Rapid Diffusion Paths Research Articles

Construction of hierarchical and core-shell structured Co3O4@MnO2@NiO nanoarrays as binder-free electrodes for high-performance asymmetric supercapacitors

Remarkable specific capacity and excellent cycle stability of the electrode materials are vital prerequisites for their practical applications. Transition metal oxide-based materials have been extensively explored and employed as electrode materials for asymmetric supercapacitors. However, the actual specific capacitances of these materials are still far lower than their theoretically predicted values. Thus, it is essential to design transition metal oxide with novel structures in order to maximize their specific capacity and cycle stability. Herein, we constructs hierarchical and core-shell structured Co3O4@MnO2@NiO arrays on nickel foam (Co3O4@MnO2@NiO/NF) through a three-step hydrothermal-annealing process, and use them as a direct binder-free electrode for pseudocapacitors. The as-prepared layered hierarchical Co3O4@MnO2@NiO/NF electrode exhibits an impressive specific capacitance of 6.42 F cm−2 (2054 F g−1) at 1 mA cm−2 in a three-electrode configuration, which is largely because of the synergistic effect among Co3O4, MnO2 and NiO. Furthermore, the 3D nanoarray structure can provides a larger specific surface area, a rapid diffusion path, and more active sites that allow to achieve improved electrochemical performance. In addition, the assembled Co3O4@MnO2@NiO/NF//AC/NF ASC all-solid-state asymmetric supercapacitor (ASC) displays a remarkable energy density (30.7 Wh kg−1 at 400.4 W kg−1), demonstrating that this all-solid-state ASC owns considerable potential for practical applications in such high-performance energy storage devices.

Oxidation Behavior of Pre-Strained Polycrystalline Ni3Al-Based Superalloy.

The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy.

FeNi nanoalloy-carbon nanotubes on defected graphene as an excellent electrocatalyst for lithium-oxygen batteries

Lithium-oxygen batteries (LOBs) promise high energy density but suffer from catalyst-related issues. We've developed FeNi-NCNT/DrGO, a novel catalyst, by integrating iron-nickel nanoalloys (FeNi) embedded in nitrogen-doped carbon nanotubes (NCNTs) grafted onto defect-rich reduced graphene oxide (DrGO). The fabrication involved freeze-drying, defect engineering, and thermal treatments. The FeNi nanoalloy within the catalyst demonstrates outstanding bifunctional activity, while the NCNTs serve as an excellent electronic conduction medium and DrGO enables favorable ion transport. The 3D open-space architecture of this catalyst provides a rapid diffusion path for the electrolyte and room for accommodating discharge products. As a result, the LOBs with FeNi-NCNT/DrGO exhibits exceptional electrochemical performance, achieving a deep discharge capacity of 21,153.6 mAh g−1 and a high round-trip efficiency of 98.7% at 200 mA g−1. Moreover, it demonstrates excellent cycling stability, exceeding 100 cycles at 200 mA g−1 with a cut-off capacity of 500 mAh g−1.

Chemical synthesis and super capacitance performance of novel CuO@Cu4O3/rGO/PANI nanocomposite electrode.

Copper oxide-based nanocomposites are promising electrode materials for high-performance supercapacitors due to their unique properties that aid electrolyte access and ion diffusion to the electrode surface. Herein, a facile and low-cost synthesis in situ strategy based on co-precipitation and incorporation processes of reduced graphene oxide (rGO), followed by in situ oxidative polymerization of aniline monomer has been reported. CuO@Cu4O3/rGO/PANI nanocomposite revealed the good distribution of CuO@Cu4O3 and rGO within the polymer matrix which allows improved electron transport and ion diffusion process. Galvanostatic charge-discharge (GCD) results displayed a higher specific capacitance value of 508 F g-1 for CuO@Cu4O3/rGO/PANI at 1.0 A g-1 in comparison to the pure CuO@Cu4O3 278 F g-1. CuO@Cu4O3/rGO/PANI displays an energy density of 23.95 W h kg-1 and power density of 374 W kg-1 at the current density of 1 A g-1 which is 1.8 times higher than that of CuO@Cu4O3 (13.125 W h kg-1) at the same current density. The retention of the electrode was 93% of its initial capacitance up to 5000 cycles at a scan rate of 100 mV s-1. The higher capacitance of the CuO@Cu4O3/rGO/PANI electrode was credited to the formation of a fibrous network structure and rapid ion diffusion paths through the nanocomposite matrix that resulted in enhanced surface-dependent electrochemical properties.

