Kirkendall Diffusion Research Articles

Hollow/porous-walled SnO2 via nanoscale Kirkendall diffusion with irregular particles

Hollow/porous structured SnO2 nanoparticles were synthesized by simple oxidation of dense metal chalcogenide precursors via nanoscale Kirkendall diffusion effect. First, tin chalcogenide (SnS, SnSe) nanoparticles were synthesized by mechanochemical method, which is considered a facile, scalable, and eco-friendly process. Hollow/porous-walled SnO2 nanoparticles were synthesized by simple oxidation of the prepared Sn chalcogenide precursors, for which the transformation mechanism was verified in detail. Nanoscale Kirkendall diffusion process was thoroughly investigated by morphological, crystallographic, and elemental analyses performed at various oxidation temperatures and times. To examine the morphological effect of hollow/porous-walled SnO2 nanoparticles on the electrochemical performance, the synthesized nanoparticles were applied as anode material in a lithium-ion battery. Anode material showed highly improved electrochemical properties compared to its dense counterpart, with 83% capacity retention from the second cycle at the 400th cycle and capacity of 302 mA h g−1 at a high current density of 30 A g−1.

Isothermal Diffusion Behavior and Surface Performance of Cu/Ni Coating on TC4 Alloy.

The poor surface performance of titanium alloys substantially limits their application in many fields, such as the petrochemical industry. To overcome this weakness, the Cu and Ni double layers were deposited on the surface of TC4 alloy by the electroplating method, and the isothermal diffusion process was performed at 700 °C to enhance the binding ability between Cu and Ni layers. The isothermal diffusion behavior and microstructure of the coating were systematically analyzed, and tribological property and corrosion resistance of the coating were also evaluated to reveal the influence of isothermal diffusion on the surface performance. It was shown that multiple diffusion layers appeared on the Cu/Ni and Ni/Ti interface, and that NixTiy and CuxTiy phases were formed in the coating with the increase of diffusion time. More importantly, Kirkendall diffusion occurred when the diffusion time increased, which led to the formation of continuous microvoids and cracks in the diffusion layer, weakening the surface performance of the Cu/Ni coatings. This paper unveils the relationship between the microstructure of the Cu/Ni coatings and isothermal diffusion behavior, providing guidelines in preparing high performance surface coatings.

Hollow/Porous-Walled SnO₂ via Nanoscale Kirkendall Diffusion with Irregular Particles

Hollow/porous structured SnO₂ nanoparticles were synthesized by simple oxidation of dense metal chalcogenide precursors via nanoscale Kirkendall diffusion effect. First, tin chalcogenide (SnS, SnSe) nanoparticles were synthesized by mechanochemical method, which is considered a facile, scalable, and eco-friendly process. Hollow/porous-walled SnO₂ nanoparticles were synthesized by simple oxidation of the prepared Sn chalcogenide precursors, for which the transformation mechanism was verified in detail. Nanoscale Kirkendall diffusion process was thoroughly investigated by morphological, crystallographic, and elemental analyses performed at various oxidation temperatures and times. To examine the morphological effect of hollow/porous-walled SnO₂ nanoparticles on the electrochemical performance, the synthesized nanoparticles were applied as anode material in a lithium-ion battery. Anode material showed highly improved electrochemical properties compared to its dense counterpart, with 83% capacity retention from the second cycle at the 400th cycle and discharge capacity of 302 mA h g⁻¹ at a high current density of 30 A g⁻¹.

Ni2+ guided phase/structure evolution and ultra-wide bandwidth microwave absorption of CoxNi1-x alloy hollow microspheres

