NC Layer Research Articles

Enabling the ability of Li storage at high rate as anodes by utilizing natural rice husks-based hierarchically porous SiO2/N-doped carbon composites

One of the greatest challenges in developing SiO2/C composites as anode materials in lithium ion batteries (LIBs) is to improve the ability of Li storage at high rate over long-term cycles. Herein, biomass rice husks-based hierarchically porous SiO2/N-doped carbon composites (BM-RH-SiO2/NC) were prepared by ball mill and thermal treatment. BM-RH-SiO2/NC can still retain a reversible capacity of 556 mAh g−1 over 1000 cycles at a high current of 1.0 A g−1. At 5.0 A g−1 the capacity is kept as high as 402 mAh g−1. This impressively long-term cyclic performance and high-rate capability of BM-RH-SiO2/NC can be ascribed to the synergetic effect between the natural SiO2 nanoparticles (< 50 nm) and the NC layer. The coating NC layer can not only effectively mitigate the volume strain during charge-discharge process to offer stably cyclic performance but also improve the electrical conductivity. Furthermore, the hierarchical porosity and better electrolyte wettability offer the rapid Li+ diffusion and electron transfer, which enhance the pseudocapacitive behavior of whole electrode material and then guarantee fast electrochemical kinetics. Importantly, the unique Li-storage mechanism of active SiO2 in BM-RH-SiO2/NC composite was formed and found, which further validates the improved electrochemical capability.

Oxygen vacancies boosting ultra-stability of mesoporous ZnO-CoO@N-doped carbon microspheres for asymmetric supercapacitors

Long-term cycling stability of pseudocapacitive materials is pursued for high-energy supercapacitors. Herein, the mesoporous zinc-cobalt oxide heterostructure@nitrogendoped carbon (ZnO-CoO@NC) microspheres with abundant oxygen vacancies are self-assembled through a hydrothermal method combined with an annealing post-treatment. The multifunctional polyvinyl pyrrolidone (PVP) is used as a structure-directing agent, the precursor of NC and the initiator of abundant oxygen vacancies in zinc-cobalt oxide microspheres. XPS demonstrates the generation of surface oxygen vacancies resulted from the reduction effect of conductive NC, and further confirms the weaker interaction between the metal ions and oxygen atoms. As a result, the electrode based on ZnO-CoO@NC in 2 mol L−1 KOH shows enhanced capacitive performance with an excellent cycle stability of 92% retention of the initial capacitance after 40,000 charge-discharge cycles at 2 A g−1, keeping the morphology unchanged. The assembled asymmetric supercapacitor, graphene//ZnO-CoO@NC, also performs good cyclic stability with 94% capacitance retention after 10,000 cycles at 2 A g−1. The remarkable electrochemical performance of the self-assembled ZnO-CoO@NC composite is attributed to the mesoporous architecture, abundant oxygen vacancies, conductive ZnO scaffold for CoO crystals forming heterostructure of ZnO-CoO and the high conductive NC layer covering outside of the multi-metal oxide nanoparticles. Hence, the ZnO-CoO@NC holds great promise for high-performance energy storage applications.

Co nanoparticles coupling induced high catalytic activity of nitrogen doped carbon towards hydrogen evolution reaction in acidic/alkaline solutions

The development of highly-efficient and noble-metal-free catalysts with low cost and high durability for hydrogen evolution reaction (HER) is of great importance to many energy-related technologies. This work reports that nitrogen-doped carbon coated Co nanoparticles encapsulated in bamboo-like nitrogen-doped carbon nanotubes (Co@NC/B-NCNTs), synthesized by a simple calcination of Co(NO3)2, melamine and P123, is a promising catalyst for HER in both acidic and alkaline solutions. In acidic solution, the Co@NC/B-NCNTs has the HER onset potential of ∼0 V and only needs an overpotential of 7 mV to drive the current density of 10 mA cm−2. Its HER catalytic activity is very close to that of Pt/C. In alkaline solution, its onset potential and overpotential to drive 10 mA cm−2 are 100 and 182 mV, respectively. Both the values are lower than those of many other catalysts reported. The DFT calculations show electronic coupling between Co nanoparticles and NC layer plays an important role in high catalytic activity of Co@NC/B-NCNTs. The Co nanoparticles can change the charge density distribution of the outer NC layer, affecting its properties for hydrogen adsorption and desorption. Additionally, the pyridinic N in the outer NC layer is calculated to be a promising active site for HER.

