(211) facet provide direct information on the effect of increasing step density, which is commonly believed to increase reactivity. Differences in reactivity on the (111) and (211) facets are subtle-quantum state specific reactivity on the (211) surface is characterized by a broader distribution of barrier heights whose average values are higher than for reaction on (111). We fully characterize the "slow channel," which has not been found in theoretical calculations although it makes up a large fraction of the reactivity in these experiments

Phosphorus stimulated unidirectional growth of TiO2 nanostructures

Previously reported TiO2 nanowire fabrication from Ni catalysts shows a surprising amount of phosphorous (P) contamination incorporated into the seed particle. We proposed this unintentional P-doping of Ni particles aids the mechanism for nanowire growth and occurs by an alternative pathway from the Vapor-Liquid-Solid (VLS) mechanism. To confirm this new mechanism, mixed phase NiP/Ni2P (NixPy) and Ni2P nanoparticles were fabricated and the central role of phosphorous in TiO 2 nanowire synthesis confirmed. This newly developed P-assisted fabrication method yielded crystalline rutile TiO2 nanowires. In this mechanism solid, quasi-spherical catalyst particles attached to the ends of nanowires and surrounded by a Ni/P liquid shell are responsible for the nanowire growth. The growing end of the nanowire appears to form a "tangent- plane" to the solid catalyst core with the liquid shell wetting and occupying the interstice between the catalyst and the nanowire. In Ni xPy assisted growth, nanowire diameters occurred as small as 12.3 nm, some of the thinnest yet reported TiO2 nanowires resulting from atmospheric-pressure chemical vapor deposition (APCVD) growth. © The Royal Society of Chemistry 2013

The kinetics of elementary thermal reactions in heterogeneous catalysis.

The kinetics of elementary reactions is fundamental to our understanding of catalysis. Just as microkinetic models of atmospheric chemistry provided the predictive power that led to the Montreal Protocol reversing loss of stratospheric ozone, pursuing a microkinetic approach to heterogeneous catalysis has tremendous potential for societal impact. However, the development of this approach for catalysis faces great challenges. Methods for measuring rate constants are quite limited, and the present predictive theoretical methods remain largely unvalidated. Here, we present a short Perspective on recent experimental advances in the measurement of rates of elementary reactions at surfaces that rely on a stroboscopic pump-probe concept for neutral matter. We present the principles behind successful measurement methods and discuss a recent implementation of those principles. The topic is discussed within the context of a specific but highly typical surface reaction, CO oxidation on Pt, which, despite more than 40 years of study, was only clarified after experiments with velocity-resolved kinetics became possible. This deceptively simple reaction illustrates fundamental lessons concerning the coverage dependence of activation energies, the nature of reaction mechanisms involving multiple reaction sites, the validity of transition-state theory to describe reaction rates at surfaces and the dramatic changes in reaction mechanism that are possible when studying reactions at low temperatures

Chemical Vapor Deposition of Graphene on a ""Peeled-Off"" Epitaxial Cu(111) Foil: A Simple Approach to Improved Properties

We present a simple approach to improving the quality of CVD grown graphene, exploiting a Cu(111) foil catalyst The catalyst is epitaxially grown by evaporation on a single crystal sapphire substrate, thickened by electroplating, and peeled off. The exposed surface is atomically fiat easily reduced, and exclusively of (111) orientation. Graphene grown on this catalyst under atmospheric CVD conditions and without wet chemical prereduction produces single crystal domain sizes of several hundred micrometers in samples that are many centimeters in size. The graphene produced in this way can easily be transferred to other substrates using well established techniques. We report mobilities extracted using field-effect (as high as 29 000 cm(2) V-1 s(-1)) and Hall bar measurement (up to 10 100 cm(2) V-1 s(-1)).X113737sciescopu