Alloy Nanosheets Research Articles

Concurrent Vacancy and Adatom Defects of Mo1-xNbxSe2 Alloy Nanosheets Enhance Electrochemical Performance of Hydrogen Evolution Reaction.

Earth-abundant transition metal dichalcogenide nanosheets have emerged as an excellent catalyst for electrochemical water splitting to generate H2. Alloying the nanosheets with heteroatoms is a promising strategy to enhance their catalytic performance. Herein, we synthesized hexagonal (2H) phase Mo1-xNbxSe2 nanosheets over the whole composition range using a solvothermal reaction. Alloying results in a variety of atomic-scale crystal defects such as Se vacancies, metal vacancies, and adatoms. The defect content is maximized when x approaches 0.5. Detailed structure analysis revealed that the NbSe2 bonding structures in the alloy phase are more disordered than the MoSe2 ones. Compared to MoSe2 and NbSe2, Mo0.5Nb0.5Se2 exhibits much higher electrocatalytic performance for hydrogen evolution reaction. First-principles calculation was performed for the formation energy in the models for vacancies and adatoms, supporting that the alloy phase has more defects than either NbSe2 or MoSe2. The calculation predicted that the separated NbSe2 domain at x = 0.5 favors the concurrent formation of Nb/Se vacancies and adatoms in a highly cooperative way. Moreover, the Gibbs free energy along the reaction path suggests that the enhanced HER performance of alloy nanosheets originates from the higher concentration of defects that favor H atom adsorption.

Ultrathin PdCu alloy nanosheet-assembled 3D nanoflowers with high peroxidase-like activity toward colorimetric glucose detection.

Enzyme-mimetic properties of nanomaterials can be efficiently tuned by controlling their size, composition, and structure. Here, ultrathin PdCu alloy nanosheet-assembled three-dimensional (3D) nanoflowers (Pd1Cux NAFs) with tunable surface composition are obtained via a generalized strategy. In presence of H2O2, the as-synthesized Pd1Cux NAFs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to the oxidized form of TMB (oxTMB) with a characteristic absorption peak at 652 nm. Interestingly, Pd1Cux NAFs show obviously composition-dependent peroxidase-like catalytic activities because of the synergistic interaction of nanoalloy. Additionally, different from 2D Pd nanosheets, the distinctive 3D superstructures are featured with rich approachable sites and proper layer spacing, which are in favor of fast mass transport and electron transfers during the catalytic process. Among the studied Pd1Cux NAFs, the Pd1Cu1.7 NAFs show the highest enzyme-like activities and can be successfully applied for the colorimetric detection of glucose with a low detection limit of 2.93 ± 0.53μM. This work provides an efficient avenue to fabricate PdCu NAF nanozymes in biosensing toward glucose detection. Two-dimensional (2D) PdCu ultrathin nanosheet-assembled 3D nanoflowers (Pd1Cux NAFs) with tunable surface composition exhibit substantially enhanced intrinsic peroxidase-like catalytic activities. The Pd1Cu1.7 NAFs are successfully used as peroxidase mimic catalyst for the colorimetric detection of glucose with low detection limit of 2.93μM.

Highly reversible lithium storage in Li2C2 nanosheets

Using Li-carbon composites as anodes in high-energy-density lithium batteries leads to significant improvements in cycling life and safety compared with lithium metal. Li2C2 consisting of dumbbell anions is the most thermodynamically stable phase in the family of lithium-carbon materials, however its low conductivity is a critical obstacle to the practical applications. sp2-hybridizing carbon is one promising option for unique electronic structures. Here, Li2C2 alloy nanosheets composed of sp2-hybridized carbon atoms are directly formed from Li element and carbon during ball milling process, presenting a metallic feature at ambient conditions. After removing lithium from these alloy nanosheets, amorphous carbon ultrathin nanosheets are obtained. A vertically aligned Li2C2 nanosheet foil prepared by pressing the milled powder, can be used as free-standing, binder-free electrodes for fabricating various types of lithium batteries, and their excellent electrochemical performance is attributed to a highly reversible Li atoms uptake in amorphous carbon nanosheets.