Fracture behaviour of nc-TiAlN/a-Si3N4 nanocomposite coatings under cyclic nano impact testing

ABSTRACTTiN, nanocomposite nc-TiAlN/a-Si3N4 (NC) and multi-layered TiN/NC coatings were deposited on commercially used tungsten carbide-cobalt (WC-Co) based tool material substrates by cathodic arc physical vapour deposition (CA-PVD) technique. The coatings were subjected to cyclic nanoimpact testing with impact loads of 1 and 5 mN. Properties such as fracture probability, (h1–hs)/(hf–h1) index and crack morphologies were analysed based on which, the performance order of the coatings was evaluated. It was observed that the multi-layer coating performed better followed by monolithic titanium nitride and nanocomposite coating (TiN/NC > TiN > NC). The order of the coatings so obtained was further compared with their relative performance during real-time machining studies. It was observed during machining that the order was changed to TiN/NC > NC > TiN. The better performance in TiN/NC coating was due to arresting of cracks formed in NC layer by TiN layer.

Structure-designed synthesis of Cu-doped Co3O4@N-doped carbon with interior void space for optimizing alkali-ion storage

Co3O4 is a promising anode candidate for Li-ion and Na-ion batteries (LIBs and SIBs) owing to its intrinsic merits. Nevertheless, drastic volume expansion upon charge/discharge causes fast capacity decay, which hugely hinders its commercial application. Introducing carbon materials as a coating layer is considered to be an effective strategy to improve the structural stability. However, the coating layer may be fractured upon repeated insertion/extraction due to the lack of void space. Therefore, constructing void space is crucial for achieving prolonged cycling stability. Herein, we design a successive coating-eching strategy to fabricate Cu-doped Co3O4@N-doped Carbon with interior void space (Cu-Co3O4@Void@NC). The void space allows the inner active material to expand freely without breaking the outer protective layer. Simultaneously, the unbroken NC layer is conductive to the formation of a stable SEI film. In addition, Cu-doping can enhance the inherent electrical conductivity of Co3O4, which is proved by the density functional theory (DFT) calculations. When evaluated as LIBs and SIBs anode, Cu-Co3O4@Void@NC delivers superior electrochemical performance (562 mAh g−1 after 1000 cycles at 5 A g−1 in LIBs and 312 mAh g−1 after 300 cycles at 2 A g−1 in SIBs).

Tailoring sandwich-like CNT@MnO@N-doped carbon hetero-nanotubes as advanced anodes for boosting lithium storage

Currently, constructing an advanced structure to address the weaknesses of MnO-based anode materials in regard to large volume variation upon cycling and inferior conductivity still needs to be further improved for endowing the MnO anode with a desirable lithium-storage performance. Herein, an ingenious sandwich-like CNT@MnO@N-doped carbon coating (NC) hetero-nanotube architecture with partial MnO being inlaid into CNT is synthesized through an elaborate route including template and coating strategy and utilized as a hopeful lithium-ion anode material exhibiting large specific capacity, long-term cyclability, and high rate capacity synchronously. The outer NC layer could not only enhance the electro-conductibility of MnO as well as efficiently confine the reaggregation and ameliorate the volume variation of MnO nanoparticles upon cycling, but also avert the direct contact between MnO and electrolyte which could lead to the unexpected depletion of lithium. The inner CNT could ensure the 1D hetero-nanotube structure benefiting to preserve the structural integrity during cycling, and also facilitate the electron transport. Additionally, the inlaying of MnO nanoparticles into CNT could boost the transfer and storage of lithium ion. Therefore, the CNT@MnO@NC electrode reveals a high Li+ storage capacity (665 mAh g−1 at 0.1 A g−1), outstanding cycling performance (617 mAh g−1 after 500 cycles at 1 A g−1) and superior rate capability (421 mAh g−1 at 2.0 A g−1), calculating based on the weight of CNT@MnO@NC composite. According to kinetic study, it is uncovered that the CNT@MnO@NC electrode presents an enhanced capacitive effect towards Li+ storage, featuring with the characteristic faradaic surface pseudocapacitive charge-storage mechanism. This work puts forward a promising strategy to prepare 1D heterostructured anode materials with improved conductivity and structure stability for boosting lithium-storage.

