Mechanistic Analysis of Urea Electrooxidation Pathways: Key to Rational Catalyst Design.

Urea electrolysis is an emerging approach to treating urea-enriched wastewater and an attractive alternative anodic process to the oxygen evolution reaction (OER) in electrochemical clean energy conversion and storage technologies (e. g., hydrogen production and CO electroreduction).

Understanding the Mechanism of Urea Oxidation from First-Principles Calculations.

Developing electrocatalysts for urea oxidation reaction (UOR) works toward sustainably treating urea-enriched water. Without a clear understanding of how UOR products form, advancing catalyst performance is currently hindered. This work examines the thermodynamics of UOR pathways to produce N, NO , and NO on a (0001) β-Ni(OH) surface using density functional theory with the computational hydrogen electrode model.

The effect of tensile strain in Pd-Ni core-shell nanocubes with tuneable shell thickness on urea electrolysis selectivity.

Expanding our understanding of the structure-performance relationship in nanoscale electrocatalysts for urea electrolysis is crucial for efficient urea waste treatment and concomitant cathodic hydrogen production or CO reduction. Here, we elucidate the effect of the lattice strain in Pd-Ni core-shell nanocubes on the dominance of urea overoxidation pathway.

Simulating electric field and current density in nanostructured electrocatalysts.

The electrocatalytic performance of nanostructured heterogeneous electrocatalysts can be tailored by adjusting their geometries due to the morphologically dependent physicochemical effects, such as field-induced reagent concentration near high-curvature nanoscale features and the confinement of reaction intermediates in a nanocavity. However, the theoretical studies on these physicochemical effects in various nanoscale structures are considerably less common in comparison to the density functional theory calculations on the atomic structure design due to the absence of consistent simulation protocols in this area. This tutorial review presents the theory, models, and protocols for the simulation of the electrochemical properties of nanoelectrocatalysts with complex morphologies using the finite element method (FEM), including the local electric field (E-field) and the current density in the electrolyte adjacent to the electrode () and in the electrode ().

Nickel-Catalyzed Urea Electrolysis: From Nitrite and Cyanate as Major Products to Nitrogen Evolution.

The electrochemical urea oxidation reaction (UOR) to N represents an efficient route to simultaneous nitrogen removal from N-enriched waste and production of renewable fuels at the cathode. However, the overoxidation of urea to NO usually dominates over its oxidation to N at Ni(OH) -based anodes. Furthermore, detailed reaction mechanisms of UOR remain unclear, hindering the rational catalyst design.

Reaction-intermediate-induced atomic mobility in heterogeneous metal catalysts for electrochemical reduction of CO.

Improving the activity and selectivity of heterogeneous metal electrocatalysts has been the primary focus of CO electroreduction studies, however, the stability of these materials crucial for practical application remains less understood. In our work, the impact of the reaction intermediates (RIs) on the energetics and mechanism of metal-atom migration is studied with a combination of density functional theory (DFT) and molecular dynamics (AIMD) on pure transition metals Cu, Ag, Au, Pd, as well as three CuPd ( = 1,2, and 3) alloys. Reaction intermediates (RIs) for the CO reduction reaction, H evolution, and O reduction were considered.

Low-Frequency Oscillations in Optical Measurements of Metal-Nanoparticle Vibrations.

Time-resolved optical measurements of vibrating metal nanoparticles have been used extensively to probe the ultrafast mechanical properties of the nanoparticles and of the surrounding liquid, but nearly all investigations so far have been limited to the linear regime. Here, we report the observation of a low-frequency oscillating signal in transient-absorption measurements of nanoparticles with octahedral gold cores and cubic silver shells; the signal appears at the difference of two mechanical vibrational frequencies in the particles, suggesting a nonlinear mixing process. We tentatively attribute this proposed mixing to a nonlinear coupling between a vibrational mode of the nanoparticle and its optical-frequency plasmon resonance.

Interparticle gap geometry effects on chiroptical properties of plasmonic nanoparticle assemblies.

Chiral linear assemblies of plasmonic nanoparticles with chiral optical activity often show low asymmetry factors. Systematic understanding of the structure-property relationship in these systems must be improved to facilitate rational design of their chiroptical response. Here we study the effect of large area interparticle gaps in chiral linear nanoparticle assemblies on their chiroptical properties using a tetrahelix structure formed by a linear face-to-face assembly of nanoscale Au tetrahedra.