Ultrathin Amorphous/Crystalline Heterophase Rh and Rh Alloy Nanosheets as Tandem Catalysts for Direct Indole Synthesis.

Heterogeneous noble-metal-based catalysis plays an essential role in the production of fine chemicals. Rh-based catalysts are one of the most active candidates for indole synthesis. However, it is still highly desired to develop heterogeneous Rh-based catalysts with high activity and selectivity. In this work, a general, facile wet-chemical method is reported to synthesize ultrathin amorphous/crystalline heterophase Rh and Rh-based bimetallic alloy nanosheets (NSs), including RhCu, RhZn, and RhRu. Impressively, the amorphous/crystalline heterophase Rh NSs exhibit enhanced catalytic activity toward the direct synthesis of indole compared to the crystalline counterpart. Importantly, the obtained amorphous/crystalline heterophase RhCu alloy NSs can further enhance the selectivity to indole of >99.9% and the conversion is 100%. This work demonstrates the importance of phase engineering and metal alloying in the rational design and synthesis of tandem heterogeneous catalysts toward fine chemical synthesis.

Chemical conversion synthesis of magnetic Fe1-xCox alloy nanosheets with controlled composition.

Chemical conversion provides a versatile platform for the synthesis of advanced nanomaterials with targeted phase, composition, and architecture. Here, we report a trioctylphosphine (TOP)-driven chemical conversion route to transform lamellar Fe1-xCoxS1.2-DETA (x = 0.1, 0.3, 0.5, 0.7, DETA = diethylenetriamine) inorganic-organic hybrid solid solutions into two-dimensional (2D) single-crystal Fe1-xCox alloy with controllable composition and dimensionality. Synergetic transformation coupled with DETA removal and sulfur extraction of lamellar Fe0.9Co0.1S1.2-DETA hybrids was examined in detail. The highest magnetization of 175 emu g-1 was recorded for the prepared Fe0.7Co0.3. Our results not only provide a new lamellar inorganic-organic hybrid solid solution but also extend the chemical conversion strategy to the synthesis of previously unavailable magnetic alloy nanosheets.

Hierarchical defective palladium-silver alloy nanosheets for ethanol electrooxidation

Tuning the chemical composition and surface structure of electrodes is demonstrated as a feasible and effective strategy to tailor advanced catalysts for energy electrocatalysis. In this work, hierarchical palladium-silver alloy nanosheets (PdAg NS) with the thickness ~7 atoms and rich atomic defects are successfully prepared, using the carbon monoxide (CO) confinement approach. The optimized Pd7Ag3 NS/C exhibits 8.8 times higher catalytic peak current density and much better stability toward ethanol electrooxidation than Pd NS/C catalyst. The catalytic enhancement mechanism could be attributed to the synergetic effects among optimized electronic structure of Pd, novel architecture, and rich atomic defects.

Assembly of Bimetallic PdAg Nanosheets and Their Enhanced Electrocatalytic Activity toward Ethanol Oxidation.

The direct ethanol fuel cells in an alkaline medium have a broad vision of applications because of their large energy density, reasonable power density, and environmentally friendly features. Herein, we present a facile one-step method to synthesize PdAg nanosheet assemblies (NSAs) in a mixed solution of N,N-dimethylformamide and water with the addition of molybdenum hexacarbonyl and cetyltrimethylammonium bromide. Pure Pd NSA shows an irregular shape while PdAg NSAs gradually undergo a process from solid assembly to a hollow structure with the Pd/Ag molar ratio changing from 3:1 to 2:1 to 1:1. The formation of alloy nanosheets in the assemblies combined with the introduction of Ag in the Pd catalyst enhances the catalytic activity toward ethanol electrooxidation from 1524 mA mg-1 of pure Pd NSA to 1866 mA mg-1 of PdAg NSA with a Pd/Ag molar ratio of 2:1. On the basis of the experimental data, compared with pure Pd structures, both the nature of a thin nanosheet of PdAg NSAs and the structural changes in the alloy assemblies play key roles in determining the electrocatalytic activity of these Pd-based catalysts.

