Showing papers in "Chemistry of Materials in 2019"
TL;DR: This work develops, for the first time, universal MatErials Graph Network (MEGNet) models for accurate property prediction in both molecules and crystals and demonstrates the transfer learning of elemental embeddings from a property model trained on a larger data set to accelerate the training of property models with smaller amounts of data.
Abstract: Graph networks are a new machine learning (ML) paradigm that supports both relational reasoning and combinatorial generalization. Here, we develop universal MatErials Graph Network (MEGNet) models ...
513 citations
TL;DR: In this article, the electronic properties of Ti3C2Tx for different surface terminations, as achieved by different annealing temperatures, with the help of photoelectron spectroscopy, inverse photo-electron, and density functional theory calculations, were investigated.
Abstract: MXenes, an emerging family of 2D transition metal carbides and nitrides, have shown promise in various applications, such as energy storage, electromagnetic interference shielding, conductive thin films, photonics, and photothermal therapy. Their metallic nature, wide range of optical absorption, and tunable surface chemistry are the key to their success in those applications. The physical properties of MXenes are known to be strongly dependent on their surface terminations. In this study, we investigated the electronic properties of Ti3C2Tx for different surface terminations, as achieved by different annealing temperatures, with the help of photoelectron spectroscopy, inverse photoelectron spectroscopy, and density functional theory calculations. We find that fluorine occupies solely the face-centered cubic adsorption site, whereas oxygen initially occupies at least two different adsorption sites, followed by a rearrangement after fluorine desorption at high annealing temperatures. The measured electroni...
290 citations
TL;DR: In this article, the authors developed a novel type of multifunctional conductive polymer hydrogel, of which high conductivity is integrated with excellent stretchability, injectability, and rapid self-healing capability, by incorporating multiple hydrogen-bonding 2-ureido-4[1H]-pyrimidinone (UPy) groups as cross-linking points into a brittle polyaniline/poly(4-styrenesulfonate) (PANI/PSS) network.
Abstract: Conducting polymer hydrogels have been employed in diverse fields such as energy storage and bioelectronics, which possess both the mechanical properties of hydrogels and electronic transport properties of conducting polymers. However, the rigid and fragile nature of conducting polymers hinders the long-time stability of the hydrogels and limits their applications in emerging flexible electronic devices. In this work, we have developed a novel type of multifunctional conductive polymer hydrogel, of which high conductivity is integrated with excellent stretchability, injectability, and rapid self-healing capability, by incorporating multiple hydrogen-bonding 2-ureido-4[1H]-pyrimidinone (UPy) groups as cross-linking points into a brittle polyaniline/poly(4-styrenesulfonate) (PANI/PSS) network. The formation of the interpenetrating PANI/PSS network offers the hydrogel electronic conduction assisted by ionic transport, showing a conductivity of 13 S/m and a linear response (gauge factor = 3.4) to external str...
280 citations
TL;DR: The near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have great potential in food industry and medical fields as mentioned in this paper.
Abstract: The near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have great potential in food industry and medical fields. For applications based on NIR spectroscopy, the next generation of...
267 citations
TL;DR: In this paper, the surface terminations of three transition metal carbide MXenes (Ti3C2Tx, Mo2CTx, and Nb2CTX) were investigated up to 1500 °C under a He atmosphere.
Abstract: Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) have attracted significant attention due to their electronic, electrochemical, chemical, and optical properties. However, understanding of their thermal stability is still lacking. To date, MXenes are synthesized via top-down wet chemical etching, which intrinsically results in surface terminations. Here, we provide detailed insight into the surface terminations of three carbide MXenes (Ti3C2Tx, Mo2CTx, and Nb2CTx) by performing thermal gravimetric analysis with mass spectrometry analysis (TA–MS) up to 1500 °C under a He atmosphere. This specific technique enables probing surface terminations including hydroxyl (−OH), oxy (═O), and fluoride (−F) and intercalated species, such as salts and structural water. The MXene hydrophilicity depends on the type of etching (hydrofluoric acid concentration and/or mixed acid composition) and subsequent delamination conditions. We show that the amount of structural water in Ti3C2Tx increases with decre...
250 citations
TL;DR: Li0.98Mg0.02Ni0.94Co0.06O2 (NC-Mg) with 2% Mg doping is presented in this article.
