Pressure-Modulated Interface Engineering toward Realizing Core@Shell Configuration Transition.

The strained interface of core@shell nanocrystals (NCs) can effectively modulate the energy level alignment, thereby significantly affecting the optical properties. Herein, the unique photoluminescence (PL) response of doped Mn ions is introduced as a robust probe to detect the targeted pressure-strain relation of CdS@ZnS NCs. Results show that the core experiences actually less pressure than the applied external pressure, attributed to the pressure-induced optimized interface that reduces the compressive strain on core. The pressure difference between core and shell increases the conduction band and valence band offsets and further achieves the core@shell configuration transition from quasi type II to type I. Accordingly, the PL intensity of CdS@ZnS NCs slightly increases, along with a faster blue-shift rate of PL peak under low pressure. This study elucidates the interplay between external physical pressure and interfacial chemical stress for core@shell NCs, leading to precise construction of interface engineering for practical applications.

Harvesting PdH Employing Pd Nano Icosahedrons via High Pressure.

Palladium hydrides (PdHx ) have important applications in hydrogen storage, catalysis, and superconductivity. Because of the unique electron subshell structure of Pd, quenching PdHx materials with more than 0.706 hydrogen stoichiometry remains challenging. Here, the 1:1 stoichiometric PdH ( F m 3 ¯ m ) $Fm\bar{3}m)$ is successfully synthesized using Pd nano icosahedrons as a starting material via high-pressure cold-forging at 0.2 GPa. The synthetic initial pressure is reduced by at least one order of magnitude relative to the bulk Pd precursors. Furthermore, PdH is quenched at ambient conditions after being laser heated ≈2000 K under ≈30 GPa. Corresponding ab initio calculations demonstrate that the high potential barrier of the facets (111) restricts hydrogen atoms' diffusion, preventing hydrogen atoms from combining to generate H2 . This study paves the way for the high-pressure synthesis of metal hydrides with promising potential applications.

Stabilizing Interface pH by Mixing Electrolytes for High-Performance Aqueous Zn Metal Batteries.

Aqueous zinc metal batteries with mild acidic electrolytes are considered promising candidates for large-scale energy storage. However, the Zn anode suffers from severe Zn dendrite growth and side reactions due to the unstable interfacial pH and the absence of a solid electrolyte interphase (SEI) protective layer. Herein, a novel and simple mixed electrolyte strategy is proposed to address these problems. The mixed electrolytes of 2 M ZnSO4 and 2 M Zn (CF3 SO3 )2 can efficiently buffer the interfacial pH and induce the in situ formation of the organic-inorganic SEI layer, which eliminates dendrite growth and prevents side reactions. As a result, Zn anodes in mixed electrolyte exhibit a lifespan enhancement over 400 times, endure stable cycling over 270 h at a high DOD of 62% and achieve high Zn plating/stripping reversibility with an average CE of 99.5% for 1000 cycles at 1 mA cm-2 . The findings pave the way for developing practical electrolyte systems for Zn batteries.

Pressure-stimulus-responsive behaviors of core-shell InP/ZnSe nanocrystals: remarkable piezochromic luminescence and structural assembly.

Piezochromic luminescence materials with optical properties can be adjusted (the colors most sensitive to the human eye range from red to green) to provide powerful means for information acquisition in various applications. Inorganic quantum dots, typically based on heavy metals such as cadmium and lead, have congenital advantages as luminescence materials, including strong inoxidizability and excellent photoelectric properties. However, small band-gap shifts under pressure have hindered the development of inorganic-based piezochromic materials. Herein, we combined in situ high-pressure photoluminescence (PL) and absorption measurements with synchrotron X-ray scattering spectra to elucidate the remarkable modulation of optical properties and morphologies by pressure, particularly that of the piezochromic luminescence, in all-inorganic core-shell InP/ZnSe nanocrystals (NCs). We observed a stepwise PL color change from red to green, and an ultrabroad bandgap tunability of 0.46 eV was observed from 1.99 to 2.45 eV in the pressure range of 14.2 GPa for InP/ZnSe NCs. Moreover, two-dimensional (2D) InP/ZnSe nanosheets were synthesized by the stress-driven attachment of nanoparticles. These results demonstrate the ability of the pressure-stimulus response to trigger remarkable piezochromic luminescence and 2D nanosheet assembly in InP/ZnSe NCs, which paves the way for new applications of all-inorganic InP-based semiconductor NCs.

