Alloy Nanocrystals Research Articles

Fcc/hcp PtNi heterostructured alloy nanocrystals with ultrathin Pt shell for enhanced catalytic performance towards hydrogen evolution reaction

Fcc/hcp PtNi heterostructured alloy nanocrystals with ultrathin Pt shell for enhanced catalytic performance towards hydrogen evolution reaction

Deciphering the Atomic-Scale Structural Origin for Photoluminescence Quenching in Tin-Lead Alloyed Perovskite Nanocrystals.

The development of tin-lead alloyed halide perovskite nanocrystals (PNCs) is highly desirable for creating ultrastable, eco-friendly optoelectronic applications. However, the current incorporation of tin into the lead matrix results in severe photoluminescence (PL) quenching. To date, the precise atomic-scale structural origins of this quenching are still unknown, representing a significant barrier to fully realizing the potential of these materials. Here, we uncover the distinctive defect-related microstructures responsible for PL quenching using atomic-resolution scanning transmission electron microscopy and theoretical calculations. Our findings reveal an increase in point defects and Ruddlesden-Popper (RP) planar faults with increasing tin content. Notably, the point defects include a spectrum of vacancies and previously overlooked antisite defects with bromide vacancies and cation antisite defects emerging as the primary contributors to deep-level defects. Furthermore, the RP planar faults exhibit not only the typical rock-salt stacking pattern found in pure Pb-based PNCs but also previously undocumented microstructures rich in bromide vacancies and deep-level cation antisite defects. Direct strain imaging uncovers severe lattice distortion and significant inhomogeneous strain distributions caused by point defect aggregation, potentially breaking the local force balance and driving RP planar fault formation via lattice slippage. Our work illuminates the nature and evolution of defects in tin-lead alloyed halide perovskite nanocrystals and their profound impact on PL quenching, providing insights that support future material strategies in the development of less toxic tin-lead alloyed perovskite nanocrystals.

Crystal-Phase- and B-Content-Dependent Electrochemical Behavior of Pd─B Nanocrystals toward Oxygen Reduction Reaction.

The manipulation of crystal phases in metal-nonmetal interstitial alloy nanostructures has attracted considerable attention due to the formation of unique electronic structures and surface atomic arrangements, resulting in unprecedented catalytic performances. However, achieving simultaneous control over crystal phase and nonmetal elements in metal-nonmetal interstitial alloy nanostructures has remained a formidable challenge. Here, a novel synthesis approach is presented for Pd─B interstitial alloy nanocrystals (NCs) that allows investigation of the crystal-phase- and B-content-dependent catalytic performance. Through comparison of the oxygen reduction reaction (ORR) properties of Pd─BX interstitial alloy NCs with different crystal phases and B contents, achieved by precise control of reaction temperature and time, the influences of crystal phase and B contents in the Pd─BX interstitial alloy NCs on ORR are precisely investigated. The hexagonal closed packed (hcp) PdB0.5 NCs exhibit superior catalytic activity, with mass activities reaching 2.58 A mg-1, surpassing Pd/C by 10.3 times, attributed to synergistic effects by the hcp crystal phase and relatively high B contents. This study not only provides a novel approach to fabricate interstitial alloy nanostructures with unconventional crystal phases and finely controlled nonmetal elements but also elucidates the importance of crystal phase and nonmetal element content in optimizing electrocatalytic efficiency.

Spin occupancy regulation of the Pt d-orbital for a robust low-Pt catalyst towards oxygen reduction

Disentangling the limitations of O-O bond activation and OH* site-blocking effects on Pt sites is key to improving the intrinsic activity and stability of low-Pt catalysts for the oxygen reduction reaction (ORR). Herein, we integrate of PtFe alloy nanocrystals on a single-atom Fe-N-C substrate (PtFe@FeSAs-N-C) and further construct a ferromagnetic platform to investigate the regulation behavior of the spin occupancy state of the Pt d-orbital in the ORR. PtFe@FeSAs-N-C delivers a mass activity of 0.75 A mgPt−1 at 0.9 V and a peak power density of 1240 mW cm−2 in the fuel-cell, outperforming the commercial Pt/C catalyst, and a mass activity retention of 97%, with no noticeable current drop at 0.6 V for more than 220 h, is attained. Operando spectroelectrochemistry decodes the orbital interaction mechanism between the active center and reaction intermediates. The Pt dz2 orbital occupation state is regulated to t2g6eg3 by spin-charge injection, suppressing the OH* site-blocking effect and effectively inhibiting H2O2 production. This work provides valuable insights into designing high-performance and low-Pt catalysts via spintronics-level engineering.