Complementary use of atom probe tomography (APT) and differential hall effect metrology (DHEM) for activation loss in phosphorus-implanted polycrystalline silicon

The objectives of this study are to explore the activation ratios of implanted phosphorus dopants in polycrystalline silicon (poly-Si), and to reveal the role of grain boundary segregation in incomplete activation using atom probe tomography (APT) and differential Hall effect metrology (DHEM). After implantation and rapid thermal annealing, the results of APT revealed pronounced segregation toward grain boundaries that provides rapid diffusion paths for phosphorus. Peak concentrations of phosphorus segregations in the grain boundaries of the regrown and non-regrown regions were measured to be 4.38E21 and 2.17E21 atoms/cm³ that correspond to activation ratios of 6 % and 1 %, respectively. In contrast, phosphorus concentrations within grain interiors were found to be 6.86E20 and 1.72E19 atoms/cm³, corresponding to activation ratios of 39 % and nearly 100 % in the regrown and non-regrown regions, respectively. This research highlights a novel approach for evaluating site-specific activation ratios in poly-Si through the integrated use of DHEM and APT.

Irradiation damage and corrosion performance of proton irradiated 304 L stainless steel fabricated by laser-powder bed fusion

The irradiation-induced microstructure and corrosion performance of proton irradiated 304 L stainless steel (SS) fabricated by laser powder bed fusion (LPBF) is investigated. Irradiation-induced dislocation loops are observed in both LPBF and traditionally manufactured (TM) 304 L SS following 2 MeV proton irradiation at 360 °C. A comparison analysis of the oxide scales formed on proton irradiated LPBF and TM 304 L SS is conducted along with the unirradiated counterparts. The irradiation-induced defects accelerate the corrosion by providing a rapid diffusion path to form a thicker and more porous film with a double-layer structure and herein the oxide film thickness of TM 304 L SS is approximately twice that of the LPBF 304 L SS. The unique microstructure of high dislocation densities, cellular sub-grains boundaries and dispersed nanoscale inclusions provides large amounts of interfaces in LPBF samples, which is benefit to absorb the irradiation-induced point defects. The irradiation induced fast diffusion paths and the nucleation points of oxides are thus reduced, resulting in a thinner oxide film thickness and a better corrosion resistance revealed by the more Cr enrichment of inner scale in LPBF 304 L SS.

Synergistic Effect of Zn–Co Bimetallic Selenide Composites for Lithium–Sulfur Battery

Compared with monometallic selenides, heterogeneous bimetallic selenides have rich phase boundaries and superior electrical conductivity. ZnSe/CoSe2 composites were prepared by introducing Zn metal and using ZIF-8/67 as the precursor through the synergistic effect between Zn and Co after selenification. The electrocatalytic conversion of polysulfide is accelerated by ZnSe through chemical adsorption and the catalytic effect. The conductive CoSe2 surface provides a rapid diffusion path for lithium ions, accelerating the conversion of the polysulfide. On the basis of their individual strengths, ZnSe and CoSe2 can jointly promote the smooth adsorptive–diffuse–catalytic conversion process of polysulfide and induce the growth of lithium sulfide around its heterogeneous interface, thus enhancing the electrochemical performance of the lithium–sulfur battery cathode materials. The ZnSe/CoSe2–S electrode, at the optimal Zn-to-Co ratio of 1:1, has a 790.06 mAh g−1 initial specific capacity at 0.2 C and excellent cycling stability at 1 C. After 300 cycles, the final capacity is 300.85 mAh g−1, and the capacity retention rate reaches 82.71%.

