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.

High-precision single-axis rotation measurement method of multi-rudders based on monocular vision.

To evaluate the assembly accuracy of rudders during the production of aerospace vehicles, a measurement method based on monocular vision is proposed in this paper. Compared with existing methods that adopt cooperative targets pasted manually, the proposed method avoids pasting cooperative targets on the surface of rudders and calibrating the original position of rudders in advance. First, we use two known position markers on the surface of the vehicle and multiple feature points of the rudder to solve the relative pose between the camera and the rudder by employing the PnP algorithm. Then, we measure the rotation angle by converting the change of the camera's pose to the rotation angle of the rudder. Finally, a tailored error compensation model is introduced into the proposed method to increase the accuracy of the measurement. Experiment results show that the average measurement absolute error of the proposed method is less than 0.08° overall, which is remarkably superior to existing methods and satisfies the requirement of practical industrial production.

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.

Low-Temperature Potassium Batteries Enabled by Electric and Thermal Field Regulation.

Recharging batteries operate at sub-zero temperature is usually limited by the slow ion diffusion and uneven charge distribution at low temperature. Here, we report a strategy to regulate electric field and thermal field simultaneously, creating a fast and uniform deposition surroundings for potassium ion in potassium metal batteries (PMBs). This regulation is achieved by using a highly ordered 1D nanoarray electrode which provides a dense and flat surface for uniforming the electric field and high thermal conductivity for reducing the temperature fluctuation. Consequently, this electrode could achieve high-areal capacity of 10 mAh cm-2 . Besides, the dependence of potassium nucleation on temperature is unveiled. Furthermore, a full-cell could steady operate with over 80 % of its room-temperature capacity at -20 °C. Those respectable performances demonstrate that this strategy is valid, potentially providing guidelines for the rational design of advanced electrodes toward PMBs.

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.

Balancing Strength and Ductility in Al Matrix Composites Reinforced by Few-Layered MoS2 through In-Situ Formation of Interfacial Al12Mo.

In this work, few-layered MoS2 (FLM) nanosheet-reinforced Al matrix composites are developed through powder metallurgy and hot extrusion. The microstructure, mechanical properties, and strengthening mechanisms have been systematically investigated. It is found that Al12Mo and Al2S3 can be formed in-situ during the sintering process, resulting in the improvement of interfacial bonding between FLM and Al matrix. With 1.5 wt.% of FLM addition, an improved tensile strength of 234 MPa with a high elongation of 17% can be obtained. Moreover, the strengthening mechanisms are also demonstrated to be grain refinement, dislocation strengthening, and load transfer, and the calculation indicates that load transfer is the main contribution factor. This work will inspire more new designs of metal matrix composites with balanced strength and ductility.

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.

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.

Ultra-Stiff Graphene Foams as Three-Dimensional Conductive Fillers for Epoxy Resin.

Conductive epoxy composites are of great interest due to their applications in electronics. They are usually made by mixing powdered conductive fillers with epoxy. However, the conductivity of the composite is limited by the low filler content because increasing filler content causes processing difficulties and reduces the mechanical properties of the epoxy host. We describe here the use of ultra-stiff graphene foams (uGFs) as three-dimensional (3D) continuous conductive fillers for epoxy resins. The powder metallurgy method was used to produce the dense uGFs monoliths that resulted in a very high filler content of 32 wt % in the uGF-epoxy composite, while the density of epoxy was only increased by 0.09 g/cm3. The composite had an electrical conductivity of 41.0 ± 6.3 S/cm, which is among the highest of all of the polymer-based composites with non-conductive polymer matrices and comparable with the conductive polymer matrices reported to date. The compressive modulus of the composite showed a remarkable improvement of >1700% compared to pure epoxy. We have demonstrated that the 3D uGF filler substantially improves the conductivity and reinforces the polymer matrix with a high filler content while retaining a density similar to that of the epoxy alone.

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.

Preparation of MoS2/TiO2 based nanocomposites for photocatalysis and rechargeable batteries: progress, challenges, and perspective.