Memristive Properties of Structures Based on (Co41Fe39B20) x (LiNbO3)100–x Nanocomposites

The current‒voltage characteristics of the metal/nanocomposite (NC)/metal structures based on (Co41Fe39B20) x (LiNbO3)100–x NCs 2.4 and 3 μm thick are investigated in the fields of up to ~104 V/cm. The structures are synthesized via ion-beam sputtering of a composite target, in which NCs of different composition are formed in the single cycle at x = 5‒48 at %. The memristive effect (ME) manifesting itself during resistive switching of structures and the storage of incipient states has been detected at x ≈ 10 at %. It is ascertained that the ME depends weakly on used metal (Cu or Cr) contacts and the NC layer thickness, the number of switching cycles (without degradation) exceeds 105, and the ratio between the resistances of high- and low-resistance states, i.e., the Roff/Ron ratio, reaches approximately 65. The detected ME is explained by the fact that oxygen vacancies substantially affect the tunneling conductance of metal-granule chains determining the electric resistance of structures below the percolation threshold.

Dopamine-derived N-doped carbon decorated titanium carbide composite for enhanced supercapacitive performance

Two-dimensional transition metal carbides, MXenes, with large surface area, excellent electrical conductivity and chemical stability, have proved promising for energy storage. However, the irreversible re-stacking and low capacity of MXenes restrict their development and practical applications. Here, the N-doped carbon decorated MXene (Ti3C2Tx@NC) composites were synthesized via an in-situ self-polymerization of dopamine on the surface of Ti3C2Tx followed by a carbonization process. The Ti3C2Tx and Ti3C2Tx@NC were systematically characterized, which have been manifested that NC were equably decorated on the surface and interlayer of Ti3C2Tx sheets and a unique three-dimensional composited nanostructure was fabricated. Such nanostructure can confer both high surface area of NC layer and effective avoidance of the restacking of Ti3C2Tx sheets, whilst, importantly, rendering the composites good conductivity and additional pseudocapacitance. As a result, the optimized Ti3C2Tx@NC-2 composite exhibited a high specific capacitance of 442.2Fg−1 under a current density of 1Ag−1, which is 281% higher than that of Ti3C2Tx. As a further description, Ti3C2Tx@NC achieved an excellent cycling stability with capacitance retaining 91.9% after 5000 cycles and a high rate capability of 92.5% at 10Ag−1. Besides, the Ti3C2Tx@NC-2-based symmetric supercapacitor presents a delighted energy density and power density. Therefore, the elaborately designed Ti3C2Tx@NC composites provided a pregnant exploration for energy-related applications.

A Hybrid Perovskite Solar Cell Modified With Copper Indium Sulfide Nanocrystals to Enhance Hole Transport and Moisture Stability

Lead halide perovskite solar cells have attracted tremendous attention for their impressive power conversion efficiencies. However, stability is still one of the most significant concerns for perovskite solar cells. Here, a layer of copper indium sulfide nanocrystals (CIS NCs) has been introduced into the perovskite solar cell, giving rise to enhanced charge transfer property as well as longer lived films and devices. Ultrafast photoluminescence studies on the charge transfer behavior have revealed that the CIS NC layer can modify the interface between perovskite and hole transporting material, suppressing charge recombination pathways. The degradation mechanism in this system is also studied under various simulated environmental conditions. Devices without CIS NCs show significant degradation after exposure to high humidity (over 80%) without device encapsulation. In contrast, the perovskite thin films with a CIS layer show superior resistance to humidity, while perovskite-CIS NC solar cells exhibit significantly improved photovoltaic stability.