Crumpling Carbon‐Pillared Atomic‐Thin Dichalcogenides and CNTs into Elastic Balls as Superior Anodes for Sodium/Potassium‐Ion Batteries

AbstractWith abundant electroactive sites and rapid ion diffusion paths, ultrathin dichalcogenides such as MoS2 demonstrate enormous potential as anodes for sodium/potassium‐ion batteries (SIBs/PIBs). However, ultrahigh‐aspect‐ratio nanosheets are very easy to aggregate and re‐stack, drastically weakening their intrinsic merits. Here a sustainable dichalcogenide anode is designed via crumpling carbon‐pillared atomic‐thin MoS2 nanosheets with CNTs into an elastic ball structure (C‐p‐MoS2/CNTs). In this architecture, the glucose‐derived carbon pillars atomic‐thin MoS2 nanosheets and broadens interlayer spacing, ensuring fast Na+/K+ diffusion; CNTs act as 3D scaffolds to impede re‐stacking of MoS2 while providing high‐speed pathways for electrons; the integration of flexible atomic‐thin sheets and high‐toughness CNTs further endows the balls with great elasticity to release the cycling stress. Consequently, the C‐p‐MoS2/CNTs material delivers high reversible capacities, outstanding cycling stability, and superior rate performance as anodes for both SIBs and PIBs. Pairing with Na3V2(PO4)2F3 cathode, the sodium‐ion coin‐cell could operate at a rate up to 50 C at high mass loading of 9.4 mg cm−2 and manifest ultrastable cycling stability at 40 C over 600 cycles. Impressively, the assembled pouch cell can be cycled stably with a high energy density of 188 Wh kg−1. This study is anticipated to provide inspiration for designing innovative metal dichalcogenides as battery anodes.

Cellulose nanofibers carbon aerogel based single-cobalt-atom catalyst for high-efficiency oxygen reduction and zinc-air battery

Single-atom catalysts (SACs) have opened up unprecedented possibilities for expediting oxygen reduction reaction (ORR) kinetics owing to their ultrahigh intrinsic activities. However, precisely controlling over the atomically dispersed metal-Nx sites on carbon support while fulfilling the utmost utilization of metal atoms remain the key obstacles. Here, atomically distributed Co-N4 sites anchored on N-doped carbon nanofibers aerogel (Co SAs/NCNA) is controllably attained through a direct pyrolysis of metal-chelated cellulose nanofibers (TOCNFs-Cd2+/Co2+) hydrogel precursor. The usage of Cd salt assists the assembly of cross-linked aerogel, creates a large number of interior micropores and defects, and favors the physical isolation of Co atoms. The hierarchically porous biomass carbon aerogel (2265.1 m2/g) offers an advantageous platform to facilitate accessibility of the catalytic centers, also renders rapid mass diffusion and electron-transfer paths throughout its 3D architecture. Notably, Co SAs/NCNA affords a paramount ORR activity and respectable durability when integrated into zinc-air battery devices.

High-temperature oxidation performance of Ni-based GH3536 superalloy fabricated by laser powder bed fusion

This study investigates the effect of microstructure on short-term and long-term oxidation behaviours of GH3536 superalloy fabricated by laser powder bed fusion (LPBF), in which the superalloy is isothermally oxidised at 950 °C for 6 h and 500 h in air. The LPBF sample exhibits improved oxidation resistance compared with a wrought counterpart after long-term exposure. The effect of microstructure diversity between LPBF and wrought samples on oxidation behaviour is discussed. The cellular structure produced during the LPBF process acts as a rapid diffusion path to accelerate the formation of a protective film in the initial stage, leading to an enhancement in oxidation resistance for extended exposure.

