Synthesis,Structure Transformation,and Electrochemical Properties of Li2MgSi as a Novel Anode for Li‐lon Batteries

In this work, a novel hexagonal Li₂MgSi anode is successfully prepared through a hydrogen‐driven chemical reaction technique. Electrochemical tests indicate significantly improved cycling stability for the as‐synthesized Li₂MgSi compared with that of Mg₂Si. Ball‐milling treatment induces a polymorphic transformation of Li₂MgSi from a hexagonal structure to a cubic structure, suggesting that the cubic Li₂MgSi is a metastable phase. The post‐24‐h‐milled Li₂MgSi delivers a maximum capacity of 807.8 mAh g^?1, which is much higher than that of pristine Li₂MgSi. In particular, the post‐24‐h‐milled Li₂MgSi retains 50% of its capacity after 100 cycles, which is superior to cycling stability of Mg₂Si. XRD analyses correlated with CV measurements do not demonstrate the dissociation of metallic Mg and/or Li–Mg alloy involved in the lithiation of Mg₂Si for the Li₂MgSi anode, which contributes to the improved lithium storage performance of the Li₂MgSi anode. The findings presented in this work are very useful for the design and synthesis of novel intermetallic compounds for lithium storage as anode materials of Li‐ion batteries.     

A Highly Stretchable Cross‐Linked Polyacrylamide Hydrogel as an Effective Binder for Silicon and Sulfur Electrodes toward Durable Lithium‐Ion Storage

Despite the recent advancement in the in‐practical active materials (e.g., silicon, sulfur) in the rechargeable lithium‐ion energy storage systems, daunting challenges still remain for these high‐capacity electrode material candidates to overcome the severe volume changes associated with the repeated lithiation/delithiation process. Herein, developing a room‐temperature covalently cross‐linked polyacrylamide (c‐PAM) binder with high stretchability and abundant polar groups targeting the construction of high‐performance Si and sulfur electrodes is focused on. The robust 3D c‐PAM binder network enables not only significant enhancement of the strain resistance for working electrodes but also strong affinity to bonding with nano‐Si surface as well as effective capture of the soluble Li₂S_n intermediates, thereby giving rise to remarkably improved cycling performances in both types of electrodes. This rational design of such an effective and multifunctional binder offers a pathway toward advanced energy storage implementations.     

Theoretical Insights into the Mechanism of Selective Nitrate-to-Ammonia Electroreduction on Single-Atom Catalysts

Selective nitrate-to-ammonia electrochemical conversion is an efficient pathway to solve the pollution of nitrate and an attractive strategy for low-temperature ammonia synthesis. However, current studies for nitrate electroreduction (NO₃RR) mainly focus on metal-based catalysts, which remains challenging because of the poor understanding of the catalytic mechanism. Herein, taking single transition metal atom supported on graphitic carbon nitrides (g-CN) as an example, the NO₃RR feasibility of single-atom catalysts (SACs) is first demonstrated by using density functional theory calculations. The results reveal that highly efficient NO₃RR toward NH₃ can be achieved on Ti/g-CN and Zr/g-CN with low limiting potentials of −0.39 and −0.41 V, respectively. Furthermore, the considerable energy barriers are observed during the formation of byproducts NO₂, NO, N₂O, and N₂ on Ti/g-CN and Zr/g-CN, guaranteeing their high selectivity. This work provides a new route for the application of SACs and paves the way to the development of NO₃RR.     

