Showing papers on "Amorphous solid published in 2019"

Scaled-Up Synthesis of Amorphous NiFeMo Oxides and Their Rapid Surface Reconstruction for Superior Oxygen Evolution Catalysis.

Abstract: The anode oxygen evolution reaction (OER) is known to largely limit the efficiency of electrolyzers owing to its sluggish kinetics. While crystalline metal oxides are promising as OER catalysts, their amorphous phases also show high activities. Efforts to produce amorphous metal oxides have progressed slowly, and how an amorphous structure benefits the catalytic performances remains elusive. Now the first scalable synthesis of amorphous NiFeMo oxide (up to 515 g in one batch) is presented with homogeneous elemental distribution via a facile supersaturated co-precipitation method. In contrast to its crystalline counterpart, amorphous NiFeMo oxide undergoes a faster surface self-reconstruction process during OER, forming a metal oxy(hydroxide) active layer with rich oxygen vacancies, leading to superior OER activity (280 mV overpotential at 10 mA cm-2 in 0.1 m KOH). This opens up the potential of fast, facile, and scale-up production of amorphous metal oxides for high-performance OER catalysts.

Breaking Long-Range Order in Iridium Oxide by Alkali Ion for Efficient Water Oxidation.

Abstract: Oxygen electrochemistry plays a critical role in clean energy technologies such as fuel cells and electrolyzers, but the oxygen evolution reaction (OER) severely restricts the efficiency of these devices due to its slow kinetics. Here, we show that via incorporation of lithium ion into iridium oxide, the thus obtained amorphous iridium oxide (Li–IrOx) demonstrates outstanding water oxidation activity with an OER current density of 10 mA/cm2 at 270 mV overpotential for 10 h of continuous operation in acidic electrolyte. DFT calculations show that lithium incorporation into iridium oxide is able to lower the activation barrier for OER. X-ray absorption characterizations indicate that both amorphous Li–IrOx and rutile IrO2 own similar [IrO6] octahedron units but have different [IrO6] octahedron connection modes. Oxidation of iridium to higher oxidation states along with shrinkage in the Ir–O bond was observed by in situ X-ray absorption spectroscopy on amorphous Li–IrOx, but not on rutile IrO2 under OER oper...

Electrosynthesis of high-entropy metallic glass nanoparticles for designer, multi-functional electrocatalysis.

Abstract: Creative approaches to the design of catalytic nanomaterials are necessary in achieving environmentally sustainable energy sources. Integrating dissimilar metals into a single nanoparticle (NP) offers a unique avenue for customizing catalytic activity and maximizing surface area. Alloys containing five or more equimolar components with a disordered, amorphous microstructure, referred to as High-Entropy Metallic Glasses (HEMGs), provide tunable catalytic performance based on the individual properties of incorporated metals. Here, we present a generalized strategy to electrosynthesize HEMG-NPs with up to eight equimolar components by confining multiple metal salt precursors to water nanodroplets emulsified in dichloroethane. Upon collision with an electrode, alloy NPs are electrodeposited into a disordered microstructure, where dissimilar metal atoms are proximally arranged. We also demonstrate precise control over metal stoichiometry by tuning the concentration of metal salt dissolved in the nanodroplet. The application of HEMG-NPs to energy conversion is highlighted with electrocatalytic water splitting on CoFeLaNiPt HEMG-NPs.

Advantageous crystalline-amorphous phase boundary for enhanced electrochemical water oxidation

Abstract: The development of cost-effective and high-performance electrocatalysts for water oxidation has attracted intense research interest. It was reported recently that the interface between the amorphous and crystalline phases plays a significant role in the electrocatalytic activity of transition metal compounds. It was reckoned therefore that an increase in the density of the crystalline–amorphous phase boundary would enhance the electrochemical water oxidation on the catalyst. In this work we develop a new and facile strategy for inducing high density crystalline–amorphous phase boundaries via selective fluorination surface doping. This resulted in excellent characteristics of the engineered material for electrochemical water splitting. An initial computational simulation is carried out to design the crystalline–amorphous phase boundary material and an experimental verification follows for demonstration and optimization of the impact of surface doping. We conclude that the engineering of the interface using this facile and cost-effective strategy maximizes the crystalline and amorphous phases of metal–metalloids, which can be used to fabricate low-cost and efficient electrocatalysts for water oxidation.