Phase Evolution of Re1-xMoxSe2 Alloy Nanosheets and Their Enhanced Catalytic Activity toward Hydrogen Evolution Reaction.

Two-dimensional ReSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), but its catalytic activity needs to be further improved. Herein, we synthesized Re1-xMoxSe2 alloy nanosheets with the whole range of x (0-100%) using a hydrothermal reaction. The phase evolved in the order of 1T″ (triclinic) → 1T' (monoclinic) → 2H (hexagonal) upon increasing x. In the nanosheets with x = 10%, the substitutional Mo atoms tended to aggregate in the 1T″ ReSe2 phase with Se vacancies. The incorporation of the 1T' phase makes the alloy nanosheets more metallic than the end compositions. The 10% Mo substitution significantly enhanced the electrocatalytic performance toward HER (in 0.5 M H2SO4), with a current of 10 mA cm-2 at an overpotential of 77 mV (vs RHE) and a Tafel slope of 42 mV dec-1. First-principles calculations of the three phases (1T″, 2H, and 1T') predicted a phase transition of 1T″-2H at x ≈ 65% as well as the production of a 1T' phase along the composition tuning, which are consistent with the experiments. At x = 12.5%, two Mo atoms prefer to form a pair along the Re4 chains. Gibbs free energy along the reaction path indicates that the best HER performance of nanosheets with 10% Mo originates from the Mo atoms that form Mo-H when there are adjacent Se vacancies.

Versatile Synthesis of Pd−M (M=Cr, Mo, W) Alloy Nanosheets Flower‐like Superstructures for Efficient Oxygen Reduction Electrocatalysis

AbstractPd‐based nanoalloys are promising electrocatalysts for replacing Pt‐based ones toward oxygen reduction reaction. Despite that great progress has been achieved, universally synthesizing Pd‐based alloy nanosheets and further integrating them into porous or hierarchical superstructures remain a challenge, and their ORR performances are not systematically investigated. Herein, novel ultrathin and highly wrinkled Pd−M (M=Cr, Mo, W) alloy nanosheets flower‐like superstructures (NSFSs) are universally fabricated via a polyether and small molecules/ions ligand assisted solvothermal method. Such Pd−M NSFSs possess mesoporous structures and co‐exist single‐atom‐like and cluster‐like M species on their surfaces. Compared with pure Pd NSFSs, those Pd−M NSFSs show greatly enhanced ORR activity in alkaline media. Due to the unique microstructure feature, proper alloy constituent and stronger interatomic polarization or electronic coupling, the Pd−W NSFSs show the highest ORR activity with the half‐wave potential of 0.89 V (vs. RHE) and mass activity of 0.46 A mgPd−1 at 0.90 V (vs. RHE), outperforming commercial Pt/C, and most of reported Pd(or Pt)‐based catalysts. Moreover, the Pd−W NSFSs manifest outstanding durability and anti‐CO poisoning ability yet. This work may spur the development of 2D Pd‐based nanoalloy superstructures and promote their applications in fuel cells or other clean energy fields.

Ultrathin RuRh Alloy Nanosheets Enable High-Performance Lithium-CO2 Battery

Summary The aprotic Li-CO2 battery with high energy density is an attractive energy-storage technology. However, its development is largely impeded by the sluggish kinetics of CO2 reduction and evolution reactions. Here, we demonstrate a class of ultrathin triangular RuRh alloy nanosheets as an exceptionally active catalyst for greatly accelerating the kinetics of CO2 reduction and evolution reactions and achieving a high-performance Li-CO2 battery. The RuRh alloy nanosheets-based battery can achieve the lowest voltage gap of 1.35 V during the charge-discharge process and stably cycle for 180 cycles with a cutoff capacity of 1,000 mAh g−1 at 1,000 mA g−1. Density functional theory calculations demonstrate the pivotal roles of Rh introduction in RuRh alloy nanosheets, which evidently activate the electron-transfer ability of surface Ru and balance the CO2 binding near Ru sites. We find that the d-d correlation between Rh and Ru contributes to the energetically favorable cycle of the Li-CO2 battery.

