High-Pressure-Field Induced Synthesis of Ultrafine-Sized High-Entropy Compounds with Excellent Sodium-Ion Storage.

Emerging high entropy compounds (HECs) have attracted huge attention in electrochemical energy-related applications. The features of ultrafine size and carbon incorporation show great potential to boost the ion-storage kinetics of HECs. However, they are rarely reported because high-temperature calcination tends to result in larger crystallites, phase separation, and carbon reduction. Herein, using the NaCl self-assembly template method, by introducing a high-pressure field in the calcination process, the atom diffusion and phase separation are inhibited for the general formation of HECs, and the HEC aggregation is inhibited for obtaining ultrafine size. The general preparation of ultrafine-sized (<10 nm) HECs (nitrides, oxides, sulfides, and phosphates) anchored on porous carbon composites is realized. They are demonstrated by combining advanced characterization technologies with theoretical computations. Ultrafine-sized high entropy sulfides-MnFeCoCuSnMo/porous carbon (HES-MnFeCoCuSnMo/PC) as representative anodes exhibit excellent sodium-ion storage kinetics and capacities (a high rating capacity of 278 mAh g-1 at 10 A g-1 for full cell and a high cycling capacity of 281 mAh g-1 at 20 A g-1 after 6000 cycles for half cell) due to the combining advantages of high entropy effect, ultrafine size, and PC incorporation. Our work provides a new opportunity for designing and fabricating ultrafine-sized HECs.

Heat-resistant super-dispersed oxide strengthened aluminium alloys.

Oxided-dispersion-strengthened (ODS) alloys are promising high-strength materials used in extreme environments such as high-temperature and radiation tolerance applications. Until now, ODS alloys have been developed for reducible metals by chemical processing methods, but there are no commercially available ODS alloys for unreducible metals, namely, Al, Mg, Ti, Zr and so on, owing to the challenge of uniformly dispersing oxide particles in these alloys by traditional techniques. Here we present a strategy to achieve ODS Al alloys containing highly dispersive 5 nm MgO nanoparticles by powder metallurgy, using nanoparticles that have in situ-grown graphene-like coatings and hence largely reduced surface energy. Notably, the densely dispersed MgO nanoparticles, which have a fully coherent relationship with an Al matrix, show effective suppression of interfacial vacancy diffusion, thus leading to unprecedented strength (~200 MPa) and creep resistance at temperatures as high as 500 °C. Our processing approach should enable the dispersion of ultrafine nanoparticles in a wide range of alloys for high-temperature-related applications.

The Synthesis of Three-Dimensional Hexagonal Boron Nitride as the Reinforcing Phase of Polymer-Based Electrolyte for All-Solid-State Li Metal Batteries.

Powdery hexagonal boron nitride (h-BN), as an important material for electrochemical energy storage, has been typically synthesized in bulk and one/two-dimensional (1/2D) nanostructured morphologies. However, until now, no method has been developed to synthesize powdery three-dimensional (3D) h-BN. This work introduces a novel NaCl-glucose-assisted strategy to synthesize micron-sized 3D h-BN with a honeycomb-like structure and its proposed formation mechanism. We propose that NaCl acts as the template of 3D structure and promotes the nitridation reaction by adsorbing NH3 . Glucose facilitates the homogeneous coating of boric acid onto the NaCl surface via functionalizing the NaCl surface. During the nitridation reaction, boron oxides (BO4 and BO3 ) form from a dehydration reaction of boric acid, which is then reduced to O2 -B-N and O-B-N2 intermediates before finally being reduced to BN3 by NH3 . When incorporated into polyethylene oxide-based electrolytes for Li metal batteries, 5 wt % of 3D h-BN significantly enhances ionic conductivity and mechanical strength. Consequently, this composite electrolyte demonstrates superior electrochemical stability. It delivers 300 h of stable cycles in the Li//Li cell at 0.1 mA cm-2 and retains 89 % of discharge capacity (138.9 mAh g-1 ) after 100 cycles at 1 C in the LFP//Li full cell.

