The bulk chemistry has been successfully used as a descriptor for oxygen reduction reaction (ORR) activities of various metal oxides. However, as the size of oxides becomes small, the bulk chemistry ...may not be sufficient to describe the activities. Here, we report a systematic study on Mn-substituted ferrite Mn x Fe3–x O4 (x = 0.5–2.5) nanoparticles and the roles of surface Mn in determining their ORR activities. Gradual Mn substitution induced changes in Mn valence and crystal structure. However, there is no remarkable correlation that can be found between their bulk chemistry and ORR activities. Instead, the surface Mn density and valency were found to play dominant roles in determining the ORR. This work shows that, at a small particle size, the bulk chemistry of oxides may not be the descriptor for their electrochemical properties. Due to the significantly high surface/bulk ratio, the surface chemistry has to be carefully characterized to interpret the activities of oxide nanoparticles.
The design of MoS2‐based electrocatalysts with exceptional reactivity and robustness remains a challenge due to thermodynamic instability of active phases and catalytic passiveness of basal planes. ...This study details a viable in situ reconstruction of zinc–nitrogen coordinated cobalt–molybdenum disulfide from structure directing metal–organic framework (MOF) to constitute specific heteroatomic coordination and surface ligand functionalization. Comprehensive experimental spectroscopic studies and first‐principle calculations reveal that the rationally designed electron‐rich centers warrant efficient charge injection to the inert MoS2 basal planes and augment the electronic structure of the inactive sites. The zinc–nitrogen coordinated cobalt–molybdenum disulfide shows exceptional catalytic activity and stability toward the hydrogen evolution reaction with a low overpotential of 72.6 mV at −10 mA cm−2 and a small Tafel slope of 37.6 mV dec−1. The present study opens up a new opportunity to stimulate catalytic activity of the in‐plane MoS2 basal domains for enhanced electrochemistry and redox reactivity through a “molecular reassembly‐to‐heteroatomic coordination and surface ligand functionalization” based on highly adaptable MOF template.
Assembly of a metal–organic framework organometallic network via weak intramolecular bonds allows reconstruction of a functionalized molybdenum disulfide molecular structure elaborated with heteroatom doping and ligand conjugation. Heteroatomic coordination and an electron‐donating functional ligand act as electron‐rich centers to warrant efficient charge injection to the inert MoS2 basal planes and augment the electronic structure of the inactive sites.
Abstract
Developing efficient catalysts is of paramount importance to oxygen evolution, a sluggish anodic reaction that provides essential electrons and protons for various electrochemical processes, ...such as hydrogen generation. Here, we report that the oxygen evolution reaction (OER) can be efficiently catalyzed by cobalt tetrahedra, which are stabilized over the surface of a Swedenborgite-type YBCo
4
O
7
material. We reveal that the surface of YBaCo
4
O
7
possesses strong resilience towards structural amorphization during OER, which originates from its distinctive structural evolution toward electrochemical oxidation. The bulk of YBaCo
4
O
7
composes of corner-sharing only CoO
4
tetrahedra, which can flexibly alter their positions to accommodate the insertion of interstitial oxygen ions and mediate the stress during the electrochemical oxidation. The density functional theory calculations demonstrate that the OER is efficiently catalyzed by a binuclear active site of dual corner-shared cobalt tetrahedra, which have a coordination number switching between 3 and 4 during the reaction. We expect that the reported active structural motif of dual corner-shared cobalt tetrahedra in this study could enable further development of compounds for catalyzing the OER.
The effect of oxygen on the local structure of Ge atoms in GeTe-O materials has been investigated. Oxygen leads to a significant modification to the vibrational modes of Ge octahedra, which results ...from a decrease in its coordination. We find that a defective octahedral Ge network is the crucial fingerprint for rapid and reversible structural transitions in GeTe-based phase change materials. The appearance of oxide Raman modes confirms phase separation into GeO and TeO at high level O doping. Counterintuitively, despite the increase in crystallization temperature of oxygen doped GeTe-O phase change materials, when GeTe-O materials are used in electrical phase change memory cells, the electrical switching energy is lower than the pure GeTe material. This switching energy reduction is ascribed to the smaller change in volume, and therefore smaller enthalpy change, for the oxygen doped GeTe materials.
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•Vβ with atomically dispersed tetrahedral V species is directly synthesized.•Incorporated V species own the intermediate covalence state close to +5.•Vβ efficiently and stably ...catalyzes methylation of phenol at low temperature.•High chemoselectivity towards cresols is exclusively observed over Vβ.•Acid-oxidation bifunctional mechanism accounts for the catalysis behavior.
V-containing BEA zeolite (Vβ) with the V/Si molar ratio of 1‰ was hydrothermally synthesized and fully characterized. It delivered the tetrahedral, highly isolated atomically dispersed V species owning the intermediate covalence state between +4 and +5 (closer to +5) within zeolite matrix, endowing oxidation capability without compromising acidity. In the low-temperature liquid-phase methylation of phenol with methanol, Vβ showed high yield (turnover number up to 5946), good reusability and preferential chemoselectivity towards the C-alkylation products (o- and p-cresols). In situ FTIR spectra suggested an acid-oxidation bifunctional mechanism involving the oxidative activation of methanol via formaldehyde. Moreover, alkylation of phenol with various other alcohols was also efficiently catalyzed by Vβ, wherein the large-sized alkylation agency showed special regioselectivity. This work not only achieves selective production of cresols through methylation of phenol at low temperature, but highlights the potential of designing high performance heterogeneous catalyst with highly dispersed active sites via controlling the chemical composition of heteroatom zeolite.