A series of bimetallic hexagonal close-packed (HCP) and face-centered cubic (FCC) CoxNi1−x (x = 1, 0.858, 0.813, 0.714, 0.662, 0.137) alloy hollow microspheres (AHMs) with continuously tunable composition and wall thickness were successfully synthesized via one-pot liquid phase reduction. In addition to prolonged reaction time, decreased metal ion concentration, and elevated reaction temperature, Ni2+ addition favors an inside-out Ostwald ripening and Kirkendall diffusion, leading to the formation of CoxNi1−x AHMs with thin wall thickness. Moreover, Ni2+ addition induced the phase transformation from HCP Co to FCC Co and modulated crystal size, internal strain, lattice constant, composition, and wall thickness. Accordingly, Ms decreased linearly as Ni content increased. Alloying of Ni with Co induced significantly enhanced μ″, negative ε′ and ultra-wide bandwidth microwave absorption due to the Plasmon resonance, defect polarization and lattice polarization. The wax-based composites containing 35 wt% Co0.81Ni0.19, 45 wt% Co0.86Ni0.14, or 50 wt% Co0.66Ni0.34 AHMs possessed significantly enhanced absorption capability with maximum RL values of −35.3, −47.3, and −54.6 dB and ultra-wide bandwidths (RL ≤ −10 dB) of 8.16, 9.2, and 10.08 GHz, corresponding to layer thicknesses of 1.9, 1.8, and 2.6 mm, respectively. CoxNi1−x AHMs exhibited stronger absorption, broader bandwidth, and lighter weight than those of other absorbers. Superior microwave absorption performance (MAP) were mainly creditable to the synergy of enhanced permittivity and permeability, high attenuation, and good impedance matching caused by hollow structure, Ni incorporation, and Plasmon resonance. CoxNi1−x AHMs with tunable Ms and excellent MAP might solve electromagnetic pollution and interference problems for further applications in microwave absorption and shielding fields.

Superior lithium-ion storage performances of SnO2 powders consisting of hollow nanoplates

Hierarchical structured transition metal oxides have attracted considerable attention as anode materials for lithium-ion batteries because they possess large surface area that can provide large contact area with the electrolyte and short diffusion distance for Li ions. Here, a hierarchical structured assembly of hollow SnO2 nanoplates is synthesized by one-step oxidation of SnS2 powders. The SnS2 powders comprising of dense nanoplates synthesized by the hydrothermal method transform into SnO2 powders comprising of hollow nanoplates by nanoscale Kirkendall diffusion at the oxidation temperature of 500 °C. After the transformation of SnS2 into SnO2 powders, the Brunauer-Emmett-Teller surface area of the powders increases from 22.8 to 82.7 m2 g−1. The hierarchical structured SnO2 powders show superior lithium-ion storage performances compared to SnS2 powders with the same structure. The discharge capacities of SnS2 and SnO2 powders at a current density of 1 A g−1 for the 300th cycle are 273 and 754 mA h g−1, respectively. The SnO2 powders show a high reversible capacity of 169 mA h g−1 even at an extremely high current density of 30 A g−1. The outstanding electrochemical properties of the SnO2 powders can be attributed to their unique morphological structure having hollow nanoplates and optimum crystallite size, which increases the contact area between the active materials and the electrolyte and the buffered stress caused by the volume expansion during cycling.

Thermodynamics of Dual Doping in Quantum Dots.

Dual doping is a powerful way to tailor the properties of semiconductor quantum dots (QDs) arising out of host-dopant and dopant-dopant interactions. Nevertheless, it has seldom been explored due to a variety of thermodynamic challenges, such as the differential bonding strength and diffusion constant within the host matrix that integrates with the host in dissimilar ways. This work discusses the challenges involved in administering them within the constraints of one host under similar conditions of temperature, time, and chemical parameters such as solubility and reactivity using CoPt-doped CdS QDs as a model system. In addition, the various forces in play, such as Kirkendall diffusion, solid- and liquid-state diffusion, hard acid soft base interaction with the host, and the effect of lattice strain due to lattice mismatch, are studied to understand the feasibility of the core to doped transformation. These findings suggest a potential approach for manipulating the properties of semiconductors by dual doping engineering.

In situ S-doped ultrathin gC3N4 nanosheets coupled with mixed-dimensional (3D/1D) nanostructures of silver vanadates for enhanced photocatalytic degradation of organic pollutants

A novel plasmonic Z-scheme sulphur doped gC3N4/Ag3VO4/β-AgVO3/Ag (SGA-x) hybrid quaternary photocatalyst was successfully fabricated via the ultrasonic assisted Kirkendall effect and diffusion processes followed by low temperature phase conversion.