Abstract: High-nickel layered oxide cathodes with a Ni content of >90% show substantial potential for next-generation lithium-ion batteries (LIBs) due to their high capacity and lower cost. However, they are plagued by rapid capacity decay and poor thermal stability, which hamper their practical viability. We present here Li0.98Mg0.02Ni0.94Co0.06O2 (NC-Mg) with 2% Mg doping, aiming to provide a strategic guideline for solving the issues. The Mg2+ ions occupy the lithium layer and are proposed to act as pillar ions, which substantially enhance the structural reversibility and reduce the anisotropic lattice distortion upon cycling, thereby greatly improving the electrochemical and thermal stability of NC-Mg compared to the undoped LiNi0.94Co0.06O2 (NC). Specifically, NC-Mg delivers 214 mA h g–1 with a capacity retention of 80.1% after 500 cycles in pouch-type full cells, much higher than the retention of NC (56.3%). A discharge capacity of 158 mA h g–1 at 10C rate demonstrates its remarkable rate capability. Addition...
241 citations
TL;DR: In this paper, a simple "Same-A-Strategies" (SAS) strategy for constructing p-type and n-type photovoltaic materials with the same electron-accepting (A) unit of benzotriazole was adopted to initially control the energ...
Abstract: Herein, a simple “Same-A-Strategy” (SAS), constructing p-type and n-type photovoltaic materials with the same electron-accepting (A) unit of benzotriazole, is adopted to initially control the energ...
222 citations
TL;DR: In this paper, the authors demonstrate LEDs made from in situ grown CsPbX3 quasi 2D/3D thin films that are color tunable across the entire visible spectrum.
Abstract: Ruddlesden–Popper phase inorganic metal halide perovskites are promising candidates for efficient light-emitting diodes (LEDs) with high brightness and color purity. Here, we demonstrate LEDs made from in situ grown CsPbX3 quasi 2D/3D thin films that are color tunable across the entire visible spectrum. CsPbX3 nanosheets are used to produce RP phase perovskites using butylammonium as a separating ligand to create BA2Csn–1Pbn(Br/Y)3n+1 2D/3D mixed halide thin films, where Y = Cl or I. The number of CsPbBr3 monolayers in these crystals was optimized by changing the butylammonium concentration. We demonstrate a stable perovskite phase with thin emission line widths providing points covering the edge of the CIE triangle and a maximum red/green/blue coverage of ∼130% of the National Television System Committee color standard. Additionally, we are able to report record efficiencies for blue emitting perovskite nanocrystal LEDs with a maximum external quantum efficiency (EQE) of 2.4% and 6.2% at 465 and 487 nm a...
219 citations
TL;DR: In this article, high quality single crystals of MnBi2Te4 were grown for the first time by slow cooling within a narrow range between the melting points of Bi2Te3 (586 °C) and MnBi 2Te4 (600 °C).
Abstract: High-quality single crystals of MnBi2Te4 are grown for the first time by slow cooling within a narrow range between the melting points of Bi2Te3 (586 °C) and MnBi2Te4 (600 °C). Single-crystal X-ray...
207 citations
TL;DR: All-solid-state lithium-ion batteries (ASSBs) are expected to represent a future alternative compared to conventional lithium ion batteries with liquid electrolytes (LIBs) as discussed by the authors.
Abstract: All-solid-state lithium-ion batteries (ASSBs) are expected to represent a future alternative compared to conventional lithium-ion batteries with liquid electrolytes (LIBs). The excellent performanc...
203 citations
TL;DR: In this paper, aqueous zinc ion batteries (ZIBs) composed of inexpensive zinc anode and nontoxic electrolyte are attractive candidates for large-scale energy storage applications.
Abstract: The aqueous zinc ion batteries (ZIBs) composed of inexpensive zinc anode and nontoxic aqueous electrolyte are attractive candidates for large-scale energy storage applications. However, their development is limited by cathode materials, which often deliver inferior rate capability and restricted cycle life. Herein, the VO2 nanorods show significant electrochemical performance when used as an intercalation cathode for aqueous ZIBs. Specifically, the VO2 nanorods display high initial capacity of 325.6 mAh g–1 at 0.05 A g–1, good rate capability, and excellent cycling stability of 5000 cycles at 3.0 A g–1. Furthermore, the VO2 unit cell expands in a, b, and c directions sequentially during the discharge process and contracts back reversibly during the charge process, and the zinc storage mechanism is revealed to be a highly reversible single-phase reaction by operando techniques and corresponding qualitative analyses. Our work not only opens a new door to the practical application of VO2 in ZIB systems but a...
