Yolk-shell Nanostructures Research Articles

Magneto-plasmonic Co@M (M = Au/Ag/Au-Ag) core-shell nanoparticles for biological imaging and therapeutics

In this paper, the optical properties of magnetic-plasmonic core-shell nanoparticles are studied using the Mie theory and DDA method. DDA results are compared with Mie theory results for spherical core-shell NPs as it gives the exact solution. It is observed that the position of LSPR peak in core-shell nanostructures is tuned by changing the cores and shell thickness in the core-shell spherical nanostructures and aspect ratio as well as shell thickness in spheroidal core-shell nanostructures. In addition, the yolk-shell nanostructures exhibit enhancement of LSPR peaks, bandwidth, and their corresponding intensities, as compared to spherical core-shell nanostructures. The calculated absorption spectra at λmax are obtained in the wavelength range of 336-698 nm. This study opens up the new potential of appropriate core-shell nanostructures in bio-imaging, drug delivery, biomedicine, and therapeutic uses.

Magnetic-plasmonic yolk-shell nanostructure-based plasmon-enhanced electrochemiluminescence sensor

In this work, plasmon-enhanced electrochemiluminescence (ECL) nanosensor based on magnetic-plasmonic Fe3O4 yolk/Au shell (M@Au) is designed for Kirsten rat sarcoma (K-RAS) gene detection. K-RAS is a mouse sarcoma virus oncogene, which mutation occurs in the initial phase of malignant tumor transformation. Thus, the detection of KAS is meaningful for the diagnosis of early cancer. Graphite phase carbon nitride quantum dots (g-C3N4 QDs) have low toxicity, and stable chemical properties. However, the low ECL intensity of g-C3N4 QDs limits its sensing application. Herein, a sandwich-typed sensor with a combination of M@Au and g-C3N4 QDs is constructed. In yolk-shell M@Au, the internal Fe3O4 nanoparticle (NP) has good magnetic property. The outer Au shell has better surface plasmon coupling (SPC) effect than conventional Au NPs. Furthermore, the middle cavity in the yolk-shell nanostructure solves the problem of electron transfer between Fe3O4 NP and Au shell. Therefore, the yolk-shell M@Au shows strong surface SPC effect, which amplifies the ECL signal of g-C3N4 QDs 2.8-fold. Based on the plasmon-enhanced ECL mode, this sensor performs well with a wide range (1 fM−1 nM) for nucleic acid detection. It also shows the high stability and selectivity of the sensing system in human serum test.

Fabrication of Silver Yolk@Porous Janus Polymer Shell Nanospheres for Synergistic Catalysis

Yolk-shell nanostructures have recently attracted tremendous research interests in various areas because of their unique structural merits. Currently, there is an urgent need for developing porous shells with multifunctional features to enhance their performance in various applications. Herein, advanced yolk-shell nanospheres have been facilely prepared by encapsulating silver nanoparticles with porous Janus polymer shells that consist of a hypercrosslinked polystyrene (xPS) outer layer and a tethered poly(acrylic acid) (PAA) brush lining. The xPS outer layer possesses well-developed porosity as mass diffusion pathways. More importantly, the tethered PAA brushes with customized carboxyl groups exhibit great affinity toward specific species (e.g., cationic dyes), leading to their enrichment from the bulk solution into the interior cavity. The unusual combination of highly porous outer layers with customizable inbuilt polymer linings in the porous Janus shells endows them with great promise for synergistically catalytic degradation of cationic dyes.

Single-cell yolk-shell nanoencapsulation for long-term viability with size-dependent permeability and molecular recognition.