Strategy for synthesizing mesoporous NiO polyhedra with empty nanovoids via oxidation of NiSe polyhedra by nanoscale Kirkendall diffusion and their superior lithium-ion storage performance

A novel strategy for the synthesis of mesoporous metal oxide polyhedra with empty nanovoids by introducing nanoscale Kirkendall diffusion into a spray pyrolysis process is suggested. In this study, NiSe polyhedra with high index facets synthesized by one-pot spray pyrolysis were transformed into mesoporous NiO polyhedra with empty nanovoids by a facile oxidation process at 500 °C through nanoscale Kirkendall diffusion. Details of the formation mechanism of these uniquely structured NiO polyhedra were also studied. In the initial oxidation step, a thin NiO layer was formed on the surface of the NiSe polyhedra. The fast diffusion of Ni cations out through the NiO layer and the melting of the remaining metalloid Se formed a porous Se layer. The formation of a mesoporous NiO layer then enabled the penetration of oxygen gas by gas phase diffusion. The diffusion of metalloid Se into the mesopores of NiO and its reaction with oxygen gas formed SeO2 nanocrystals which then evaporated into the gas phase. The step-by-step oxidation of the NiSe crystals therefore resulted in mesoporous NiO polyhedra with empty nanovoids. When used as an anode material in a lithium ion battery, mesoporous NiO polyhedra with empty nanovoids showed superior cycling and rate performance compared to anodes fabricated from dense-structured NiSe polyhedra and commercial NiO nanopowders. The mesoporous NiO polyhedra showed a high discharge capacity of 1072 mA h g−1 after 200 cycles at a current density of 1.0 A g−1 and they showed a high reversible capacity of 453 mA h g−1, even at a high current density of 15.0 A g−1.

Thickness-dependent photoelectrochemical properties of a semitransparent Co3O4 photocathode

Co3O4 has been widely studied as a catalyst when coupled with a photoactive material during hydrogen production using water splitting. Here, we demonstrate a photoactive spinel Co3O4 electrode grown by the Kirkendall diffusion thermal oxidation of Co nanoparticles. The thickness-dependent structural, physical, optical, and electrical properties of Co3O4 samples are comprehensively studied. Our analysis shows that two bandgaps of 1.5 eV and 2.1 eV coexist with p-type conductivity in porous and semitransparent Co3O4 samples, which exhibit light-induced photocurrent in photoelectrochemical cells (PEC) containing the alkaline electrolyte. The thickness-dependent properties of Co3O4 related to its use as a working electrode in PEC cells are extensively studied and show potential for the application in water oxidation and reduction processes. To demonstrate the stability, an alkaline cell was composed for the water splitting system by using two Co3O4 photoelectrodes. The oxygen gas generation rate was obtained to be 7.17 mL·h−1 cm−1. Meanwhile, hydrogen gas generation rate was almost twice of 14.35 mL·h−1·cm−1 indicating the stoichiometric ratio of 1:2. We propose that a semitransparent Co3O4 photoactive electrode is a prospective candidate for use in PEC cells via heterojunctions for hydrogen generation.

Superior electrochemical properties of micron-sized aggregates of (Co0.5Fe0.5)3O4 hollow nanospheres and graphitic carbon

Morphology-controlled micron-sized aggregates consisted of hollow nanospheres and graphitic carbon are considered to be efficient electrode materials for lithium-ion batteries because the advantages of hollow nanospheres are combined with those of micron-size powders with easy processability. In this study, carbon microspheres with extremely large surface area of 3350 m2 g−1 are successfully used as templates to synthesize (Co0.5Fe0.5)3O4-graphitic carbon (CoFeO-GC) composite microspheres, which in turn, are composed of hollow nanospheres. The CoFe alloy nanospheres act as catalyst in formation of graphitic carbon during reduction process and transform into metal oxide hollow nanospheres after oxidation by nanoscale Kirkendall diffusion. Owing to their unique structure, CoFeO-GC composite microspheres show lithium-ion storage performances superior to those of the CoFeO-amorphous carbon composites with ultrafine nanocrystals and dense structure. The CoFeO-GC composite microspheres have extremely high capacities of 1072 and 681 mA h g−1 at current densities of 1 and 3 A g−1, respectively, after 350 cycles. This hybrid structure employs synergistic effect of the hollow nanosphere aggregate and high content of graphitic carbon with high electrical conductivity, resulting in superior cycling and rate performances, when tested as anode materials for lithium-ion batteries.

