1,720,991 research outputs found
Understanding Surface Modulation to Improve the Photo/Electrocatalysts for Water Oxidation/Reduction
No full textWater oxidation and reduction reactions play vital roles in highly efficient hydrogen production conducted by an electrolyzer, in which the enhanced efficiency of the system is apparently accompanied by the development of active electrocatalysts. Solar energy, a sustainable and clean energy source, can supply the kinetic energy to increase the rates of catalytic reactions. In this regard, understanding of the underlying fundamental mechanisms of the photo/electrochemical process is critical for future development. Combining light-absorbing materials with catalysts has become essential to maximizing the efficiency of hydrogen production. To fabricate an efficient absorber-catalysts system, it is imperative to fully understand the vital role of surface/interface modulation for enhanced charge transfer/separation and catalytic activity for a specific reaction. The electronic and chemical structures at the interface are directly correlated to charge carrier movements and subsequent chemical adsorption and reaction of the reactants. Therefore, rational surface modulation can indeed enhance the catalytic efficiency by preventing charge recombination and prompting transfer, increasing the reactant concentration, and ultimately boosting the catalytic reaction. Herein, the authors review recent progress on the surface modification of nanomaterials as photo/electrochemical catalysts for water reduction and oxidation, considering two successive photogenerated charge transfer/separation and catalytic chemical reactions. It is expected that this review paper will be helpful for the future development of photo/electrocatalysts
Functional Molecular Junctions Derived from Double Self-Assembled Monolayers
No full textInformation processing using molecular junctions is becoming more important as devices are miniaturized to the nanoscale. Herein, we report functional molecular junctions derived from double self-assembled monolayers (SAMs) intercalated between soft graphene electrodes. Newly assembled molecular junctions are fabricated by placing a molecular SAM/(top) electrode on another molecular SAM/(bottom) electrode by using a contact-assembly technique. Double SAMs can provide tunneling conjugation across the van der Waals gap between the terminals of each monolayer and exhibit new electrical functions. Robust contact-assembled molecular junctions can act as platforms for the development of equivalent contact molecular junctions between top and bottom electrodes, which can be applied independently to different kinds of molecules to enhance either the structural complexity or the assembly properties of molecules. (c) 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim1111sciescopu
Tunable Sub-nanopores of Graphene Flake Interlayers with Conductive Molecular Linkers for Supercapacitors
No full textAlthough there are numerous reports of high performance supercapacitors with porous graphene, there are few reports to control the interlayer gap between graphene sheets with conductive molecular linkers (or molecular pillars) through a π-conjugated chemical carbon-carbon bond that can maintain high conductivity, which can explain the enhanced capacitive effect of supercapacitor mechanism about accessibility of electrolyte ions. For this, we designed molecularly gap-controlled reduced graphene oxides (rGOs) via diazotization of three different phenyl, biphenyl, and para-terphenyl bis-diazonium salts (BD1-3). The graphene interlayer sub-nanopores of rGO-BD1-3 are 0.49, 0.7, and 0.96 nm, respectively. Surprisingly, the rGO-BD2 0.7 nm gap shows the highest capacitance in 1 M TEABF4 having 0.68 nm size of cation and 6 M KOH having 0.6 nm size of hydrated cation. The maximum energy density and power density of the rGO-BD2 were 129.67 W h kg-1 and 30.3 kW kg-1, respectively, demonstrating clearly that the optimized sub-nanopore of the rGO-BDs corresponding to the electrolyte ion size resulted in the best capacitive performance. © 2016 American Chemical Society171911sciescopu
Efficient ammonia synthesis via electroreduction of nitrite using single-atom Ru-doped Cu nanowire arrays
