Intimate Intermixing Research Articles

Metal Selenide Anchored Carbon Nanotube for Boosted Oxygen Evolution Reaction

The oxygen evolution represents an important reaction in electrochemical water splitting and metal-air batteries. To deal with the increasing energy crisis and demand for sustainable clean energy, production of low-cost, high-efficiency, and robust oxygen evolution reaction (OER) electrocatalysts is urgently needed. Recently, transition metal chalcogenides (TMCs) have been used as active electrocatalysts for OER because of their high electrical conductivity and enhanced electrochemical activity. These chalcogenides based electrocatalysts show unprecedented high efficiency for OER exhibiting very low overpotentials, thereby surpassing state-of-the-art precious metal oxides or hydroxide-based catalysts. Carbon nanostructures have been shown to significantly improve their electrocatalytic performance even further. In the present work, nickel selenide nanorods (NRs) were grown inside carbon nanotubes (NiSe@CNT) through chemical vapor deposition (CVD) wherein, the carbon nanotube formed in-situ wrapping around the growing nickel selenide nanorods. Such intimate intermixing is expected to aid in rapid electron transfer from the catalyst composite and yield significantly higher current density. The encapsulation with a CNT shell can also expectedly increase stability of the selenide phase with respect to corrosion and anion leaching. Electrocatalytic behavior was explored by various electrochemical studies, including linear sweep voltammetry (LSV), chronoamperometric experiments, electrochemical surface area determination, and Tafel slope determination, under highly alkaline condition. It was observed that this NiSe@CNT composites showed enhanced electrocatalytic activity for OER. Our results indicate that the self-grown CNT around nickel selenide increases catalytic activity of this hybrid nanostructure due to an increased number of catalytic sites and electronic conductivity of the nanocomposite. The overpotential at 10 mA cm-2 for the as-synthesized NiSe@CNT catalyst is 270 mV which is much better than precious metal based electrocatalysts for OER, such as RuO2 and IrO2. In addition, the current-voltage plots were superimposable before and after 40 h of chronoamperometry test, confirming that the as-synthesized catalyst gives stable electrocatalytic OER activity in 1 M KOH medium for an extended time period. The as-synthesized catalyst was characterized by XRD, Raman spectroscopy, XPS and TEM for morphology, elemental and chemical compositions.Keywords: oxygen evolution reaction, carbon nanotubes, In-situ wrapping Figure 1

Shape-Directed Co-Assembly of Lead Halide Perovskite Nanocubes with Dielectric Nanodisks into Binary Nanocrystal Superlattices.

Self-assembly of colloidal nanocrystals (NCs) holds great promise in the multiscale engineering of solid-state materials, whereby atomically engineered NC building blocks are arranged into long-range ordered structures—superlattices (SLs)—with synergistic physical and chemical properties. Thus far, the reports have by far focused on single-component and binary systems of spherical NCs, yielding SLs isostructural with the known atomic lattices. Far greater structural space, beyond the realm of known lattices, is anticipated from combining NCs of various shapes. Here, we report on the co-assembly of steric-stabilized CsPbBr3 nanocubes (5.3 nm) with disk-shaped LaF3 NCs (9.2–28.4 nm in diameter, 1.6 nm in thickness) into binary SLs, yielding six columnar structures with AB, AB2, AB4, and AB6 stoichiometry, not observed before and in our reference experiments with NC systems comprising spheres and disks. This striking effect of the cubic shape is rationalized herein using packing-density calculations. Furthermore, in the systems with comparable dimensions of nanocubes (8.6 nm) and nanodisks (6.5 nm, 9.0 nm, 12.5 nm), other, noncolumnar structures are observed, such as ReO3-type SL, featuring intimate intermixing and face-to-face alignment of disks and cubes, face-centered cubic or simple cubic sublattice of nanocubes, and two or three disks per one lattice site. Lamellar and ReO3-type SLs, employing large 8.6 nm CsPbBr3 NCs, exhibit characteristic features of the collective ultrafast light emission—superfluorescence—originating from the coherent coupling of emission dipoles in the excited state.

Spray Flame Synthesis (SFS) of Lithium Lanthanum Zirconate (LLZO) Solid Electrolyte.

A spray-flame reaction step followed by a short 1-h sintering step under O2 atmosphere was used to synthesize nanocrystalline cubic Al-doped Li7La3Zr2O12 (LLZO). The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline La2Zr2O7 (LZO) pyrochlore phase while Li was present on the nanoparticles’ surface as amorphous carbonate. However, a short annealing step was sufficient to obtain phase pure cubic LLZO. To investigate whether the initial mixing of all cations is mandatory for synthesizing nanoparticulate cubic LLZO, we also synthesized Li free LZO and subsequently added different solid Li precursors before the annealing step. The resulting materials were all tetragonal LLZO (I41/acd) instead of the intended cubic phase, suggesting that an intimate intermixing of the Li precursor during the spray-flame synthesis is mandatory to form a nanoscale product. Based on these results, we propose a model to describe the spray-flame based synthesis process, considering the precipitation of LZO and the subsequent condensation of lithium carbonate on the particles’ surface.