The rapidly increasing severity of the energy crisis and environmental degradation are stimulating the rapid development of photocatalysts and rechargeable lithium/sodium ion batteries. In particular, MoS2/TiO2 based nanocomposites show great potential and have been widely studied in the areas of both photocatalysis and rechargeable lithium/sodium ion batteries due to their superior combination properties. In addition to the low-cost, abundance, and high chemical stability of both MoS2 and TiO2, MoS2/TiO2 composites also show complementary advantages. These include the strong optical absorption of TiO2vs. the high catalytic activity of MoS2, which is promising for photocatalysis; and excellent safety and superior structural stability of TiO2vs. the high theoretic specific capacity and unique layered structure of MoS2, thus, these composites are exciting as anode materials. In this review, we first summarize the recent progress in MoS2/TiO2-based nanomaterials for applications in photocatalysis and rechargeable batteries. We highlight the synthesis, structure and mechanism of MoS2/TiO2-based nanomaterials. Then, advancements and strategies for improving the performance of these composites in photocatalytic degradation, hydrogen evolution, CO2 reduction, LIBs and SIBs are critically discussed. Finally, perspectives on existing challenges and probable opportunities for future exploration of MoS2/TiO2-based composites towards photocatalysis and rechargeable batteries are presented. We believe the present review would provide enriched information for a deeper understanding of MoS2/TiO2 composites and open avenues for the rational design of MoS2/TiO2 based composites for energy and environment-related applications.

Efficient Water-Splitting Electrodes Based on Laser-Induced Graphene.

Electrically splitting water to H2 and O2 is a preferred method for energy storage as long as no CO2 is emitted during the supplied electrical input. Here we report a laser-induced graphene (LIG) process to fabricate efficient catalytic electrodes on opposing faces of a plastic sheet, for the generation of both H2 and O2. The high porosity and electrical conductivity of LIG facilitates the efficient contact and charge transfer with the requisite electrolyte. The LIG-based electrodes exhibit high performance for hydrogen evolution reaction and oxygen evolution reaction with excellent long-term stability. The overpotential reaches 100 mA/cm2 for HER, and OER is as low as 214 and 380 mV with relatively low Tafel slopes of 54 and 49 mV/dec, respectively. By serial connecting of the electrodes with a power source in an O-ring setup, H2 and O2 are simultaneously generated on either side of the plastic sheet at a current density of 10 mA/cm2 at 1.66 V and can thereby be selectively captured. The demonstration provides a promising route to simple, efficient, and complete water splitting.

Single-Atomic Ruthenium Catalytic Sites on Nitrogen-Doped Graphene for Oxygen Reduction Reaction in Acidic Medium.

The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH3 atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO4, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N4 structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.

Three-Dimensional Printed Graphene Foams.

An automated metal powder three-dimensional (3D) printing method for in situ synthesis of free-standing 3D graphene foams (GFs) was successfully modeled by manually placing a mixture of Ni and sucrose onto a platform and then using a commercial CO2 laser to convert the Ni/sucrose mixture into 3D GFs. The sucrose acted as the solid carbon source for graphene, and the sintered Ni metal acted as the catalyst and template for graphene growth. This simple and efficient method combines powder metallurgy templating with 3D printing techniques and enables direct in situ 3D printing of GFs with no high-temperature furnace or lengthy growth process required. The 3D printed GFs show high-porosity (∼99.3%), low-density (∼0.015g cm-3), high-quality, and multilayered graphene features. The GFs have an electrical conductivity of ∼8.7 S cm-1, a remarkable storage modulus of ∼11 kPa, and a high damping capacity of ∼0.06. These excellent physical properties of 3D printed GFs indicate potential applications in fields requiring rapid design and manufacturing of 3D carbon materials, for example, energy storage devices, damping materials, and sound absorption.

Lithium Batteries with Nearly Maximum Metal Storage.

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene-carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g-1GCNT-Li approaches that of bare Li metal (3861 mAh g-1Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm-2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg-1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm-2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

Graphene Carbon Nanotube Carpets Grown Using Binary Catalysts for High-Performance Lithium-Ion Capacitors.

Here we show that a versatile binary catalyst solution of Fe3O4/AlOx nanoparticles enables homogeneous growth of single to few-walled carbon nanotube (CNT) carpets from three-dimensional carbon-based substrates, moving past existing two-dimensional limited growth methods. The binary catalyst is composed of amorphous AlOx nanoclusters over Fe3O4 crystalline nanoparticles, facilitating the creation of seamless junctions between the CNTs and the underlying carbon platform. The resulting graphene-CNT (GCNT) structure is a high-density CNT carpet ohmically connected to the carbon substrate, an important feature for advanced carbon electronics. As a demonstration of the utility of this approach, we use GCNTs as anodes and cathodes in binder-free lithium-ion capacitors, producing stable devices with high-energy densities (∼120 Wh kg-1), high-power density capabilities (∼20,500 W kg-1 at 29 Wh kg-1), and a large operating voltage window (4.3 to 0.01 V).