Layered H2Ti6O13‐Nanowires: A New Promising Pseudocapacitive Material in Non‐Aqueous Electrolyte

Layered H₂Ti₆O₁₃‐nanowires are prepared using a facile hydrothermal method and their Li‐storage behavior is investigated in non‐aqueous electrolyte. The achieved results demonstrate the pseudocapacitive characteristic of Li‐storage in the layered H₂Ti₆O₁₃‐nanowires, which is because of the typical nanosize and expanded interlayer space. The as‐prepared H₂Ti₆O₁₃‐nanowires have a high capacitance of 828 F g^?1 within the potential window from 2.0 to 1.0 V (vs. Li/Li⁺). An asymmetric supercapacitor with high energy density is developed successfully using H₂Ti₆O₁₃‐nanowires as a negative electrode and ordered mesoporous carbon (CMK‐3) as a positive electrode in organic electrolyte. The asymmetric supercapacitor can be cycled reversibly in the voltage range of 1 to 3.5 V and exhibits maximum energy density of 90 Wh kg^?1, which is calculated based on the mass of electrode active materials. This achieved energy density is much higher than previous reports. Additionally, H₂Ti₆O₁₃//CMK‐3 asymmetric supercapacitor displays the highest average power density of 11 000 W kg^?1. These results indicate that the H₂Ti₆O₁₃//CMK‐3 asymmetric supercapacitor should be a promising device for fast energy storage.     

Structural Lithium Incorporated with the Crystalline Poly(Triazine Imide) Frameworks for Selective Catalytic Oxidative Desulfurization

Carbon nitride (CN) materials have been employed as catalysts in many scientific fields. Moreover, highly crystalline CN as an ideal model material for key problems in catalytic reaction research has received a lot of attention. Herein, the Li⁺ incorporated highly crystalline poly(triazine imide) (PTI–Li⁺) with a well-defined structure is successfully fabricated through the ionothermal method. The atomically dispersed Li in the PTI–Li⁺ serve as the active sites in the selective catalytic oxidation of H₂S, and the interaction between Li ions and PTI–Li⁺ framework extends electron delocalization and modulate electronic band structure resulting in improved O₂ and H₂S adsorption and activation ability. Consequently, PTI–Li⁺ shows excellent selective catalytic desulfurization activity and durability. This work not only designs an efficient desulfurization catalyst but also demonstrates the role of these atomically dispersed Li ions in PTI–Li⁺ during the catalytic reaction, enlightening the deeper understanding and wider application of carbon nitride materials.     

Syntheses,Li Insertion,and Photoactivity of Mesoporous Crystalline TiO2

Ordered mesoporous rutile and anatase TiO₂ samples are prepared using mesoporous silica SBA‐15 as template and freshly synthesized titanium nitrate and titanium chloride solutions as precursors. The rutile material formed from the nitrate solution is monocrystalline and contains minimal amounts of Si with a Si:Ti ratio of 0.031(4), whereas the anatase material formed from the chloride solution comprises nanocrystals and contains a higher content of Si with a Si:Ti ratio of 0.18(3). It is found that control of temperature and selection of Ti‐containing precursor play important roles in determining the crystal phase and crystallinity. A possible formation mechanism of porous crystalline TiO₂ is suggested. Characterization of these porous materials is performed by XRD, HRTEM, and nitrogen adsorption/desorption. SBA‐15‐templated mesoporous rutile TiO₂ exhibits a higher Li ion insertion capability than KIT‐6‐templated TiO₂ due to its larger surface area. Likewise mesoporous anatase TiO₂:SiO₂ composite has a better photoactivity than bulk TiO₂ or TiO₂‐loaded SBA‐15 for bleaching methylene blue.     

A Molecular‐Cage Strategy Enabling Efficient Chemisorption–Electrocatalytic Interface in Nanostructured Li2S Cathode for Li Metal‐Free Rechargeable Cells with High Energy