Octahedral Nanocrystals of Ru-Doped PtFeNiCuW/CNTs High-Entropy Alloy: High Performance Toward pH-Universal Hydrogen Evolution Reaction.

Integrating high-entropy philosophy and nanocrystal-specific orientation into a single catalyst represents a promising strategy in development of high-performance catalysts. Nonetheless, shape-controlled synthesis of high-entropy alloy (HEA) nanocrystals is challenging owing to the distinct redox potentials and growth dynamics of metal elements. Herein, a one-pot co-reduction method is developed to fabricate ruthenium (Ru)-doped PtFeNiCuW octahedral HEA nanocrystals onto carbon nanotubes (Ru-PtFeNiCuW/CNTs). It is demonstrated that Ru dopants and W(CO)6 promote the concurrent reduction and growth of other metal precursors to obtain higher yield and larger size of HEA nanocrystals, despite low Ru content in Ru-PtFeNiCuW/CNTs. As an electrocatalyst toward hydrogen evolution reaction (HER), Ru-PtFeNiCuW/CNTs exhibits low overpotentials of 9, 16, and 34mV at a current density of 10mA cm-2 and Tafel slopes of 19.2, 27.9, and 23.1mV dec-1 in acidic, alkaline, and neutral electrolytes, respectively. As a cathodic catalyst, Ru-PtFeNiCuW/CNTs operates for up to 1500 and 1200 h in acidic and alkaline electrolyte, respectively, at a current density of 50mA cm-2 in a two-electrode system for full water splitting. Theoretical calculations reveal accelerated kinetics of H2O dissociation on W sites and *H desorption on hollow Cu-Cu-Cu and Cu-Cu-Pt sites.

C3N5 nanosheets decorated with Cu–Pt alloy nanoparticles toward efficient photocatalytic hydrogen evolution

The construction of highly efficient photocatalysts for generating high-purity hydrogen (H2) through a sustainable water decomposition system is a feasible option to replace conventional non-renewable energy resources. Here, we report a simple chemical reduction approach to embed Cu–Pt alloy nanocrystals on the C3N5 (CN) matrix, creating a Schottky heterojunction. The structural morphology, crystal phase, light-harvesting capacity, and photo-electrochemical properties of as-prepared heterostructures were investigated. The uniformly anchored Cu–Pt alloy nanocrystals improve the photocatalytic H2 evolution (PHE) activity by promoting the separation and transfer of photogenerated carriers and inhibiting recombination. Meanwhile, the alloyed nanocrystals strengthen the absorption of incident light energy, inducing photothermal energy. This improves the charge carrier separation and promotes the surface reaction kinetics. The PHE performance of as-developed catalysts could be adjusted by optimizing the molar ratio of Cu/Pt ions. Among them, the optimal Cu1Pt3/CN photocatalyst yields a higher PHE performance (672.85 μmol g−1 h−1). Notably, the Cu1Pt3/CN catalyst also reveals an enhanced photocatalytic activity for H2 evolution in natural seawater. The possible PHE mechanism in CuPt/CN heterostructures is discussed toward the role of CuPt alloy deposition in boosting photocatalytic efficiency.