Plasmonic photocatalytic reactor design: Use of multilayered films for improved organic degradation rates in a recirculating flow reactor

Plasmonic photocatalysis was investigated by examining both the arrangement of the photocatalyst and plasmonic components, and the structure and composition of the plasmonic phase. Pd was epitaxially grown on to 50nm Ag nanocubes. The Ag:Pd ratio was optimized to blue-shift the plasmonic absorption peak to match the bandgap of TiO2 (∼405nm). A∼5nm Pd coating on the Ag nanocubes (Ag:Pd=9:1) led to the observation of the Ag nanocube’s plasmonic feature. The arrangement of the photocatalyst components was tested for degradation of model organics in a slurry and a recirculating thin film photoreactor. The results demonstrated that both the arrangement of the components and the structure and composition of the plasmonic material influenced the conversion. The TiO2/Ag composite catalysts yielded slight improvement (in thin film reactor) or had a negative effect (slurry reactor) compared to TiO2 which was attributed to scattering light away from the semiconductor photocatalyst and/or covering some active sites. The addition of the Pd shell on the Ag nanocube yielded improved performance compared to the TiO2/Ag composite catalysts, likely due to electron trapping. A factor of 2 enhancement in rate and apparent quantum yield compared to TiO2 was achieved for the Ag NC layer underneath the TiO2 layer and was attributed to light scattering of absorbed photons. The addition of the Pd shell to the Ag nanocube still provided enhancement compared to TiO2, but was lesser compared to Ag layer due to lower scattering efficiency. The results of this study provide insights for plasmonic photocatalytic reactor design. Best utilization of plasmonic enhancement to photocatalysis is indicated via a layered design of the plasmonic and photocatalytic phases.

Nitriding of nanocrystalline pure Fe induced by surface mechanical attrition treatment

Properties of nanocrystalline (nc) materials are different from, and often superior to those of conventional coarse-grained counterparts. Unfortunately, it is still difficult to obtain ideal (e.g. full-density, residual stress-free, flaw-free, porosity-free and contamination-free) nc bulk sample by using the present preparation methods. Recently, a new technique named surface mechanical attrition treatment (SMAT) was developed. SMAT enables the fabrication of an nc surface layer on various bulk metals. The nc layer is free of contamination and porosity because the nanocrystallization process is induced by the severe plastic deformation at very high strain rates. In this work, a pure Fe plate was subjected to the SMAT and its microstructure were characterized. The effect of the surface nanocrystalline layer on the gas nitriding process at a lower temperature was also investigated by using structural analysis. The surface nanocrystallization evidently enhances nitriding kinetics and promotes the formation of an ultra-fine polycrystalline compound layer. The results of the investigation showed that this new gas nitriding technique can effectively increase the hardness of the resulting surface layer in comparison with conventional nitriding, demonstrating a significant advancement for materials processing.

Improved corrosion resistance in simulated concrete pore solution of surface nanocrystallized rebar fabricated by wire-brushing

Continuous surface nanocrystallization (SNC) of rebar was achieved through wire-brushing process. A uniform NC layer with thickness of 25μm and average grain size of 50nm was formed on the rebar surface. Due to the enhanced passivation performance of the NC layer, corrosion resistance of the SNC rebar was significantly improved in Cl−-containing saturated Ca(OH)2 solution. High-energetic crystal defects of the nano-grains leads to the faster passivation and enhanced stability of the passive film of the SNC rebar.