Like nanomaterials, bacteria have been unknowingly used for centuries. They hold significant economic potential for fuel and medicinal compound production. Their full exploitation, however, is impeded by low biological activity and stability in industrial reactors. Though cellular encapsulation addresses these limitations, cell survival is usually compromised due to shell-to-cell contacts and low permeability. Here, we report ordered packing of silica nanocolloids with organized, uniform and tunable nanoporosities for single cyanobacterium nanoencapsulation using protamine as an electrostatic template. A space between the capsule shell and the cell is created by controlled internalization of protamine, resulting in a highly ordered porous shell-void-cell structure formation. These unique yolk-shell nanostructures provide long-term cell viability with superior photosynthetic activities and resistance in harsh environments. In addition, engineering the colloidal packing allows tunable shell-pore diameter for size-dependent permeability and introduction of new functionalities for specific molecular recognition. Our strategy could significantly enhance the activity and stability of cyanobacteria for various nanobiotechnological applications.

Simple synthesis of the Au-GQDs@AgPt Yolk-shell nanostructures electrocatalyst for enhancing the methanol oxidation

Au-GQDs@AgPt Yolk-shell nanostructures with Au-GQDs yolk and AgPt alloy shell have been synthesized through a green wet chemical reduction method. In this process employed Au-GQDs as a yolk to obtain Au-GQDs@Ag nanoparticles (NPs), and then galvanic replacement reaction occurred between PtCl 6 2- and Ag to fabricate Au-GQDs@AgPt Yolk-shell nanostructures. GQDs served as a structure-directing and dispersing agent to prepare homogeneous shell. The electrocatalytic performance of the as-synthesized Au-GQDs@AgPt Yolk-shell nanostructures for methanol oxidation reaction (MOR) is studied by cyclic voltammetry (CV) and chronoamperometry (CA). The catalyst has displayed excellent specific activity (33.20 mA cm −2 ), which is approximately 7 times higher than those of commercial Pt/C. And its CO tolerance and stability for MOR are also greatly improved. The results attribute to their particular structure (Yolk-shell nanostructures), electron effect with Ag and Pt, electron transport between GQDs and AgPt shell. The present strategy can provide an environment-friendly and valuable way to fabricate multicomponent nanostructures with Yolk-shell nanostructures. Schematic illustration demonstrates the structural and compositional features of the porosity Au-GQDs@AgPt Yolk-shell nanostructures as an efficient MOR catalyst. • The unique Au-GQDs@AgPt Yolk-shell nanostructures were synthesized through a green wet chemical reducation method. • GQDs serve as a structure-directing and dispersing agent to prepare homogenous shell. • Au-GQDs@AgPt Yolk-shell enhanced catalytic performance, CO tolerance and stability for methanol oxidation reaction. • The Yolk-shell nanostructures, electron effect and electron transport are imporatant for improving catalytic performance.

A novel strategy for the design of Au@CdS yolk-shell nanostructures and their photocatalytic properties

Abstract Nanomaterials with well-defined morphologies are of significant interest from fundamental research to technical applications because of their novel physicochemical properties. Here, a novel strategy is developed to fabricate monodisperse Au@CdS yolk-shell nanostructure (YSNs). First, Au@Cd-cysteine core-shell nanostructure (CSNs) are prepared and used as precursors. Subsequently, the Cd-cysteine shells are transformed into CdS hollow nanostructures through anion exchange process. The prepared Au@CdS YSNs have well-defined morphology and exhibit excellent visible light absorption capacity due to their unique structures. Investigations using FESEM, TEM and powder XRD are conducted to monitor the structure evolution and crystallization process. XPS is carried out to further determine the chemical composition and the surface states of the samples before and after sulfidation. The adsorption capacity of Au@CdS YSNs is stronger than that of Au@CdS CSNs. Compared with CdS nanoparticles and Au@CdS CSNs, Au@CdS YSNs exhibit excellent photocatalytic activity for photodegradation R6G solution due to their unique structures and the synergistic effect between Au and CdS. The developed synthetic strategy may inspire the design and fabrication of complex yolk-shell structures for efficiently solar energy utilization.

Enhancing the Charge Transportation Ability of Yolk-Shell Structure for High-Rate Sodium and Potassium Storage.