An Amorphous Nickel–Iron-Based Electrocatalyst with Unusual Local Structures for Ultrafast Oxygen Evolution Reaction

Abstract: Rationally designing active and durable catalysts for the oxygen evolution reaction (OER) is of primary importance in water splitting. Perovskite oxides (ABO3 ) with versatile structures and multiple physicochemical properties have triggered considerable interest in the OER. The leaching of A site cations can create nanostructures and amorphous motifs on the perovskite matrix, thus facilitating the OER process. However, selectively dissolving A site cations and simultaneously obtaining more active amorphous motifs derived from the B site cations remains a great challenge. Herein, a top-down strategy is proposed to transform bulk crystalline perovskite (LaNiO3 ) into a nanostructured amorphous hydroxide by FeCl3 post-treatment, resulting in an extremely low overpotential of 189 mV at 10 mA cm-2 . The top-down-constructed amorphous catalyst with a large surface area has dual NiFe active sites, where high-valence Ni3+ -based edge-sharing octahedral frameworks are surrounded by interstitial distorted Fe octahedra and contribute to the superior OER performance. This top-down strategy provides a valid way to design novel perovskite-derived catalysts.

Effects of ball milling on the structure of cotton cellulose

Abstract: Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.

A general synthesis approach for amorphous noble metal nanosheets.

Abstract: Noble metal nanomaterials have been widely used as catalysts. Common techniques for the synthesis of noble metal often result in crystalline nanostructures. The synthesis of amorphous noble metal nanostructures remains a substantial challenge. We present a general route for preparing dozens of different amorphous noble metal nanosheets with thickness less than 10 nm by directly annealing the mixture of metal acetylacetonate and alkali salts. Tuning atom arrangement of the noble metals enables to optimize their catalytic properties. Amorphous Ir nanosheets exhibit a superior performance for oxygen evolution reaction under acidic media, achieving 2.5-fold, 17.6-fold improvement in mass activity (at 1.53 V vs. reversible hydrogen electrode) over crystalline Ir nanosheets and commercial IrO2 catalyst, respectively. In situ X-ray absorption fine structure spectra indicate the valance state of Ir increased to less than + 4 during the oxygen evolution reaction process and recover to its initial state after the reaction. While noble metal usage in catalysis is ubiquitous, the metals’ scarcity necessitates new materials designs for efficient utilization. Here, authors report a general strategy to prepare amorphous noble metal nanosheets and find the nanomaterials to act as efficient water-splitting electrocatalysts.

Amorphization activated ruthenium-tellurium nanorods for efficient water splitting.

Abstract: Pursuing active and durable water splitting electrocatalysts is of vital significance for solving the sluggish kinetics of the oxygen evolution reaction (OER) process in energy supply. Herein, theoretical calculations identify that the local distortion-strain effect in amorphous RuTe2 system abnormally sensitizes the Te-pπ coupling capability and enhances the electron-transfer of Ru-sites, in which the excellent inter-orbital p-d transfers determine strong electronic activities for boosting OER performance. Thus, a robust electrocatalyst based on amorphous RuTe2 porous nanorods (PNRs) is successfully fabricated. In the acidic water splitting, a-RuTe2 PNRs exhibit a superior performance, which only require a cell voltage of 1.52 V to reach a current density of 10 mA cm-2. Detailed investigations show that the high density of defects combine with oxygen atoms to form RuOxHy species, which are conducive to the OER. This work offers valuable insights for constructing robust electrocatalysts based on theoretical calculations guided by rational design and amorphous materials.

