skip to main content

Title: Progress in catalytic synthesis of advanced carbon nanofibers
Carbon nanofibers (CNFs) have wide applications in various high-tech areas. The demand for CNFs can exponentially increase due to the rapid development of advanced functional materials. Accordingly, a transformational progress is being made in synthesizing CNFs, especially functionalized CNFs. A dominant CNF synthesis pathway is catalytic chemical vapor deposition (CCVD). Therefore, the goal of this work is to review the most recent progress in CCVD synthesis of functional CNFs and to understand how the process conditions and catalysts, especially metal catalysts, affect the physical and chemical properties of the produced CNFs.
; ; ; ; ; ; ;
Award ID(s):
Publication Date:
Journal Name:
Journal of Materials Chemistry A
Page Range or eLocation-ID:
13863 to 13881
Sponsoring Org:
National Science Foundation
More Like this
  1. The development of synthetic, metal-based catalysts to perform intracellular bioorthogonal reactions represents a relatively new and important area of research that combines transition metal catalysis and chemical biology. The ability to perform reactions in cellulo , especially those transformations without a natural counterpart, offers a versatile tool for medicinal chemists and chemical biologists. With proper modification of the metal catalysts, it is even possible to direct a reaction to certain intracellular sites. This review highlights advances in this new area, from early work on intracellular functional group conversions to recent advances in intracellular synthesis of drugs, including cytotoxic agents. Both the fundamental and applied aspects of this approach to intracellular synthesis are reviewed.
  2. Conspectus By using transition metal catalysts, chemists have altered the “logic of chemical synthesis” by enabling the functionalization of carbon–hydrogen bonds, which have traditionally been considered inert. Within this framework, our laboratory has been fascinated by the potential for aldehyde C–H bond activation. Our approach focused on generating acyl-metal-hydrides by oxidative addition of the formyl C–H bond, which is an elementary step first validated by Tsuji in 1965. In this Account, we review our efforts to overcome limitations in hydroacylation. Initial studies resulted in new variants of hydroacylation and ultimately spurred the development of related transformations (e.g., carboacylation, cycloisomerization, and transfer hydroformylation). Sakai and co-workers demonstrated the first hydroacylation of olefins when they reported that 4-pentenals cyclized to cyclopentanones, using stoichiometric amounts of Wilkinson’s catalyst. This discovery sparked significant interest in hydroacylation, especially for the enantioselective and catalytic construction of cyclopentanones. Our research focused on expanding the asymmetric variants to access medium-sized rings (e.g., seven- and eight-membered rings). In addition, we achieved selective intermolecular couplings by incorporating directing groups onto the olefin partner. Along the way, we identified Rh and Co catalysts that transform dienyl aldehydes into a variety of unique carbocycles, such as cyclopentanones, bicyclic ketones, cyclohexenyl aldehydes, andmore »cyclobutanones. Building on the insights gained from olefin hydroacylation, we demonstrated the first highly enantioselective hydroacylation of carbonyls. For example, we demonstrated that ketoaldehydes can cyclize to form lactones with high regio- and enantioselectivity. Following these reports, we reported the first intermolecular example that occurs with high stereocontrol. Ketoamides undergo intermolecular carbonyl hydroacylation to furnish α-acyloxyamides that contain a depsipeptide linkage. Finally, we describe how the key acyl-metal-hydride species can be diverted to achieve a C–C bond-cleaving process. Transfer hydroformylation enables the preparation of olefins from aldehydes by a dehomologation mechanism. Release of ring strain in the olefin acceptor offers a driving force for the isodesmic transfer of CO and H2. Mechanistic studies suggest that the counterion serves as a proton-shuttle to enable transfer hydroformylation. Collectively, our studies showcase how transition metal catalysis can transform a common functional group, in this case aldehydes, into structurally distinct motifs. Fine-tuning the coordination sphere of an acyl-metal-hydride species can promote C–C and C–O bond-forming reactions, as well as C–C bond-cleaving processes.« less
  3. Catalysis plays a significant role in most processes of the chemical industry, especially in the emerging areas of sustainable energy and clean environment. A major challenge is the design of catalysts with the desired synergies in terms of activity, selectivity, stability, and cost. New insights into many fundamental questions related to the challenge have sparked a surge of interest in recent years in the area of exploring copper-based alloy catalysts. In this review, the most recent progress in the explorations of copper-alloy catalysts will be highlighted, with a focus on the structural and mechanistic characterizations of the catalysts in different catalytic reactions. The fundamental understanding of the detailed catalytic synergies of the catalysts for the targeted heterogeneous catalytic reactions depends strongly on the utilization of various analytical techniques for the characterization. Significant progress has been made in utilizing advanced techniques, both ex situ and in situ / operando characterizations, demonstrating the abilities to gain atomic/molecular level insights into the morphological, structural, electronic and catalytic properties of copper alloy catalysts, especially the dynamic surface active sites under the reaction conditions or during the catalytic processes. The focus on structural characterization in this review serves as a forum for discussions on structuralmore »and mechanistic details, which should provide useful information for identifying challenges and opportunities in future research and development of copper-alloy catalysts.« less