Facile synthesis of g-C3N4/ LaMO3 (M: Co, Mn, Fe) composites for enhanced visible-light-driven photocatalytic water splitting

C3N4 was used as a base semiconductor for the formation of composites with LaMO3 (M: Co, Mn, Fe) perovskite powders prepared by sol-gel (SG) and solid-state (SS) through an easy impregnation method. The optical analysis showed a redshift displacement in the case of C3N4/LaMnO3 and C3N4/LaCoO3 composites due to perovskite particles act as electron traps. By photoluminescence, we elucidate that LaFeO3 generates intermediate states inside the structure of C3N4 indicating an intimate intermixing, which is also corroborated by electrochemical characterizations. The activity of the composites towards the hydrogen evolution reaction was tested under simulated solar irradiation without sacrificial agent neither noble metals. Incorporation of 2% of perovskite over C3N4 showed the best efficiencies. C3N4/2%LaFeO3 SG and C3N4/2%LaFeO3 SS showed the highest activities (140 μmol h−1 g−1 and 40 μmol h−1 g−1 respectively). These results are attributed to the better coupling between C3N4 and LaFeO3 and the formation of a type II heterostructure. Meanwhile, the activity of C3N4/LaMnO3 and C3N4/LaCoO3 composites exhibited lower performance compared with composites prepared with LaFeO3 particles, related to the creation of a type I heterostructure where the flow of charges is not efficient, limiting the photocatalytic performance.

Organic solar cells based on anthracene-containing PPE–PPVs and non-fullerene acceptors

Lately, non-fullerene acceptors (NFAs) have received increasing attention for use in polymer-based bulk-heterojunction (BHJ) organic solar cells (OSCs), as improved photovoltaic performance compared to classical polymer–fullerene blends could be demonstrated. In this study, polymer solar cells based on a statistically substituted anthracene-containing poly(p-phenylene ethynylene)-alt-poly(p-phenylene vinylene)s (PPE–PPVs) copolymer (AnE-PVstat) as donor in combination with a number of different electron accepting materials were investigated. Strong photoluminescence quenching of the polymer donor indicates intimate intermixing of both materials. However, the photovoltaic performances were found to be poor compared to blends that use fullerene as acceptor. Time-delayed collection field (TDCF) measurements demonstrate: charge generation is field-independent, but bimolecular recombination processes limit the fill factor and thus the efficiency of devices.

Epoxy/polysiloxane intimate intermixing networks driven by intrinsic motive force to achieve ultralow-temperature damping properties

We propose a facial strategy to design a ‘forced’ intermixing epoxy/polysiloxane network by utilizing a novel epoxy/polysiloxane monomer (SH-EP) in a one-pot synthesis.

Ultrafast Energy Transfer between Disordered and Highly Planarized Chains of Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV).

Upon cooling a solution of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), a phase transition occurs, leading to the formation of aggregates. We have studied the dynamics of singlet excitons in MEH-PPV solution below the critical temperature of the phase transition using steady-state photoluminescence measurements and pump-probe fs-spectroscopy at different temperatures. Spectral analysis indicates the coexistence of disordered chromophores with highly planarized chromophores. The high planarity is evidenced by a remarkably high 0-0/0-1 peak ratio in the spectra. By spectrally separating the contributions of either type of chromophore to the pump-probe signal we find that energy transfer takes place within less than 1 ps from disordered, unaggregated chain segments to highly planarized, aggregated chain segments. The short time scale of the energy transfer indicates intimate intermixing of the planarized and disordered polymeric chromophores.

Efficient and stable Ni–Ce glycerol reforming catalysts: Chemical imaging using X-ray electron and scanning transmission microscopy

Nickel–ceria composite catalysts prepared by a microemulsion method showed outstanding catalytic behavior in hydrogen production by glycerol steam reforming. Contrarily to usual Ni-based catalysts, the system allows long-term stability and nearly absence of by-products, particularly methane and carbon monoxide. With the help of scanning transmission electron microscopy and energy dispersive X-ray spectroscopy we confirmed the key role played by an intimate intermixing of Ni and Ceria components at reaction conditions. In addition, chemical imaging maps as well as more conventional techniques, such as Temperature Programmed Oxidation (TPO) and X-ray Photoelectron Spectroscopy (XPS) were used to identify the carbon containing (including coke) species nature and to establishing their chemical relevance. Combination of these techniques points out that the optimum interphase contact, reached for a specific 20:80 molar Ni:Ce formulation, allows; (i) to keep the Ni particle size controlled with absence of significant formation of coke and thus without deleterious effects on the long-term stability of the catalysts; and (ii) to eliminate undesirable side reactions such as methanation.

Composites from Aqueous Polyethylene Nanocrystal/Graphene Dispersions

Aqueous high molecular weight linear polyethylene nanocrystal/graphene composite dispersions were produced in situ by ethylene insertion polymerization in water or alternatively via a postpolymerization technique. Graphene was used without any prior compatibilizing surface modification. Remarkably, the Ni(II) salicylaldiminato catalyst employed is polymerization active in the presence of the functional groups of graphene in the absence of any scavengers or activating agents in the aqueous system. The intimate intermixing between the polyethylene nanocrystals and graphene in dispersion enables the formation of a uniformly dispersed graphene framework upon precipitation. Because of the very small size of the polyethylene nanocrystals, no segregation of the graphene on the particle surface is possible. The composites obtained feature a low electrical percolation threshold of the highly dispersed graphene. Commercially available graphene is compared with thermally reduced graphene oxide (TRGO) regarding its d...