Nanostructured polymer films with metal-like thermal conductivity.

Abstract: Due to their unique properties, polymers – typically thermal insulators – can open up opportunities for advanced thermal management when they are transformed into thermal conductors. Recent studies have shown polymers can achieve high thermal conductivity, but the transport mechanisms have yet to be elucidated. Here we report polyethylene films with a high thermal conductivity of 62 Wm−1 K−1, over two orders-of-magnitude greater than that of typical polymers (~0.1 Wm−1 K−1) and exceeding that of many metals and ceramics. Structural studies and thermal modeling reveal that the film consists of nanofibers with crystalline and amorphous regions, and the amorphous region has a remarkably high thermal conductivity, over ~16 Wm−1 K−1. This work lays the foundation for rational design and synthesis of thermally conductive polymers for thermal management, particularly when flexible, lightweight, chemically inert, and electrically insulating thermal conductors are required. Thermally conductive polymers can be used for advanced thermal management applications but the transport mechanisms have yet to be elucidated. Here the authors report the synthesis of polyethylene films with high thermal conductivity, which is attributed to the amorphous regions of the nanofibers.

Accumulation of Glassy Poly(ethylene oxide) Anchored in a Covalent Organic Framework as a Solid-State Li+ Electrolyte

Abstract: Design of molecular structures showing fast ion conductive/transport pathways in the solid state has been a significant challenge. The amorphous or glassy phase in organic polymers works well for fast ion conductivity because of their dynamic and random structure. However, the main issue with these polymers has been the difficulty in elucidating the mechanisms of ion conduction and thus low designability. Furthermore, the amorphous or glassy state of ion conductive polymers often confronts the problems of structural/mechanical stabilities. Covalent organic frameworks (COFs) are an emerging class of crystalline organic polymers with periodic structure and tunable functionality, which exhibit potential as a unique ion conductor/transporter. Here, we describe the use of a COF as a medium for all-solid-state Li+ conductivity. A bottom-up self-assembly approach was applied to covalently reticulate the flexible, bulky, and glassy poly(ethylene oxide) (PEO) moieties that can solvate Li+ for fast transport by the...

Solvent-Engineered Design of Argyrodite Li6PS5X (X = Cl, Br, I) Solid Electrolytes with High Ionic Conductivity

Abstract: Argyrodites, Li6PS5X (X = Cl, Br), are considered to be one of the most promising solid-state electrolytes for solid-state batteries. However, while traditional ball-mill approaches to prepare these materials do not promote scale-up, solution-based preparative methods have resulted in poor ionic conductivity. Herein, we report a solution-engineered, scalable approach to these materials, including the new argyrodite solid solution phase Li6–yPS5–yCl1+y (y = 0–0.5), that shows very high ionic conductivities (up to 3.9 mS·cm–1) and negligible electronic conductivities. These properties are almost the same as their analogues prepared by solid-state methods, owing to a lack of amorphous contributions and low impurity contents ranging from 3 to 10%. Electrochemical performance is demonstrated for Li6PS5Cl in a prototype solid-state battery and compared to that of the same solid electrolyte derived from classic ball-milling processing.

Bone mineral: new insights into its chemical composition.

Abstract: Some compositional and structural features of mature bone mineral particles remain unclear. They have been described as calcium-deficient and hydroxyl-deficient carbonated hydroxyapatite particles in which a fraction of the PO43− lattice sites are occupied by HPO42− ions. The time has come to revise this description since it has now been proven that the surface of mature bone mineral particles is not in the form of hydroxyapatite but rather in the form of hydrated amorphous calcium phosphate. Using a combination of dedicated solid-state nuclear magnetic resonance techniques, the hydrogen-bearing species present in bone mineral and especially the HPO42− ions were closely scrutinized. We show that these HPO42− ions are concentrated at the surface of bone mineral particles in the so-called amorphous surface layer whose thickness was estimated here to be about 0.8 nm for a 4-nm thick particle. We also show that their molar proportion is much higher than previously estimated since they stand for about half of the overall amount of inorganic phosphate ions that compose bone mineral. As such, the mineral-mineral and mineral-biomolecule interfaces in bone tissue must be driven by metastable hydrated amorphous environments rich in HPO42− ions rather than by stable crystalline environments of hydroxyapatite structure.