The microstructure of large-capacity anodes is of great importance in determining the performance of sodium- and potassium-ion batteries. Yolk-shell nanostructures promise excellent structural stability but suffer from insufficient charge transfer rate during cycles. Herein, we tackle this challenge by constructing a single-walled carbon nanotube (SWNT) internally bridged yolk-shell structure, inside which SWNTs cover the surface of the yolk and connect the yolk and shell, for better electron/ion transportation. Combining the merits of both yolk-shell structure and conductive SWNT channels, the as-prepared Fe1-xS/SWNT@C composite manifests high reversible capacity and ultralong cycling stability up to 8700 cycles. Moreover, it displays the best rate capability (317 mA h g-1 at 20 A g-1 for Na+ and 236 mA h g-1 at 10 A g-1 for K+) among the reported yolk-shell structures and iron-sulfide-based anodes thus far. The kinetic analysis and density functional theory calculations further reveal that the Fe1-xS/SWNT heterointerface can effectively enhance the reversibility of K+ storage and decrease the K+ diffusion energy barrier, leading to excellent pseudocapacitive behavior and fast ion transportation for outstanding rate capability.

Yolk-Shell Nanostructures: Syntheses and Applications for Lithium-Ion Battery Anodes.

Yolk–shell nanostructures have attracted tremendous research interest due to their physicochemical properties and unique morphological features stemming from a movable core within a hollow shell. The structural potential for tuning inner space is the focal point of the yolk–shell nanostructures in a way that they can solve the long-lasted problem such as volume expansion and deterioration of lithium-ion battery electrodes. This review gives a comprehensive overview of the design, synthesis, and battery anode applications of yolk–shell nanostructures. The synthetic strategies for yolk–shell nanostructures consist of two categories: templating and self-templating methods. While the templating approach is straightforward in a way that the inner void is formed by removing the sacrificial layer, the self-templating methods cover various different strategies including galvanic replacement, Kirkendall effect, Ostwald ripening, partial removal of core, core injection, core contraction, and surface-protected etching. The battery anode applications of yolk–shell nanostructures are discussed by dividing into alloying and conversion types with details on the synthetic strategies. A successful design of yolk–shell nanostructures battery anodes achieved the improved reversible capacity compared to their bare morphologies (e.g., no capacity retention in 300 cycles for Si@C yolk–shell vs. capacity fading in 10 cycles for Si@C core–shell). This review ends with a summary and concluding remark yolk–shell nanostructures.

Yolk-shelled Sn@C@MnO hierarchical hybrid nanospheres for high performance lithium-ion batteries

Metallic tin exhibits great potential as an alternative to commercial graphite anode materials. However, its tremendous volume change during cycles leads to significant capacity fading, which hampers its practical application. In this work, Sn nanoparticles are confined to a carbon nanocage to form Sn@C@MnO yolk-shell hierarchical hybrid nanospheres as anode nanomaterials for Li-ion battery. In the novel nanostructures, the yolk-shell nanostructures can well buffer the volume contraction/expansion of Sn nanocores during cycles; the carbon shell can provide high conductivity and inhibit Sn and MnO nanocrystals from stacking; MnO nanocrystals on the C shell can not only offer sufficient active sites for Li-ion adsorption, but also validly consolidate the structural stability of the shell in the yolk-shell nanostructure. Benefiting from the unique nanostructures, Sn@C@MnO yolk-shell hierarchical hybrid nanospheres exhibit superior electrochemical lithium storage performances (822mAhg−1 after 250 cycles at 0.1Ag-1) and long-term cyclic stability (603mAhg−1 after 500 cycles at 0.5Ag-1). This work offers valuable insight into the synthetic strategy of Sn-based anode materials with novel hierarchical hybrid nanostructures.