Enhanced electrochemical detection of thrombin via a dual signal amplification strategy based on Au Nanoparticles@Carbon nanosheets and PtCu3 nanoparticles

Thrombin (TB) is an enzyme involved in blood coagulation and associated with various diseases such as thromboembolic disease, Alzheimer's disease, and cancer. This study introduces an electrochemical biosensor with a sandwich-type structure designed for the highly sensitive detection of TB. The working electrode (WE) was modified with gold nanoparticles loaded onto the carbonization product of two-dimensional Cu-bond tetrakis(4-carboxyphenyl)porphyrin (Cu-TCPP) nanosheets (referred to as Au@CNSs), enhancing the electrical conductivity and specific surface area of the WE. The modified electrode exhibited notable catalytic activity for H2O2 reduction. One aptamer of TB (Apt1), with a sulfhydryl group (-SH-) at the end, can tightly bound to Au@CNSs through a S-Au bond. Additionally, PtCu3 alloy nanocrystals, possessing high electrocatalytic activity towards H2O2 reduction, were prepared and modified with another TB aptamer (Apt2). In the presence of TB, a sandwich-type biosensing interface formed, resulting in an increased reduction current for H2O2. Under optimized conditions, the proposed aptasensor demonstrated a broad linear range from 0.01 pM to 32 nM and a low detection limit of 0.005 pM. Furthermore, the aptasensor exhibited excellent performance in terms of stability, reproducibility, and sensitivity, making it a promising tool for TB detection in human serum.

Unveiling the Growth Mechanism of Ordered-Phase within Multimetallic Nanoplates.

Tuning the crystal phase of alloy nanocrystals (NCs) offers an alternative way to improve their electrocatalytic performance, but, how heterometals diffuse and form ordered-phase remains unclear. Herein, for the first time, the mechanism for forming tetrametallic ordered-phase nanoplates (NPLs) is unraveled. The observations reveal that the intermetallic ordered-phase nucleates through crystallinity alteration of the seeds and then propagates by reentrant grooves. Notably, the reentrant grooves act as intermediate NCs for ordered-phase, eventually forming intermetallic PdCuIrCo NPLs. These NPLs substantially outperform for oxygen evolution reaction (221mV at 10mA cm-2) and hydrogen evolution reaction (19mV at 10mA cm-2) compared to commercial Ir/C and Pd/C catalysts in acidic media. For OER at 1.53V versus RHE, the PdCuIrCo/C exhibits an enhanced mass activity of 9.8 A mg-1 Pd+Ir (about ten times higher) than Ir/C. For HER at -0. 2V versus RHE, PdCuIrCo/C shows a remarkable mass activity of 1.06 A mg-1 Pd+Ir, which is three-fold relative to Pd/C. These improvements can be ascribed to the intermetallic ordered-structure with high-valence Ir sites and tensile-strain. This approach enabled the realization of a previously unobserved mechanism for ordered-phase NCs. Therefore, this strategy of making ordered-phase NPLs can be used in diverse heterogeneous catalysis.

Plasmonic Au3Cu Ordered Nanocrystals Induced Phase Transformation in 2D‐MoS2 for Efficient Hydrogen Evolution

AbstractThe synthesis of ordered gold‐copper (Au3Cu) alloy nanocrystals (≈10 nm) is reported and used in the semiconductor (2H) to metallic (1T) phase transformation of an atomically thin large‐area 2D‐MoS2 grown via CVD technique. The ordered Au3Cu nanocrystals are dispersed over 2D‐MoS2, and the phase transformation is confirmed via Raman spectroscopy followed by X‐ray photoelectron spectroscopy (XPS), while the surface properties of the Au3Cu/2D‐MoS2 is determined by the XPS valence band analysis and ultra‐violet photoemission spectroscopy (UPS). By comparing overpotential and Tafel slopes for Hydrogen Evolution Reaction (HER), a decrease is observed in overpotential by 83.2 mV and Tafel slope by ≈58.25 mV per decade for Au3Cu/MoS2 on light irradiation. This electrocatalytic enhancement of Au3Cu/MoS2 refers to the transformation of semiconducting 2D‐MoS2 to metallic phase under light illumination, thereby altering the surface electronic structures, improving carrier concentrations, lowering the valence band edge, and lowering the free energy of H* adsorption/desorption. Density functional theory (DFT) calculations, along with other surface characterizations, further illustrate that the ordered nanocrystal‐induced phase transformation in 2D‐MoS2 leads to a more durable metallic characteristic, thus, enhancing the surface electrical conductivity, reducing surface potential and Gibbs free energy, and improving the kinetics of photoelectrocatalytic performance of the hybrid structure.