Three-Dimensional Rebar Graphene.

Free-standing robust three-dimensional (3D) rebar graphene foams (GFs) were developed by a powder metallurgy template method with multiwalled carbon nanotubes (MWCNTs) as a reinforcing bar, sintered Ni skeletons as a template and catalyst, and sucrose as a solid carbon source. As a reinforcement and bridge between different graphene sheets and carbon shells, MWCNTs improved the thermostability, storage modulus (290.1 kPa) and conductivity (21.82 S cm-1) of 3D GF resulting in a high porosity and structurally stable 3D rebar GF. The 3D rebar GF can support >3150× the foam's weight with no irreversible height change, and shows only a ∼25% irreversible height change after loading >8500× the foam's weight. The 3D rebar GF also shows stable performance as a highly porous electrode in lithium ion capacitors (LICs) with an energy density of 32 Wh kg-1. After 500 cycles of testing at a high current density of 6.50 mA cm-2, the LIC shows 78% energy density retention. These properties indicate promising applications with 3D rebar GFs in devices requiring stable mechanical and electrochemical properties.

Rivet Graphene.

Large-area graphene has emerged as a promising material for use in flexible and transparent electronics due to its flexibility and optical and electronic properties. The anchoring of transition metal nanoparticles on large-area single-layer graphene is still a challenge. Here, we report an in situ preparation of carbon nano-onion-encapsulated Fe nanoparticles on rebar graphene, which we term rivet graphene. The hybrid film, which allows for polymer-free transfer and is strong enough to float on water with no added supports, exhibits high optical transparency, excellent electric conductivity, and good hole/electron mobility under certain tensile/compressive strains. The results of contact resistance and transfer length indicate that the current in the rivet graphene transistor does not just flow at the contact edge. Carbon nano-onions encapsulating Fe nanoparticles on the surface enhance the injection of charge between rivet graphene and the metal electrode. The anchoring of Fe nanoparticles encapsulated by carbon nano-onions on rebar graphene will provide additional avenues for applications of nanocarbon-based films in transparent and flexible electronics.

Graphene Oxide-Assisted Synthesis of Microsized Ultrathin Single-Crystalline Anatase TiO2 Nanosheets and Their Application in Dye-Sensitized Solar Cells.

High-quality microsized ultrathin single-crystalline anatase TiO2 nanosheets (MS-TiO2) with exposed {001} facets were synthesized by a facile and low-cost two-step process that combines a graphene oxide (GO)-assisted hydrothermal method with calcination. Both GO and HF play an important role in the formation of well dispersed MS-TiO2. As a novel microsized (1-4 µm) ultrathin two-dimensional (2D) material, MS-TiO2 possesses much higher lateral size and aspect ratio compared to common 2D nanosized (30-60 nm) ultrathin TiO2 nanosheets (NS-TiO2), resulting in excellent electronic conductivity and superior electron transfer and diffusion properties. Here, we fabricated MS-TiO2 and NS-TiO2, both of which were incorporated with the TiO2 nanoparticles (P25) to constitute the hybrid photoanode of dye-sensitized solar cells (DSSCs), and explored the effect of the lateral size (nano- and micro-) of ultrathin TiO2 nanosheets on their electron transfer and diffusion properties. Benefiting from the faster electron transfer rate and short diffusion path of the MS-TiO2, the MS-TiO2/P25 gains the more superior performance compared to pure P25 and NS-TiO2/P25 in the application of DSSCs. Moreover, it is expected that the novel high aspect ratio MS-TiO2 may be applied in diverse fields including photocatalysis, photodetectors, lithium-ion batteries and others concerning the environment and energy.

Preparation of Three-Dimensional Graphene Foams Using Powder Metallurgy Templates.

A simple and scalable method which combines traditional powder metallurgy and chemical vapor deposition is developed for the synthesis of mesoporous free-standing 3D graphene foams. The powder metallurgy templates for 3D graphene foams (PMT-GFs) consist of particle-like carbon shells which are connected by multilayered graphene that shows high specific surface area (1080 m(2) g(-1)), good crystallization, good electrical conductivity (13.8 S cm(-1)), and a mechanically robust structure. The PMT-GFs did not break under direct flushing with DI water, and they were able to recover after being compressed. These properties indicate promising applications of PMT-GFs for fields requiring 3D carbon frameworks such as in energy-based electrodes and mechanical dampening.