Reaction-driven restructuring of defective PtSe into ultrastable catalyst for the oxygen reduction reaction.

PtM (M = S, Se, Te) dichalcogenides are promising two-dimensional materials for electronics, optoelectronics and gas sensors due to their high air stability, tunable bandgap and high carrier mobility. However, their potential as electrocatalysts for the oxygen reduction reaction (ORR) is often underestimated due to their semiconducting properties and limited surface area from van der Waals stacking. Here we show an approach for synthesizing a highly efficient and stable ORR catalyst by restructuring defective platinum diselenide (DEF-PtSe) through electrochemical cycling in an O-saturated electrolyte.

Kinetic Modeling Analysis of Ar Addition to Atmospheric Pressure N-H Plasma for Plasma-Assisted Catalytic Synthesis of NH.

Zero-dimensional kinetic modeling of atmospheric pressure Ar-N-H nonthermal plasma was carried out to gain mechanistic insights into plasma-assisted catalytic synthesis of ammonia. Ar dilution is a common technique for tailoring plasma discharge properties and has been shown to enhance NH formation when added to N-H plasma. The kinetic model was developed for a coaxial dielectric barrier discharge quartz wool-packed bed reactor operating at near room temperature using a kHz-frequency plasma source.

Ion concentration ratio measurements of ion beams generated by a commercial microwave electron cyclotron resonance plasma source.

A commercially available electron cyclotron resonance (ECR) plasma source (GenII Plasma Source, tectra GmbH) is widely used for surface processing. This plasma source is compatible with ultrahigh vacuum systems, and its working pressure is relatively low, around 10-6-10-4 Torr even without differential pumping. Here, we report ion flux concentration ratios for each ion species in an ion beam from this source, as measured by a mass/energy analyzer that is a combination of a quadrupole mass spectrometer, an electrostatic energy analyzer, and focusing ion optics.

Enhanced Feammox activity and perfluorooctanoic acid (PFOA) degradation by Acidimicrobium sp. Strain A6 using PAA-coated ferrihydrite as an electron acceptor.

Acidimicrobium sp. Strain A6 (A6) can degrade perfluoroalkyl acids (PFAAs) by oxidizing NH while reducing Fe(Ⅲ). However, supplying and distributing Fe(III) phases in sediments is challenging since surface charges of Fe(III)-phases are typically positive while those of sediments are negative.

Mechanistic Elucidations of Highly Dispersed Metalloporphyrin Metal-Organic Framework Catalysts for CO Electroreduction.

Immobilization of porphyrin complexes into crystalline metal-organic frameworks (MOFs) enables high exposure of porphyrin active sites for CO electroreduction. Herein, well-dispersed iron-porphyrin-based MOF (PCN-222(Fe)) on carbon-based electrodes revealed optimal turnover frequencies for CO electroreduction to CO at 1 wt.% catalyst loading, beyond which the intrinsic catalyst activity declined due to CO mass transport limitations.

Effect of Porous Catalyst Support on Plasma-Assisted Catalysis for Ammonia Synthesis.

We report on the effect of catalyst support particle porosity on the conversion of NH synthesis from N and H in a coaxial dielectric barrier discharge (DBD) plasma reactor. The discharge was created using an AC applied voltage with the reactor at room temperature and near atmospheric pressure (550 Torr). Two different particles of almost equal diameter (∼1.

Spectroscopic observation and structure-insensitivity of hydroxyls on gold.

The O-H stretching vibration of surface hydroxyls remained at 3691 cm for gold structures ranging in size from clusters to nanoparticles, to non-flat bulk surfaces. In contrast, this vibration was not observed on flat gold surfaces. Therefore, this vibration can serve as an indicator of the roughness of the gold surface and associated functional properties, such as catalytic activity.

Increasing Iridium Oxide Activity for the Oxygen Evolution Reaction with Hafnium Modification.

Synthesis and implementation of highly active, stable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is a major challenge in developing energy efficient and economically viable energy conversion devices such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. The current benchmark electrocatalyst for OER is based on iridium oxide (IrO) due to its superior performance and excellent stability. However, large scale applications using IrO are impractical due to its low abundance and high cost.

Acetic Acid Adsorption and Reactions on Ni(110).