TL;DR: This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area- selective ALD processes can be improved.
Abstract: Bottom-up nanofabrication by area-selective atomic layer deposition (ALD) is currently gaining momentum in semiconductor processing, because of the increasing need for eliminating the edge placement errors of top-down processing. Moreover, area-selective ALD offers new opportunities in many other areas such as the synthesis of catalysts with atomic-level control. This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area-selective ALD processes can be improved. A general cause for the loss of selectivity during deposition is that the character of surfaces on which no deposition should take place changes when it is exposed to the ALD chemistry. A solution is to implement correction steps during ALD involving for example surface functionalization or selective etching. This leads to the development of advanced ALD cycles by combining conventional two-step ALD cycles with correction steps in multistep cycle and/or supercycle recipes.
TL;DR: In this paper, the photoluminescent behavior of cubic double perovskite Cs2NaBiCl6-xBrx:Mn2+ doped with Mn2+ ions was investigated.
Abstract: In this work, we report on the promising photoluminescent behavior of the cubic double perovskite Cs2NaBiCl6 doped with Mn2+ ions. Localized excitations centered on Bi3+ ions in the host lattice strongly absorb near-UV light. In the undoped host compound, only very weak photoluminescence is observed, but in manganese-doped samples, energy transfer from Bi3+ to Mn2+ leads to intense orange-red photoluminescence. A broad emission peak centered at 590 nm is assigned to the 4T1 → 6A1 transition of octahedrally coordinated Mn2+. The excitation spectrum contains peaks at 294 and 354 nm that arise from 6s2 → 6s16p1 excitations of Bi3+ ions. If the chloride ions are partially replaced by bromide ions, the strongest excitation peak red-shifts to 375 nm. The lack of expensive reagents and toxic elements and the ability to tune the excitation and emission spectra through chemical substitution make Cs2NaBiCl6–xBrx:Mn2+ a promising phosphor system.
TL;DR: In this article, the colloidal synthesis of lead-free halide double perovskites was optimized to achieve the stability and nontoxicity compared to lead-based perovsites.
Abstract: Lead-free halide double perovskites continue to draw increasing attention in view of their nontoxicity and stability compared to lead-based perovskites. Herein, we optimized the colloidal synthesis...
TL;DR: In this paper, a new class of ultrastiff and tough supramolecular hydrogels facilely prepared by copolymerization of methacrylic acid and methacrylamide was reported.
Abstract: Design of tough hydrogels has made great progress in the past two decades. However, the synthetic tough gels are usually much softer than some biotissues (e.g., skins with modulus up to 100 MPa). Here we report a new class of ultrastiff and tough supramolecular hydrogels facilely prepared by copolymerization of methacrylic acid and methacrylamide. The gels with water content of approximately 50–70 wt % possessed remarkable mechanical properties, with Young’s modulus of 2.3–217.3 MPa, tensile breaking stress of 1.2–8.3 MPa, breaking strain of 200–620%, and tearing fracture energy of 2.9–23.5 kJ/m2, superior to most existing hydrogels, especially in terms of modulus. Typical yielding and crazing were observed in the gel under tensile loading, indicating the forced elastic deformation of these hydrogels in a glassy state, as confirmed by dynamic mechanical analysis. The ultrahigh stiffness was attributed to the dense cross-linking and reduced segmental mobility caused by the robust intra- and interchain hydr...
TL;DR: In this article, the authors proposed elastic carbon aerogels (CECAs) as new two-dimensional materials with extraordinary proper properties for applications in wearable electronics and electronic skins.
Abstract: Compressible and elastic carbon aerogels (CECAs) hold great promise for applications in wearable electronics and electronic skins. MXenes, as new two-dimensional materials with extraordinary proper...
TL;DR: In this paper, the authors proposed a method for fabrication of conductive hydrogels at room or low temperatures, without external stimuli, which is a challenge in the field of biomedical applications.
Abstract: Tough and conductive hydrogels are the promising materials for various applications. However, fabrication of these hydrogels at room or low temperatures, without external stimuli, is a challenge. H...
