Oxygen reduction reaction (ORR) is a key step that determines the performance of a variety of energy storage and conversion devices, such as fuel cells and metal–air batteries. Heteroatom‐doped ...carbon nanotubes (CNTs) and graphenes have attracted increasing interest and hold great promise as efficient ORR catalysts to replace noble‐metal‐based catalysts, owing to their unique structure characteristics, excellent physicochemical properties, low cost, and rich resources. In this review, recent progress on the design, fabrication, and performance of heteroatom‐doped CNT‐ and graphene‐based catalysts is summarized, aiming to provide insights into the working mechanism of these heteroatom‐doped nanocarbons in ORR. The advantages, challenges that remain, and possible solutions of these nanocarbon‐based electrocatalysts are discussed. Finally, future developing trends of the CNT‐ and graphene‐based ORR catalysts are proposed.
Carbon nanotubes (CNTs)/graphenes are unique one‐dimensional/two‐dimensional structures composed of sp2 hybridized carbon atoms and excellent physicochemical properties. Heteroatom‐doped CNT/graphene‐based catalysts show advantages of high‐content active sites, good electron/ion transport capability, excellent durability, and low cost. These catalysts demonstrate attractive oxygen reduction reaction performance and therefore may find applications in metal–air batteries and fuel cells.
Floating catalyst chemical vapor deposition (FCCVD) has been one of the most important techniques for the synthesis of high‐quality single‐, double‐, and multi‐wall carbon nanotubes (CNTs). The ...method is characterized of simple processing, good controllability, and desirable scalability. The bulk morphologies of the synthesized CNTs can be sponge‐like, an array, a thin film, or fiber by simply changing the growth parameters and the way they are collected, which facilitates a wide range of applications. The authors comprehensively review the state‐of‐the‐art progress on the controlled growth of CNTs by FCCVD which have a defined number of walls, and controlled diameter, bundle size, and type of conductivity. The properties and possible applications for the CNTs and their hybrids are summarized. Finally, insights into the key challenges and prospects for CNTs synthesized by FCCVD are discussed.
Floating catalyst chemical vapor deposition (FCCVD) method is widely used to produce high quality carbon nanotubes (CNTs) due to its simple processing, good controllability, and desirable scalability. This review summarizes the state‐of‐the‐art progress in the controlled growth and applications of the CNTs and their macrostructures by FCCVD. The critical challenges and future perspectives are also discussed.
The great interest in rechargeable Zn–air batteries (ZABs) arouses extensive research on low‐cost, high‐active, and durable bifunctional electrocatalysts to boost the sluggish oxygen reduction ...reaction (ORR) and oxygen evolution reaction (OER). It remains a great challenge to simultaneously host high‐active and independent ORR and OER sites in a single catalyst. Herein a dual‐phasic carbon nanoarchitecture consisting of a single‐atom phase for the ORR and nanosized phase for the OER is proposed. Specifically, single Co atoms supported on carbon nanotubes (single‐atom phase) and nanosized Co encapsulated in zeolitic‐imidazole‐framework‐derived carbon polyhedron (nanosized phase) are integrated together via carbon nanotube bridges. The obtained dual‐phasic carbon catalyst shows a small overpotential difference of 0.74 V between OER potential at 10 mA cm−2 and ORR half‐wave potential. The ZAB based on the bifunctional catalyst demonstrates a large power density of 172 mW cm−2. Furthermore, it shows a small charge‐discharge potential gap of 0.51 V at 5 mA cm−2 and outstanding discharge‐charge cycling durability. This study provides a feasible design concept to achieve multifunctional catalysts and promotes the development of rechargeable ZABs.
A dual‐phasic carbon nanoarchitecture consisting of a single‐atom phase for oxygen reduction reaction (ORR) and nanosized phase for oxygen evolution reaction (OER) is proposed to boost the oxygen electrode performance for rechargeable Zn–air batteries, showing a small OER‐ORR overpotential difference (0.74 V), large power density (172 mW cm–2), a small charge‐discharge potential gap (0.51 V at 5 mA cm–2), and outstanding discharge‐charge cycling durability.
•A novel hybrid-honeycomb structure with enhanced stiffness is proposed.•It exhibits negative Poisson ratio and negative thermal expansion coefficient.•Its effective thermoelastic properties are ...widely tunable.•Analytical expressions of its effective thermoelastic constants are derived.
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Most metamaterials with negative Poisson’s ratio and/or negative thermal expansion coefficient possess relatively low stiffness. In this work, a novel hybrid-honeycomb structure with enhanced stiffness is proposed. It consists of two merged hexagonal honeycombs. Analytical and computational homogenization methods are used to evaluate the effective thermoelastic properties. Analytical expressions of the effective Young’s modulus, Poisson’s ratio, and thermal expansion coefficient are given. We show that the effective thermoelastic properties of the structure are widely tunable by tailoring the microstructural geometry and the constituent materials. In particular, the in-plane effective Poisson’s ratio and thermal expansion coefficient are adjustable over a wide range, from negative to positive. By properly choosing the geometrical and material parameters, the structure can be designed to concurrently possess an enhanced stiffness and a high degree of auxeticity and negative thermal expansion.