Acetic acid adsorption and reactions at multiple surface coverage values on Ni(110) were studied with temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) at 90-500 K. The experimental measurements were interpreted with density functional theory (DFT) calculations that provided information on adsorbate geometries, energies, and vibrational modes. Below the monolayer saturation coverage of 0.

Nitrogen-plasma treated hafnium oxyhydroxide as an efficient acid-stable electrocatalyst for hydrogen evolution and oxidation reactions.

Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in strong acids represents a great challenge for developing high efficiency, durable, and cost effective electrolyzers and fuel cells. We report herein that hafnium oxyhydroxide with incorporated nitrogen by treatment using an atmospheric nitrogen plasma demonstrates high catalytic activity and stability for both hydrogen evolution and oxidation reactions in strong acidic media using earth-abundant materials. The observed properties are especially important for unitized regenerative fuel cells using polymer electrolyte membranes.

Self-assembling of formic acid on the partially oxidized p(2 × 1) Cu(110) surface reconstruction at low coverages.

Carbon dioxide (CO) reduction for synthetic fuel generation could be an integral part of a sustainable energy future. Copper (Cu) is the leading electrocatalyst for CO reduction to produce multiple C-containing products such as C1 and C2 hydrocarbons and oxygenates. Understanding the mechanisms leading to their production could help optimize these pathways further.

Shear-Induced Changes of Electronic Properties in Gallium Nitride.

We show that sliding on the surface of GaN can permanently change the surface band structure, resulting in an increased degree of band bending by more than 0.5 eV. We hypothesize that shear and contact stresses introduce vacancies that cause a spatially variant band bending.

The promoting effect of tetravalent cerium on the oxygen evolution activity of copper oxide catalysts.

A new catalyst is presented for the oxygen evolution reaction (OER) based on cerium-modified copper oxide (CuO) prepared using a facile electrodeposition procedure. Incorporation of Ce into CuO leads to greatly improved OER activity, which reached an optimal value at a surface concentration of 6.9 at% Ce.

Hydrogenation of CO to Methanol on Ni(110) through Subsurface Hydrogen.

We present a combined theoretical and experimental study of CO hydrogenation on a Ni(110) surface, including studies of the role of gas-phase atomic hydrogen, surface hydrogen, and subsurface hydrogen reacting with adsorbed CO. Reaction mechanisms leading both to methane and methanol are considered. In the reaction involving surface or subsurface hydrogen, we investigate four possible pathways, using density functional theory to characterize the relative energetics of each intermediate, including the importance of further hydrogenation versus C-O bond breaking, where the latter may lead to methane production.

Investigation of Water Dissociation and Surface Hydroxyl Stability on Pure and Ni-Modified CoOOH by Ambient Pressure Photoelectron Spectroscopy.

Water adsorption and reaction on pure and Ni-modified CoOOH nanowires were investigated using ambient pressure photoemission spectroscopy (APPES). The unique capabilities of APPES enable us to observe water dissociation and monitor formation of surface species on pure and Ni-modified CoOOH under elevated pressures and temperatures for the first time. Over a large range of pressures (UHV to 1 Torr), water dissociates readily on the pure and Ni-modified CoOOH surfaces at 27 °C.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge.

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm, is above the boron melting point (2350 K).

Effect of Temperature on the Desorption of Lithium from Molybdenum(110) Surfaces: Implications for Fusion Reactor First Wall Materials.

Determining the strength of Li binding to Mo is critical to assessing the survivability of Li as a potential first wall material in fusion reactors. We present the results of a joint experimental and theoretical investigation into how Li desorbs from Mo(110) surfaces, based on what can be deduced from temperature-programmed desorption measurements and density functional theory (DFT). Li desorption peaks measured at temperatures ranging from 711 K (1 monolayer, ML) to 1030 K (0.

Facet-dependent activity and stability of Co₃O₄ nanocrystals towards the oxygen evolution reaction.

The electrocatalytic activities and stabilities of spinel cobalt oxides with different morphologies have been investigated for the oxygen evolution reaction (OER) in an alkaline environment. Spinel cobalt oxide nanoparticles with well-defined cubic and octahedral morphologies were prepared, which predominantly expose the (100) and (111) surfaces, respectively. The OER activity of spinel cobalt oxide, measured in terms of current density, increases with higher relative proportion of the (111) surface, which can be attributed to the higher density of cobalt ions on the (111) surface compared to that on the (100) surface.