TL;DR: In this paper, the authors performed a guided search of materials space with a machine learning (ML)-based prediction model for material selection and density functional theory molecular dynamics (DFT-MD) simulations for calculating ionic conductivity.
Abstract: We discover many new crystalline solid materials with fast single crystal Li ion conductivity at room temperature, discovered through density functional theory simulations guided by machine learning-based methods. The discovery of new solid Li superionic conductors is of critical importance to the development of safe all-solid-state Li-ion batteries. With a predictive universal structure–property relationship for fast ion conduction not well understood, the search for new solid Li ion conductors has relied largely on trial-and-error computational and experimental searches over the last several decades. In this work, we perform a guided search of materials space with a machine learning (ML)-based prediction model for material selection and density functional theory molecular dynamics (DFT-MD) simulations for calculating ionic conductivity. These materials are screened from over 12 000 experimentally synthesized and characterized candidates with very diverse structures and compositions. When compared to a r...
TL;DR: In this paper, the authors combine electrochemistry, operando synchrotron X-ray diffraction (XRD), and ex situ solid-state NMR spectroscopy to provide new insights into the structural changes and lithium dynamics of NMC811 during electrochemical charge and discharge, which are essential for a better understanding of its fast degradation.
Abstract: The nickel-rich layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) is a promising future cathode material for lithium-ion batteries in electric vehicles due to its high specific energy density. However, it exhibits fast voltage and capacity fading. In this article, we combine electrochemistry, operando synchrotron X-ray diffraction (XRD), and ex situ solid-state NMR spectroscopy to provide new insights into the structural changes and lithium dynamics of NMC811 during electrochemical charge and discharge, which are essential for a better understanding of its fast degradation. The evolution of the interlayer spacing is tracked by XRD, showing that it gradually increases upon delithiation before collapsing at high state-of-charge (SOC). Importantly, no two-phase O3 → O1 transition is observed at high SOC, demonstrating that this cannot be a major cause of degradation. A strong increase of Li dynamics accompanies the increase of the interlayer spacing, which is shown by 7Li NMR and electrochemical characterization. A...
TL;DR: Tumor microenvironment-mediated cancer therapy, such as chemodynamic therapy (CDT) based on Fenton reaction, has attracted extensive attention in recent years, but efficient Fenton reactivity is still a challenge.
Abstract: Tumor microenvironment (TME)-mediated cancer therapy, such as chemodynamic therapy (CDT) based on Fenton reaction, has attracted extensive attention in recent years. However, efficient Fenton react...
TL;DR: LiNiO2, NCA and NMC materials with various chemistrie as discussed by the authors are widely used in electric vehicle and energy storage applications, and are derived from LiNiO 2, NCA 2, and LiNi1−x−yCoxAlyO2 (NCA).
Abstract: LiNi1–x–yCoxAlyO2 (NCA) and LiNi1–x–yMnxCoyO2 (NMC) materials are widely used in electric vehicle and energy storage applications. Derived from LiNiO2, NCA and NMC materials with various chemistrie...
TL;DR: In this article, a composite strategy to enhance the stability of water-sensitive CsPbBr3 quantum dots by embedding the QDs into the super-hydrophobic porous organic polymer frameworks (CPB@S...
Abstract: We present a novel composite strategy to enhance the stability of water-sensitive CsPbBr3 quantum dots (QDs) by embedding the QDs into the super-hydrophobic porous organic polymer frameworks (CPB@S...
TL;DR: In this article, the authors show that both H+/Zn2+ intercalation and conversion reactions occur at different voltages and that the rapid capacity fading can clearly be attributed to the rate-limiting and irreversible conversion reactions at a lower voltage.
Abstract: Rechargeable aqueous Zn-ion batteries (ZIBs) are very promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. Their usage, however, is largely hampered by the fast capacity fade. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways of Zn/MnO2 system. In this study, we find that both H+/Zn2+ intercalation and conversion reactions occur at different voltages and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By limiting the irreversible conversion reactions at ∼1.26 V, we successfully demonstrate ultrahigh power and long life that are superior to most of the reported ZIBs or even some lithium-ion batteries.
TL;DR: Biomimetic skin-like electric materials have been rapidly developed for human–machine interfaces, health monitoring, and soft robots, but achieving a combination of mechanical and sensory prop...