A multisite dynamic synergistic oxygen evolution reaction mechanism of Fe-doped NiOOH: a first-principles study.

Changing the composition is an important way to regulate the electrocatalytic performance of the oxygen evolution reaction (OER) for metallic compounds. Clarifying the synergistic mechanism among different compositions is a key scientific problem to be solved urgently. Here, based on first-principles calculations, a Ni-O-Fe multisite dynamic synergistic reaction mechanism (MDSM) for the OER of Fe-doped NiOOH (NiFeOOH) has been discovered. Based on the MDSM, Fe/O/Ni are triggered as the active sites in turn, resulting in an overpotential of 0.33 V. The factors affecting the deprotonation, O-O coupling, and O2 desorption during the OER process are analyzed. The electron channels related to the magnetic states among Fe-O-Ni is revealed, which results in the decoupling between OER sites and the oxidation reaction sites. O-O coupling and O2 desorption are affected by ferromagnetic coupling and the instability of the lattice O during the OER process, respectively. The results give a comprehensive understanding of the active sites in NiFeOOH and provide a new perspective on the synergistic effects among different compositions in metal compounds during the OER process.

Decreasing Interfacial Pitfalls with Self-Grown Sheet-Like Li2 S Artificial Solid-Electrolyte Interphase for Enhanced Cycling Performance of Lithium Metal Anode.

Constructing a 3D composite Li metal anode (LMA) along with the engineering of artificial solid electrolyte interphase (SEI) is a promising strategy for achieving dendrite-free Li deposition and high cycling stability. The nanostructure of artificial SEI is closely related to the performance of the LMA. Herein, the self-grown process and morphology of in situ formed Li2 S during lithiation of Cux S is studied systematically, and a large-sized sheet-like Li2 S layer as an artificial SEI is in situ generated on the inner surface of a 3D continuous porous Cu skeleton (3DCu@Li2 S-S). The sheet-like Li2 S layer with few interfacial pitfalls (Cu/Li2 S heterogeneous interface) possesses enhanced diffusion of Li ions. And the continuous porous structure provides transport channels for lithium-ion transport. As a result, the 3DCu@Li2 S-S presents a high Coulombic efficiency (99.3%), long cycle life (500 cycles), and high-rate performance (10 mA cm-2 ). Furthermore, Li/3DCu@Li2 S anode fabricated by thermal infusion method inherits the synergistic advantages of sheet-like Li2 S and continuous porous structure. The Li/3DCu@Li2 S anode shows significantly enhanced cycling life in both liquid and solid electrolytes. This work provides a new concept to design artificial SEI for LMA with high safe and high performance.

Single-Atom Cobalt Supported on Nitrogen-Doped Three-Dimensional Carbon Facilitating Polysulfide Conversion in Lithium-Sulfur Batteries.

Single-atom catalysts (SACs) have demonstrated catalytic efficacy toward lithium polysulfide conversion in Li-S batteries. However, achieving high-density M-Nx sites with rational design by a simple method is still challenging to date. Herein, an ultrathin porous 3D carbon-supported single-atom catalyst (SACo/NDC) is synthesized with a salt-template strategy via a facile freeze-drying and one-step pyrolysis procedure and serves well as a sulfur host. The well-defined 3D carbon structure can effectively alleviate volume stress and confine polysulfides inside. Moreover, the dispersed Co-Nx sites exhibit strong chemical adsorption function and valid catalytic efficiency to LiPSs redox conversion. As a result, the SACo/NDC cathodes display enhanced long-term cycling stability and better rate capability.

W Clusters In Situ Assisted Synthesis of Layered Carbon Nanotube Arrays on Graphene Achieving High-Rate Performance.