Generalized preparation of Au NP @ Ni(OH)2 yolk-shell NPs and their enhanced catalytic activity

Yolk-shell nanostructures have attracted considerable attention because of their unique properties and promising applications. Yet, synthesis of well-defined yolk-shell structures with controllable composition remains a major challenge. Here, we report a general method to fabricate Au NP @ Ni(OH)2 yolk-shell NPs. Au cores with various diameters and shapes can be successfully encapsulated into the Ni(OH)2 shells by a similar approach. When the diameter of the core Au NPs changed from ~15 to ~90 nm, the size of the yolk-shell NPs accordingly grew from ~110 to ~380 nm, however, the shell thickness of the final yolk-shell NPs is in the narrow range of 18–20 nm. The synergistic contribution from both Au and Ni(OH)2 has endowed the yolk-shell heterostructure with enhanced catalytic activity. As shown in the oxygen-evolution reactions (OER) tests, the OER activity of Au NP @ Ni(OH)2 yolk-shell NPs is 8.7 and 86-fold higher than that of hollow Ni(OH)2 NPs alone and Au NP @C (5%) (Au NPs (5%) mixed with Carbon Black), respectively. In general, our method provides a simple and novel strategy towards the fabrication of yolk-shell structures with superior catalytic activity for OER.

γ-Al2O3 yolk–shell porous microspheres with superior Congo red removal performance

γ-Aluminum oxide (γ-Al2O3) yolk–shell meso–macroporous microspheres (AOYSs) were prepared using the glucose-assisted hydrothermal method followed by an annealing process, and were characterized by X-ray diffraction, scanning electron microscopy and Brunauer–Emmett–Teller nitrogen (N2) adsorption–desorption analysis. The hierarchical AOYSs showed a high specific surface area (201 m2/g) with highly porous structures. Compared with solid and hollow microspheres, the hierarchical AOYSs showed an excellent adsorption performance toward Congo red, which can be attributed to their unique yolk–shell structures and hierarchical meso–macroporous structures with a high specific surface area. Furthermore, the Langmuir isotherm model and pseudo-second-order kinetic model well represented the adsorption of Congo red on the surface of hierarchical AOYSs. This study provides a new insight into the design and synthesis of yolk–shell nanostructures, which can offer various applications, such as those in adsorption, energy storage, catalysis and sensor fields.

Carbon Pseudocubes from Iron Oxide Templates for Capacitive Energy Storage

A surface-protected etching approach was used to synthesize monodisperse partially hollow carbon nanostructures with pseudocubic shapes. Monodisperse chemical templates (α-Fe2O3, MF) were synthesized by the gel-sol method and coated with a polyvinylpyrrolidone (PVP) protective layer. Pyrrole monomers were dispersed around the PVP-protected α-Fe2O3 templates. Upon acidic etching, Fe3+ ions were released to initiate in situpolymerization of pyrrole to form Fe2O3@PPy (MFP) core–shell intermediates. The MFP particles were calcined to obtain partially hollow 3D pseudocubic carbon nanoparticles (PCC). The PCC delivered a high specific capacitance (395 F g−1 at 0.2 A g−1) and enhanced cycling stability (5000 cycles at 4 A g−1). The superior electrochemical properties of the PCC is attributed to its cubic and partially hollow structure, which increases electric double layer capacitance by increasing charge storage surface, facilitates effective ion diffusion by reducing interparticle distances, and buffers volumetric changes associated with ion insertion through void space/pores. The simple and highly reproducible method presented in this work can be extended to produce various hollow or yolk-shell nanostructures as high-performance supercapacitor electrode materials.

Rational design of yolk-shell nanostructures for drug delivery.

Yolk–shell nanoparticles (YSNPs) are a new class of hollow nanostructures, and their unique properties can be utilized in drug delivery systems. The recent progress in YSNPs-based carriers is highlighted in drug delivery systems. Doxorubicin hydrochloride, ceftriaxone sodium, and methotrexate are three of the most common drugs that are used in this field. According to the reported studies, the materials used most often as yolk–shells are magnetic nanoparticles and polymers. The used methods for synthesizing a diverse array of YSNPs are classified based on their core structures. Various properties of YSNPs include their high drug-loading capacity, and their ability to decrease drug toxicity and satisfactorily and efficiently release drugs.