Using high‐capacity and metallic Li‐free lithium sulfide (Li₂S) cathodes offers an alternative solution to address serious safety risks and performance decay caused by uncontrolled dendrite hazards of Li metal anodes in next‐generation Li metal batteries. Practical applications of such a cathode, however, still suffer from low redox activity, unaffordable cost, and poor processability of infusible and moisture‐sensitive Li₂S. Herein, these difficulties are addressed by developing a molecular cage–engaged strategy that enables low‐cost production and interfacial engineering of Li₂S cathodes for rechargeable Li₂S//Si cells. An efficient chemisorption–electrocatalytic interface is built in extremely nanostructured Li₂S cathodes by harnessing the confinement/separation effect of metal–organic molecular cages on ionic clusters of air‐stable, soluble, and low‐cost Li salt and their chemical transformation. It effectively boosts the redox activity toward Li₂S activation/dissociation and polysulfide chemisorption–conversion in Li‐S batteries, leading to low activation voltage barrier, stable cycle life of 1000 cycles, ultrafast current rate up to 8 C, and high areal capacities of Li₂S cathodes with high mass loading. Encouragingly, this highly active Li₂S cathode can be applied for constructing truly workable Li₂S//Si cells with a high specific energy of 673 Wh kg^?1 and stable performance for 200 cycles at high rates against hollow nanostructured Si anode.     

Precious‐Metal‐Free Nanocatalysts for Highly Efficient Hydrogen Production from Hydrous Hydrazine

Hydrous hydrazine (H₂NNH₂·H₂O) has generally been considered a promising hydrogen storage carrier because of inherent advantages such as its high hydrogen content and easy recharging as a liquid. Unfortunately, the decomposition of hydrous hydrazine to H₂ is terribly sluggish and/or not entirely favored—a competing decomposition to ammonia may be preferred. This has been the case using noble‐metal catalysts and using non‐precious‐metal‐based catalysts, even at elevated temperatures. To overcome this challenge, non‐precious‐metal‐based Cu@Fe₅Ni₅ core@shell nanocatalysts are prepared using an in situ seeding‐growth approach. Unexpectedly, the catalyst exerts 100% H₂ selectivity and excellent activity and stability toward the complete decomposition of hydrous hydrazine, which is due to the synergistic effect of the core@shell structure. These promising results will certainly promote the effective application of hydrous hydrazine as a potential hydrogen storage material.     

The self-formation graded diffusion barrier of Zr/ZrN

In this paper, the 5 nm ZrN diffusion barrier was deposited by high vacuum magnetron sputtering method on Si substrate and the 300 nm Cu(Zr) alloy film or Cu film was sputtered on ZrN barrier without break vacuum. The self-formation graded Zr/ZrN diffusion barrier was obtained by annealing Cu(Zr)/ZrN bilayer system in N₂/H₂ (10% H₂) atmosphere. The X-ray diffraction (XRD) and four-point probe method were used to study graded Zr/ZrN diffusion barrier. The results revealed that the self-formation Zr barrier and ZrN barrier all obviously improved the thermal stability of Cu/Si system.     

Anomalous Enhancement of Li‐O2 Battery Performance with Li2O2 Films Assisted by NiFeOx Nanofiber Catalysts: Insights into Morphology Control

It is generally understood that particle‐shaped Li₂O₂ is preferred in Li‐O₂ batteries (LOBs) because the dominance of Li₂O₂ films may lead to poor electrochemical performance. The influence of Li₂O₂ morphology and its nucleation mechanism are probed by experiments along with the first‐principle calculations. It is revealed that the LOBs with Li₂O₂ films deliver unexpectedly improved capacities, longer cycles, and significantly reduced overpotentials assisted by NiFeO_x nanofiber catalysts. The energetically favored Li 2a vacancies under LiO₂‐rich conditions, small crystallites, and large contact areas with the electrode/electrolyte explain the anomalous performance enhancement. Li₂O₂ films are formed by a heterogeneous nucleation mechanism and the voltage applied, electrolyte, electrode surface, and use of catalysts are identified as the parameters controlling the mechanisms. The mapped correlations among these parameters shed light on the control of Li₂O₂ morphology for developing high‐performance LOBs.     

