202 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
Universal assembly of liquid metal particles in polymers enables elastic printed circuit board
No full text© 2022 American Association for the Advancement of Science. All rights reserved.An elastic printed circuit board (E-PCB) is a conductive framework used for the facile assembly of system-level stretchable electronics. E-PCBs require elastic conductors that have high conductivity, high stretchability, tough adhesion to various components, and imperceptible resistance changes even under large strain. We present a liquid metal particle network (LMPNet) assembled by applying an acoustic field to a solid-state insulating liquid metal particle composite as the elastic conductor. The LMPNet conductor satisfies all the aforementioned requirements and enables the fabrication of a multilayered high-density E-PCB, in which numerous electronic components are intimately integrated to create highly stretchable skin electronics. Furthermore, we could generate the LMPNet in various polymer matrices, including hydrogels, self-healing elastomers, and photoresists, thus showing their potential for use in soft electronics.11Nsciescopu
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
Surface silanol sites in mesoporous MFI zeolites for catalytic Beckmann rearrangement
No full textSilanol groups were generated in siliceous MFI zeolite nanosheets, via alkali-free synthesis routes, for catalytic application for gas-phase Beckmann rearrangement. The catalytic conversion by the zeolite nanosheets was investigated at 310 or 350 degrees C with cyclohexanone oxime, 4-phenylcyclohexanone oxime and cyclododecanone oxime. Here, cyclohexanone oxime was chosen as a small reactant that should be able to diffuse into the zeolite micropores, while the others were too bulky to diffuse. The catalytic conversion was analyzed in reference to a previous method used to generate hydrogen-bonded silanol nests in bulk-crystalline MFI zeolites using NH3/NH4+. The result of the analysis indicated that the silanol nest was necessary for the catalytic conversion of cyclohexanone oxime and 4-phenylcyclohexanone oxime, but isolated silanols on the external surface were sufficient for the reaction of cyclododecanone oxime.11Nsciescopu
Influence of catalyst pelletization on propane dehydrogenation over hierarchical MFI zeolite supported with platinum-yttrium nanoparticles
No full textPlatinum-yttrium (PtY) nanoparticles supported on a siliceous form of mesoporous MFI zeolite (MZ) were recently found to exhibit excellent catalytic performance in propane dehydrogenation (PDH). Herein, potential shaping of the PtY/MZ catalyst is investigated from the laboratory-synthesized powder form into industrially preferable pellets. The MZ zeolite powder was synthesized using multi-ammonium surfactants as a structure-directing agent and then pelletized in a hydraulic press by itself or with inorganic binders (i.e., pseudoboehmite, fumed silica, or hydrotalcite). As a part of the sequential pelletization process, pressing was followed by a high-temperature treatment (923 K). Addition of 20 wt% pseudoboehmite resulted in the highest mechanical strength without a significant loss of the initial zeolite mesoporosity. The pseudoboehmite-bound pellet also showed high catalytic activity and longevity in PDH application when simultaneously impregnated with 1 wt% Pt [Pt(NH3)4(NO3)2] and 1 wt% Y [Y(NO3)2·6H2O]. Notwithstanding the observed high propane conversion, the pseudoboehmite-bound catalyst produced an unsatisfactory result of low propylene selectivity (∼60%). Image analyses of HAADF-STEM EDS and solid-state 31P NMR spectroscopic data suggest that such findings could be attributed to Al migration from pseudoboehmite onto zeolite regime during the phase transformation of pseudoboehmite in the shaping process. Alternatively, the uses of non-acidic binders, such as fumed silica and hydrotalcite binders were also demonstrated. The silica-bound catalyst yielded high propane conversion with high propylene selectivity although mechanical strengths of the pellet were compromised to a moderate level. © 2023 Elsevier Inc.11Nsciescopu
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
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
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
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
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