Immobilizing ultrafine PtRu alloy nanoparticles onto 3D interconnected MXene-graphene frameworks for highly efficient methanol oxidation

Although direct methanol fuel cell (DMFC) is regarded as a promising power source to establish green energy conversion system, its overall performance is largely limited by the slow methanol oxidation kinetics of current anode catalysts. Herein, we demonstrate a robust and facile bottom-up strategy for the controllable construction of ultrafine PtRu alloy nanoparticles immobilized onto three-dimensional (3D) interconnected Ti3C2Tx MXene-graphene frameworks (PtRu/MXene-G) through a co-assembly process. Interestingly, the utilization of 3D porous MXene-G matrix provides strong interfacial interactions with alloy nanocrystals and promotes the transportation of both reactant and electron during the electrocatalytic process, while the introduction of Ru atoms ameliorates the Pt electronic structure and generates plentiful hydroxyl species for the oxidative removal of CO byproducts. Working together, the resulting PtRu/MXene-G nanoarchitecture with an appropriate Pt/Ru atomic ratio exhibits exceptional methanol oxidation properties in terms of a large electrochemically active surface area of 101.8 m2 g−1, a high mass (specific) activity of 1779.5 mA mg−1 (1.75 mA cm−2), and good long-term stability, all of which are significantly superior to those of conventional Pt/carbon black, Pt/G, Pt/MXene, and Pt/MXene-G catalysts with an identical Pt usage.

Facet-Defined Dilute Metal Alloy Nanorods for Efficient Electroreduction of CO2 to n-Propanol.

Electroreduction of CO2 into liquid fuels is a compelling strategy for storing intermittent renewable energy. Here, we introduce a family of facet-defined dilute copper alloy nanocrystals as catalysts to improve the electrosynthesis of n-propanol from CO2 and H2O. We show that substituting a dilute amount of weak-CO-binding metals into the Cu(100) surface improves CO2-to-n-propanol activity and selectivity by modifying the electronic structure of catalysts to facilitate C1-C2 coupling while preserving the (100)-like 4-fold Cu ensembles which favor C1-C1 coupling. With the Au0.02Cu0.98 champion catalyst, we achieve an n-propanol Faradaic efficiency of 18.2 ± 0.3% at a low potential of -0.41 V versus the reversible hydrogen electrode and a peak production rate of 16.6 mA·cm-2. This study demonstrates that shape-controlled dilute-metal-alloy nanocrystals represent a new frontier in electrocatalyst design, and precise control of the host and minority metal distributions is crucial for elucidating structure-composition-property relationships and attaining superior catalytic performance.

Smartphone-assisted colorimetric biosensor for the determination of organophosphorus pesticides on the peel of fruits

Nowadays, the widespread use of organophosphorus pesticides (OPs) in agricultural production leads to varying degrees of residues in crops, which pose a potential threat to human health. Conventional methods used in national standard for the detection of OPs in fruits and vegetables require expensive instruments or cumbersome sample pretreatment steps for the analysis. To address these challenges, in this work, we took advantage of the peroxidase-like activity of PtCu3 alloy nanocrystals (NCs) for a colorimetric and smartphone assisted sensitive detection of OPs. With the assist of a smartphone, the concentration of OPs on the peel of fruits could be obtained by comparing the B/RG value (the brightness value of blue divided by those of red and green) of a test strip with a calibration curve. This work not only provides a facile and cost-effective method to detect pesticides but also makes a positive contribution to food safety warning.

Atomic intimacy in Pd1Ni/SiO2 single-atom alloy prepared by galvanic replacement for enhanced semi-hydrogenation of acetylene