W atoms/clusters are employed to in situ assist the development of layered vertically aligned carbon nanotube arrays (VACNTs) through hot-filament-assisted chemical vapor deposition (HFCVD) with liquid binary Fe3O4/AlOx catalysts. The hot W filament was utilized to in situ evaporate atomic W and form W clusters on Fe catalysts, which have a strong impact on the growth of layered VACNT arrays. The migration and Ostwald ripening of Fe catalysts are found to be suppressed immediately with more W clusters deposition during CNT growth. Through controlling the deposition of W clusters, the electrochemical energy storage performance of as-prepared layered VACNT arrays is also tunable as electrodes of ion-based supercapacitors. The layered VACNT arrays can achieve a high capacity of 83.1 mF cm-2 and possess desirable rate performance due to the suitable hot filament condition (55 W for 90 s). This work provides a new perspective to in-depth understand the behavior of W filament during HFCVD and the significant role of the in situ generated W clusters on the growth of CNTs by maintaining the catalytic activity and structure of catalysts.

A powder-metallurgy-based strategy toward three-dimensional graphene-like network for reinforcing copper matrix composites.

Three-dimensional graphene network is a promising structure for improving both the mechanical properties and functional capabilities of reinforced polymer and ceramic matrix composites. However, direct application in a metal matrix remains difficult due to the reason that wetting is usually unfavorable in the carbon/metal system. Here we report a powder-metallurgy based strategy to construct a three-dimensional continuous graphene network architecture in a copper matrix through thermal-stress-induced welding between graphene-like nanosheets grown on the surface of copper powders. The interpenetrating structural feature of the as-obtained composites not only promotes the interfacial shear stress to a high level and thus results in significantly enhanced load transfer strengthening and crack-bridging toughening simultaneously, but also constructs additional three-dimensional hyperchannels for electrical and thermal conductivity. Our approach offers a general way for manufacturing metal matrix composites with high overall performance.

Effect of Isothermal Transformation Times below Ms and Tempering on Strength and Toughness of Low-Temperature Bainite in 0.53 C Bainitic Steel.

This study aims to investigate the microstructures, strength, and impact toughness of low-temperature bainite obtained by isothermal transformation at temperature below Ms (Martensite Starting temperature) for different times and tempering process in 0.53 C wt% bainitic steel. By using the optical microscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), electron back scatter diffraction (EBSD), and mechanical property test, it was found that the microstructures after heat treatment consist of small amounts of martensite, fine bainite, and film retained austenite. After tempered at 250 °C for 2 h, the volume fraction of retained austenite (10.9%) in the sample treated by isothermal transformation at 220 °C for three hours is almost the same as that of the sample without tempering. In addition, the retained austenite fraction decreases with the increase of holding times and is reduced to 6.8% after holding for 15 h. The ultimate tensile strength (1827 MPa), yield strength (1496 MPa), total elongations (16.1%), and impact toughness (up to 58 J/cm2) were obtained by isothermal transformation at 220 °C for three hours and tempered at 250 °C. Whereas, the impact toughness of sample without tempering is 28 J/cm2. After holding for 15 h, the impact toughness raises to 56 J/cm2, while the ductility and strength decreases. These results indicate that the tempering process is helpful to improve the impact toughness of low-temperature bainite.

Octopus-Inspired Design of Apical NiS2 Nanoparticles Supported on Hierarchical Carbon Composites as an Efficient Host for Lithium Sulfur Batteries with High Sulfur Loading.

Developing high-performance Li-S batteries with high sulfur loading is highly desirable for practical application and remains a major challenge. To achieve this goal, the following requirements for designing carbon/metal compound composites need to be met: (i) the carbon materials need to exhibit suitable specific surface area, void structure, and electrical conductivity; (ii) the weight content of the metal compounds should be low; and (iii) the metal compounds need to show a strong adsorption and efficient electrocatalytic function for LiPSs. In this study, inspired by the body structure of an octopus, a new carbon/NiS2 hierarchical composite is reported, in which the apical NiS2 nanoparticles (0D) on a 1D carbon nanotubes (CNTs) are supported on a three-dimensional carbon (3DC) framework (3DC-CNTs-NiS2). The 3DC-CNTs-NiS2 composite has a high specific surface area (271 m2 g-1), good electrical conductivity, and low NiS2 content (9.2 wt %), and the apical NiS2 nanoparticles are capable of adsorption and electrocatalysis toward LiPSs, demonstrated by both electrochemical characterization and theoretical calculation. When used as a cathode host of the Li-S battery, it exhibits an ultra-stable cycling performance with a fade rate of 0.043% per cycle over 1000 cycles; even with a high S loading (6.5 mg cm-2 with 90 wt % of S), the soft package battery delivers a high area capacity of 5.0 mAh cm-2 under the E/S ratio of 5 µLE mg-1s. This work provides a new approach to design and fabricate multi-functional S hosts with high S loading.