Use of Au@Void@TiO2 yolk-shell nanostructures to probe the influence of oxide crystallinity on catalytic activity for low-temperature oxidations.

A series of Au@Void@TiO2 yolk-shell structures were synthesized and characterized, and their catalytic activity was tested for the oxidation of carbon monoxide. The target of this work was to evaluate the effects of (1) the crystallinity of the TiO2 shell and (2) the presence of titanate phases. Transmission electron microscopy and X-ray diffraction data show that increasing calcination temperatures, from 850 to 1250 K, leads to the formation of larger titania crystallites. These crystallites are typically in the form of anatase, but some rutile is also made at high temperatures. The general yolk-shell nanostructures retain their basic characteristics upon calcination and upon treatment with HCl (used to remove the titanate phases), but a few structural and chemical changes do take place: (1) the void-space diameter is reduced by approximately 10% when going from TCalc = 850 K to TCalc = 1250 K, a change that is accompanied by a decrease in the surface area (estimated from N2 adsorption-desorption isotherms); (2) the shell thickness remains unaffected by either calcination or HCl treatment; (3) the pore volume also remains approximately constant with increasing calcination temperature in the catalysts free of titanates but diminishes significantly in the samples with titanate phases; (4) the mesoporosity is minimal in all yolk-shell nanostructures but more noticeable with the pure TiO2 shells; (5) the titanates have high Na content (measured by X-ray photoelectron spectroscopy), but that Na is fully removed upon treatment with HCl; (6) no Ti3+ was detectable in any of the samples, but silica, together with C and (minor amounts of) N, was present in all; (7) all Au is in metallic form; (8) two temperature regimes were observed for the catalytic oxidation of CO, as reported for other similar samples in the past, an Arrhenius regime around or above room temperature, and a cryogenic range going to temperatures as low as 120 K; (9) the latter regime is only seen with the samples containing titanate phases; (10) the titanates seem to also aid in the oxidation at higher temperatures; and (11) in general, increasing titania crystallinity leads to a decrease the catalytic activity.

Heteroatoms-doped 3D carbon nanosphere cages embedded with MoS2 for lithium-ion battery

A facile route for the N/P doped MoS2@ poly (cyclotriphosphazene-co-4,4-sulfonyldiphenol)-C (MoS2@PZS-C) yolk shell nanostructure has been presented. The obtained MoS2@PZS-C nanospheres has a unique advantage of yolk shell morphology, due to the internal void space (floc porous structure formed by oligomers) with a high surface area (573.9 m2 g−1), which can not only provide enough reaction sites to store electrical charge, but also accelerate the reaching of reaction sites by ions flux permeation. Even if the volume expansion causes the structure to be destroyed, the pulverized active material is still wrapped in the conductive material to achieve stable electrical contact. Using the MoS2@PZS-C nanospheres as anode material in lithium-ion batteries (LIBs), it presented enhanced cycle stability with high specific capacity (1245 mA h·g−1) and good rate capability. At the same time, DFT calculations showed that N, P, S doped modified carbon structure can improve the binding energy of materials and lithium ion/atoms, and change the local charge density of materials to produce more active sites. What’s more, the defects caused by doping can increase the electron chemical activity and electron transport rate of the material. It reveals the cause of the PZS-C electrode with high electrochemical performance.

