DIMENSIONALITY BASED SCALE SELECTION IN 3D LIDAR POINT CLOUDS

International audienceThis papers presents a multi-scale method that computes robust geometric features on lidar point clouds in order to retrieve the optimal neighborhood size for each point. Three dimensionality features are calculated on spherical neighborhoods at various radius sizes. Based on combinations of the eigenvalues of the local structure tensor, they describe the shape of the neighborhood, indicating whether the local geometry is more linear (1D), planar (2D) or volumetric (3D). Two radius-selection criteria have been tested and compared for finding automatically the optimal neighborhood radius for each point. Besides, such procedure allows a dimensionality labelling, giving significant hints for classification and segmentation purposes. The method is successfully applied to 3D point clouds from airborne, terrestrial, and mobile mapping systems since no a priori knowledge on the distribution of the 3D points is required. Extracted dimensionality features and labellings are then favorably compared to those computed from constant size neighborhoods

Potential-Dependent Adsorption of CO and Its Low-Overpotential Reduction to CH_3CH_2OH on Cu(511) Surface Reconstructed from Cu(pc): Operando Studies by Seriatim STM-EQCN-DEMS

Operando scanning tunneling microscopy first revealed that application of a CO_2-reduction potential to a Cu(pc) electrode in 0.1 M KOH resulted in the reconstruction of the selvedge to an x-layer stack of well-ordered Cu(100) terraces, Cu(pc)-x[Cu(100)]. Subsequent Cu↔Cu_2O oxidation-reduction cycles between −0.90 V and 0.10 V SHE converted the reconstructed region to a stepped Cu(S)-[3(100) × (111)], or Cu(511), surface. Differential electrochemical mass spectrometry showed that reduction of CO produced only CH_3CH_2OH at the lowest overpotential. Later application of STM and surface infrared spectroscopy uncovered a potential, above which no CO adsorption occurs. In this study, electrochemical quartz crystal nanobalance was combined with STM and DEMS as a prelude to the acquisition of CO coverages as continuous functions of concentration and potential; in heterogeneous catalysis, surface coverage are important since the reaction rate are functions of those quantities. Also equally critical is the knowledge of the packing arrangement at the onset of the reaction because, if “CO dimers” were indeed the precursors to C_(2+) products, reduction can only be initiated when the adlayer consists of closely packed CO; otherwise, dimerization will not transpire if the molecules were far apart. The results indicate that the catalysis lags the adsorption, and starts only when CO adsorption is saturated

Ordered Porous Electrodes by Design: Towards Enhancing the Effective Utilization of Platinum in Electrocatalysis

Platinum‐nanoparticle‐functionalized, ordered, porous support electrodes are prepared and characterized as a potential new class of oxygen reduction reaction (ORR) electrocatalysts. This study aims to develop electrode materials that enhance the effective utilization of Pt in electrocatalytic reactions through improved mass transport properties, high Pt mass specific surface area, and increased Pt electrochemical stability. The electrodes are prepared using modular sacrificial templates, producing a uniform distribution of Pt nanoparticles inside ordered porous Au electrodes. This method can be further fine‐tuned to optimize the architecture for a range of characteristics, such as varying nanoparticle properties, pore size, or support material. The Pt‐coated Au, ordered, porous electrodes exhibit several improved characteristics, such as enhanced Pt effective utilization for ORR electrocatalysis. This includes a nearly twofold increase in Pt mass specific surface area over other ultrathin designs, superior mass transport properties in comparison to traditional catalyst layers of C black supported Pt nanoparticles mixed with ionomer, good methanol tolerance and exceptional stability toward Pt chemical and/or electrochemical dissolution through interfacial interactions with Au. The methods to prepare Pt‐coated ordered porous electrodes can be extended to other architectures for enhanced catalyst utilization and improved performance of Pt in electrochemical processes

Platinum Ordered Porous Electrodes: Developing a Platform for Fundamental Electrochemical Characterization

High surface area platinum electrodes with an ordered porous structure (Pt-OP electrodes) have been prepared and characterized by electrochemical methods. This study builds a foundation upon which we can seek an in-depth understanding of the limitations and design considerations to make efficient and stable Pt-OP electrodes for use in electrochemical applications. A set of Pt-OP electrodes were prepared by controlled electrodeposition of Pt through a self-assembled array of spherical particles and subsequent removal of the spherical templates by solvent extraction. The preparation method was shown to be reproducible and the resulting electrodes were found to have clean Pt surfaces and a large electrochemical surface area (A ecsa) resulting from both the porous structure, as well as the nano- and micro-scale surface roughness. Additionally, the Pt-OP electrodes exhibit a surface area enhancement comparable to commercially available electrocatalysts. In summary, the Pt-OP electrodes prepared herein show properties of interest for both gaining fundamental insights into electrocatalytic processes and for use in applications that would benefit from enhanced electrochemical response