Galvanic Replacement-Driven Transformations of Atomically Intermixed Bimetallic Colloidal Nanocrystals: Effects of Compositional Stoichiometry and Structural Ordering.

Galvanic replacement reactions dictated by deliberately designed nanoparticulate templates have emerged as a robust and versatile approach that controllably transforms solid monometallic nanocrystals into a diverse set of architecturally more sophisticated multimetallic hollow nanostructures. The galvanic atomic exchange at the nanoparticle/liquid interfaces induces a series of intriguing structure-transforming processes that interplay over multiple time and length scales. Using colloidal Au-Cu alloy and intermetallic nanoparticles as structurally and compositionally fine-tunable bimetallic sacrificial templates, we show that atomically intermixed bimetallic nanocrystals undergo galvanic replacement-driven structural transformations remarkably more complicated than those of their monometallic counterparts. We interpret the versatile structure-transforming behaviors of the bimetallic nanocrystals in the context of a unified mechanistic picture that rigorously interprets the interplay of three key structure-evolutionary pathways: dealloying, Kirkendall diffusion, and Ostwald ripening. By deliberately tuning the compositional stoichiometry and atomic-level structural ordering of the Au-Cu bimetallic nanocrystals, we have been able to fine-maneuver the relative rates of dealloying and Kirkendall diffusion with respect to that of Ostwald ripening through which an entire family of architecturally distinct complex nanostructures are created in a selective and controllable manner upon galvanic replacement reactions. The insights gained from our systematic comparative studies form a central knowledge framework that allows us to fully understand how multiple classic effects and processes interplay within the confinement by a colloidal nanocrystal to synergistically guide the structural transformations of complex nanostructures at both the atomic and nanoparticulate levels.

Design and Synthesis of Spherical Multicomponent Aggregates Composed of Core-Shell, Yolk-Shell, and Hollow Nanospheres and Their Lithium-Ion Storage Performances.

Micrometer-sized spherical aggregates of Sn and Co components containing core-shell, yolk-shell, hollow nanospheres are synthesized by applying nanoscale Kirkendall diffusion in the large-scale spray drying process. The Sn2 Co3 -Co3 SnC0.7 -C composite microspheres uniformly dispersed with Sn2 Co3 -Co3 SnC0.7 mixed nanocrystals are formed by the first-step reduction of spray-dried precursor powders at 900 °C. The second-step oxidation process transforms the Sn2 Co3 -Co3 SnC0.7 -C composite into the porous microsphere composed of Sn-Sn2 Co3 @CoSnO3 -Co3 O4 core-shell, Sn-Sn2 Co3 @CoSnO3 -Co3 O4 yolk-shell, and CoSnO3 -Co3 O4 hollow nanospheres at 300, 400, and 500 °C, respectively. The discharge capacity of the microspheres with Sn-Sn2 Co3 @CoSnO3 -Co3 O4 core-shell, Sn-Sn2 Co3 @CoSnO3 -Co3 O4 yolk-shell, and CoSnO3 -Co3 O4 hollow nanospheres for the 200th cycle at a current density of 1 A g-1 is 1265, 987, and 569 mA h g-1 , respectively. The ultrafine primary nanoparticles with a core-shell structure improve the structural stability of the porous-structured microspheres during repeated lithium insertion and desertion processes. The porous Sn-Sn2 Co3 @CoSnO3 -Co3 O4 microspheres with core-shell primary nanoparticles show excellent cycling and rate performances as anode materials for lithium-ion batteries.