Co-doped 1T′/T phase dominated MoS1+XSe1+Y alloy nanosheets as bifunctional electrocatalyst for overall water splitting

The electrocatalytic overall water splitting is currently regarded as an efficient method for reservation and conversion of sustainable energy sources. The earth-abundant transition-metal chalcogenides (TMCs) possess unique properties to realize hydrogen evolution reaction (HER), but the semiconductor 2H phase behaves a medial activity for HER and even worse performance for oxygen evolution reaction (OER). To date, developing the efficient and bifunctional TMCs electrocatalyst is an attractive but difficult task. Herein, Co-doped 1T′/T phase dominated MoS1+XSe1+Y alloy (Co-MoS1+XSe1+Y) nanosheets electrocatalysts were synthesized by a one-step facial hydrothermal method. Meanwhile, the crystal structures and element composition of the Co-MoS1+XSe1+Y were determined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Importantly, the as-prepared catalysts Co-MoS1+XSe1+Y with the atomic ratio of Co: Mo = 1: 5 (Co-MoS1+XSe1+Y1-5) shows superior electrochemical activity, achieving current density (j) of 10 mA cm−2 at small overpotentials of 119 mV and 280 mV for HER and OER in 1.0 M KOH, respectively. Moreover, applying the bifunctional electrode in an alkaline water electrolytic cell allows a high-efficiency electrocatalyst with only 1.60 V at j = 10 mA cm−2, which could be practical in electrocatalytic overall water splitting reaction devices.

Self‐Supporting Ni‐M (M = Mo, Ge, Sn) Alloy Nanosheets via Topotactic Transformation of Oxometallate Intercalated Layered Nickel Hydroxide Salts: Synthesis and Application for Electrocatalytic Hydrogen Evolution Reaction

AbstractMetal alloys are valuable for achieving energy‐ and cost‐efficient electrocatalysis. To maximize active sites exposure and electron transport, a general method to prepare binder‐free Ni‐M (M = Mo, Ge, Sn) bimetallic alloy nanosheets electrocatalyst for the hydrogen evolution reaction (HER) is successfully developed for the first time, via topotactic transformation of layered nickel hydroxide salts (Ni‐LHS). The obtained bimetallic alloys show much improved HER performance to that of Ni. In particular, Ni4Mo alloy nanosheets exhibit HER activity with an overpotential of only 69.6 mV at 100 mA cm−2 and a low Tafel slope of 37 mV decade−1 in alkaline medium, due to large electrochemical active surface area and low charge transfer resistance. Moreover, Ni4Mo alloy nanosheets also show high HER activity in both acidic and neutral electrolytes with long‐term stability, demonstrating superior activity comparable to or better than state‐of‐the‐art commercial Pt/C catalyst. This topotactic transformation method using LHS precursors provides a way to design and fabricate cost‐effective and energy‐efficient ultrathin 2D bimetallic alloy nanosheets for electrocatalysis, greatly broadening the scope of the currently available self‐supporting metal alloy electrocatalysts.

Anisotropic alloying of Re1−xMoxS2 nanosheets to boost the electrochemical hydrogen evolution reaction

Anisotropic atomic distribution of Re1−xMoxS2 alloy nanosheets enhanced their electrocatalytic performance toward the hydrogen evolution reaction.

General synthesis of Pd-pm (pm = Ga, In, Sn, Pb, Bi) alloy nanosheet assemblies for advanced electrocatalysis.