Electrochemically Active Nickel Foams as Support Materials for Nanoscopic Platinum Electrocatalysts

Platinum is deposited on open-cell nickel foam in low loading amounts via chemical reduction of Pt cations (specifically, Pt2+ or Pt4+) originating from aqueous Pt salt solutions. The resulting Pt-modified nickel foams (Pt/Ni foams) are characterized using complementary electrochemical and materials analysis techniques. These include electron microscopy to examine the morphology of the deposited material, cyclic voltammetry to evaluate the electrochemical surface area of the deposited Pt, and inductively coupled plasma optical emission spectrometry to determine the mass of deposited Pt on the Ni foam substrate. The effect of potential cycling in alkaline media on the electrochemical behavior of the material and the stability of Pt deposit is studied. In the second part of this paper, the Pt/Ni foams are applied as electrode materials for hydrogen evolution, hydrogen reduction, oxygen reduction, and oxygen evolution reactions in an aqueous alkaline electrolyte. The electrocatalytic activity of the electrodes toward these processes is evaluated using linear sweep voltammetry curves and Tafel plots. The results of these studies demonstrate that nickel foams are acceptable support materials for nanoscopic Pt electrocatalysts and that the resulting Pt/Ni foams are excellent electrocatalysts for the hydrogen evolution reaction. An unmodified Ni foam is shown to be a highly active electrode for the oxygen evolution reaction

Potential-Dependent Adsorption of CO and Its Low-Overpotential Reduction to CH_3CH_2OH on Cu(511) Surface Reconstructed from Cu(pc): Operando Studies by Seriatim STM-EQCN-DEMS

Operando scanning tunneling microscopy first revealed that application of a CO_2-reduction potential to a Cu(pc) electrode in 0.1 M KOH resulted in the reconstruction of the selvedge to an x-layer stack of well-ordered Cu(100) terraces, Cu(pc)-x[Cu(100)]. Subsequent Cu↔Cu_2O oxidation-reduction cycles between −0.90 V and 0.10 V SHE converted the reconstructed region to a stepped Cu(S)-[3(100) × (111)], or Cu(511), surface. Differential electrochemical mass spectrometry showed that reduction of CO produced only CH_3CH_2OH at the lowest overpotential. Later application of STM and surface infrared spectroscopy uncovered a potential, above which no CO adsorption occurs. In this study, electrochemical quartz crystal nanobalance was combined with STM and DEMS as a prelude to the acquisition of CO coverages as continuous functions of concentration and potential; in heterogeneous catalysis, surface coverage are important since the reaction rate are functions of those quantities. Also equally critical is the knowledge of the packing arrangement at the onset of the reaction because, if “CO dimers” were indeed the precursors to C_(2+) products, reduction can only be initiated when the adlayer consists of closely packed CO; otherwise, dimerization will not transpire if the molecules were far apart. The results indicate that the catalysis lags the adsorption, and starts only when CO adsorption is saturated

Cyclic-voltammetry behavior of Pt(1 1 1) in aqueous HClO4+C6H6 Influence of C6H6 concentration, scan rate and temperature

Pt(1 1 1) is modified with an overlayer of C6H6 ads by immersion in 005 or 050 M HClO4 + 1 mM C6H6 and cycling in the 0 05-0 80 V vs RHE potential range The influence of the C6H6 concentration (1-20 mM) scan rate (10-100 mV s(-1)) and temperature (278-318 K) on cyclic-voltammetry (CV) features of Pt(1 1 1) and C6H6 surface excess are examined The surface excess of C6H6 Gamma(C6H6) is evaluated through its oxidative desorption The amount of adsorbed C6H6 corresponds to a sub-monolayer with C6H6 molecules being parallel to the Pt(1 1 1) surface As the amount of dissolved C6H6 increases the surface excess of C6H6 increases to ca 2 monolayers indicating that the C6H6 ads molecules adopt a tilted orientation on Pt(1 1 1) Increase of the scan rate from 10 to 100 mV s(-1) does not result in any shift of the anodic peak but induces a shift of the cathodic peak towards lower potentials An increase of temperature from 278 to 318 K shifts both cathodic and anodic peaks towards higher potentials while at the same time reducing the peak current density However it does not modify the peaks charge density or the C6H6 surface excess The cathodic and anodic CV peaks obtained in 005 or 0 50 M HClO4 + 1 mM C6H6 are assigned to H-UPD adsorption and desorption Repetitive cycling of C6H6-modified Pt(1 1 1) in 005 or 050 M HClO4 (free of C6H6) regenerates the CV profile characteristic of a well ordered Pt(1 1 1) electrode thus indicating that C6H6 adsorption and desorption does not disorder Pt(1 1 1