Rational design and synthesis of hierarchically structured SnO2 microspheres assembled from hollow porous nanoplates as superior anode materials for lithium-ion batteries

Herein, hierarchically structured SnO2 microspheres are designed and synthesized as an efficient anode material for lithium-ion batteries using hollow SnO2 nanoplates. Three-dimensionally ordered macroporous (3-DOM) SnOx-C microspheres synthesized by spray pyrolysis are transformed into hierarchically structured SnO2 microspheres by a two-step post-treatment process. Sulfidation produces hierarchically structured SnS-SnS2-C microspheres comprising tin sulfide nanoplate and carbon building blocks. A subsequent oxidation process produces SnO2 microspheres from hollow SnO2 nanoplate building blocks, which are formed by Kirkendall diffusion. The discharge capacity of the hierarchically structured SnO2 microspheres at a current density of 5 A·g−1 for the 600th cycle is 404 mA·h·g−1. The hierarchically structured SnO2 microspheres have reversible discharge capacities of 609 and 158 mA·h·g−1 at current densities of 0.5 and 30 A·g−1, respectively. The ultrafine nanosheets contain empty voids that allow excellent lithium-ion storage performance, even at high current densities.

Application of Porous Nanofibers Comprising Hollow α-Fe 2 O 3 Nanospheres Prepared by Applying Both PS Template and Kirkendall Diffusion Effect for Anode Materials in Lithium-ion Batteries

Application of Porous Nanofibers Comprising Hollow α-Fe 2 O 3 Nanospheres Prepared by Applying Both PS Template and Kirkendall Diffusion Effect for Anode Materials in Lithium-ion Batteries

Lithium-ion storage performances of sunflower-like and nano-sized hollow SnO2 spheres by spray pyrolysis and the nanoscale Kirkendall effect.

Nanostructured metal selenides with a variety of morphologies are crucial for fabricating porous, hollow metal-oxide nanomaterials by nanoscale Kirkendall diffusion. Herein, SnSe-SnO2 composite powders and SnSe nanospheres were synthesized via one-pot spray pyrolysis by optimizing the concentration of the Se precursor in the spray solution; these were then used to fabricate sunflower-like SnO2 and hollow SnO2 nanospheres, respectively, via nanoscale Kirkendall diffusion. Post-treatment of the SnSe-decorated SnO2 under air produced sunflower-like SnO2, in which ray and disk florets consisting of hollow nanoplates and dense nanospheres, respectively, were present. The mean diameter of the homogeneous hollow SnO2 nanospheres was 150 nm. The hollow morphology shortens the diffusion length, increasing the contact area between the electrolyte and voids and buffering large volume changes during repeated cycling. As anode materials for lithium-ion batteries, the hollow SnO2 nanospheres showed excellent cycling and rate performances. The discharge capacity of the hollow SnO2 nanospheres, after 500 cycles from 0.001 V to 3.0 V, was 1043 mA h g-1, at a current density of 3.0 A g-1. The hollow SnO2 nanospheres showed a high reversible capacity of 638 mA h g-1, even at current density as high as 10 A g-1.

Electrochemical properties of uniquely structured Fe2O3 and FeSe2/graphitic-carbon microrods synthesized by applying a metal-organic framework

Uniquely structured Fe2O3 and FeSe2/graphitic-carbon (GC) microrods composed of hollow Fe2O3 and FeSe2 nanospheres, respectively, were successfully prepared by applying a metal-organic framework (MOF, MIL-88) as the precursor and template. This strategy involves the fabrication of Fe@GC microrods by the thermal reduction of MIL-88 microrods followed by transformation into hollow Fe2O3 nanosphere aggregate (H-Fe2O3-NSA) microrods and hollow FeSe2 nanosphere aggregate/GC (H-FeSe2/GC) microrods by means of oxidation and selenization, respectively. During the post-treatment step, metallic Fe nanocrystals embedded in GC are converted into hollow metal compound nanospheres through nanoscale Kirkendall diffusion. This novel structure makes it possible to achieve a superior electrochemical performance by alleviating the volume variation and providing ample ion reaction sites. In addition, in the case of H-FeSe2/GC, the carbon framework not only prevents the structural collapse but also ensures sufficient electron transport during repeated cycles. Thus, the H-Fe2O3-NSA and H-FeSe2/GC microrods have high specific discharge capacities of 973 mA h g−1 after 400 cycles at 1 A g−1 and 587 mA h g−1 after 100 cycles at 0.2 A g−1 when applied as anode materials for lithium-ion and sodium-ion batteries, respectively.