Owing to the synergistic compositional and structural advantages, ultrathin bimetallic nanosheet assembly nanostructures are widely recognized as advanced catalysts for alcohol electrooxidation reaction. Although numerous efforts have been made, the fabrication of well-defined ultrathin bimetallic nanosheet assemblies (NSAs) at large scale is still a tough challenge. Herein, a universal synthetic approach has been proposed to produce a series of well-defined Pd-pm (pm = Ga, In, Sn, Pb, Bi) alloy NSAs. Due to multiple merits of their unique 3D flower-like nanostructure and alloyed crystalline features, the self-supported Pd-pm NSAs show excellent electrocatalytic performance for the methanol oxidation reaction (MOR) and glycerol oxidation reaction (GOR). Given the eco-friendly synthetic concept, facile universality, and outstanding electrocatalytic properties of the generated bimetallic Pd-pm NSAs, we believe that this method could be employed for building more advanced nanocatalysts toward efficient electrocatalytic applications.

2D AuPd alloy nanosheets: one-step synthesis as imaging-guided photonic nano-antibiotics

The complicated synthesis and undesirable biocompatibility of nanomaterials hinder the synergistic photothermal/photodynamic therapy for bacterial infections. Herein, we develop a one-step preparation method of 2D AuPd alloy nanosheets as imaging-guided photonic nano-antibiotics. 2D AuPd alloy nanosheets with an extremely small thickness (∼1.5 nm) exhibit prominent photothermal effects (η = 76.6%), excellent ROS generation, strong photoacoustic signals and desirable biocompatibility. AuPd nanosheets can eliminate 100% of representative Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) when irradiated using an 808 nm laser at 1 W cm−2 for 5 minutes. After being modified with a bacterial targeting peptide, under the guidance of photoacoustic imaging, AuPd nanosheets achieve promising synergistic photothermal/photodynamic therapeutic efficacy in treating Staphylococcus aureus infected mice. This work expands the biomedical application of 2D noble metal nanomaterials to the field of photonic nano-antibiotics.

Ultrathin Pd-based nanosheets: syntheses, properties and applications.

Two-dimensional (2D) noble metal-based nanosheets (NSs) have received considerable interest in recent years due to their unique properties and widespread applications. Pd-based NSs, as a typical member of 2D noble metal-based NSs, have been most extensively studied. In this review, we first summarize the research progress on the synthesis of Pd-based NSs, including pure Pd NSs, Pd-based alloy NSs, Pd-based core-shell NSs and Pd-based hybrid NSs. The synthetic strategy and growth mechanism are systematically discussed. Then their properties and applications in catalysis, biotherapy, gas sensing and so on are introduced in detail. Finally, the challenges and opportunities towards the rational design and controlled synthesis of Pd-based NSs are proposed.

Superior intracluster conductivity of metallic lithium-ion battery anode achieved by high-pressure torsion

Researchers have always hoped to increase the capacity of lithium-ion battery electrodes. Given the unique plastic characteristic of alloy anodes, this paper puts forward the application of high-pressure torsion and subsequent high-energy ball milling to produce a secondary cluster metallic anode system. A common germanium cooper eutectic alloy nanosheet is used for typical illustration, and after high-pressure torsion processing, the bulk nanocrystalline cluster with density of 14.7 g/cm3 was achieved, which is much higher than the original powder’s density (4.6 g/cm3). Meanwhile, it is also observed that the conductivity and the cycle performance of the processed samples are greatly improved, and the sample’s capacity retention after 2800 cycles is surprisingly remaining at 96%. Therefore, as a pure mechanical processing method, high-pressure torsion has a bright prospect in improving the tap density and the conductivity of existing functional nanomaterials.

Three-dimensional PdCuM (M = Ru, Rh, Ir) Trimetallic Alloy Nanosheets for Enhancing Methanol Oxidation Electrocatalysis.