New-phase retention in colloidal core/shell nanocrystals via pressure-modulated phase engineering.

Core/shell nanocrystals (NCs) integrate collaborative functionalization that would trigger advanced properties, such as high energy conversion efficiency, nonblinking emission, and spin-orbit coupling. Such prospects are highly correlated with the crystal structure of individual constituents. However, it is challenging to achieve novel phases in core/shell NCs, generally non-existing in bulk counterparts. Here, we present a fast and clean high-pressure approach to fabricate heterostructured core/shell MnSe/MnS NCs with a new phase that does not occur in their bulk counterparts. We determine the new phase as an orthorhombic MnP structure (B31 phase), with close-packed zigzagged arrangements within unit cells. Encapsulation of the solid MnSe nanorod with an MnS shell allows us to identify two separate phase transitions with recognizable diffraction patterns under high pressure, where the heterointerface effect regulates the wurtzite → rocksalt → B31 phase transitions of the core. First-principles calculations indicate that the B31 phase is thermodynamically stable under high pressure and can survive under ambient conditions owing to the synergistic effect of subtle enthalpy differences and large surface energy in nanomaterials. The ability to retain the new phase may open up the opportunity for future manipulation of electronic and magnetic properties in heterostructured nanostructures.

Effect of the Inherent Structure of Rh Nanocrystals on the Hydriding Behavior under Pressure.

Tailoring the inherent structure of materials is an effective way to improve the hydrogen storage capacity of metal materials. In this work, we report the effect of rhodium (Rh) nanocrystals (NCs) on the hydrogenation reaction. We found that Rh NCs could form rhodium monohydride (RhH) at a lower pressure than the bulk Rh because of its high specific surface area and structure defects. In addition, Rh NCs in the form of icosahedrons exhibited a much higher hydrogen absorption efficiency than Rh nanocubes. Furthermore, much smaller irregular Rh nanoparticles are even partially converted to RhH at lower pressure because of the nanosize effect. We thus believe that it is possible to design materials with excellent hydrogen storage properties under mild conditions.

Phosphine-free engineering toward the synthesis of metal telluride nanocrystals: the role of a Te precursor coordinated at room temperature.

A colloidal strategy offers opportunities for the rational design and synthesis of metal telluride nanocrystals (NCs) with the desired crystal structure, uniform geometry, and composition. However, it remains a challenge to use the paradigm to construct metal telluride NCs by a phosphine-free synthesis procedure for promising applications such as luminescence, photovoltaics and thermoelectricity. Here, we developed a new strategy for fabricating metal telluride nanocrystals, e.g. CdTe and PbTe NCs, by using a highly reactive phosphine-free Te precursor. The ability to reduce a TeO2 powder with dodecanethiol (DDT) has been achieved in the presence of oleylamine (OLA) to generate a soluble alkylammonium telluride at room temperature. We provide direct experimental evidence that the OLA-Te complexes were formed in an order of second magnitude kinetic process based on an in situ UV-vis absorption test. In the case of the CdTe NC system, the straightforward measurement of luminescence and the fabrication of LED devices are presented that can semiquantitatively assess the quality of preparation and the reactivity of this air-stable precursor. The proposed strategy highlights several unique features of this solution-based green chemistry that can be useful for synthesizing other metal telluride NCs to develop novel functional materials.

Moving to Aqueous Binder: A Valid Approach to Achieving High-Rate Capability and Long-Term Durability for Sodium-Ion Battery.

Polyanionic Na3V2(PO4)2F3 with a NASICON-type structure is heralded as a promising cathode material for sodium-ion batteries due to its fast ionic conduction, high working voltage, and favorable structural stability. However, a number of challenging issues remain regarding its rate capability and cycle life, which must be addressed to enable greater application compatibility. Here, a facile and effective approach that can be used to overcome these disadvantages by introducing an aqueous carboxymethyl cellulose (CMC) binder is reported. The resulting conductive network serves to accelerate the diffusion of Na+ ions across the interface as well as in the bulk. The strong binding force of the CMC and stable solid permeable interface protect the electrode from degradation, leading to an excellent capacity of 75 mA h g-1 at an ultrahigh rate of 70 C (1 C = 128 mA g-1) and a long lifespan of 3500 cycles at 30 C while sustaining 79% of the initial capacity value. A full cell based on this electrode material delivers an impressive energy density as high as 216 W h kg-1, indicating the potential for application of this straightforward and cost-effective route for the future development of advanced battery technologies.

