1,720,974 research outputs found
Thin Nickel Layer with Embedded WC Nanoparticles for Efficient Oxygen Evolution
No full textDeveloping active and stable electrocatalysts for the oxygen evolution reaction (OER) is essential to enhance the efficiency of water splitting. Herein, we report a nickel/tungsten carbide (Ni/WC) composite catalyst in which WC nanoparticles are embedded underneath thin Ni layers as a highly active OER catalyst in an alkaline electrolyte. The thin Ni layer has a modulated electronic structure stemming from the interaction with the WC. The Ni/WC composite exhibits excellent OER activity and durability in a 1 M KOH solution. The turnover frequency of the Ni/WC composite (0.58 s(-1)) is increased by approximately 5.8 times relative to that of the Ni nanoparticles (0.10 s(-1)). The significant increase in catalytic activity of the Ni/WC composite can be attributed to the adsorption property change originating from the interaction between the Ni layers and the WC nanoparticles. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation results show that the electronic structure of the Ni layers can change due to electron transfers from the WC nanoparticles to the Ni layer across their interfaces. This electronic structure change reduces the kinetic barrier of the rate-determining step of the OER pathway by lowering the O* binding energy that impedes the OER kinetics. As a result, the overall OER on the Ni/WC surface is accelerated. These findings suggest a unique strategy by which to enhance the catalytic activity of the OER in an alkaline electrolyte.
Metal-Organic Framework-Derived Magnesium Oxide@Carbon Interlayer for Stable Lithium-Sulfur Batteries
No full textLithium sulfur (Li-S) batteries represent a promising future battery technology. However, the low electrical conductivity of solid-state sulfur species (S, Li2S2, and Li2S) and the polysulfide shuttle effect deteriorate their practical capacity and cycling retention. Herein, we present an interlayer composed of magnesium oxide (MgO) nanoparticles and carbon matrix for the Li-S batteries. In the composite, MgO can capture dissolved polysulfides that diffuse to the carbon matrix along the oxide surface for further reduction reactions. As a novel precursor to produce the composite structure, a Mg metal-organic-framework, Mg-MOF-74, is adopted and synthesized on a free-standing carbon paper (MOF/C-paper). Through pyrolysis, Mg-MOF-74 is converted into highly porous carbon containing uniformly distributed MgO nanoparticles (MgO@C/C-paper). The Li-S cells assembled with MgO@C/C-paper and C-paper interlayer show significantly higher initial capacities (980 and 898 mAh g-1, respectively) than the interlayer-free cell (729 mAh g-1) owing to the conductive interlayers. After 200 cycles at 0.2 C, the MgO@C/C-paper cell presents a cycle retention (78.3%) superior to that of the C-paper cell (76.5%). With a higher sulfur loading of 3.3 mg cm-2, the MgO@C/C-paper cell exhibits an even higher capacity retention (80.1%) than the C-paper cell (54.6%) after 100 cycles. The excellent cycle stability of the MgO@C/C-paper cell over the C-paper cell demonstrates that the unique structure of the MOF-derived MgO@C is highly effective in anchoring and reutilizing dissolved polysulfides.