Owing to their intrinsically high activity and rich active sites on the surface, noble metal materials with an ultrathin two-dimensional nanosheet structure are emerging as ideal catalysts for boosting fuel cell reactions. However, the realization of controllable synthesis of multimetallic Pd-based alloy ultrathin nanosheets (NSs) for achieving enhanced electrocatalysis evolved from compositional and structural advantages remains a grand challenge. Herein, we report a universal method for the construction of a new series of the three-dimensional (3D) multimetallic PdCuM (M = Ru, Rh, Ir) superstructures that consist of ultrathin alloy NSs. Different from the conventional 2D ultrathin nanostructure, the 3D PdCuM NSs that endowed with abundant routes for fast mass transport, high noble material utilization efficiency, and ligand effect from M to PdCu display large promotion in electrocatalytic performance for the methanol oxidation reaction. Impressively, the composition-optimized Pd59Cu33Ru8 NSs, Pd57Cu34Rh9 NSs, and Pd63Cu29Ir8 NSs show the mass activities of 1660.8, 1184.4, and 1554.8 mA mg-1 in alkaline media, which are 4.9, 3.5, and 4.6-fold larger than that of commercial Pd/C, respectively. More importantly, all of the PdCuM NSs are also very stable for long-term electrochemical tests.

Self-Powered SnS1-xSex Alloy/Silicon Heterojunction Photodetectors with High Sensitivity in a Wide Spectral Range.

Alloy engineering and heterostructures designing are two efficient methods to improve the photosensitivity of two-dimensional (2D) material-based photodetectors. Herein, we report the first-principle calculation about the band structure of SnS1-xSex (0 ≤ x ≤ 1) and synthesize these alloy nanosheets. Systematic measurements indicate that SnS0.25Se0.75 exhibits the highest hole mobility (0.77 cm2·V-1·s-1) and a moderate photoresponsivity (4.44 × 102 A·W-1) with fast response speed (32.1/57.5 ms) under 635 nm irradiation. Furthermore, to reduce the dark current and strengthen the light absorption, a self-driven SnS0.25Se0.75/n-Si device has been fabricated. The device achieved a preeminent photo-responsivity of 377 mA·W-1, a detectivity of ∼1011 Jones and Ilight/Idark ratio of ∼4.5 × 102. In addition, the corresponding rising/decay times are as short as 4.7/3.9 ms. Moreover, a broadband sensitivity from 635 to 1200 nm is obtained and the related photoswitching curves are stable and reproducibility. Noticeably, the above parameters are comparable or superior to the most of reported group IVA layered materials-based self-driven photodetectors. Last, the synergistic effects between the SnS0.25Se0.75 nanosheets and the n-Si have been discussed by the band alignment. These brilliant results will pave a new pathway for the development of next generation 2D alloy-based photoelectronic devices.

High-efficiency bifunctional electrocatalyst based on 3D freestanding Cu foam in situ armored CoNi alloy nanosheet arrays for overall water splitting

It is highly desired to design and develop highly efficient and durable electrocatalysts for hydrogen evolution reaction and oxygen evolution reaction under alkaline condition. In this study, three dimensional freestanding porous Cu foam in situ armored CoNi alloy nanosheet arrays with tunable compositions is synthesized via a facile and cost-efficient electrodeposition strategy. With the optimal nanosheet composition (Co81Ni19), highly exposed active surface, improved electrical conductivity, the as-fabricated composite exhibits intriguing properties for efficient overall water splitting in alkaline media. Such freestanding Co81Ni19 alloy nanosheet arrays demonstrate superior electrocatalytic performances with the overpotentials of only 132 and 240 mV for hydrogen evolution and oxygen evolution to reach a catalytic current density of 10 mA cm−2 in 1.0 M KOH. Meanwhile, the Co81Ni19 exhibits high electrochemical stability with almost no detectable activity decay after 36,000 s of continuous operation. Remarkably, this study paves the way to design high-performance and easy-accessible transition metal alloy-based bifunctional catalysts for overall water splitting. Meanwhile, these transition metal-based macroscopic assemblies may be attractive candidates for a wide range of practical energy conversion and storage applications.