1,720,979 research outputs found
Engineering Active Sites in Three-Dimensional Hierarchically Porous Graphene-Like Carbon with Co and N-Doped Carbon for High-Performance Zinc-Air Battery
No full text© 2021 Wiley-VCH GmbHThe design of active sites plays an important role in developing highly active oxygen electrocatalysts in Zn-air batteries (ZnABs). Here, we report the formation of cobalt (Co) nanoparticles and thin graphitic N-doped carbon (NC) supported on three-dimensional hierarchically porous graphene-like carbon (Co-NC/3DHPGC) to maximize the accessibility of Co-NC active sites for oxygen reduction/evolution reactions (ORR/OER). The produced Co-NC/3DHPGC exhibits a broad size distribution (5–30 nm) of Co nanoparticles dispersed on the external surface of 3DHPGC and coated with NC to a thickness of ∼2 nm. We attributed the formation of Co nanoparticles with broad size distribution to the hierarchical porosity of 3DHPGC, which served as a cage to stabilize the Co nanoparticles and increase the metal dispersion; the produced Co nanoparticles catalyze the formation of graphitic NC. Compared with commercial Pt/C and RuO2 catalysts, the resultant Co-NC/3DHPGC exhibits excellent bifunctional ORR/OER electrocatalytic activity and high durability. The high electrocatalytic performance is ascribed to the accessibility of highly active Co-NC sites through mesopores of 3DHPGC. The ZnAB assembled with Co-NC/3DHPGC exhibits high energy density and efficiency. This systematic engineering and rational synthesis strategy may provide new insight into the development of high-performance oxygen electrocatalysts for metal-air batteries and fuel cell technology.11Nsciescopu
Co 3 O 4 nanosheets on zeolite-templated carbon as an efficient oxygen electrocatalyst for a zinc-air battery
No full text© The Royal Society of Chemistry. Zinc-air batteries (ZnABs) are among the most promising energy storage devices, offering multiple advantages of high energy density, low manufacturing cost, high safety, and environmental benignity. However, challenges remain in the development of ZnAB electrode materials due to the lack of efficient air-electrode catalysts for solving the problems regarding slow kinetics of the oxygen reduction/evolution reactions (ORR/OER) and poor durability. Here, we report the formation of Co 3 O 4 nanosheets with rich oxygen-vacancy defects grown on zeolite-templated carbon (ZTC) for electrocatalytic application in a ZnAB. Hydrophobic ZTC serves as a substrate for the growth of the Co 3 O 4 nanosheets. Oxygen vacancies are generated by the borohydride reduction of Co 2+ , followed by oxidation with oxygen in atmospheric air. The resultant oxygen-vacancy defective Co 3 O 4 nanosheets on ZTC (Co 3 O 4 NS/ZTC) exhibits excellent bifunctional electrocatalytic activity towards the ORR/OER and high durability, compared with commercial Pt/C and RuO 2 catalysts. The high bifunctional electrocatalytic activity is attributed to the sheet-like structure and oxygen-vacancy defects of Co 3 O 4 and the high surface area and uniform microporosity of ZTC. The ZnAB with the bifunctional electrocatalyst exhibits excellent discharge performance and long-term charge/discharge cycling stabilit
Sulfonium-based organic structure-directing agents for microporous aluminophosphate synthesis
No full textSulfur-centered phenyl, n-butyl, p-tolyl, and benzyl sulfoniums and sulfides were tested as organic structure-directing agents (SDAs) for the synthesis of crystalline microporous aluminophosphates (AlPOs) over various ranges of gel compositions, hydrothermal treatment temperatures, and crystallization times. Among the investigated compounds, triphenylsulfonium gave single-phase products of ATS-type AlPO and silicoaluminophosphate. Other sulfoniums yielded only non-porous, dense crystalline AlPOs. On the other hand, diaryl sulfides gave a tiny amount of AFI-type AlPO amid tridymite and amorphous phases. Based on the results, it was found to be reasonable that weakly basic sulfide could hardly act as a zeotype SDA due to the low protonation to sulfonium at the present synthesis pH. © 2019 Elsevier Inc. All rights reserved.11sciescopu
Anomalously High Lithium Storage in Three-Dimensional Graphene-like Ordered Microporous Carbon Electrodes
No full textZeolite-templated
carbon, having a three-dimensional graphene-like
ordered microporous structure with high electrical conductivity, is
a fascinating anode material for Li-ion batteries (LIBs). Herein,
we report an extremely high Li capacity of 2950 mA h g–1 (equivalent to Li1.3/C), which is 7.9 times the maximum
capacity of graphite, Li/C6. This is equivalent to the
crowded packing of 20 Li+ per pore with 0.9 nm diameter.