Pressure Effects on Structure and Optical Properties in Cesium Lead Bromide Perovskite Nanocrystals.

Metal halide perovskites (MHPs) are gaining increasing interest because of their extraordinary performance in optoelectronic devices and solar cells. However, developing an effective strategy for achieving the band-gap engineering of MHPs that will satisfy the practical applications remains a great challenge. In this study, high pressure is introduced to tailor the optical and structural properties of MHP-based cesium lead bromide nanocrystals (CsPbBr3 NCs), which exhibit excellent thermodynamic stability. Both the pressure-dependent steady-state photoluminescence and absorption spectra experience a stark discontinuity at ∼1.2 GPa, where an isostructural phase transformation regarding the Pbnm space group occurs. The physical origin points to the repulsive force impact due to the overlap between the valence electron charge clouds of neighboring layers. Simultaneous band-gap narrowing and carrier-lifetime prolongation of CsPbBr3 trihalide perovskite NCs were also achieved as expected, which facilitates the broader solar spectrum absorption for photovoltaic applications. Note that the values of the phase change interval and band-gap red-shift of CsPbBr3 nanowires are between those for CsPbBr3 nanocubes and the corresponding bulk counterparts, which results from the unique geometrical morphology effect. First-principles calculations unravel that the band-gap engineering is governed by orbital interactions within the inorganic Pb-Br frame through structural modification. Changes of band structures are attributed to the synergistic effect of pressure-induced modulations of the Br-Pb bond length and Pb-Br-Pb bond angle for the PbBr6 octahedral framework. Furthermore, the significant distortion of the lead-bromide octahedron to accommodate the Jahn-Teller effect at much higher pressure would eventually lead to a direct to indirect band-gap electronic transition. This study enables high pressure as a robust tool to control the structure and band gap of CsPbBr3 NCs, thus providing insight into the microscopic physiochemical mechanism of these compressed MHP nanosystems.

Compressed few-layer black phosphorus nanosheets from semiconducting to metallic transition with the highest symmetry.

The high-pressure response of few-layer black phosphorus (BP) nanosheets remains elusive, despite the special interest in it particularly after the achievement of an exotic few-layer BP based field effect transistor. Here, we identified a pressure-induced reversible phase transition on few-layer BP nanosheets by performing in situ ADXRD and Raman spectroscopy with the assistance of DAC apparatus. The few-layer BP nanosheets transformed from orthorhombic semiconductors to simple cubic metal with increasing pressure, which is well interpreted using the pressure-induced inverse Peierls distortion. The obtained simple cubic BP nanosheets exhibited an enhanced isothermal bulk modulus of 147.0(2) GPa, and negative Grüneisen parameters that were attributed to the pressure-driven softening of phonon energies. Note that the simple cubic BP nanosheets adopted the highest symmetry which is in stark contrast to the general phase transformation under high pressure. First-principles calculations indicated that the metallic BP was significantly related to the band overlapped metallization, resulting from the traversing of density of states across the Fermi level at high pressure. Such findings paved a potential pathway to design targeted BP nanostructures with functional properties at extremes, and opened up possibilities for conceptually new devices.

Kinetically controlled synthesis of nanoporous Au and its enhanced electrocatalytic activity for glucose-based biofuel cells.

Nanoporous gold (NPG) structures, which possess abundant high-index facets, kinks, and steps, have been demonstrated as effective catalysts for the glucose electrooxidation in biofuel cells. Herein, we designed surface-clean NPG structures with high-index facets by a trisodium citrate (Na3Cit) self-initiated reduction of chloroauric acid (HAuCl4) in a water-ice bath followed by a kinetically controlled self-assembly manner. This strategy breaks through the traditional trisodium citrate thermal-reducing chloroauric acid approach where solutions are required to heat to a certain temperature for the reaction to initiate. However, herein, the surface-clean NPG structures yielded highly enhanced catalytic activity in glucose electrooxidation with approximately 9 A cm-2 mg-1 current density, which is over 20 times higher than that of Au nanoparticles devised by Turkevich (Turkevich-Au NPs) under the same conditions. This remarkable electrocatalytic activity could be ascribed to the large electrochemically active surface area, clean surface, and high-index facets or highly active sites of the porous structure. The employment of the surface-clean NPG with high-index facets for glucose electrooxidation promises a substantial improvement in the current biofuel cell technology and indicates the potential of biofuel cells in practical applications.

Cu Nanowires with Clean Surfaces: Synthesis and Enhanced Electrocatalytic Activity.