Enhancing the interlayer tensile strength of 3D printed short carbon fiber reinforced PETG and PLA composites via annealing

Abstract: Previous studies have shown that 3D printed composites exhibit an orthotropic nature with inherently lower interlayer mechanical properties. This research work is an attempt to improve the interlayer tensile strength of extrusion-based 3D printed composites. Annealing was identified as a suitable post-processing method and was the focus of this study. Two distinct thermoplastic polymers, which are common in 3D printing, were selected to study the enhancement of interlayer tensile strength of composites by additive manufacturing: a) an amorphous polyethylene terephthalate-glycol (PETG), and b) a semi-crystalline poly (lactic acid) (PLA). It was determined that short carbon fiber reinforced composites have lower interlayer tensile strength than the corresponding neat polymers in 3D printed parts. This reduction in mechanical performance was attributable to an increase in melt viscosity and the consequential slower interlayer diffusion bonding. However, the reduction in interlayer tensile strength could be recovered by post-processing when the annealing temperature was higher than the glass transition temperature of the amorphous polymer. In the case of the semi-crystalline polymer, the recovery of the interlayer tensile strength was only observed when the annealing temperature was higher than the glass transition temperature but lower than the cold-crystallization temperature. This study utilized rheological and thermal analysis of 3D printed composites to provide a better understanding of the interlayer strength response and, therefore, overcome a mechanical performance limitation of these materials.

Novel Black BiVO4/TiO2−x Photoanode with Enhanced Photon Absorption and Charge Separation for Efficient and Stable Solar Water Splitting

Abstract: Recent advances in solar water splitting by using BiVO4 as a photoanode have greatly optimized charge carrier and reaction dynamics, but relatively wide bandgap and poor photostability are still bottlenecks. Here, an excellent photoanode of black BiVO4@amorphous TiO2−x to tackle both problems is reported. Its applied bias photon‐to‐current efficiency for solar water splitting is up to 2.5%, which is a new record for a single oxide photon absorber. This unique core–shell structure is fabricated by coating amorphous TiO2 on nanoporous BiVO4 with the aid of atomic layer deposition and further hydrogen plasma treatment at room temperature. The black BiVO4 with moderate oxygen vacancies reveals a bandgap reduction of ≈0.3 eV and significantly enhances solar utilization, charge transport and separation simultaneously, compared with conventional BiVO4. The amorphous layer of TiO2−x acts as both oxygen‐evolution catalyst and protection layer, which suppresses anodic photocorrosion to stabilize black BiVO4. This configuration of black BiVO4@amorphous TiO2−x may provide an effective strategy to prompt solar water splitting toward practical applications.

One-step controllable synthesis of amorphous (Ni-Fe)Sx/NiFe(OH)y hollow microtube/sphere films as superior bifunctional electrocatalysts for quasi-industrial water splitting at large-current-density