FeS2@C-ICG-PEG nanostructure with intracellular O2 generation for enhanced photo-dynamic/thermal therapy and imaging

Here, photodynamic therapy (PDT), photothermal therapy (PTT) and multimode imaging have been integrated in to one-nanoplatform. The FeS2@C-PEG yolk-shell nanostructures (200 nm) have been synthesized, which possesses strong NIR absorption and high photothermal conversion (42.3%), ascribing to the narrow band gap and the novel hollow structure. Moreover, FeS2@C-PEG also reveals the NIR-triggered ROS (OH and O2–) generation, and the mechanism was investigated in detail, showing that the photo-excited electrons and dissolved O2 determine the ROS generation. Moreover, by evaluating the energy band of FeS2, the VB potential is enough to oxidize water to form O2 under NIR irradiation that relieves tumor hypoxia and enhances PDT. Besides, the Fenton reaction of Fe ion also makes FeS2 would degrade intracellular H2O2 to produce ·OH and O2 to assist PDT. To make the best of the hollow structure, photosensitizer ICG was loaded to further improve the PTT and PDT. Furthermore, FeS2@C-PEG possess high relaxivity (424.9 mM−1 s−1), making the potential contrast agent for MRI. And the synergistic effect of PTT and PDT further insures the enhanced anticancer efficacy.

Yolk-shell manganese oxide nanostructures for lithium-ion battery anodes

Nowadays, anodes based on graphitic materials are struggling with the ever-stringent requirements on lithium ion batteries (LIBs) in terms of energy and power densities, life-span, and deformability, from their extended applications such as automobiles, power grids and wearable electronics. As one of the promising alternates, transition metal oxides (TMOs) hold great perspectives. Unlike the lithium insertion mechanism of graphite, the lithiation/delithiation of TMOs is through redox conversion, imparting higher capacity and better safety. Among the numerous TMOs that have been extensively studied for LIB anodes, manganese oxides (MnO x ) are particularly attractive due to their high natural abundance, environmental benignity, tunable oxidation states, and low fabrication costs. However, as common to most of the TMOs, MnO x are essentially non-conductive and suffer from severe volume expansion upon lithiation, which greatly limit their rate capability and cycle performance. To overcome the above problems of MnO x (as well as other TMOs), many solutions have been attempted and can be majorly classified into two strategies: nanostructuring and carbon-compositing. The former based on developing diverse nanostructures brings in numerous benefits such as shortened ion diffusion path, enlarged electrochemically active surface, promoted electrolyte infiltration, as well as relieved lattice stress. The later based on hybridizing with various kinds of carbonaceous materials enables to greatly enhance electronic conductivity, buffer the cyclic volume fluctuation, and reinforce the electrode stability by providing structural supports for the active materials. Of the explored nanostructures, the yolk-shell structure has gained increasing attentions due to the prominent advantages in buffering the volume expansion and promoting the utilization of active materials. On one hand, when compared to solid nanoparticles the void spaces in the yolk-shell structure can accommodate the cyclic volume change during charge/discharge, effectively preventing the pulverization of active materials. On the other hand, in comparison to the hollow nanospheres and nanocages, the volumetric specific capacity of the yolk-shell structure is obviously superior. Nevertheless, despite of these apparent benefits, previous reported fabrications of yolk-shell nanostructures have been quite complex and typically involved multi-step synthesis with both high material and energy inputs. Besides, the structural stability and integrity of the yolk-shell structure itself pose an issue, in which the nanostructures might crack and collapse due to mechanical stress, especially in the prolonged charge/discharge process. Therefore, a rational design and facile fabrication of yolk-shell nanostructures for optimizing their utilization and stability in LIB anodes are highly desired for achieving the outstanding electrochemical and cycle performance. In this paper, a simple method involving polypyrrole-coated metal organic framework is adopted to synthesize manganese oxides with yolk-shell structure and use them as the anodes for lithium ion batteries. The as-prepared yolk-shell MnO x nanoparticles exhibit good specific capacity during charge/discharge, and demonstrate high specific capacities of 723, 651, 384 mAh g–1 at current densities of 0.1, 0.5 and 2 A g–1, respectively. Great stability and rate performance are also achieved with minimal capacity attenuation for over 200 cycles. Both the fabrication methodology and electrochemical understandings gained here for nanostructured manganese oxides can also extend to the other TMOs towards their ultimate implementation in high-performance LIBs.