Abstract: Biomimetic skin-like electric materials have been rapidly developed for human–machine interfaces, health monitoring, and soft robots. However, achieving a combination of mechanical and sensory prop...
TL;DR: In this article, near-infrared organic photodetectors (NIR OPDs) own some unique properties such as tailorable optoelectronic properties, ease of processing, compatibility with flexible substrates, and operation at high temperature.
Abstract: Near-infrared organic photodetectors (NIR OPDs) own some unique properties such as tailorable optoelectronic properties, ease of processing, compatibility with flexible substrates, and operation at...
TL;DR: In this paper, the first demonstration of a general concept for achieving facile proton conduction within a class of layered two-dimensional aza-fused π-conjugated covalent organic frameworks is presented.
Abstract: This paper describes the first demonstration of a general concept for achieving facile proton conduction within a class of layered two-dimensional aza-fused π-conjugated covalent organic frameworks...
TL;DR: In this article, three series of conjugated microporous polymers (CMPs) were used as photocatalysts for hydrogen production from water using a sacrificial hole scavenger.
Abstract: Three series of conjugated microporous polymers (CMPs) were studied as photocatalysts for hydrogen production from water using a sacrificial hole scavenger. In all cases, dibenzo[b,d]thiophene sulfone polymers outperformed their fluorene analogues. A porous network, S-CMP3, showed the highest hydrogen evolution rates of 6076 μmol h–1 g–1 (λ > 295 nm) and 3106 μmol h–1 g–1 (λ > 420 nm), with an external quantum efficiency of 13.2% at 420 nm. S-CMP3 outperforms its linear structural analogue, P35, whereas in other cases, nonporous linear polymers are superior to equivalent porous networks. This suggests that microporosity might be beneficial for sacrificial photocatalytic hydrogen evolution, if suitable linkers are used that do not limit charge transport and the material can be wetted by water as studied here by water sorption and quasi-elastic neutron scattering.
TL;DR: In this article, the authors summarized the latest developments with regard to the applications of PDAs as a class of sensing materials presented in the literature since 2014 and sorted them into categories based on the structural differences of diacetylene monomers from which PDAs are generated.
Abstract: Conjugated polymers are intriguing materials that have potential practical applications in diverse interdisciplinary subjects. Among them, polydiacetylenes (PDAs) have been extensively studied due to their interesting structural, spectral, and optical features. In particular, the unique colorimetric and fluorescent transition of PDAs in response to different external stimuli makes them a novel class of sensing materials, and numerous applications of PDAs as bio- or chemosensors have been explored in the past few decades. In this review, we summarize the latest developments with regard to the applications of PDAs as a class of sensing materials presented in the literature since 2014. This review is sorted into categories based on the structural differences of diacetylene monomers, from which PDAs are generated. In addition, different forms of PDAs and various methods for improving the sensing performance of PDAs are also emphasized.
TL;DR: It is found that the choice of the halide as well as subtle details of the crystal structure profoundly govern the photoluminescence peak positions and emission line widths and radiative lifetimes through the altered ligand-field effects and degrees of spin–orbit coupling.
Abstract: Finding narrow-band light emitters for the visible spectral region remains an immense challenge. Such phosphors are in great demand for solid-state lighting and display application. In this context...
TL;DR: In this paper, the authors highlight the scientific and engineering challenges to enhance the conductivity of n-type polymer thermoelectric materials, including n-doping efficiency in N-type polymers, factors influencing charge carrier mobilities after doping, and stability of N-Type conducting polymers.
Abstract: In the past several decades, conducting polymers have achieved remarkable progress and have been widely applied as the active materials for optoelectronics. So far, p-type conducting polymers exhibit high conductivities over 1000 S cm–1 and thermoelectric performance comparable to that of inorganic materials; however, only a few n-type conducting polymers showed conductivities over 1 S cm–1 after doping. The low conductivity of n-type conducting polymers is considered as the major barrier for further enhancing their thermoelectric performances. In this perspective, we highlight the scientific and engineering challenges to enhance the conductivity of n-type polymer thermoelectric materials, including n-doping efficiency in n-type polymers, factors influencing charge carrier mobilities after doping, and stability of n-type conducting polymers. Recent development and strategies to address these issues and enhance the conductivity of n-type conjugated polymers are summarized and discussed, providing materials...