An in-plane Co9S8@MoS2 heterostructure for the hydrogen evolution reaction in alkaline media.

Transition metal sulfides have emerged as promising hydrogen evolution reaction (HER) electrocatalysts in acidic media due to high intrinsic activity. They exhibit inferior HER activity in alkaline media, however, owing to the sluggish water dissociation kinetics. Herein, in-plane MoS2/Co9S8 heterostructures are in situ grown on three-dimensional carbon network substrates with interconnected hierarchical pores by one-step pyrolysis to enhance the alkaline HER activity. The experiment results reveal that the HER kinetics of MoS2 is accelerated after the construction of heterostructures. The synthesized MoS2/Co9S8 heterostructures anchored on a three-dimensional interconnected hierarchical pore carbon network exhibit a lower overpotential of 177 mV than MoS2 (252 mV) at 10 mA cm-2 for the HER in 1 M KOH. The enhanced catalytic performance is mainly attributed to the accelerated water dissociation kinetics on the interface of MoS2 and Co9S8. In combination with DFT calculations, it is revealed that assembling the interface construction synergistically favors the chemisorption of protons and the cleavage of the O-H bonds of the H2O molecule, thus accelerating the kinetics of the HER. Moreover, the three-dimensional interconnected hierarchical pore carbon (3DC) network structure is beneficial for the circulation of the electrolyte and H2 spillover. This study demonstrates the present strategy as a facile route for fabricating efficient HER catalysts.

Orientation Relationships and Interface Structure in MgAl2O4 and MgAlB4 Co-Reinforced Al Matrix Composites.

Ceramic phase reinforced aluminum matrix composites (CAMCs) are widely used in high-tech fields represented by aerospace industry due to their advantages of high specific strength, high specific modulus, high thermal stability, and light weight. Strong interface bonding is a prerequisite for high performance of multiphase materials. Herein, a novel CAMC in situ reinforced by MgAl2O4 particles and MgAlB4 nanorods was prepared by vacuum hot-pressing combined with hot-extrusion process. A high-resolution transmission electron microscope was used to characterize the orientation relationship and interface structure between the ceramic phases and the aluminum matrix. Two orientation relationships (OR1 and OR2) of MgAl2O4/Al and one (OR3) of MgAlB4/Al are determined: OR1-[011]p//[011]Al, (11̅1)p//(11̅1)Al; OR2-[211]p//[011]Al, (113̅)p//(022̅)Al; OR3-[101̅0]R//[001]Al, (0002)R//(2̅20)Al. The MgAl2O4 in OR1 forms a coherent interface with the aluminum matrix at (111) surface, while they form a 4 × 5 near coincidence site lattice (CSL) interface structure for OR2. In OR3, the MgAlB4 forms an approximate coherent interface with Al matrix at its (0002) surface and a 2 × 5 CSL interface structure at its (011̅0) surface. First-principles calculations suggest that MgAl2O4 combines to aluminum at (111) plane through covalent bonds, which means high interfacial bonding strength. The hot-extrusion process makes the ceramic phase evenly distributed in the matrix. The mechanical properties of the composites are greatly improved compared with pure aluminum.

Enhanced Hydrogen Evolution Reaction Performance of NiCo2P by Filling Oxygen Vacancies by Phosphorus in Thin-Coating CeO2.