Abstract: Crystalline transition-metal chalcogenides with (oxy)-hydroxides hybrids multiple nanoarchitectures are a new type of promising bifunctional electrocatalysts for electrolysis of water, but their amorphous states are scarcely studied. Herein, a facile electrodeposited approach is presented to fabricate hierarchically amorphous (Ni-Fe)Sx/NiFe(OH)y films on Nickel foam. By accurately tuning multi-components and electrochemical-parameters resulting in abundant micro-tube/sphere morphologies and phase evolution to obtain unique amorphous nano-cluster architectures, the (Ni-Fe)Sx/NiFe(OH)y catalyst performs super electrocatalytic performance, driving the current density of 100 mA·cm−2 at ultralow overpotential of 124 mV and 290 mV for hydrogen and oxygen evolution reaction in 1 M KOH solution with first-class long-term stability for at least 50 h, respectively. In addition, the bimetallic Ni-Fe sulfides and NiFe hydroxides are confirmed to be highly-intrinsic active components for HER and OER. More importantly, the (Ni-Fe)Sx/NiFe(OH)y material directly as cathode and anode electrodes, achieves 10 mA·cm−2 at low electrolytic voltage of 1.46 V in 1 M KOH, even at large current density of 1200 mA·cm-2 only needing 2.2 V as well as super-durability at 1000 mA·cm-2 for 50 h in quasi-industrial conditions. Further experimental results reveal that both temperature and appropriate alkalinity are in favour of reducing the overall hydrolytic overpotential due to accelerating sluggish thermodynamics and dynamics. Parallelly, the bifunctional (Ni-Fe)Sx/NiFe(OH)y electrode is one of the best efficient electrocatalysts in alkaline electrolyte up to now and expected for large-scale industrial water-splitting at large-current-density.

Spin coating epitaxial films.

Abstract: Spin-coated films, such as photoresists for lithography or perovskite films for solar cells, are either amorphous or polycrystalline. We show that epitaxial films of inorganic materials such as cesium lead bromide (CsPbBr3), lead(II) iodide (PbI2), zinc oxide (ZnO), and sodium chloride (NaCl) can be deposited onto a variety of single-crystal and single-crystal-like substrates by simply spin coating either solutions of the material or precursors to the material. The out-of-plane and in-plane orientations of the spin-coated films are determined by the substrate. The thin stagnant layer of supersaturated solution produced during spin coating promotes heterogeneous nucleation of the material onto the single-crystal substrate over homogeneous nucleation in the bulk solution, and ordered anion adlayers may lower the activation energy for nucleation on the surface. The method can be used to produce functional materials such as inorganic semiconductors or to deposit water-soluble materials such as NaCl that can serve as growth templates.

Flexible X-ray Detectors Based on Amorphous Ga2O3 Thin Films

Abstract: Ga2O3, as an emerging optoelectronic material, is very appealing for the detection of ionizing radiation because of its low cost, wide band gap (4.5–5.0 eV) and radiation hardness. In this work, a ...

Glassy Li Metal Anode for High-Performance Rechargeable Li Batteries

Abstract: Controlling nanostructure from molecular, crystal lattice to the electrode level remains as arts in practice, where nucleation and growth of the crystals still require more fundamental understanding and precise control to shape the microstructure of metal deposits and their properties. This is vital to achieve dendrite-free Li metal anodes with high electrochemical reversibility for practical high-energy rechargeable Li batteries. Here, cryogenic-transmission electron microscopy was used to capture the dynamic growth and atomic structure of Li metal deposits at the early nucleation stage, in which a phase transition from amorphous, disordered states to a crystalline, ordered one was revealed as a function of current density and deposition time. The real-time atomic interaction over wide spatial and temporal scales was depicted by the reactive-molecular dynamics simulations. The results show that the condensation accompanied with the amorphous-to-crystalline phase transition requires sufficient exergy, mobility and time to carry out, contrary to what the classical nucleation theory predicts. These variabilities give rise to different kinetic pathways and temporal evolutions, resulting in various degrees of order and disorder nanostructure in nano-sized domains that dominate in the morphological evolution and reversibility of Li metal electrode. Compared to crystalline Li, amorphous/glassy Li outperforms in cycle life in high-energy rechargeable batteries and is the desired structure to achieve high kinetic stability for long cycle life.

Interfacial Engineering of Nickel Boride/Metaborate and Its Effect on High Energy Density Asymmetric Supercapacitors.