No full text© The Royal Society of Chemistry 2022. Here, we report the highly active and selective electrocatalytic reduction of NO2- ions to value-added NH3 over a single-atom Ru-modified Cu nanowire array on three-dimensional copper foam (Ru-Cu NW/CF) under ambient conditions. The obtained Ru-Cu NW/CF catalyst exhibited a maximum faradaic efficiency of 94.1% and an NH3 yield up to 211.73 mg h(-1) cm(-2) (0.732 mmol h(-1) cm(-2)), which was approximately five times higher than that of the Cu NW/CF catalyst.11Nsciescopu
Uncovering the Role of Countercations in Ligand Exchange of WSe2: Tuning the d-Band Center toward Improved Hydrogen Desorption
No full textCopyright © 2021 American Chemical Society. The role of countercations that do not bind to core nanocrystals (NCs) but rather ensure charge balance on ligand-exchanged NC surfaces has been rarely studied and even neglected. Such a scenario is unfortunate, as an understanding of surface chemistry has emerged as a key factor in overcoming colloidal NC limitations as catalysts. In this work, we report on the unprecedented role of countercations in ligand exchange for a colloidal transition metal dichalcogenide (TMD), WSe2, to tune the d-band center toward the Fermi level for enhanced hydrogen desorption. Conventional long-chain organic ligands, oleylamine, of WSe2 NCs are exchanged with short atomic S2- ligands having countercations to preserve the charge balance (WSe2/S2-/M+, M = Li, Na, K). Upon exchange with S2- ligands, the charge-balancing countercations are intercalated between WSe2 layers, thereby serving a unique function as an electrochemical hydrogen evolution reaction (HER) catalyst. The HER activity of ligand-exchanged colloidal WSe2 NCs shows a decrease in overpotential by down-shift of d-band center to induce more electron-filling in antibonding orbital and an increase in the electrochemical active surface area (ECSA). Exchanging surface functionalities with S2- anionic ligands enhances HER kinetics, while the existence of intercalated countercations improves charge transfer with the electrolyte. The obtained results suggest that both anionic ligands and countercationic species in ligand exchange must be considered to enhance the overall catalytic activity of colloidal TMDs.11Nsciescopu
Inductive Effect of Lewis Acidic Dopants on the Band Levels of Perovskite for a Photocatalytic Reaction
No full textBand-edge modulation of halide perovskites as photoabsorbers
plays
significant roles in the application of photovoltaic and photochemical
systems. Here, Lewis acidity of dopants (M) as the new descriptor
of engineering the band-edge position of the perovskite is investigated
in the gradiently doped perovskite along the core-to-surface (CsPbBr3–CsPb1–xMxBr3). Reducing M–bromide bond
strength with an increase in hardness of acidic M increases the electron
ability of basic Br, thus strengthening the Pb–Br orbital coupling
in M–Pb–Br, noted as the inductive effect of dopants.
Especially, the highly hard Lewis acidic Mg localized in the outer
position of the perovskite induces the increase of work function and
then shifts band edge upward along the core-to-surface of the perovskite.
Thus, charge separation driven by the dopant-induced internal electric
field induces the slow annihilation of the excited holes, improving
the slow aromatic Csp3–H dissociation
in the photocatalytic oxidation process by ∼211% (491.39 μmol
g–1 h–1) enhancements, compared
with undoped nanocrystals
Layer-Dependent Band Structure of Ternary Metal Chalcogenides: Thickness-Controlled Hexagonal FeIn2S4
No full textTwo-dimensional (2D) transition metal dichalcogenides have received considerable attention due to their exotic electrical, chemical, and physical properties. Here, we report a layer-dependent band structure of a 2D semiconducting ternary metal chalcogenide (TMC), hexagonal FeIn2S4 (hFIS), which is prepared through thickness-controlled colloidal solution synthesis. The controlled dissociation rate of chalcogen precursors caused the growth of the different thicknesses of hFIS, which is coincident with mechanisms established in conventional 2D nanomaterial colloidal synthesis. The various thickness-dependent band structures of hFIS were investigated from the corresponding optical band gap and redox potentials. The unveiled layerdependent band structure of hFIS showed band gaps of approximately 1.02, 1.26, and 1.52 eV, corresponding to synthesis of the 7-8, 5-6, and 2-3 layers, respectively. This study will contribute to the exploration of other layer-dependent TMCs (MIn2X4, M = Fe, Co, Mn, and Zn and X = S, Se, and Te) for new optical and electronic device applications.11Nsciescopu