Low activity and high cost of electrocatalysts are the major challenge for the commercialization of the direct fuel cells (DFCs) and biofuel cells. In this work, we demonstrate the desirable "clean surfaces" effect of Cu nanocrystals in electrocatalysis. By a new reaction route of Cu2O nanospheres (Cu2O NSs), Cu nanowires (Cu NWs) with high purity and "clean surfaces" are first obtained under mild conditions. Benefiting from the path directing effects and abundant (100) facets, the as-prepared Cu NWs exhibit a lower overpotential to achieve the methanol electro-oxidation reaction (MOR) than that of analogous Cu nanoparticles (Cu NPs). Moreover, the "clean surfaces" provide more available active sites for the efficient transfer of electrons, enabling the Cu NWs to show their enhanced electrocatalytic activity. In the MOR, forward peak current density for the surface-cleaned Cu NWs is 2839 µA cm-2, which is ca. 6.45-fold higher than that of the Cu NWs with residual capping molecules on their surface. The "clean surfaces" effect can also be extended to the glucose electro-oxidation reaction (GOR), and the enhancement in specific surface area activity for the Cu NWs is 11.3-fold. This work enhances the electrocatalytic performance of Cu nanocrystals without the need for additional noble metals, which opens up new avenues for utilizing non-noble metals in the DFC or biofuel cell applications.

Alternative motif toward high-quality wurtzite MnSe nanorods via subtle sulfur element doping.

The manipulated synthesis of high-quality semiconductor nanocrystals (NCs) is of high significance with respect to the exploration of their properties and their corresponding applications. Nevertheless, the preparation of metastable-phase NCs still remains a great challenge due to their high kinetic barriers and harsh synthetic conditions. Herein, we demonstrated the fabrication of high-quality MnSe nanorods with a metastable wurtzite structure via a subtle sulfur-doping strategy. Based on the UV-vis absorption spectra, manganese polysulfide clusters were formed by mixing oleylamine-sulfur and oleylamine-manganese solutions at room temperature. The existence of manganese polysulfide clusters with polymeric sulfur structures makes the system more reactive, inducing fast wurtzite-phase nucleation. This can overcome the natural kinetic barrier of wurtzite MnSe and lead to subsequent growth of targeted NCs. On the other hand, no sulfur doping would produce MnSe NCs in a thermodynamically favorable rock-salt phase. As expected, different doping contents and sulfur sources also resulted in the formation of high-quality wurtzite MnSe nanorods. This success establishes that a facile strategy can be anticipated to synthesize high-quality metal chalcogenide NCs with a metastable phase, especially wurtzite nanorods, for potential applications from spintronics to solar cells.

Synthesis of dendritic iridium nanostructures based on the oriented attachment mechanism and their enhanced CO and ammonia catalytic activities.

Branched iridium nanodendrites (Ir NDs) have been synthesized by a simple method based on the oriented attachment mechanism. Transmission electron microscopy images reveal the temporal growth process from small particles to NDs. Precursor concentrations and reaction temperatures have a limited effect on the morphology of Ir NDs. Metal oxide and hydroxide-supported Ir NDs exhibit enhanced activity for catalytic CO oxidation. Particularly, the Fe(OH)x-supported Ir NDs catalyst with a 4 wt% Ir loading show superior CO oxidation catalytic activity with a full conversion of CO at 120 °C. Furthermore, compared with Ir NPs and commercial Ir black, Ir NDs exhibit higher activity and stability for ammonia oxidation. The specific activity and mass activity of Ir NDs for ammonia oxidation are 1.7 and 7 times higher than that of Ir NPs. The improved catalytic activities of Ir NDs are attributed not only to their large specific surface area, but also to their considerably high index facets and rich edge and corner atoms. Hence, the obtained Ir NDs provide a promising alternative for direct ammonia fuel cells and proton-exchange membrane fuel cells.

A one-step green route to synthesize copper nanocrystals and their applications in catalysis and surface enhanced Raman scattering.

A nontoxic, simple, inexpensive, and reproducible strategy, which meets the standard of green chemistry, is introduced for the synthesis of copper nanocrystals (Cu NCs) with olive oil as both reducing agent and capping agent. By changing the reaction parameters, the shape, size and surface structure of the Cu NCs can be well controlled. The obtained Cu nanocubes show excellent catalytic properties for the catalytic reduction of dyes and CO oxidation. Moreover, the prepared Cu nanocubes as substrates exhibit surface enhanced Raman scattering (SERS) activity for 4-mercaptopyridine (4-Mpy). Therefore, this facile route provides a useful platform for the fabrication of Cu NCs which have the potential to replace noble metals for certain applications.