Approximately 59% of the capacity was reversible. According to the
characterizations by electron energy loss spectroscopy, 7Li NMR, and 13C NMR, most of the Li species existed as
Li+ within the carbon micropores. Contrary to the often-made
assumption, only a small amount of solid–electrolyte interphase
layers was detected at the external surface of the carbon particles
but not inside the micropores. The anomalously high Li capacity is
attributed to the extremely narrow pore environment, where Li+ would be difficult to be fully solvated. Tailoring of the
carbon pores to a subnanometric range would therefore be exciting
for future advancement of LIBs
Facile synthesis of mesoporous zeolite Y using seed gel and amphiphilic organosilane
No full text© 2019 Elsevier Inc.Zeolite Y is widely used as an industrial catalyst for catalytic cracking of heavy feedstocks to lighter olefins. However, incorporation of uniform mesoporosity in zeolite Y without compromising the microporous characteristics is required to improve the catalyst efficiency and minimize catalyst deactivation. Here, we report a facile synthesis method for mesoporous zeolite Y (MPYsg) using seed gel and amphiphilic organosilane, that results in mesoporous zeolite showing a narrow mesopore size distribution (3–4 nm) with high external surface area (110 m2g-1) and high micropore surface area (654 m2g-1). During the crystallization of MPYsg, the organosilane acted as a mesopore-generating agent, and the seed gel provided secondary nuclei that created a uniform mesoporous structure in the zeolite Y nanocrystals. Analysis of aluminosilicate precursors collected during the crystallization revealed that the crystallization process starts with a long nucleation period, followed by rapid crystal growth. Due to the highly accessible strong acid sites present on its external surface, MPYsg shows catalytic activity in the decalin cracking reaction higher than that of conventional microporous zeolite Y11sciescopu
Template dissolution with NaOH–HCl in synthesis of zeolite-templated carbons: Effects on oxygen functionalization and electrical energy storage characteristics
Full text link© 2019 Elsevier LtdZeolite-templated synthesis is a versatile route to ordered microporous carbons built with single-walled sp2 framework of various structures, but the use of hazardous HF to dissolve the zeolite template is still a critical safety issue. We investigated the template-removal process using NaOH and HCl, which are safer than HF. The results indicated that the residual ash content in the carbon could be lowered to less than 5 wt% when the template was removed by consecutive treatments using NaOH and HCl in a proper sequence depending on the zeolite framework type. The carbon obtained in this manner exhibited a rather increased supercapacitance in aqueous media at high current density, as compared to carbons from HF-washing. In the case of the non-aqueous supercapacitor, however, the washing with NaOH–HCl resulted in low capacitance. This was due to the effect of NaOH to generate oxygen-functional groups, which could lead to an increase in the hydrophilicity, and a decrease in the electrical conductivity. Furthermore, the oxygen-functional groups could serve as a base to graft organic amines. When the carbon was heated in H2, the oxygen content decreased to a similar level to that of the HF-washed carbon, restoring the conductivity and electrochemical energy storage characteristics11sciescopu
Highly dispersed Pt nanoclusters supported on zeolite-templated carbon for the oxygen reduction reaction
No full text© The Royal Society of Chemistry 2020. The formation of highly dispersed Pt nanoclusters supported on zeolite-templated carbon (PtNC/ZTC) by a facile electrochemical method as an electrocatalyst for the oxygen reduction reaction (ORR) is reported. The uniform micropores of ZTC serve as nanocages to stabilize the PtNCs with a sharp size distribution of 0.8-1.5 nm. The resultant PtNC/ZTC exhibits excellent catalytic activity for the ORR due to the small size of the Pt clusters and high accessibility of the active sites through the abundant micropores in ZTC11sciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Sodium-free synthesis of mesoporous zeolite to support Pt-Y alloy nanoparticles exhibiting high catalytic performance in propane dehydrogenation
No full text© 2021 Elsevier Inc.Mesoporous zeolite-supported Pt3Y catalyst deactivates slowly in propane dehydrogenation, maintaining high propane conversion and propylene selectivity, but the formation of the intermetallic compound requires atomistic migration of yttrium through silanol nests on the zeolite. Compared to the cumbersome generation of silanols via framework demetallation, we report a direct synthesis of mesoporous MFI zeolite possessing silanol nests. The synthesis procedure employed a diammonium-type bromide surfactant [C18H37–N(CH3)2–C6H12–N(CH3)2–C4H9Br2] and a sodium-free silica source. The basicity of the synthesis mixture was adjusted by the addition of readily available N(CH3)4OH, instead of converting the surfactant to hydroxyl form. The presence of silanol nests in the resultant zeolite was confirmed by IR and NMR spectroscopies. When the zeolite was supported with 0.50 wt% Pt and 0.50 wt% Y using nitrate precursors, a remarkably long catalytic lifetime of 20 days was obtained with high propane conversion and propylene selectivity under the reaction condition using neat propane gas at 853 K.11Nsciescopu
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