Investigation of Zr–N thin films for use as diffusion barrier in Cu metallization

Zr–N thin films as a barrier in Cu/Si contact were investigated. The Cu/Zr–N/Si specimens were prepared and annealed at temperatures up to 700 °C in N₂ ambient for an hour. Characterization of phase composition and crystallite structure of the barriers was performed by XRD, the film morphology was examined using atomic force microscopy (AFM), and the composition profiles of the as-deposited and annealed samples of Cu/Zr–N/Si were identified by Auger electron spectroscopy (AES). It is evident that the Zr–N film structure is very sensitive to the deposition conditions. Cu/Zr–N/Si contact systems showed better thermal stability so that the Cu₃Si phase could not be detected. It is indicated from the comparison analysis results that the Zr–N film showed better thermal stability with increasing N₂ flow ratio and/or negative substrate bias.     

MoS2‐Quantum‐Dot‐Interspersed Li4Ti5O12 Nanosheets with Enhanced Performance for Li‐ and Na‐Ion Batteries

Rational nanoscale surface engineering of electroactive nanoarchitecture is highly desirable, since it can both secure high surface‐controlled energy storage and sustain the structural integrity for long‐time and high‐rate cycling. Herein, ultrasmall MoS₂ quantum dots (QDs) are exploited as surface sensitizers to boost the electrochemical properties of Li₄Ti₅O₁₂ (LTO). The LTO/MoS₂ composite is prepared by anchoring 2D LTO nanosheets with ultrasmall MoS₂ QDs using a simple and effective assembly technique. Impressively, such 0D/2D heterostructure composites possess enhanced surface‐controlled Li/Na storage behavior. This unprecedented Li/Na storage process provides a LTO/MoS₂ composite with outstanding Li/Na storage properties, such as high capacity and high‐rate capability as well as long‐term cycling stability. As anodes in Li‐ion batteries, the materials have a stable specific capacity of 170 mAhg^?1 after 20 cycles and are able to retain 94.1% of this capacity after 1000 cycles, i.e., 160 mAhg^?1, at a high rate of 10 C. Due to these impressice performance, the presented 0D/2D heterostructure has great potential in high‐performance LIBs and sodium‐ion batteries.     

Empowering Metal Phosphides Anode with Catalytic Attribute toward Superior Cyclability for Lithium‐Ion Storage

Due to high capacity, moderate redox voltage, and relatively low polarization, metal phosphides (MPs) attract much attention as viable anode materials for lithium‐ion storage. However, severe capacity decay induced by the poor reversibility of discharge product (Li₃P) in these anodes suppresses their practical applications. Herein, it is first revealed that N‐doped carbon can effectively catalyze the oxidation of Li₃P by density functional theory calculations and activation experiments. By anchoring Ni₂P nanoparticles on N‐doped carbon sheets (Ni₂P@N‐C) via a facile method, an MP‐based anode rendered with a catalytic attribute is successfully fabricated for improving the reversibility of Li₃P during lithium‐ion storage. Benefiting from this design, not only can high capacity and rate performance be reached, but also an extraordinary cyclability and capacity retention be realized, which is the best among all other phosphides reported so far. By employing such a Ni₂P@N‐C composite and a commercialized active carbon as the anode and cathode, respectively, hybrid lithium‐ion capacitors can be fabricated with an ultrahigh energy density of 80 Wh kg^?1 at a power density of 12.5 kW kg^?1. This strategy of designing electrodes may be generalized to other energy storage systems whose cycling performance needs to be improved.     

Resistive Random Access Memory Cells with a Bilayer TiO2/SiOX Insulating Stack for Simultaneous Filamentary and Distributed Resistive Switching

In order to fulfill the information storage needs of modern societies, the performance of electronic nonvolatile memories (NVMs) should be continuously improved. In the past few years, resistive random access memories (RRAM) have raised as one of the most promising technologies for future information storage due to their excellent performance and easy fabrication. In this work, a novel strategy is presented to further extend the performance of RRAMs. By using only cheap and industry friendly materials (Ti, TiO₂, SiO_X, and n⁺⁺Si), memory cells are developed that show both filamentary and distributed resistive switching simultaneously (i.e., in the same I–V curve). The devices exhibit unprecedented hysteretic I–V characteristics, high current on/off ratios up to ≈5 orders of magnitude, ultra low currents in high resistive state and low resistive state (100 pA and 125 nA at –0.1 V, respectively), sharp switching transitions, good cycle‐to‐cycle endurance (>1000 cycles), and low device‐to‐device variability. We are not aware of any other resistive switching memory exhibiting such characteristics, which may open the door for the development of advanced NVMs combining the advantages of filamentary and distributed resistive switching mechanisms.     