Application of a Silicon Nanocrystal Down-shifter to a c-Si Solar Cell

Silicon nanocrystals (Si NCs) in a matrix of SiO2 were applied to the front of a p-type c-Si solar cell as down-shifter. The down-shifting action of the Si NCs was confirmed from the analysis of spectral response measurements with the help of ray tracing simulations. Ray tracing simulations were performed to simulate the application of a Si NC layer with varying emission quantum efficiencies to the glass coversheet in a solar module with EVA as encapsulant. It is found that gain in Jsc is only achieved for a Si NC layer with high emission quantum efficiencies, which requires efficient quantum cutting. The most important loss factors identified are the low Si NC emission coupling efficiency in combination with parasitic absorption in the spectral range of high solar cell internal quantum efficiency.

Silicon nanocrystals from high‐temperature annealing: Characterization on device level

AbstractSilicon nanocrystals (Si NCs) embedded in Si‐based dielectrics provide a Si‐based high band gap material (1.7 eV) and enable the construction of all‐crystalline Si tandem solar cells. However, Si nanocrystal formation involves high‐temperature annealing which deteriorates the properties of any previously established selective contacts. The inter‐diffusion of dopants during high‐temperature annealing alters Si NC formation and limits the built‐in voltage. Furthermore, most devices presented so far also involve electrically active bulk Si and therefore do not allow a clear separation of the observed photovoltaic effect of the nanocrystal layer from that of the bulk Si substrate. A membrane route is presented for nanocrystal based p–i–n solar cells to overcome these limitations. In this approach, the formation of both selective contacts is carried out after high‐temperature annealing and therefore not affected by the latter. p–i–n Solar cells are investigated with Si NCs embedded in silicon carbide in the intrinsic region. Device failure due to damaged insulation layers is analyzed by electron‐ and light beam induced current measurements. Open‐circuit voltages of 176 mV are shown for the NC layer. An optical model of the device is presented for improving the cell current. Comparison of the optical limit and the measured short circuit current demonstrates that the device is governed by recombination within the absorber layer. magnified imageVertical p–i–n solar cell with a Si nanocrystal thin film in the intrinsic region and selective electron and hole contacts by doped amorphous silicon carbide (a‐SixC1−x:H).

Core–shell Si–N-doped C assembled via an oxidative template for lithium-ion anodes

The Si-NC core-shell composite was synthesized by a modified oxidative template assembly route using a facile carbonization process. The images of the obtained Si-NC composites showed that an amorphous NC layer adsorbed stably and tightly on the nano-Si surface with an only several nanometers thickness to the formation of the Si-NC core-shell structure, which was beneficial for the electronic contact of Si nanoparticles. For the Si-NC-700 anode, it could be calculated that the initial charge capacity was 986.2 mA h g(-1) at a rate of 0.2 C. And it could still be kept at 764.4 mA h g(-1) over 100 cycles, with a little capacity loss of 0.22% per cycle. Moreover, it was concluded that the Si-NC-700 anode could achieve a capacity of 790.8 mA h g(-1) for the first cycle, and significantly remain at 778.2 mA h g(-1) over 500 cycles at a rate of 0.5 C. These excellent electrochemical performances could probably be due to the N-doping generating the extrinsic defects and the absorption of Li ions, and hence result in a superior long-term cycling stability and rate capability. This suggests that the core-shell Si-NC composite is a promising material for improving the electrochemical performance of lithium-ion anodes.

Enhancing the Performance of Solid‐State Dye‐Sensitized Solar Cells Using a Mesoporous Interfacial Titania Layer with a Bragg Stack