Metal single-atom alloys (SAAs) are important catalysts in many catalytic reactions, while the preparation of metal SAA catalysts is a major challenge because the metal species can inevitably deposit on both support and the host metal when using conventional preparation methods, leading to decreased catalytic performances. In this work, we report the preparation of metal SAA by the galvanic replacement (GR) to selectively deposit metal species on the host nanocrystals (NCs) prior to loading on a support. It includes the first synthesis of Ni NCs by colloidal method and the following deposition of Pd atoms onto Ni NCs via GR. After that, the Pd1Ni nanocrystal alloys were deposited onto SiO2 and the atomic intimacy of Pd with Ni was confirmed by multiple characterization techniques. The Pd1Ni/SiO2 SAA prepared by GR presented improved catalytic reactivity in semi-hydrogenation of acetylene, as compared to the reference PdNi/SiO2 catalyst prepared by impregnation. Moreover, the Pd1Ni/SiO2-GR catalyst showed higher C2H4 selectivity in a wide range of temperatures (30–180 °C), which was better than Pd1Ni/SiO2-I SAA, Pd/NiO-I and Pd/SiO2-I catalysts prepared by impregnation. The DFT explains the enhanced selectivity, which is due to the electron transfer from Ni nanocrystal to Pd single atoms. The electron transfer was resulted from the improved intimacy of Pd atoms and Ni nanocrystals.

Mixed-ligand-functionalized silicon-germanium alloy nanocrystals with improved carrier mobilities.

Silicon-germanium (SiGe) alloy nanocrystals (NCs) are promising for advanced optoelectronic applications due to their highly tunable composition and photophysical behaviors. The homogenous dispersion of Si and Ge atoms on the surfaces of SiGe NCs adds a degree of freedom for manipulating the surface chemistry of this type of alloy material. However, the difference in the reactivity between Si and Ge atoms brings additional difficulty in selecting appropriate surface ligands to passivate SiGe NCs. Here we report a mixed-ligand functionalization approach to passivate SiGe NCs effectively. Octadecene and oleylamine molecules serve as co-ligands to cap the surface Si and Ge atoms, respectively, yielding colloidally stable SiGe NCs with high solution dispersity and stable intrinsic near-infrared emission with a microsecond-scale lifetime decay. The resulting particles also show improved hole and electron mobilities of up to 1.1 × 10-6 cm2 V-1 s-1 and 6.3 × 10-6 cm2 V-1 s-1, 2.2 and 1.2 times improvement over the particles only passivated by octadecene ligands.

Cyanosol-enabled ultrafine alloy nanocrystals on graphene as a hybridization matrix for long-life and high-rate silicon anodes

A cyanosol-derived electrostatic assembly and pyrolysis route has been developed to construct homogeneous silicon/metal/carbon (Si/M/C) ternary materials, enabling improved lithium-storage kinetics and performance.

Component-controlled synthesis of PdxSny nanocrystals on carbon nanotubes as advanced electrocatalysts for oxygen reduction reaction.

Pd-based bimetallic or multimetallic nanocrystals are considered to be potential electrocatalysts for cathodic oxygen reduction reaction (ORR) in fuel cells. Although much advance has been made, the synthesis of component-controlled Pd-Sn alloy nanocrystals or corresponding nanohybrids is still challenging, and the electrocatalytic ORR properties are not fully explored. Herein, component-controlled synthesis of PdxSny nanocrystals (including Pd3Sn, Pd2Sn, Pd3Sn2, and PdSn) has been realized, which are in situ grown or deposited on pre-treated multi-walled carbon nanotubes (CNTs) to form well-coupled nanohybrids (NHs) by a facile one-pot non-hydrolytic system thermolysis method. In alkaline media, all the resultant PdxSny/CNTs NHs are effective at catalyzing ORR. Among them, the Pd3Sn/CNTs NHs exhibit the best catalytic activity with the half-wave potential of 0.85 V (vs. RHE), good cyclic stability, and excellent methanol-tolerant capability due to the suited Pd-Sn alloy component and its strong interaction or efficient electronic coupling with CNTs. This work is conducive to the advancement of Pd-based nanoalloy catalysts by combining component engineering and a hybridization strategy and promoting their application in clean energy devices.