Self-Rolling-Up Enabled Ultrahigh-Density Information Storage in Freestanding Single-Crystalline Ferroic Oxide Films

Ferroelectric memory is one of the most attractive emerging nonvolatile memory. Conventional methods to increase storage density in ferroelectrics include reducing the storage bit size or fabricating 3D stacks. However, the former will face a physical limit finally, and the integration of single-crystalline ferroelectric oxide following the latter still remains a great challenge. Here, a new method is introduced to construct a scroll-like 3D memory structure by self-rolling-up single-crystalline ferroelectric oxides. PbZr_0.3Ti_0.7O₃ single-crystalline thin film is chosen as a prototype and epitaxially grown on another oxide stressor layer with a few lattice-mismatch. Releasing such “Pb(Zr, Ti)O₃/stressor” bilayered structure from the substrate induces self-rolling-up due to the internal stress from the lattice-mismatch. High-density information can be written in the form of switched ferroelectric domains on those flat “Pb(Zr, Ti)O₃/stressor” membranes via piezoelectric force microscopy. In self-rolling-up membranes, information density can be experimentally enhanced up to 45 times. Theoretically, the freestanding “Pb(Zr, Ti)O₃/stressor” membranes have a strongly driven force to self-rolling-up, and the area ratio can enhance 100–450 times, corresponding to an ultra-high density information storage of 10² Tbit In⁻². This study provides a new and general method to develop compact, high-density, and 3D memories from oxide materials.     

Resonant Tunneling through Monolayer Si Colloidal Quantum Dots and Ge Nanocrystals

Resonant tunneling through a 4 nm nanocrystal Ge (nc‐Ge) layer and a 2.4 nm monolayer of Si colloidal quantum dots (QD) is achieved with 0.7 nm amorphous Al₂O₃ (a‐Al₂O₃) barriers. The nc‐Ge resonant tunneling diode (RTD) demonstrates a peak‐to‐valley current ratio (PVCR) of 8 and a full width at half maximum (FWHM) of 30 mV at 300 K, the best performance among RTDs based on annealed nanocrystals. The Si QD RTD is first achieved with PVCRs up to 47 and FWHMs as small as 10 mV at room temperature, confirming theoretically expected excellences of 3D carrier confinements. The high performances are partially due to the smooth profile of nc‐Ge layer and the uniform distribution of Si QDs, which reduce the adverse influences of many‐body effects. More importantly, carrier decoherence is avoided in the 0.7 nm a‐Al₂O₃ barriers thinner than the phase coherence length (≈1.5 nm). Ultrathin a‐Al₂O₃ also passivates well materials and suppresses leakage currents. Additionally, the interfacial bandgap of ultrathin a‐Al₂O₃ is found to be similar to the bulk, forming deep potential wells to sharpen transmission curves. This work can be easily extended to other materials, which may enable resonant tunneling in various nanosystems for diverse purposes.     

A MoS2 and Graphene Alternately Stacking van der Waals Heterostructure for Li+/Mg2+ Co-Intercalation