Ni Enrichment and Stability of Al-Free Garnierite Solid-Solutions: A Thermodynamic Approach

AbstractGarnierites represent significant Ni ore minerals in the many Ni-laterite deposits worldwide. The occurrence of a variety of garnierite minerals with variable Ni content poses questions about the conditions of their formation. From an aqueous-solution equilibrium thermodynamic point of view, the present study examines the conditions that favor the precipitation of a particular garnierite phase and the mechanism of Ni-enrichment, and gives an explanation to the temporal and spatial succession of different garnierite minerals in Ni-laterite deposits. The chemical and structural characterization of garnierite minerals from many nickel laterite deposits around the world show that this group of minerals is formed essentially by an intimate intermixing of three Mg-Ni phyllosilicate solid solutions: serpentine-népouite, kerolite-pimelite, and sepiolite-falcondoite, without or with very small amounts of Al in their composition. The present study deals with garnierites which are essentially Al-free. The published experimental dissolution constants for Mg end-members of the above solid solutions and the calculated constants for pure Ni end-members were used to calculate Lippmann diagrams for the three solid solutions, on the assumption that they are ideal. With the help of these diagrams, congruent dissolution of Ni-poor primary minerals, followed by equilibrium precipitation of Ni-rich secondary phyllosilicates, is proposed as an efficient mechanism for Ni supergene enrichment in the laterite profile. The stability fields of the solid solutions were constructed using [log aSiO2(aq), log ((aMg2+aNi2+)/(aH+)2)] (predominance) diagrams. These, combined with Lippmann diagrams, give an almost complete chemical characterization of the solution and the precipitating phase(s) in equilibrium. The temporal and spatial succession of hydrous Mg- Ni phyllosilicates encountered in Ni-laterite deposits is explained by the small mobility of silica and the increase in its activity.

Observation of Co nanoparticle dispersions in WC nanograins in WC-Co cermets consolidated from chemically synthesized powders

Abstract High resolution, and analytical electron microscopy has been used to analyze morphological features in consolidated specimens of nanostructured tungsten carbide-cobalt cermet materials prepared from chemically synthesized nanostructured WC-Co powder. The investigation includes studying materials produced by consolidation (i) above, and (ii) below the eutectic temperature by thermo-mechanical working. In the case of liquidphase sintered material, the study includes examining the influence of a vanadium carbide additive on morphological features, as well as its effect in inhibiting grain growth. Electron microscope examination of all consolidated materials reveals a dispersion of nanoprecipitates within the WC nanograins of the WC-Co cermet. Micro-diffraction and analytical studies show that these nanoprecipitates are f.c.c. cobalt. This novel discovery is consistent with the concept that the nanoprecipitates nucleate from cobalt retained within the WC nanograins, which is a consequence of the intimate intermixing of tungsten and cobalt in the original chemical synthesis process.

Variation in peperite textures associated with differing host-sediment properties

Peperites formed by mixing of magma and wet sediment are well exposed along Punta China, Baja California, Mexico, where two sills intrude a section of lava flows, limestones, and volcaniclastic rocks. Irregular lobes and dikes extend from the sills several meters into host sediments, including highly comminuted flow top breccias (lithic lapilli tuff breccias) and shelly micrites, whereas intrusive contacts with lava flows are sharp and planar. Where one sill intruded both coarse-grained volcaniclastic rock and fine-grained limestone, textural differences between the hosts produced strikingly different styles of peperite. Blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias; the blocks consequently underwent in situ fragmentation as they were rapidly quenched. The high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse-grained permeable host. Elutriation of fine-grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter-scale fluidization of the host. The contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous, immiscible fluids (fluidal peperite). Intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off “grain by grain” as magma advanced into the host. Thin-section-scale elutriation pipes formed. Microglobular peperite represents a “frozen” example of a fuel-coolant interaction (FCI) between basaltic magma and fluidized micrite host. The intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma-vapor-host interface. Such intimate intermixing of magma and water-bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism.

XPS and AES quantitative surface analysis: Comparison on oxide powder systems

AbstractXPS and AES quantitative surface analyses on several oxide systems, containing two or three metal elements, are compared. Both single‐phase and multi‐phase systems have been investigated, representative of a variety of situations regarding surface v. bulk composition relationships. Metal‐to‐metal ratios obtained via the two techniques have been compared. A very intimate intermixing of cations, as it happens in single‐phase systems (i.e. solid solutions), appears a necessary but not sufficient condition for obtaining good correlation between the results of the two spectroscopies. Slopes of the straight lines correlationg XPS and AES data are generally far from the expected value of 1, suggesting the existence of strong matrix effects for at least one of the two techniques.