Rationally tailoring the coordination environments of metal single atoms (SAs) is an effective approach to promote their catalytic performances, which, however, remains as a challenge to date. Here, ...we report a novel misplaced deposition strategy for the fabrication of differently coordinated dual-metal hetero-SAs. Systematic characterization results imply that the as-synthesized dual-metal hetero-SAs (exemplified by Cu and Co) are affixed to a hierarchical carbon support via Cu–C4 and Co–N4 coordination bonds. Density functional theory studies reveal that the strong synergistic interactions between the asymmetrically deployed CuC4 and CoN4 sites lead to remarkably polarized charge distributions, i.e., electron accumulation and deficiency around CuC4 and CoN4 sites, respectively. The obtained CuC4/CoN4@HC catalyst exhibits significantly enhanced capability in substrate adsorption and O2 activation, achieving superior catalytic performances in the oxidative esterification of aromatic aldehydes in comparison with the Cu- and Co-based SA counterparts.
COVID-19 has become a global pandemic caused by the novel coronavirus SARS-CoV-2. Understanding the origins of SARS-CoV-2 is critical for deterring future zoonosis, discovering new drugs, and ...developing a vaccine. We show evidence of strong purifying selection around the receptor binding motif (RBM) in the spike and other genes among bat, pangolin, and human coronaviruses, suggesting similar evolutionary constraints in different host species. We also demonstrate that SARS-CoV-2's entire RBM was introduced through recombination with coronaviruses from pangolins, possibly a critical step in the evolution of SARS-CoV-2's ability to infect humans. Similar purifying selection in different host species, together with frequent recombination among coronaviruses, suggests a common evolutionary mechanism that could lead to new emerging human coronaviruses.
Biocompatible and self-healing hydrogels that mimic the functions of human skin have attracted much attention for skin-like electronics and human motion detection. Integrating high stretchability and ...improving sensing sensitivity are current challenges. In this study, a nanocomposite hydrogel comprised of polyacrylic acid (PAA) and reduced graphene oxide (rGO) prepared via mussel-inspired chemistry integrates high stretchability (higher than 600%), strong mechanical strength (as high as 400 kPa), excellent self-healing properties, and superior sensing abilities. The outstanding performance of this autonomous self-healing hydrogel originates from its dual-crosslinked networks, which include both physically crosslinked networks and chemically crosslinked networks. The physical crosslinking formed by the ionic interactions between the carboxylic groups of polyacrylic acid and the ferric ions provide reversible self-healing properties for the hydrogel, whereas the covalent bonds provide a stable and strong chemical network for the hydrogel. Due to the effective electric pathways provided via rGO, the hydrogel exhibited strain sensitivity and was able to detect multiple human motions. Moreover, HEF1 fibroblasts differentiated from human embryonic stem cells showed a flourishing living state on the biocompatible hydrogel. The preparation method is simple, easily scaled-up, which will allow for the low cost fabrication of electronic skins and bio-sensors.
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We developed an integrated workflow for circulating tumor cell (CTC) detection and downstream single‐cell analysis based on a novel ChimeraX®‐i120 platform. The platform facilitates negative ...enrichment, immunofluorescent labeling, and machine learning‐based identification of CTCs. The CTC captured by the platform is also compatible for single‐cell molecular analysis. In this study, potential utility of our workflow was validated in clinical setting.
Circulating tumor cell (CTC) analysis holds great potential to be a noninvasive solution for clinical cancer management. A complete workflow that combined CTC detection and single‐cell molecular analysis is required. We developed the ChimeraX®‐i120 platform to facilitate negative enrichment, immunofluorescent labeling, and machine learning‐based identification of CTCs. Analytical performances were evaluated, and a total of 477 participants were enrolled to validate the clinical feasibility of ChimeraX®‐i120 CTC detection. We analyzed copy number alteration profiles of isolated single cells. The ChimeraX®‐i120 platform had high sensitivity, accuracy, and reproducibility for CTC detection. In clinical samples, an average value of > 60% CTC‐positive rate was found for five cancer types (i.e., liver, biliary duct, breast, colorectal, and lung), while CTCs were rarely identified in blood from healthy donors. In hepatocellular carcinoma patients treated with curative resection, CTC status was significantly associated with tumor characteristics, prognosis, and treatment response (all P < 0.05). Single‐cell sequencing analysis revealed that heterogeneous genomic alteration patterns resided in different cells, patients, and cancers. Our results suggest that the use of this ChimeraX®‐i120 platform and the integrated workflow has validity as a tool for CTC detection and downstream genomic profiling in the clinical setting.
A
bstract
The study of Rényi mutual information (RMI) sheds light on the AdS/CFT correspondence beyond classical order. In this article, we study the Rényi mutual in- formation between two intervals ...at large distance in two-dimensional holographic warped conformal field theory, which is conjectured to be dual to gravity on AdS
3
or warped AdS
3
spacetimes under Dirichlet-Neumann boundary conditions. By using the operator product expansion of twist operators up to level 3, we read the leading oder and the next-to-leading order RMI in the large central charge and small cross-ratio limits. The leading order result is furthermore confirmed using the conformal block expansion. Finally, we match the next-to-leading order result by a 1-loop calculation in the bulk.
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