Abstract: Solid materials with special atomic and electronic structures are deemed desirable platforms for establishing clear relationships between surface/interface structure characteristics and electrochemical activity. In this work, nickel boride (NixB) and nickel boride/graphene (NixB/G) are chosen as positive materials of supercapacitors. The NixB/G displays higher specific capacitance (1822 F g-1) than that of NixB (1334 F g-1) at 1 A g-1, and it still maintains 1179 F g-1 at 20 A g-1, suggesting the high rate performance. The asymmetric supercapacitor device (NixB/G//activated carbon) also delivered a very high energy density of 50.4 Wh kg-1, and the excellent electrochemical performance is ascribed to the synergistic effect of NixB, Ni(BO2)2, and graphene that fully enhances the diffusion of OH- and the electron transport. During the cycles, the prepared ultrafine NixB nanoparticles will be gradually in situ converted into β-Ni(OH)2 which has a smaller particle size than that prepared by other methods. This will enhance the utilization of Ni(OH)2 and decrease the ion diffusion distance. The electron deficient state of B in Ni(BO2)2 amorphous shell will make it easy to accept extra electrons, enhancing the adsorption of OH- at the shell surface. Moreover, Ni(BO2)2 makes strong adhesion between NixB (or β-Ni(OH)2) and graphene and protects the core structure in a stable state, extending the cycle life. The above properties of NixB/G endow the electrode good capacitive performance.

Promoting photoluminescence quantum yields of glass-stabilized CsPbX3 (X = Cl, Br, I) perovskite quantum dots through fluorine doping

Abstract: In the last few years, all-inorganic cesium lead halide (CsPbX3) quantum dots have shown unprecedented radical progress for practical applications in the optoelectronic field, but they quickly decompose when exposed to air. The in situ growth of the CsPbX3 particles inside amorphous glass can significantly improve their stability. Unfortunately, it is formidably difficult to precipitate whole-family CsPbX3 from a glass matrix and their photoluminescence quantum yields require further improvement. Herein, fluoride additives were introduced into oxyhalide borosilicate glasses to break the tight glass network, which promoted the nucleation/growth of CsPbX3 (X = Cl, Cl/Br, Br, Br/I and I) inside the glass. Importantly, the quantum efficiencies of glass-stabilized CsPbBr3, CsPb(Br/I)3 and CsPbI3 reached 80%, 60% and 50%, respectively, which are the highest efficiencies reported so far. Benefiting from the effective protection of robust glass, CsPbX3 quantum dots exhibited superior water resistance with more than 90% luminescence remaining after immersing them in water for 30 days, and halogen anion exchange among different CsPbX3 materials was completely inhibited. Two prototype light-emitting diodes were constructed by coupling green/red and green/orange/red quantum dots with InGaN blue chips, yielding bright white light with optimal luminous efficiency of 93 lm W−1, tunable color temperature of 2000–5800 K and high color rendering index of 90.

Wear and corrosion resistant performance of thermal-sprayed Fe-based amorphous coatings: A review

Abstract: Thermal sprayed Fe-based amorphous coatings exhibit excellent wear and corrosion resistance, and thus have been widely utilized for enhancing the performance of material surfaces. In this paper, important research progresses achieved in regards to deposition technologies and properties of thermal sprayed Fe-based amorphous coatings are reviewed. In particular, the dependence of wear and corrosion resistance of the coatings on processing parameters, e.g., kinetic energy, particle size, gas flow rate, and heat treatment temperature are summarized. Moreover, the utilization of reinforced phases and alloy elements for enhancing the wear and corrosion resistance of the coatings are presented. It is expected that future endeavors will be dedicated to the formation mechanism of amorphous phase and “processing parameter-microstructure-macroscopic property” relationship of Fe-based amorphous coatings.

Unraveling the Reaction Mechanisms of SiO Anodes for Li-Ion Batteries by Combining in Situ 7Li and ex Situ 7Li/29Si Solid-State NMR Spectroscopy.