Shape control in seed-mediated synthesis of non-elongated Cu nanoparticles and their optical properties.

Shape and surface chemistry control in copper nanoparticle synthesis is an important research area due to a wide range of developing applications of this material in catalysis, energy conversion, sensing and many others. In addition to being an inexpensive and abundant metal, copper is an attractive photocatalyst due to its optical properties in the visible range. Here, we report a facile, tunable and sustainable methodology for synthesizing Pd-seeded Cu nanoparticles with various shapes, including cubes, spheres, raspberry-like particles and cages stabilized with a bilayer of a cationic surfactant in aqueous media.

Inductive effects in cobalt-doped nickel hydroxide electronic structure facilitating urea electrooxidation.

Electrochemical oxidation of urea provides an approach to prevent excess urea emissions into the environment while generating value by capturing chemical energy from waste. Unfortunately, the source of high catalytic activity in state-of-the-art doped nickel catalysts for urea oxidation reaction (UOR) activity remains poorly understood, hindering the rational design of new catalyst materials. In particular, the exact role of cobalt as a dopant in Ni(OH) to maximize the intrinsic activity towards UOR remains unclear.

Reductive and Coordinative Effects of Hydrazine in Structural Transformations of Copper Hydroxide Nanoparticles.

Shape-specific copper oxide nanostructures have attracted increasing attention due to their widespread applications in energy conversion, sensing, and catalysis. Advancing our understanding of structure, composition, and surface chemistry transformations in shaped copper oxide nanomaterials during changes in copper oxidation state is instrumental from both applications and preparative nanochemistry standpoints. Here, we report the study of structural and compositional evolution of amorphous copper (II) hydroxide nanoparticles under hydrazine reduction conditions that resulted in the formation of crystalline CuO and composite CuO-NH branched particles.

Trapping a Photoelectron behind a Repulsive Coulomb Barrier in Solution.

Multiply charged anions (MCAs) display unique photophysics and solvent-stabilizing effects. Well-known aqueous species such as SO and PO experience spontaneous electron detachment or charge-separation fragmentation in the gas phase owing to the strong Coulomb repulsion arising from the excess of negative charge. Thus, anions often present low photodetachment thresholds and the ability to quickly eject electrons into the solvent via charge-transfer-to-solvent (CTTS) states.

Pd-CNT-SiO nanoskein: composite structure design for formic acid dehydrogenation.

High energy density and low toxicity of formic acid makes it a promising hydrogen energy carrier. Here we report a Pd/CNT-based formic acid dehydrogenation catalyst that shows a significant decrease in the apparent activation energy compared to benchmark Pd catalysts and provide a mechanistic insight into its catalytic performance.

Cu(ii)-nanoparticle-derived structures under CO reduction conditions: a matter of shape.

Uncovering the nature and formation mechanisms of active sites in electrocatalysts is crucial for advancing energy conversion technologies. Cu(ii)-derived electrodes show unique activity in CO2 electroreduction, but its origins are not fully understood. We investigate the structural evolution of Cu(OH)2 nanoparticle-derived electrodes and its effect on their performance in CO2 electroreduction.

An aligned octahedral core in a nanocage: synthesis, plasmonic, and catalytic properties.

Plasmonic metal nanostructures with complex morphologies provide an important route to tunable optical responses and local electric field enhancement at the nanoscale for a variety of applications including sensing, imaging, and catalysis. Here we report a high-concentration synthesis of gold core-cage nanoparticles with a tethered and structurally aligned octahedral core and examine their plasmonic and catalytic properties. The obtained nanostructures exhibit a double band extinction in the visible-near infrared range and a large area electric field enhancement due to the unique structural features, as demonstrated using finite difference time domain (FDTD) simulations and confirmed experimentally using surface enhanced Raman scattering (SERS) tests.

Self-Assembly and Surface Patterning of Polyferrocenylsilane-Functionalized Gold Nanoparticles.

Chemical and topographic surface patterning of inorganic polymer-functionalized nanoparticles (NPs) and their self-assembly in nanostructures with controllable architectures enable the design of new NP-based materials. Capping of NPs with inorganic polymer ligands, such as metallopolymers, can lead to new synergetic properties of individual NPs or their assemblies, and enhance NP processing in functional materials. Here, for gold NPs functionalized with polyferrocenylsilane, two distinct triggers are used to induce attraction between the polymer ligands and achieve NP self-assembly or topographic surface patterning of individual polymer-capped NPs.