Effect of HfO2 framework on steam oxidation behavior of HfO2 doped Si coating at high temperatures

HfO2 doped Si is designed as bond coat material in thermal/environmental barrier coatings (TEBCs). In this work, the HfO2-Si composite coatings with different HfO2 contents were prepared by atmospheric plasma spraying (APS). The steam oxidation behavior of the coatings was comparatively studied at 1300 °C and 1400 °C. Volatilization of Si occurred during spraying, leading to the deviation of coating compositions. The sprayed coatings contained different HfO2 structures. During steam oxidation, HfSiO4 phase was formed at the SiO2/HfO2 interface by solid-state reaction between them. The HfSiO4 or HfO2/HfSiO4 mixture particles worked to deflect or pin micro-cracks, thus improving the resistance of the coating to cracking. At 1300 °C, a protective oxide scale was formed on the traditional Si coating or the HfO2-Si coating with isolated HfO2 particles. However, the HfO2-Si coating with inter-connected HfO2 framework revealed poor oxidation-resistance. At 1400 °C, accelerated oxidation degradation, steam corrosion volatilization, interface reaction and sintering occurred. The HfO2 framework structure played a dominating role in determining the steam oxidation resistance of the HfO2-Si coating, and the connected HfO2 framework and TGO network provided a rapid diffusion path for oxidants (H2O, O2− and OH−) and deteriorated the oxidation resistance.

Grain refinement and enhanced diffusion of W[sbnd]Cu gradient material processed by high pressure torsion with floating cavity

High-pressure torsion (HPT)processing with floating cavity was carried out under the applied pressure of 1.5 GPa with the revolution from 5 to 20 turns at the temperature of 300 °C, and the WCu gradient material with noble bonding interface and significant grain refinement was successfully obtained. The microstructure evolution and atomic diffusion around the bonding interface were analyzed by electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) in a field emission scanning electron microscope (SEM). The mechanism of large shear strain on the microstructure evolution and diffusion ability of tungsten and copper at the interface was investigated. The results show that HPT processing with floating cavity can effectively refine microstructure of tungsten and copper to submicron. After 5 turns of HPT deformation, the grain size of copper was significantly refined to 0.59 μm but experiences slight increases to 0.8 μm with the additional revolution number to 20 turns, and the ultrafine equiaxed grains with relatively straight grain boundaries and few dislocations within grains were formed under the continuous dynamic recrystallization mechanism. However, the microstructure of tungsten was continuously refined within 20 turns of HPT processing due to the accumulation shear deformation, and a lamellar microstructure was formed along the WCu bonding interface with a gradient distribution in the width of banded grains from 0.06 μm at the interface to 0.33 μm towards the tungsten matrix. In addition, with the increase of torsion strain, the diffusion lengths of tungsten and copper gradually increasing to 1.6 μm and 6.2 μm, the interdiffusion coefficient of tungsten in copper remained basically constant, while the value of copper in tungsten increases continuously. The high density of defects and ultrafine grains with high angle boundaries introduced by large shear deformation of 20 turns of HPT processing play roles in the rapid diffusion paths to accelerate the atom diffusion and the interdiffusion coefficient of tungsten and copper is enhanced by 0.48– 1.79× 108 times compared to the lattice diffusion.

A Dual‐Functional Titanium Nitride Chloride Layered Matrix with Facile Lithium‐Ion Diffusion Path and Decoupled Electron Transport as High‐Capacity Anodes

AbstractIntercalation typed electrodes are expected with low theoretical capacity, which falls behind their high rate performance and stability. In this work, α‐TiNCl, an isoelectronic system of TiO2, is designed as a promising high‐capacity intercalation anode. TiNCl features are layered TiN backbone terminated by Cl atoms. While the rocksalt TiN backbones function as electron conductors, the interlayer voids provide Cl‐coordinated Li+ sites without strong Li‐Ti repulsion, which proves to be a rapid diffusion path with a low energy barrier (0.06 vs 0.47 eV of TiO2). Therefore, a dual‐functional TiNCl matrix is established for Li+ and e– transport. To stabilize the layered structure, TiNCl is scaffolded by an in situ grown TiO2 coating, which also serves as an electron reservoir during lithiation. The TiNCl‐TiO2 anode exhibits significantly large Li+ intercalation capacity (243% of TiO2) and outstanding battery performance (231 mA h g–1 at ≈17 C for 2500 cycles, 94 mA h g–1 at ≈34 C for 10 000 cycles). The (+) LiCoO2 || TiNCl‐TiO2 (–) full battery maintains 170 mA h g–1 for 300 cycles. This work may shed light on the molecular engineering of new compounds for electrodes.