  4. Conventional lithium-ion batteries are unable to meet the increasing demands for high-energy storage systems, because of their limited theoretical capacity. 1 In recent years, intensive attention has been paid to enhancing battery energy storage capability to satisfy the increasing energy demand in modern society and reduce the average energy capacity cost. Among the candidates for next generation high energy storage systems, the lithium sulfur battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1) and potential cost reduction. In addition, sulfur is a cost effective and environmentally friendly material due to its abundance and low-toxicity. 2 Despite all of these advantages, the practical application of lithium sulfur batteries to date has been hindered by a series of obstacles, including low active material loading, poor cycle life, and sluggish sulfur conversion kinetics. 3 Achieving high mass loading cathode in the traditional 2D planar thick electrode has been challenged. The high distorsion of the traditional planar thick electrodes for ion/electron transfer leads to the limited utilization of active materials and high resistance, which eventually results in restricted energy density and accelerated electrode failure. 4 Furthermore, of the electrolyte to pores in the cathode and utilization ratiomore »of active materials. Catalysts such as MnO 2 and Co dopants were employed to accelerate the sulfur conversion reaction during the charge and discharge process. 5 However, catalysts based on transition metals suffer from poor electronic conductivity. Other catalysts such as transition metal dopants are also limited due to the increased process complexities. . In addition, the severe shuttle effects in Li-S batteries may lead to fast failures of the battery. Constructing a protection layer on the separator for limiting the transmission of soluble polysulfides is considered an effective way to eliminate the shuttle phenomenon. However, the soluble sulfides still can largely dissolve around the cathode side causing the sluggish reaction condition for sulfur conversion. 5 To mitigate the issues above, herein we demonstrate a novel sulfur electrode design strategy enabled by additive manufacturing and oxidative vapor deposition (oCVD). Specifically, the electrode is strategically designed into a hierarchal hollow structure via stereolithography technique to increase sulfur usage. The active material concentration loaded to the battery cathode is controlled precisely during 3D printing by adjusting the number of printed layers. Owing to its freedom in geometry and structure, the suggested design is expected to improve the Li ions and electron transport rate considerably, and hence, the battery power density. The printed cathode is sintered at 700 °C at N 2 atmosphere to achieve carbonization of the cathode during which intrinsic carbon defects (e.g., pentagon carbon) as catalytic defect sites are in-situ generated on the cathode. The intrinsic carbon defects equipped with adequate electronic conductivity. The sintered 3D cathode is then transferred to the oCVD chamber for depositing a thin PEDOT layer as a protection layer to restrict dissolutions of sulfur compounds in the cathode. Density functional theory calculation reveals the electronic state variance between the structures with and without defects, the structure with defects demonstrates the higher kinetic condition for sulfur conversion. To further identify the favorable reaction dynamic process, the in-situ XRD is used to characterize the transformation between soluble and insoluble polysulfides, which is the main barrier in the charge and discharge process of Li-S batteries. The results show the oCVD coated 3D printed sulfur cathode exhibits a much higher kinetic process for sulfur conversion, which benefits from the highly tailored hierarchal hollow structure and the defects engineering on the cathode. Further, the oCVD coated 3D printed sulfur cathode also demonstrates higher stability during long cycling enabled by the oCVD PEDOT protection layer, which is verified by an absorption energy calculation of polysulfides at PEDOT. Such modeling and analysis help to elucidate the fundamental mechanisms that govern cathode performance and degradation in Li-S batteries. The current study also provides design strategies for the sulfur cathode as well as selection approaches to novel battery systems. References: Bhargav, A., (2020). Lithium-Sulfur Batteries: Attaining the Critical Metrics. Joule 4 , 285-291. Chung, S.-H., (2018). Progress on the Critical Parameters for Lithium–Sulfur Batteries to be Practically Viable. Advanced Functional Materials 28 , 1801188. Peng, H.-J.,(2017). Review on High-Loading and High-Energy Lithium–Sulfur Batteries. Advanced Energy Materials 7 , 1700260. Chu, T., (2021). 3D printing‐enabled advanced electrode architecture design. Carbon Energy 3 , 424-439. Shi, Z., (2021). Defect Engineering for Expediting Li–S Chemistry: Strategies, Mechanisms, and Perspectives. Advanced Energy Materials 11 . Figure 1« less
  5. Abstract

    Nanostructured materials are critically important in many areas of technology because of their unusual physical/chemical properties due to confined dimensions. Owing to their intrinsic hierarchical micro‐/nanostructures, unique chemical/physical properties, and tailorable functionalities, hydrogels and their derivatives have emerged as an important class of functional materials and receive increasing interest from the scientific community. Bottom‐up synthetic strategies to rationally design and modify their molecular architectures enable nanostructured functional hydrogels to address several critical challenges in advanced energy technologies. Integrating the intrinsic or extrinsic properties of various functional materials, nanostructured functional hydrogels hold the promise to break the limitations of current materials, improving the device performance of energy storage and conversion. Here, the focus is on the fundamentals and applications of nanostructured functional hydrogels in energy conversion and storage. Specifically, the recent advances in rational synthesis and modification of various hydrogel‐derived functional nanomaterials as core components in batteries, supercapacitors, and catalysts are summarized, and the perspective directions of this emerging class of materials are also discussed.