A series of NiCo2P-based electrocatalysts, which were wrapped by CeO2 whose oxygen vacancies (VO) are partially filled with phosphorus atoms (named as NiCo2Px/PxFVo-CeO2, where x refers to the consumption of NaH2PO2·H2O), have been fabricated to improve the electrocatalytic reactivity of NiCo2P toward hydrogen evolution in alkaline solution. In the novel catalysts, the P atoms fill the oxygen vacancies, elevate the chemical valence state of Ni2+ and Co3+, and increase the hydride acceptors, which reinforcing the promoting effect of CeO2 in the hydrogen evolution reaction (HER). Moreover, the negatively charged P atoms capture the positively charged protons more easily, benefiting the Volmer step during HER. Furthermore, the synergistic effect between oxygen vacancies and the filled P atoms accelerates the migration rate of electrons/ions and increases the electrochemical active area. All of the above are advantageous to the hydrogen evolution of NiCo2Px/PxFVo-CeO2 in alkaline electrolyte. As a result, the overpotential as low as 33.6 mV is achieved for NiCo2P0.3/P0.3FVo-CeO2 in alkaline media to drive a current density of 10 mA cm-2. The reactivity is superior to that of Pt/C at a large current density along with a Tafel slope of 61.24 mV dec-1 and long-term durability, which giving a new technology for efficient transition-metal catalyst candidates toward HER in alkaline solution.

Distorted 1T-ReS2 Nanosheets Anchored on Porous TiO2 Nanofibers for Highly Enhanced Photocatalytic Hydrogen Production.

Recently, loading TiO2 with transition-metal disulfides (TMDs) to construct dual functional heterostructures has been widely researched as an effective strategy to improve the photocatalytic performance of a TiO2 photocatalyst. For the TMD cocatalysts, the 2H-MoS2 and 1T-MoS2 have been widely studied and researched. However, they suffer from poor catalytic activity sites/low charge transfer ability and an unstable structure. In this regard, distorted 1T-phase TMDs with a stable structure are greatly fit for the cocatalyst due to their high charge transfer ability and rich catalytic sites on both the edge and basal plane. Therefore, it is highly desirable to develop distorted 1T-phase TMD/TiO2 heterostructures with well-identified interfaces for highly enhanced photocatalytic performance. Herein, we first introduce distorted 1T-ReS2 anchored on porous TiO2 nanofibers as a promising photocatalyst for achieving an excellent photocatalytic hydrogen production. The excellent performance is attributed to the strong chemical interaction of the Ti-O-Re bond between TiO2 and ReS2, the excellent electron mobility of distorted 1T-ReS2, and the abundant catalytic activity sites on both the plane and edge of the ReS2 cocatalyst.

Effect of Interface Structure on the Mechanical Properties of Graphene Nanosheets Reinforced Copper Matrix Composites.

Currently, seldom studies have paid close attention to the impact of the defects and oxygen-containing functional groups on the surface of the graphene for composite applications. In this work, two typical graphene materials, namely graphene nanosheets synthesized by an in situ catalytic reaction and reduced graphene oxide (RGO), were adopted to fabricate reinforced copper matrix composites by spark plasma sintering. A harmful transitional interfacial layer made up of Cu/CuOx/amorphous carbon/RGO, resulted from interfacial reaction between Cu and RGO, were observed in the RGO/Cu composite. In contrast, the in situ synthesized graphene with fewer defect and lower oxygen level can realize clean graphene-Cu interface with Cu-O-C bonding and thus lead to much improved interface bonding and superior yield strength and tensile ductility. These results imply that the in situ synthesized graphene is more favorable for achievement of robust interfacial bonding for enhancing the mechanical properties of the graphene-Cu composites.

Assembly Multifunctional Three-Dimensional Carbon Networks by Controlling Intermolecular Forces.