Prevention of surface and bulk degradation of Co-free Ni-rich layered cathodes by primary-particle-level Li2SO4 coating
No full textElevating the cutoff voltage is a method that can be employed to harness the high theoretical capacity of nickelrich (Ni-rich) layered oxide cathodes. However, deep charging leads to rapid decays in voltage and capacity, primarily due to hydrogen fluoride (HF) attack on the surface and the lattice strain in the bulk. To improve the performance of cobalt-free (Co-free), nickel-rich (Ni-rich) layered oxide cathode material, LiNi0.96Mn0.04O2 (LNMO), we propose a novel primary-particle-level lithium sulfate (Li2SO4) coating method. This involves soaking the hydroxide precursor in an aqueous nickel sulfate solution before the calcination process, allowing the primary-particle-level Li2SO4 coating layer to form during calcination. In contrast to conventional coating methods, the proposed Li2SO4 coating can prevent both bulk and surface degradation. Firstly, the Li2SO4 coating layer on primary particles serves as a barrier against primary particle agglomeration during calcination, resulting in cathode materials with reduced primary-particle-size. Reducing the primary particle size lowers the lithium ion (Li+) concentration gradient, which in turn reduces lattice strain. Consequently, the formation of diffusionimpeding, diffusion-induced dislocations is significantly suppressed. Second, the Li2SO4 layer consumes the transition metal dissolutive HF and prevents the deposition of insulating metal fluoride. Subsequently, the Li2SO4-coated LNMO (SLNMO) exhibits superior electrochemical performance, demonstrating a high initial discharge capacity of 224.5 mAh g_1 and a high initial Coulombic efficiency of 94.2 % at a cutoff voltage of 4.5 V. Furthermore, the Li2SO4-coated LNMO maintains a discharge capacity of 181.9 mAh g_1 with a high energy efficiency of 94.9 % at the 100th cycle.
Achieving Enhanced High-Temperature Performance of Lithium-Ion Batteries via Salt-Inspired Interfacial Engineering
No full textElectrolyte additive engineering enables the creation of long-lasting interfacial layers that protect electrodes, thus extending the lifetime of high-energy lithium-ion batteries employing Ni-rich Li[Ni1-x-yCoxMny]O2 (NCM) cathodes. However, batteries face various limitations if existing additives are employed alone without an appropriate combination. Herein, the study reports the development of a molecular-engineered salt-type multifunctional additive, lithium bis(phosphorodifluoridate) triethylammonium ethenesulfonate (LiPENS), that leverages the different functionalities of phosphorous, nitrogen, and sulfur-embedded motifs, as well as the classical additive vinylene carbonate (VC), to construct protective interfacial layers. The thermally and electrochemically reinforced solid electrolyte interphase (SEI), achieved through the combined use of LiPENS and VC, conserves the lithiation level of the Graphite (Gr) anode with minimal SEI growth, whereas the inorganic-rich cathode-electrolyte interface (CEI) alleviates the irrevocable phase transition and mechanical fragility of the LiNi0.8Co0.1Mn0.1O2 (NCM811) secondary particles. The multifunctional roles of LiPENS are demonstrated in an NCM811/Gr full cell, showing a discharge capacity of 190.7 mAh g-1 with an enhanced capacity retention of 91.8% at 1 C and 45 degrees C after 300 cycles. This advancement in electrolyte additive engineering based on salt structures can lead to more efficient, reliable, and commercially viable batteries for high-energy applications, including electric vehicles and portable electronics.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A Deep Learning-Based Approach for Identifying the Medicinal Uses of Plant-Derived Natural Compounds
No full textMedicinal plants and their extracts have been used as important sources for drug discovery. In particular, plant-derived natural compounds, including phytochemicals, antioxidants, vitamins, and minerals, are gaining attention as they promote health and prevent disease. Although several in vitro methods have been developed to confirm the biological activities of natural compounds, there is still considerable room to reduce time and cost. To overcome these limitations, several in silico methods have been proposed for conducting large-scale analysis, but they are still limited in terms of dealing with incomplete and heterogeneous natural compound data. Here, we propose a deep learning-based approach to identify the medicinal uses of natural compounds by exploiting massive and heterogeneous drug and natural compound data. The rationale behind this approach is that deep learning can effectively utilize heterogeneous features to alleviate incomplete information. Based on latent knowledge, molecular interactions, and chemical property features, we generated 686 dimensional features for 4,507 natural compounds and 2,882 approved and investigational drugs. The deep learning model was trained using the generated features and verified drug indication information. When the features of natural compounds were applied as input to the trained model, potential efficacies were successfully predicted with high accuracy, sensitivity, and specificity.
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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