Size-controlled synthesis of bifunctional magnetic and ultraviolet optical rock-salt MnS nanocube superlattices.

Wide-band-gap rock-salt (RS) MnS nanocubes were synthesized by the one-pot solvent thermal approach. The edge length of the nanocubes can be easily controlled by prolonging the reaction time (or aging time). We systematically explored the formation of RS-MnS nanocubes and found that the present synthetic method is virtually a combination of oriented aggregation and intraparticle ripening processes. Furthermore, these RS-MnS nanocubes could spontaneously assemble into ordered superlattices via the natural cooling process. The optical and magnetic properties were investigated using measured by UV-vis absorption, photoluminescence spectra, and a magnetometer. The obtained RS-MnS nanocubes exhibit good ultraviolet optical properties depending on the size of the samples. The magnetic measurements suggest that RS-MnS nanocubes consist of an antiferromagnetic core and a ferromagnetic shell below the blocking temperatures. Furthermore, the hysteresis measurements indicate these RS-MnS nanocubes have large coercive fields (e.g., 1265 Oe for 40 nm nanocubes), which is attributed to the size and self-assembly of the samples.

Synthesis and high-pressure transformation of metastable wurtzite-structured CuGaS2 nanocrystals.

The metastable wurtzite nanocrystals of CuGaS(2) have been synthesized through a facile and effective one-pot solvothermal approach. Through the Rietveld refinement on experimental X-ray diffraction patterns, we have unambiguously determined the structural parameters and the disordered nature of this wurtzite phase. The metastability of wurtzite structure with respect to the stable chalcopyrite structure was testified by a precise theoretical total energy calculation. Subsequent high-pressure experiments were performed to establish the isothermal phase stability of this wurtzite phase in the pressure range of 0-15.9 GPa, above which another disordered rock salt phase crystallized and remained stable up to 30.3 GPa, the highest pressure studied. Upon release of pressure, the sample was irreversible and intriguingly converted into the energetically more favorable and ordered chalcopyrite structure as revealed by the synchrotron X-ray diffraction and the high-resolution transmission electron microscopic measurements. The observed phase transitions were rationalized by first-principles calculations. The current research surely establishes a novel phase transition sequence of disorder → disorder → order, where pressure has played a significant role in effectively tuning stabilities of these different phases.

Electrical properties and behaviors of cuprous oxide cubes under high pressure.

An accurate in situ electrical resistivity measurement of cuprous oxide cubes has been conducted in a diamond anvil cell at room temperature with pressures up to 25 GPa. The abnormal electrical resistivity variation found at 0.7-2.2 GPa is attributed to the phase transformation from a cubic to a tetragonal structure. Three other discontinuous changes in the electrical resistivity are observed around 8.5, 10.3, and 21.6 GPa, corresponding to the phase transitions from tetragonal to pseudocubic to hexagonal to another hexagonal phase, respectively. The first-principles calculations illustrate that the electrical resistivity decrease of the tetragonal phase is not related to band-gap shrinkage but related to a higher quantity of electrons excited from strain-induced states increasing in band gap with increasing pressure. The results indicate that the Cu(2)O cubes begin to crush at about 15 GPa and completely transform into nanocrystalline at 25 GPa.

ZnO nanorod array/CuAlO2 nanofiber heterojunction on Ni substrate: synthesis and photoelectrochemical properties.

A novel ZnO nanorod array (NR)/CuAlO(2) nanofiber (NF) heterojunction nanostructure was grown on a substrate of Ni plates using sol-gel synthesis for the NFs and hydrothermal reaction for the NRs. Compared with a traditional ZnO/CuAlO(2) laminar film nanostructure, the photocurrent of this fibrous network heterojunction is significantly increased. A significant blue-shift of the absorption edge and a favorable forward current to reverse current ratio at applied voltages of -2 to +2 V were observed in this heterojunction with the increase of Zn(2+) ion concentration in the hydrothermal reaction. Furthermore, the photoelectrochemical properties were investigated and the highest photocurrent of 3.1 mA cm(-2) was obtained under AM 1.5 illumination with 100 mW cm(-2) light intensity at 0.71 V (versus Ag/AgCl). This novel 3D fibrous network nanostructure plays an important role in the optoelectronic field and can be extended to other binary or ternary oxide compositions for various applications.