Three-dimensional (3D) carbon networks (3DCNs) enjoy the merits of high surface area, effective mass-transfer ability, and mechanical stability. The physicochemical properties of such materials not only depend on their microstructures but also rely on the assembly forms. This work achieves different assembly forms of 3DCNs on the macroscale from powder, monolith, to clay and reveals the relations between intermolecular forces and these assembly forms. With the "weak" van der Waals forces, only 3DCN powders are obtained. The N-doping effect increases the part of "strong" van der Waals forces, which enables 3DCNs assembled as a monolith and supports 43 000 times its own weight. Furthermore, the introduction of aniline molecules and the corresponding hydrogen bond connections make carbon networks to transform into a clay with superior ductility and plasticity. Considering that 3DCNs can be engineered into functionalized materials by in situ incorporation of functional components such as Fe3O4, the composites with controllable forms are treated as promising candidate materials used in various fields.

CeO x-Decorated NiFe-Layered Double Hydroxide for Efficient Alkaline Hydrogen Evolution by Oxygen Vacancy Engineering.

As a promising bifunctional electrocatalyst for water splitting, NiFe-layered double hydroxide (NiFe LDH) demonstrates an excellent activity toward oxygen evolution reaction (OER) in alkaline solution. However, its hydrogen evolution reaction (HER) activity is challenged owing to the poor electronic conductivity and insufficient electrochemical active sites. Therefore, a three-dimensional self-supporting metal hydroxide/oxide electrode with abundant oxygen vacancies is prepared by electrodepositing CeO x nanoparticles on NiFe LDH nanosheets. According to the density functional theory calculations and experimental studies, the oxygen vacancies at the NiFe LDH/CeO x interface can be introduced successfully because of the positive charges accumulation resulting from the local electron potential difference between NiFe LDH and CeO x. The oxygen vacancies accelerate the electron/ion migration rates, facilitate the charge transfer, and increase the electrochemical active sites, which give rise to an efficient activity toward HER in alkaline solution. Furthermore, NF@NiFe LDH/CeO x needs a lower potential of 1.51 V to drive a current density of 10 mA cm-2 in overall water splitting and demonstrates a superior performance compared with the benchmark Pt/C and RuO2, which is indicated to be a promising bifunctional electrode catalyst.

Boosting the Photocatalytic Activity of P25 for Carbon Dioxide Reduction by using a Surface-Alkalinized Titanium Carbide MXene as Cocatalyst.

Although they are widely used as cocatalysts in promoting photocatalysis, practical application of noble metals is limited by their high cost and rarity. Development of noble-metal-free cocatalysts is thus highly demanded. Herein titanium carbide (Ti3 C2 ) MXene is shown to be a highly efficient noble-metal-free cocatalyst with commercial titania (P25) for photocatalytic CO2 reduction. Surface alkalinization of Ti3 C2 dramatically enhances the activity; the evolution rates of CO (11.74 µmol g-1 h-1 ) and CH4 (16.61 µmol g-1 h-1 ) are 3- and 277-times higher than those of bare P25, respectively. The significantly enhanced activity is attributed to the superior electrical conductivity and charge-carrier separation ability, as well as the abundant CO2 adsorption and activation sites of surface-alkalinized Ti3 C2 MXene, indicating its promise as a highly-active noble-metal-free cocatalysts for photocatalytic CO2 reduction.

A Top-Down Strategy toward SnSb In-Plane Nanoconfined 3D N-Doped Porous Graphene Composite Microspheres for High Performance Na-Ion Battery Anode.

Engineering of 3D graphene/metal composites with ultrasmall sized metal and robust metal-graphene interfacial interaction for energy storage application is still a challenge and rarely reported. In this work, a facile top-down strategy is developed for the preparation of SnSb-in-plane nanoconfined 3D N-doped porous graphene networks for sodium ion battery anodes, which are composed of several tens of interconnected empty N-graphene boxes in-plane firmly embedded with ultrasmall SnSb nanocrystals. The all-around encapsulation (plane-to-plane contact) architecture that provides a large interface between N-graphene and SnSb nanocrystal not only effectively enhances the electron conductivity and structural integrity of the overall electrode, but also offers excess interfacial sodium storage, thus leading to much enhanced high-rate sodium storage capacity and stability, which has been proven by both experimental results and first-principles simulations. Moreover, this top-down strategy can enable new paths to the low-cost and high-yield synthesis of 3D graphene/metal composites for applications in energy-related fields and beyond.