Owing to the low-cost, dendrite-free formation, and high volumetric capacity, rechargeable Li⁺/Mg²⁺ hybrid-ion batteries (LMIBs) have attracted great attention and are regarded as promising energy storage devices. However, due to the strong Coulombic interaction of Mg²⁺ with host materials, the traditional “Daniell Type” LMIBs with only Li⁺ intercalation usually cannot ensure a satisfactory energy density. Herein, graphene monolayers are arranged intercalating into MoS₂ interlamination to construct van der Waals heterostructures (MoS₂/G VH). This operation transforms the construction of ion channels from pristine interlamination of two MoS₂ monolayers to the interlamination of MoS₂ monolayer with graphene monolayer, thereby greatly reducing ion diffusion energy barriers. Compared with pristine MoS₂, the MoS₂/G VH can obviously reduce the migration energy barriers of Li⁺ (from 0.67 to 0.09 eV) and Mg²⁺ (from 1.01 to 0.21 eV). Moreover, it is also demonstrated that MoS₂/G VHs realize Li⁺/Mg²⁺ co-intercalation even at a rate current of 1000 mA g⁻¹. As expected, the MoS₂/G VH exhibits superior electrochemical performance with a reversible capacity of 145.8 mAh g⁻¹ at 1000 mA g⁻¹ after 2200 cycles, suggesting the feasibility of potential applications for high-performance energy storage devices.     

Spin‐Coated Periodic Mesoporous Organosilica Thin Films—Towards a New Generation of Low‐Dielectric‐Constant Materials

Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C₂H₅O)₃Si–R–Si(OC₂H₅)₃ or R′–[Si(OC₂H₅)₃]₃ with R = methene (–CH₂–), ethylene (–C₂H₂–), ethene (–C₂H₄–), 1,4‐phenylene (C₆H₄), and R′ = 1,3,5‐phenylene (C₆H₃). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and ²⁹Si and ¹³C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH₂ and C₂H₄ compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.     

Facile Synthesis of Monodisperse Mesoporous Zirconium Titanium Oxide Microspheres with Varying Compositions and High Surface Areas for Heavy Metal Ion Sequestration

Monodisperse mesoporous zirconium titanium oxide microspheres with varying compositions (Zr content from 0 to 100%), high surface areas (up to 413 m²/g) and well‐interconnected mesopores are synthesized via a combined sol–gel self‐assembly and solvothermal process. Surface areas, pore diameters, crystallinity and mesostructures of the products are controlled by changing the composition of the microspheres. The resulting mesoporous microspheres are tested as adsorbents to remove Cr (VI) anions from solution and the binary oxides show very high adsorption capacities (>25.40 mg/g, that is 0.49 mmol/g) in contrast to previously reported oxides (4.25 mg/g for TiO₂, 4.47 mg/g for α‐Fe₂O₃, 5.8 mg/g for CeO₂). The maximum adsorption capacities of the mesoporous microspheres of varying compositions correlate with the amount of surface hydroxyl groups on the materials. A maximum adsorption capacity of 29.46 mg/g (0.57 mmol/g) is achieved on the microspheres containing 30% Zr due to abundant active hydroxyl groups for heavy metal ion adsorption. Owing to their integrated features (including variable compositions, high specific surface area, tunable pore size and monodisperse grain size) as well as specific acid‐base surface properties, such mesoporous zirconium titanium oxide microspheres are also expected to have potential either as catalysts or catalyst supports for industrial applications.     

Tristate Memory Using Ferroelectric–Insulator–Semiconductor Heterojunctions for 50% Increased Data Storage

Ferroelectric random‐access memory (FeRAM) is considered to be one of the best candidates for universal memory. However, difficult scaling of the memory cell size has hindered the realization of high density FeRAM. Given that size scaling is inherently limited by the complicated crystal structure and processing of ferroelectric materials, the highly stable and step‐wise three memory state of one cell can be another pathway to high‐density FeRAM. A feasible structure and actual operation of a tristate memory function for high‐density FeRAM is presented that uses stacked ferroelectric Pb(Zr,Ti)O₃/insulating Al₂O₃/semiconducting ZnO layers with Pt top and bottom electrodes. The complicated electrical responses of the stacked structure to external stimuli are well understood based on the separated trapping of the compensating charges at the Pb(Zr,Ti)O₃/Al₂O₃ and Al₂O₃/ZnO interfaces and the discrete dissipation of the trapped charges during polarization switching in one direction. This unique function of the structure induces three discrete charge states that can be used to increase the memory density by 50% compared to conventional FeRAM at a given cell size.