Effect of shot-peening on corrosion behavior of austenitic steel in supercritical carbon dioxide at 700 °C

The contribution of shot-peening treatment on the corrosion resistance of Sanicro 25 exposed to supercritical carbon dioxide (S-CO2) at 700 °C and 15 MPa was investigated. Complex corrosion layers formed on shot-peened Sanicro 25 were approximately ten times thicker than those formed on non-peened Sanicro 25. Rapid diffusion paths induced by shot-peening treatment accelerated inward diffusion of C, resulting in the formation of subsurface carbide-containing core/shell structure precipitates. Increased voids in shot-peened Sanicro 25 and the stress concentration promoted scale spallation after exposure. In summary, shot-peened Sanicro 25 exhibited worse corrosion resistance compared to non-peened Sanicro 25 in 1000 h.

In-situ reconstruction of spinel interface on Li-rich layered cathode with improved electrochemical performances

The produced inactive interface during the cycle and poor rate performance are the inevitable obstacles for the practicability of lithium-rich layered cathode. Here, we report that in-situ surface pretreatment technique with hydrazine hydrate can reconstruct epitaxial spinel possessing the rapid lithium ions diffusion path, which primarily includes the leaching of Li+/Ni2+ and redistribution of the metal ions. We confirm the generation of epitaxial spinel heterostructure on the layered matrix by kinds of characterization methods such as transmission electron microscopy and Raman spectroscopy. As a result, the epitaxial spinel substantially promotes the lithium ion diffusion coefficient from 1.98 × 10−11 cm2 s−1 to 3.76 × 10−11 cm2 s−1. Even under a discharge current 5 C, the reversible capacity still reaches up to 171.1 mAh g−1. After 200 cycles at 1 C, the modified cathode delivers a capacity retention of 84.2% with the discharge capacity of 197.8 mAh g−1. The presence of the epitaxial spinel layer exerts a positive effect on the stability of the cathode structure and suppression of side reactions at the interface via exploring the morphology and composition of the cycled cathodes. The in-situ surface reconstruction technology to generate spinel is appealing for promise prospect application of lithium-rich layered cathodes in the future.

Effect of explosive compaction on microstructure of ODS FeCrAl alloy fabricated by oxidation method

A fabrication process of 14Cr ODS FeCrAl alloy including direct oxidation treatment, explosive compaction and vacuum post-sintering was proposed herein. A thin oxide layer formed on the powder surface during a low-temperature oxidation treatment was crushed in the explosive compaction, resulting in the redistribution of oxides at prior powder boundary (PPB) and the subsequent formation of an exclusive iron oxide layer between the grains of compacted materials. A large number of defects (dislocations and grain boundaries) were also produced in the compacted particles. Through characterizing the evolution of oxide dispersoids during the course of fabrication, the contribution of explosive compaction to dislocations, nanoscale precipitates and mechanical properties was clarified. The results show that the iron oxide layer became the container for transporting oxygen and was dissolved during the post-sintering, which affected the composition of nanoscale precipitates. The high-density dislocations not only became the rapid diffusion paths of oxygen, aluminum and yttrium atom, but also became the preferential sites of Y-Al-O precipitation. With the manufacturing method, the more uniform distribution of oxide nanoparticles and the higher microhardness of ODS alloy were obtained.

GeS2 nanocomposite space-confined in an interconnected spherical graphene framework as advanced anodes for lithium storage

Although owing ultrahigh theoretic capacity, the development of germanium sulfide-based anode is severely hindered by its poor conductivity and inferior stability derived from the large volume variation, which is hardly satisfied with the vigorous demand for the high-performance lithium storage. Herein, a reliable and self-assembly synthetic technique is proposed for in-situ growth of GeS2 nanograins homogeneously distributed on interconnected spherical graphene framework, constructing a three-dimensional (3D) conductive network (GeS2@PS-G). Benefiting from the synergistic strategy of delicately-designed structure and optimized composition, the unique hierarchical GeS2@PS-G can effectively relieve the electrode pulverization and agglomeration, thus maintaining the structural integrity. Moreover, the 3D graphene framework provides rapid ions diffusion path, enabling to achieve the maximum conductivity. Systematic electrochemical results demonstrate that such GeS2@PS-G nanohybrid yields an ultrahigh reversible capacity (1172 mAh g−1 at 0.1 A g−1) and outstanding cycling stability (985 mAh g−1 at 1.0 A g−1 over 1600 cycles) for Li-storage, presenting the best reported performance to date. Notably, the detailed analysis of structural evolution and reaction mechanism of GeS2@PS-G are clearly articulated by in-situ X-ray diffraction investigation. These findings provide an insight to explore and develop high-performance anodes for next-generation energy storage.