Three-dimensional macroporous CNTs microspheres highly loaded with NiCo2O4 hollow nanospheres showing excellent lithium-ion storage performances

Three-dimensional macroporous carbon nanotubes microspheres highly loaded with phase-pure NiCo2O4 hollow nanospheres are synthesized by the spray pyrolysis process and are characterized for potential use in lithium-ion batteries. Polystyrene nanobead template and the nanoscale Kirkendall diffusion process are first combined and are applied to the spray pyrolysis process to form macroporous NiCo2O4/carbon nanotubes composite microspheres with extremely high rate performance as anode materials for lithium-ion batteries. Metallic NiCo2/carbon nanotubes composite microspheres—formed as intermediate products—are transformed into composite microspheres of phase-pure NiCo2O4 hollow nanospheres and carbon nanotubes by the nanoscale Kirkendall diffusion process. The mean size of the hollow NiCo2O4 nanospheres decorated on the carbon nanotubes backbone is 28 nm. The macroporous NiCo2O4/carbon nanotubes composite microspheres have discharge capacities of 840, 748, 677, 591, 514, 451, 391, 337, and 289 mA h g−1 at current densities of 0.5, 1, 2, 5, 10, 15, 20, 25, and 30 A g−1, respectively. The discharge capacity of the macroporous NiCo2O4/carbon nanotubes microspheres for the 500th cycle at a current density of 3 A g−1 is 572 mA h g−1. The uniquely structured hollow NiCo2O4 nanosphere/carbon nanotubes composite microspheres have superior cycling and rate performances for lithium-ion storage.

Synthesis of barium-strontium titanate hollow tubes using Kirkendall effect

(BaSr)TiO3 hexagonal hollow tubes was fabricated by a solid-state interfacial reaction including a Kirkendall diffusion. Using a co-precipitation and sol-gel process, a core@shell structure of (BaSr)CO3@TiO2 rods were prepared, and then converted to (BaSr)TiO3 hollow tubes at 750 °C. This was a first achievement of single-phase crystal hollow tube. Here, the inner diameter and wall thickness of hollow tube were about 700 nm and 130 nm, respectively. The fabrication of (BaSr)TiO3 hollow tubes was monitored with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to investigate their formation mechanism. The present synthetic approach would provide a new insight into the design and fabrication of hollow architectures of many perovskite oxides.

Facile synthesis of porous forsterite nanofibres by direct electrospinning method based on the Kirkendall effect

Porous forsterite nanofibres were prepared by direct electrospinning method. The phase composition, morphology and pore structure of nanofibres were characterized. The porous nanofibres had high-purity for forsterite phase, mesoporous structure and a high specific surface area of 31.1m2g−1. The porous formation in forsterite nanofibres was driven by the Kirkendall diffusion effect. As the Mg ions diffused into SiO2 component faster, the forsterite phase formed on the silica side, and the previous voids occupied by Mg ions left behind and evolved into the Kirkendall pore structure. The porous forsterite nanofibres had a low thermal conductivity of 0.0463W/m·K, indicating a potential application for thermal insulation.

Metal–organic framework-templated hollow Co3O4 nanosphere aggregate/N-doped graphitic carbon composite powders showing excellent lithium-ion storage performances

Hollow Co3O4 nanosphere aggregate/N-doped graphitic carbon (HCO/NGC) composite powders, exhibiting excellent Li-ion storage performances, were prepared by applying metal–organic frameworks (MOFs). Zeolitic imidazolate framework (ZIF)-67 cubes were reduced to produce Co/NGC composite powders. The Co/NGC composite powders were oxidized to produce cubic HCO/NGC composite powders, in which the hollow Co3O4 nanospheres were uniformly covered with a NGC layer. The Co nanocrystals transformed into hollow nanospheres during oxidation via the nanoscale Kirkendall diffusion process. The unique composite structure accommodates mechanical stress owing to the void spaces within the Co3O4 nanospheres; it also prevents structure collapse during cycling owing to the presence of the NGC matrix. Thus, the cubic hollow powders exhibited excellent electrochemical performances when used as an anode material in Li-ion batteries (LIBs). Following 250cycles, the HCO/NGC composite powders with 11wt% NGC delivered a discharge capacity of 1030mAhg−1 at a current density of 1Ag−1. In addition, the composite powders delivered a discharge capacity of 738mAhg−1 even at a high current density of 10Ag−1.