Unveiling surface charge on chalcogen atoms toward the high aspect-ratio colloidal growth of two-dimensional transition metal chalcogenides
No full text© Royal Society of Chemistry 2021. Controlling surface energies of each facet is essential for the anisotropic growth of two-dimensional transition metal chalcogenides (TMCs). However, it is a challenge due to stronger binding energies of ligand head groups to the edge facets compared to the planar facets. Herein, we demonstrate that the adsorption of ligands on metal positions can induce partial electron localization on the chalcogen sites, and then accelerate metal-chalcogen bond formation for enhanced anisotropic growth of nanosheets. And only in the case of trioctylphosphine oxide (TOPO)-adsorbed nanosheets, surface polarization can be unveiled on the surface of the colloidal nanosheets due to restricted development of nonpolar ligand shells by the steric effects of the ligands. Moreover, density functional theory (DFT) calculation results reveal that the decrease of surface energy on the (100) edge facets as well as the increase on the (001) basal facets by the adsorption of triorganylphosphine oxide also contribute to the preferentially lateral growth. As a result, various 2D TMCs, including MoSe2, WSe2, and SnSe2 synthesized with TOPO, show enhanced anisotropic growth.11Nsciescopu
Low Iridium Content Confined inside a Co3O4 Hollow Sphere for Superior Acidic Water Oxidation
No full textNoble-metal-oxide support catalysts have been demonstrated to be unique for electrocatalytic water oxidation in acidic media. Highly porous three-dimensional oxide supported can serve as an ideal platform to confine ultrasmall metal catalysts on specific sites and modulate their reactivity, resulting in the reduction of noble metal content in the catalyst by boosting the mass activity. However, due to poor control over the support morphology, geometric-driven shifts in mass activity of metal-oxide support catalysts for the oxygen evolution reaction in acidic media have not been realized. Herein, a nanoscale Kirkendall effect is exploited to produce and control a structural evolution yielding an oxygen-evolving catalyst that is highly efficient and robust in acidic medium. By selective reaction-diffusion under oxidizing conditions, the starting solid CoIr NC is directly transformed into an unprecedented Ir-Co3O4@Co3O4 porous-core@shell hollow nanospheres (ICO PCSHS), in which an ultrasmall Ir catalyst is spatially isolated within a porous Co3O4-backbone core, encapsulated by a hollow Co3O4 outer shell. With a low Ir content of 14 wt %, the iridium mass activity exhibited by ICO PCSHS-400 catalyst is 24 times higher than that of benchmark RuO2, substantially exceeding the known oxide-supported metal catalysts. More importantly, the electrocatalyst shows high stability during 8 h of continuous testing in acidic medium. © 2019 American Chemical Society11sciescopu
Hydrogen adsorption engineering by intramolecular proton transfer on 2D nanosheets
Full text linkProton transfer has been intensively researched in the catalysis of reactions involving hydrogen, such as the hydrogen evolution reaction (HER), oxygen evolution reaction, and carbon dioxide reduction. Recently, two-dimensional (2D) materials have gained attention as catalysts for these reactions, and their catalytic effect upon changing the size, shape, thickness, and phase has been studied. However, there are no reports on the role of proton transfer in catalysis by 2D materials. Here, a novel way to enhance the catalytic effect of 2D MoS2 was demonstrated via functionalization with four different organic moieties: phenyl–Me, phenyl–OMe, phenyl–OH, and phenyl–COOH groups. The role of proton transfer in 2D catalysis was carefully investigated via electrochemical kinetic analysis and electrical measurement. The best HER performance was observed with proton-donating COOH-functionalized active materials due to intramolecular proton transfer, which shows potential in hydrogen adsorption engineering using proton transfer. In addition, other molecularly functionalized 2D catalysts, including MoTe2 and graphene, also show proton transfer due to the incorporation of organic moieties, providing enhanced HER performance. [Figure not available: see fulltext.] © 2018 The Author(s011sciescopu
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