Manganese (Mn)‐based compounds are important materials for both energy conversion and energy storage. Unfortunately, it has been a significant challenge to develop highly ordered ...microporous/mesoporous structures for them to provide more active sites for these applications. In order to do so using the soft‐templating method, three conditions have to be met, namely, a strong interaction between the inorganic precursor and the organic templates; eliminating the formation of bulk manganese phosphate; and the preservation of the manganese phosphate framework without it collapsing upon template removal. Herein, a soft‐templating approach is reported using an organophosphonic acid (n‐hexylphosphonic acid) as both the etching and the templating agent, followed by high‐vacuum‐assisted annealing. This approach simultaneously satisfies the above conditions. Both microporous and mesoporous manganese phosphates with uniform pore sizes and well‐defined pore structures are obtained. The utilization of the organophosphonic acid is shown to be the key in the transformation from bulk manganese oxide into a highly ordered microporous phosphate. A very high surface area of 304.1 m2 g−1 is obtained for the microporous manganese phosphate, which is the highest among the reported values for Mn‐based compounds. The ultrafine micropores and high specific surface area of our manganese phosphate promote electrocatalytic activity for the oxygen evolution reaction.
The challenges in synthesizing porous manganese phosphates using the soft‐templating method are overcome by using n‐hexylphosphonic acid as both the etching and the templating agent, with high‐vacuum‐assisted annealing. Benefitting from its high surface area (304.1 m2 g−1) and ultrafine pore size, highly ordered microporous manganese phosphate is found to be a promising candidate for energy storage and electrocatalysis applications, such as the oxygen evolution reaction.
In this study, we report a series of bimetallic Ni−WOx catalyst for the ring‐opening of THFA into 15PDO. The structure‐performance relationship of the catalysts was discussed based on extensive ...characterization using techniques such as BET, H2‐TPR, NH3‐TPD, Pyr‐IR, IPA‐TPD‐MS, XRD, XPS and EXAFS/XANES. The acidity measurements show that higher W density leads to the higher amount of acid density, which could be assigned to the creation of Lewis acid sites mainly on the surface of the calcined catalysts. H2‐TPR profiles of Ni−WOx catalysts show that there is a strong interaction between Ni and W species, enhancing the reducibility of WOx. XRD measurements of calcined Ni−WOx catalysts reveal that the dispersion of Ni particles is enhanced after addition of WOx species. After reduction, different peaks corresponding to metallic Ni and WO3−x are identified for 10Ni−WOx catalysts, as well as new peak assigned to Ni−W intermetallic phase on 10Ni−30WOx catalyst. The formation of Ni−W intermetallic phase was further proved using XPS and EXAFS studies. THFA hydrogenolysis was also conducted under aqueous‐phase conditions over Ni−WOx catalysts, yielding up to 47 % selectivity to 15PDO, along with a highest combined C5 polyols (i. e., 15PDO and 125PTO) selectivity of approximately 64 %. However, the Ni−WOx catalytic system suffers from deactivation process due to the hydrothermal dissolution of the active phase. Further investigation reveals the better stability of metallic tungsten and Ni−W intermetallic phase (Ni4W) against leaching since their corresponding peaks in the XRD patterns of spent catalysts remains nearly unchanged. Finally, 1,4‐dioxane as an organic solvent was employed in THFA hydrogenolysis reaction, resulting in different product distribution, with a THP yield of around 54 %. The catalyst crystalline structure is preserved because of very low Ni and W leaching when 1,4‐dioxane is used as solvent.
Intermetallic decoration: Bi‐functional Ni−WOx catalysts exhibit high catalytic activity towards the selective hydrogenolysis of tetrahydrofurfuryl alcohol to 1,5‐pentanediol, along with 1,2,5‐pentanetriol and tetrahydropyran. Ni4W intermetallic phase formation offers a new approach to stabilize the catalyst against leaching.
Epitaxial growth is one of the most commonly used strategies to precisely tailor heterostructures with well-defined compositions, morphologies, crystal phases, and interfaces for various ...applications. However, as epitaxial growth requires a small interfacial lattice mismatch between the components, it remains a challenge for the epitaxial synthesis of heterostructures constructed by materials with large lattice mismatch and/or different chemical bonding, especially the noble metal-semiconductor heterostructures. Here, we develop a noble metal-seeded epitaxial growth strategy to prepare highly symmetrical noble metal-semiconductor branched heterostructures with desired spatial configurations, i.e., twenty CdS (or CdSe) nanorods epitaxially grown on twenty exposed (111) facets of Ag icosahedral nanocrystal, albeit a large lattice mismatch (more than 40%). Importantly, a high quantum yield (QY) of plasmon-induced hot-electron transferred from Ag to CdS was observed in epitaxial Ag-CdS icosapods (18.1%). This work demonstrates that epitaxial growth can be achieved in heterostructures composed of materials with large lattice mismatches. The constructed epitaxial noble metal-semiconductor interfaces could be an ideal platform for investigating the role of interfaces in various physicochemical processes.
Metallic nanostructures are commonly densely packed into a few packing variants with slightly different atomic packing factors. The structural aspects and physicochemical properties related with the ...vacancies in such nanostructures are rarely explored because of lack of an effective way to control the introduction of vacancy sites. Highly voided metallic nanostructures with ordered vacancies are however energetically high lying and very difficult to synthesize. Here, we report a chemical method for synthesis of hierarchical Rh nanostructures (Rh NSs) composed of ultrathin nanosheets, composed of hexagonal close-packed structure embedded with nanodomains that adopt a vacated Barlow packing with ordered vacancies. The obtained Rh NSs exhibit remarkably enhanced electrocatalytic activity and stability toward the hydrogen evolution reaction (HER) in alkaline media. Theoretical calculations reveal that the exceptional electrocatalytic performance of Rh NSs originates from their unique vacancy structures, which facilitate the adsorption and dissociation of H
O in the HER.
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