Ethanol-dependent expression of the NKG2D ligands MICA/B in human cell lines and leukocytes.

Alcohol consumption affects the human immune system, causing a variety of disorders. However, the mechanisms of development of these changes are not fully understood. We hypothesized that ethanol may influence the expression of MICA and MICB, stress-induced molecules capable of regulating the activity of cytotoxic lymphocytes through the interaction with receptor NKG2D, which substantially affects the functionality of cellular immunity.

Colloidal cholesteric liquid crystal in spherical confinement.

The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets.

Surface patterning of nanoparticles with polymer patches.

Patterning of colloidal particles with chemically or topographically distinct surface domains (patches) has attracted intense research interest. Surface-patterned particles act as colloidal analogues of atoms and molecules, serve as model systems in studies of phase transitions in liquid systems, behave as 'colloidal surfactants' and function as templates for the synthesis of hybrid particles. The generation of micrometre- and submicrometre-sized patchy colloids is now efficient, but surface patterning of inorganic colloidal nanoparticles with dimensions of the order of tens of nanometres is uncommon.

Enhanced electrocatalytic CO reduction via field-induced reagent concentration.

Electrochemical reduction of carbon dioxide (CO) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concentration of CO surrounding typical CO reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species, but the effect is restricted by the solubility of relevant salts.

Linear assembly of patchy and non-patchy nanoparticles.

Linear assemblies of nanoparticles show promising applications due to their collective electronic, optical and magnetic properties. Rational design and controllable organization of nanoparticles in one-dimensional structures can strongly benefit from the marked similarity between conventional step-growth polymerization reactions and directional step-wise assembly of nanoparticles in linear chains. Here we show different aspects of the "polymerization" approach to the solution-based self-assembly of polymer-functionalized metal nanoparticles with different chemical compositions, shapes and dimensions.

Shape-Dependent Interactions of Palladium Nanocrystals with Hydrogen.

Elucidation of the nature of hydrogen interactions with palladium nanoparticles is expected to play an important role in the development of new catalysts and hydrogen-storage nanomaterials. A facile scaled-up synthesis of uniformly sized single-crystalline palladium nanoparticles with various shapes, including regular nanocubes, nanocubes with protruded edges, rhombic dodecahedra, and branched nanoparticles, all stabilized with a mesoporous silica shell is developed. Interaction of hydrogen with these nanoparticles is studied by using temperature-programmed desorption technique and by performing density functional theory modeling.

Circular Dichroism of Chiral Nematic Films of Cellulose Nanocrystals Loaded with Plasmonic Nanoparticles.

In the search for induced chiral plasmonic activity, cholesteric films formed by cellulose nanocrystals have attracted great interest as potential hosts for plasmonic nanoparticles. Circular dichroism (CD) spectra of the composite films exhibit two peaks, one of which is ascribed to the cholesteric host and the other one to plasmonic chiroptical activity of the plasmonic nanoparticles. Here we report the results of comprehensive studies of extinction and CD properties of composite films formed by different types of cellulose nanocrystals and different types of plasmonic nanoparticles.

Structural and optical properties of self-assembled chains of plasmonic nanocubes.

Solution-based linear self-assembly of metal nanoparticles offers a powerful strategy for creating plasmonic polymers, which, so far, have been formed from spherical nanoparticles and cylindrical nanorods. Here we report linear solution-based self-assembly of metal nanocubes (NCs), examine the structural characteristics of the NC chains, and demonstrate their advanced optical characteristics. In comparison with chains of nanospheres with similar dimensions, composition, and surface chemistry, predominant face-to-face assembly of large NCs coated with short polymer ligands led to a larger volume of hot spots in the chains, a nearly uniform E-field enhancement in the gaps between colinear NCs, and a new coupling mode for NC chains due to the formation of a Fabry-Perot resonator structure formed by face-to-face bonded NCs.

Shaken, and stirred: oscillatory segmented flow for controlled size-evolution of colloidal nanomaterials.

We introduce oscillatory segmented flow as a compact microfluidic format that accommodates slow chemical reactions for the solution-phase processing of colloidal nanomaterials. The strategy allows the reaction progress to be monitored at a dynamic range of up to 80 decibels (i.e.