The (0001) surfaces of α-Fe2O3 nanocrystals are preferentially activated for water oxidation by Ni doping.

Photoelectrochemical water oxidation on hematite has been extensively studied, yet the relationship between the various facets exposed, heteroatom doping, and associated electrocatalytic activity has not been adequately explored. Here, hematite nanocrystals were synthesized with continuous tuning of the aspect-ratio and fine control of the surface area ratio of the (0001) facet with respect to other surfaces. The samples were doped with nickel, which was confirmed using the combined results of HRTEM, SEM, XRD, Raman, BET, and XPS measurements.

Water oxidation catalysis: effects of nickel incorporation on the structural and chemical properties of the α-Fe₂O₃(0001) surface.

Photoelectrochemical solar fuel synthesis devices based on photoactive hematite (α-Fe2O3) anodes have been extensively investigated, yet a fundamental understanding regarding its associated water oxidation surface reaction mechanism is still lacking. To help elucidate detailed reaction mechanisms, we studied water chemisorption and reaction as well as structural changes induced by Ni incorporation into the α-Fe2O3(0001) surface. Investigation by scanning probe and electron diffraction techniques show that vapor deposition of Ni and subsequent annealing to 700 K leads to the interdiffusion and incorporation of Ni into the near-surface region of hematite and changes the structure of the (0001) surface by the formation of FeO-like domains on the topmost layer.

Hydrogen-bonded cyclic water clusters nucleated on an oxide surface.

We report the observation and molecular-scale scanning probe electronic structure (dI/dV) mapping of hydrogen-bonded cyclic water clusters nucleated on an oxide surface. The measurements are made on a new type of cyclic water cluster that is characterized by simultaneous and cooperative bonding interactions among molecules as well as with both metal and oxygen sites of an oxide surface. Density functional theory + U + D calculations confirm the stability of these clusters and are used to discuss other potential water-oxide bonding scenarios.

Geometric requirements for hydrocarbon catalytic sites on platinum surfaces.

Vibrational spectroscopic measurements and density functional calculations were used to identify a preferential catalytic mechanism for the transformation of acetylene, HC-CH, to vinylidene, C-CH2, on surfaces of Pt-Sn ordered alloys. In this mechanism, two adjacent Pt atoms adsorb an acetylene molecule and a third neighboring Pt atom is required for stabilizing the reacting H atom during the transformation. Therefore, unlike a direct H shift along the C-C bond in organometallic compounds with a single transition-metal atom, this mechanism has a geometric site requirement of three adjacent Pt atoms in the form of a three-fold site.

WO3-α-Fe2O3 composite photoelectrodes with low onset potential for solar water oxidation.

The physical and photoelectrochemical properties of a composite oxide photoelectrode comprised of α-Fe2O3 and WO3 crystals is investigated. The composite films exhibit a water oxidation photocurrent onset potential as low as 0.43 V vs.

Alloy formation and chemisorption at Zn/Pt(111) bimetallic surfaces using alkali ISS, XPD, and TPD.

Alloy formation and chemisorption at bimetallic surfaces formed by vapor-depositing Zn on a Pt(111) single crystal were investigated primarily by using X-ray photoelectron diffraction (XPD), X-ray photoelectron spectroscopy (XPS), low-energy alkali ion scattering spectroscopy (ALISS), low electron energy diffraction (LEED), and temperature programmed desorption (TPD). A wide range of conditions were investigated to explore whether deposition and annealing of Zn films could produce well-defined, ordered alloy surfaces, similar to those encountered for Sn/Pt(111) surface alloys. These attempts were unsuccessful, although weak, diffuse (2 × 2) spots were observed under special conditions.

Iron nanoparticles for environmental clean-up: recent developments and future outlook.

Nanoscale zero-valent iron (nZVI) is one of the most extensively applied nanomaterials for groundwater and hazardous waste treatment. In the past fifteen years, progress made in several key areas has deepened our understanding of the merits and uncertainties of nZVI-based remediation applications. These areas include the materials chemistry of nZVI in its simple and modified forms, the nZVI reactivity with a wide spectrum of contaminants in addition to the well-documented chlorinated solvents, methods to enhance the colloidal stability and transport properties of nZVI in porous media, and the effects of nZVI amendment on the biogeochemical environment.