Abstract: Silicon monoxide is a promising alternative anode material due to its much higher capacity than graphite, and improved cyclability over other Si anodes. An in-depth analysis of the lithium silicide (Li xSi) phases that form during lithiation/delithiation of SiO is presented here and the results are compared with pure-Si anodes. A series of anode materials is first prepared by heating amorphous silicon monoxide (a-SiO) at different temperatures, X-ray diffraction and 29Si NMR analysis revealing that they comprise small Si domains that are surrounded by amorphous SiO2, the domain size and crystallinity growing with heat treatment. In and ex situ 7Li and 29Si solid-state NMR combined with detailed electrochemical analysis reveals that a characteristic metallic Li xSi phase is formed on lithiating a-SiO with a relatively high Li concentration of x = 3.4-3.5, which is formed/decomposed through a continuous structural evolution involving amorphous phases differing in their degree of Si-Si connectivity. This structural evolution differs from that of pure-Si electrodes where the end member, crystalline Li15Si4, is formed/decomposed through a two-phase reaction. The reaction pathway of SiO depends, however, on the size of the ordered Si domains within the pristine material. When crystalline domains of >3 nm within a SiO2 matrix are present, a phase resembling Li15Si4 forms, albeit at a higher overpotential. The continuous formation/decomposition of amorphous Li xSi phases without the hysteresis and phase change associated with the formation of c-Li15Si4, along with a partially electrochemically active SiO2/lithium silicate buffer layer, are paramount for the good cyclability of a-SiO.

Amorphous–nanocrystalline alloys: fabrication, properties, and applications

Abstract: Owing to their unique mechanical and functional properties, both amorphous and nanocrystalline alloys have attracted extensive research interest over the past decades. However, in spite of the tremendous efforts dedicated to both kinds of alloys, their engineering applications are still hindered today because some fundamental issues, such as low thermal stability and poor ductility, are yet to be solved. To overcome these issues, one recent strategy proposed is to combine both amorphous and nanocrystalline structures in a single alloy through the use of either an amorphous or a nanocrystalline alloy as a “template”. On the one hand, the derived amorphous–nanocrystalline alloys may inherit the unique properties from either the amorphous or the nanocrystalline “template”, such as outstanding magnetic properties, extraordinary wear/corrosion resistance, and superior hardness and strength. On the other hand, these amorphous–nanocrystalline alloys also exhibit enhanced thermal stability and ductility, which are difficult to achieve for either the amorphous or the nanocrystalline alloy template. In this review article, we would like to first discuss a number of experimental methods developed to fabricate amorphous–nanocrystalline alloys, including partial crystallization in amorphous precursors, grain boundary amorphization, and physical vapor deposition. After that, we will give an overview of the mechanical and functional properties of the amorphous–nanocrystalline alloys. Finally, we will have a discussion on the existing applications of the amorphous–nanocrystalline alloys in various areas such as renewable and green energy, catalysis, and surface protection.

A unique amorphous cobalt-phosphide-boride bifunctional electrocatalyst for enhanced alkaline water-splitting

Abstract: A unique cobalt-phosphide-boride (Co-P-B) catalyst was synthesized via simple chemical-reduction route. The obtained catalyst was amorphous in nature, resembling the spherical morphology of Co-B nanoparticles. X-ray photoelectron spectroscopy revealed that B loses electrons to Co while P gains electrons from Co. This unique electron transfer mechanism in Co-P-B is a combination of the characteristics showcased by Co-B and Co-P catalysts individually. The optimized catalyst (Co-P-B-5) showed overpotentials of 145 mV and 290 mV to achieve the benchmark current density of 10 mA/cm2 for HER and OER, respectively, in 1 M NaOH. From theoretical calculations, it was observed that addition of P modulates the electron density at Co sites, thereby optimizing the H-adsorption capability, leading to higher HER rate. During anodic polarization, Co-P-B-5 shows formation of large number of CoOOH species on its surface, facilitating OER. Finally, stability, recyclability and wide-pH suitability of Co-P-B-5 was established to demonstrate its industrial viability.