AbstractHigh efficiency dye‐sensitized solar cells (DSSCs) are fabricated with a heterostructured photoanode that consists of a 500‐nm‐thick organized mesoporous TiO2 (om‐TiO2) interfacial layer (IF layer), a 7 or 10‐μm thick nanocrystalline TiO2 layer (NC layer), and a 2‐μm‐thick mesoporous Bragg stack (meso‐BS layer) as the bottom, middle and top layers, respectively. An om‐TiO2 layer with a high porosity, transmittance, and interconnectivity is prepared via a sol‐gel process, in which a poly(vinyl chloride)‐g‐poly(oxyethylene methacrylate) (PVC‐g‐POEM) graft copolymer is used as a structure‐directing agent. The meso‐BS layer with large pores is prepared via alternating deposition of om‐TiO2 and colloidal SiO2 (col‐SiO2) layers. Structure and optical properties (refractive index) of the om‐TiO2 and meso‐BS layers are studied and the morphology of the heterostructured photoanode is characterized. DSSCs fabricated with the heterostructured IF/NC/BS photoanode and combined with a polymerized ionic liquid (PIL) exhibit an energy conversion efficiencies of 6.6% at 100 mW/cm2, one of the highest reported for solid‐state DSSCs and much larger than cells prepared with only a IF/NC layer (6.0%) or a NC layer (4.5%). Improvements in energy conversion efficiency are attributed to the combination of improved light harvesting, decreased resistance at the electrode/electrolyte interface, and excellent electrolyte infiltration.

Subsurface microstructural alterations during sliding wear of biomedical metals. Modelling and experimental results

Underneath contact surfaces under sliding wear distinct microstructural changes have been found in biomedical materials. These are attributed to the nature of the contact stress (and strain) field. The experimental investigation of subsurface areas of retrieved metal-on-metal hip joints and laboratory specimens revealed that the worn surfaces of these fcc CoCrMo alloys in general consist of a nano-crystalline (nc) layer with a thickness of up to 200 nm. This layer is chemically modified by mechanical mixing, which introduces the interfacial medium (e.g. proteins) into the subsurface volume. Below 200 nm one often finds a nc-layer of the same grain size but having only the chemical composition of the base material. Thus, the interface between the mechanically mixed nc-layer and the underlying one cannot be distinguished by grain size, but by chemical composition. In comparison to shear fatigue tests, these materials show a distinct tendency for ratchetting and they depict the same lattice defects as in a siding wear stress field. This contribution shows that computer simulation and experimental validation can support each other in order to understand the complicated interaction of wear mechanisms under sliding wear qualitatively. But there is no general description available and any aspect requires its own simulation method.

Wear behaviour of AZ91D magnesium alloy with a nanocrystalline surface layer

The tribological behaviour of nanocrystalline surface layer with an average grain size of 30 ± 5 nm generated by surface mechanical attrition treatment on AZ91D Mg alloy samples has been investigated under dry sliding conditions. Compared with the alloy without SMAT, nano-grained surface layer showed lower friction coefficient. An improved wear resistance of the NC layer was found at the load ranges from 3 N to 9 N due to the grain refinement strengthening effect. Examination of the worn surface and the wear debris indicated that the wear mechanism of NC layer is similar to that of the coarse-grained alloy. Cooperative effects of cutting, plowing and oxidation govern the tribological behaviour of nanocrystalline AZ91D Mg alloys.

Structural properties of Ge-implanted SiO 2 layers and related MOS memory effects

Recently, the feasibility of using ion implantation of germanium and high temperature annealing to fabricate a near-interface nanocrystal (nc) layer into a silicon dioxide (SiO 2) on Si film has been demonstrated. In this work, the influence of ion implantation parameters on the nc layer formation in SiO 2 is studied. Transmission electron microscopy and Rutherford backscattering spectroscopy have been used to study the Ge-redistribution in the SiO 2 films. Depending on the ion implantation energy and dose, the formation of a bulk nc layer in addition to the desired near-interface layer can be observed. A maximum near-interface Ge-nc density of 1.7 × 10 12 cm −2 has been measured. Capacitance–voltage measurements have been used to study electrical properties of metal-oxide-semiconductor structures containing such implanted SiO 2 films. The results indicate a strong memory effect due to the presence of near-interface Ge-nc. As an example, flat-band shifts of 4.5 V have been obtained at a programming voltage of 7 V for 1 s. For the first time, long retention properties have been demonstrated on a memory structure containing a single near-interface Ge-nc layer.