Encapsulating CoRu alloy nanocrystals into nitrogen-doped carbon nanotubes to synergistically modify lithium-sulfur batteries separator

Lithium-sulfur batteries (LSBs) have attracted considerable attention owing to their large energy density and abundant reserves of sulfur element. However, the sluggish kinetics and shuttle effects.seriously inhibit the further application of LSBs. Extensive studies have conclusively demonstrated that separator modification was an effective strategy to enhance LSBs properties through the chemical adsorption and catalytic kinetic conversion of lithium polysulfides (LiPSs). In this study, cobalt and ruthenium nanoalloys confined into nitrogen-doped carbon nanotubes (CoRu@N-CNTs) were prepared by one-step annealing method using melamine as carbon source. The obtained CoRu@N-CNTs exhibit plenty of advantages, including abundant CoRu bimetallic catalytical and nitrogen adsorption active sites, exceptional electrolyte wettability and high conductivity. Thanks to these merits, the CoRu@N-CNTs can provide ultrafast ion transfer channels, lots of anchoring for LiPSs and the catalytic conversion kinetics of LiPSs. When applied to modify Li–S batteries separator, the CoRu@N-CNTs modified separator presented an excellent initial specific capacity of 1134.22 mAh g−1 at 0.5C, good rate performance (686 mAh g−1 at 3C) and outstanding cycle performance with a capacity attenuate rate of only 0.107 % per cycle for 400 cycles. Furthermore, when the current density increased to 1C (S loading of 1.344 mg), it displayed a superior capacity attenuation rate of 0.09 %. When the S loading increased to 2.304/3.072 mg, it also demonstrated an outstanding cycle performance. This work provides a feasible strategy to modify the Li–S battery separator through synergistic integration of catalytic conversion and chemisorption of polysulfides.

Bandgap study of quantum dot-sized SiGe alloy nanocrystals prepared in a nonthermal capacitively-coupled plasma by ambient scanning tunneling spectroscopy

The manuscript aims to elucidate the evolution of the bandgap and the semiconducting nature of quantum dot-sized SiGe alloy nanocrystals prepared at different plasma conditions in VHF PECVD. The technique of scanning tunneling spectroscopy (STS) is used for this, considering its highly localized nature, and to study the individual NCs. The STS analysis gives the density of states (DOS) spectrum of the SiGe alloy NCs. The present STS study reveals a dependence of the bandgap of SiGe alloy NCs on plasma parameters. The SiGe alloy NCs also exhibited a shallow p-type character despite the fact that no dopants were used during the deposition. Besides this, the midgap defect states are also observed in some of the samples. Further, a comparative bandgap study of the SiGe alloy NCs with its bulk indicates quantum confinement. These new findings from the QD-sized SiGe alloy NCs are important for the conceptual design and practical development of quantum dot-based third-generation solar cells.

Mechanisms of modification of magnesium– manganese alloys

It is shown that the main modifying phases cannot serve as centers of crystallization of α‑phase microcrystals during solidification of magnesium‑manganese alloys.The superheating modification of these alloys is an adsorption‑nanostructural process. It is shown that adsorbed hydrogen acts as a modifying element of the structure of castings of magnesium‑manganese alloys. The mechanism of their modification by overheating consists of a significant decrease in the concentration of adsorbed hydrogen due to the predominance of its desorption processes from elementary magnesium and manganese nanocrystals in liquid magnesiummanganese alloys. The mechanism of modification of the main modifying phases of these alloys consists of a significant decrease in the concentration of adsorbed hydrogen in the melts through a significant decrease in the concentration of dissolved hydrogen.

Cu-Ni alloy nanocrystals with heterogenous active sites for efficient urea synthesis

Electrocatalytic urea synthesis from CO2 and NO3− are environmental green and energy savable. Although Cu are effective for CO2 and NO3− reduction reactions, achieving high efficiency of urea production remains challenging. Herein, Cu-Ni nanocrystals are formed to provide heterogenous active sites for promoting hydrogenation and C−N coupling reactions in urea synthesis. The carbon supported Cu-Ni nanocrystals are characterized by extended X-ray absorption fine structure and X-ray photoelectron spectroscopy spectra. The Cu-Ni nanocrystals achieves the highest urea Faradaic efficiency of 25.1 % and urea yield of 22.01 μmol h−1 cm−1, which is much higher than that of single Cu or Ni metal. The reaction mechanism is probed by in-situ Fourier transform infrared spectroscopy, revealing a C−N coupling reaction pathway between *CO and *NH2. Theoretical calculations suggest that hydrogenation of *NOx and coupling *CO with *NH2 are more easily occurred over co-existed Cu and Ni sites rather than homogeneous Cu or Ni site.