Free-standing and flexible graphene supercapacitors of high areal capacitance fabricated by laser holography reduction of graphene oxide

Photoreduction of graphene oxide (GO) holds great potential for developing graphene-based electrodes for high-performance supercapacitors (SCs). However, the insufficient micro-nanostructure on photoreduced GO (PRGO) restricts its electrochemical performance. Here, a hierarchically structured PRGO-based planar SC is reported by combining two-beam-laser-interference with the masking technique. The hierarchical structures improve the surface area between PRGO and electrolyte and contribute to format electric double-layer capacitors. Planar device structures with PRGO-based interdigital finger current collectors are beneficial for rapid ion diffusion paths. As a result, the hierarchically structured PRGO-based planar SC achieves an areal capacitance of 3.97 mF cm−2 at 10 mV s−1. The proposed strategy of employing hierarchically structured PRGO in the planar SC design offers a new route for manufacturing high-performance integrated energy storage devices.

Enhanced age hardening response and precipitation evolution of elastic stress aged Mg–Zn alloys

How to improve the age hardening response of Mg alloys in economical and effective ways is an important and interesting issue. The age hardening response and precipitation evolution of Mg–Zn alloys with and without external elastic stress are investigated. Microstructural observations of stress-free aged samples show that the low hardness is mainly due to the low number density and relatively small aspect ratio of β1′ precipitates, while a large number of nano-scale strengthening β1′ precipitates appear in the α-Mg matrix at the early stage of stress aging. In addition, the aspect ratio of β1′ precipitates in the stress aged samples is evidently higher than that of the stress-free aged samples at the same peak aged stage. Abundant dislocations introduced by the applied stress act as nucleation sites of precipitates and rapid diffusion path of solutes, which are mainly responsible for the remarkable increment in hardness and promoted kinetics. Precipitate-free zones ( PFZs) are observed in both samples with and without stress. In the stress aged samples, the formation of PFZs is mainly controlled by the motion of dislocations, which is different from the solute-vacancy depletion mechanism in the stress-free samples. Results imply that the external stress plays a similar role to that of commonly used methods in reducing the size, increasing the density, and promoting the precipitation kinetics, but has a negligible stress-orienting effect on the precipitate evolution.

In situ encapsulation of Co/Co3O4 nanoparticles in nitrogen-doped hierarchically ordered porous carbon as high performance anode for lithium-ion batteries

This work explores the fabrication of Co/Co3O4 nanoparticles encapsulated in nitrogen-doped hierarchically ordered porous carbon (Co/Co3O4/NHPC) and investigates their electrochemical performance for lithium-ion batteries (LIBs). Co/Co3O4/NHPC is obtained from a typical dual-template (silica opal is employed as a hard template and F127 (EO106PO70EO106) acts as a soft template to guide the mesoporous structure) by taking advantage of resol (phenol/formaldehyde) as carbon source, dicyandiamide as nitrogen source, and cobalt nitrate as cobalt source. We have optimized the performance of Co/Co3O4/NHPC composite base on the contents of Co/Co3O4 in composite. 0.6-Co/Co3O4/NHPC (0.6 g cobalt nitrate in precursor solution) demonstrates a high discharge capacity (1823 mAh g−1 after 200 cycles at 0.2 A g−1), excellent cycling stability, and high-rate capability (1313/1056/576 mAh g−1 after 500 cycles at 2/5/10 A g−1). This outstanding LIB anode performance can be attributed to the hierarchically ordered porous carbon that could effectively provide rapid diffusion path way for electrolyte and metallic Co that could accelerate the transmission of electrons.