Facile synthesis of yolk-shell structured Fe3O4@C-Au nanoparticles for thermotherapic application

Abstract Yolk-shell nanostructures haves promising applications in cancer therapy due to their great potential for multi-functions. However, the control over its structure and morphology still remains a big challenge. Herein, yolk-shell Fe3O4@C-Au composite nanostructure has been successfully synthesized with magnetic Fe3O4 nanoparticles encapsulated in hollow carbon shells and Au nanoparticles well dispersed. The yolk-shell structure has a uniform size of ~80 nm and a high surface area of 325.13 m2/g. The Fe3O4 and Au nanoparticles are 10 and 3 nm, respectively. The as-prepared Fe3O4@C-Au showed good biocompatibility during endocytosis process. The Fe3O4@C-Au suspension (150 μg/ml) shows efficient photothermal conversion effect and effectively damage 4T1 cells. The composite nanostructure Fe3O4@C-Au show promising applications in cancer diagnosis and therapy.

Ag nanoparticles encapsulated in carboxyl-functionalized hollow microporous organic nanospheres for highly efficient catalysis applications

In this work, we present a novel synthesis of Ag nanoparticles encapsulated in carboxyl-functionalized hollow microporous organic nanospheres (Ag@COOH-HMONs) by a combination of hyper-cross-linking mediated self-assembly and simply impregnation method, in which the COOH-HMONs supports were prepared via a Friedel-Crafts alkylation reaction by using polylactide-b-poly(tertbutyl acrylate)-b-polystyrene (PLA-b-PtBA-b-PS) triblock copolymer as precursors. Owing to the abundant carboxyl groups in the cavity of COOH-HMONs, highly dispersed silver nanoparticles can be successfully anchored into COOH-HMONs to produce Ag@COOH-HMONs via an ion exchange with AgNO3 following by an in-situ reduction of sodium borohydride (NaBH4). The obtained Ag@COOH-HMONs exhibit the high catalytic activities for the reduction of MB and nitroaromatic compounds as well as selective oxidation of thiol and styrene due to their high surface area, hierarchical porosity and yolk-shell nanostructure. This approach of constructing novel metal@porous organic polymers is expected to open doors for new types of yolk-shell structural catalysts for practical applications.

Interface control and catalytic performances of Au-NiSx heterostructures

Nickel sulfides (NiSx) as promising catalysts for hydrogen evolution reaction (HER) have attracted much interest. However, the HER catalytic activities of NiSx reported are relatively low for their poor electrical conductivity. The HER catalytic performance of NiSx is expected to be further enhanced by increasing their electronic conductivity. Constructing heterostructures consisting of noble metal and semiconductor has been proven to be an efficient method to promote their physicochemical performances benefitting from synergistic effects along the metal-semiconductor interface. Here, Au-NiSx heterostructures including core@shell, yolk-shell, and oligomer-like structures have been designed and synthesized by different solvothermal methods. A formation mechanism involving the Kirkendall effect has been proposed for the yolk-shell structure with an empty space around the Au core rather than the seeded grown core@shell structure. Catalytic performance measurements indicate that the Au@NiSx core@shell nanoparticles (NPs) exhibit superior HER catalytic property to Au-NiSx yolk-shell, oligomer-like structures, and “pure” NiSx NPs, resulting from the electron transfer between Au and NiSx interfaces. The overpotentials of Au-NiSx NPs with core@shell and yolk-shell nanostructures are 253 mV and 263 mV at 10 mA/cm2, respectively, which are lower than those of oligomer-like Au-NiSx (283 mV) and pure NiSx (321 mV) NPs. The Tafel slope of Au@NiSx core@shell structure (43.7 mV/dec) is also the lowest. These results demonstrate that the core@shell NPs possess the best HER performances, followed by their yolk-shell and oligomer-like counterparts. These findings confirm that the physicochemical performances of the metal-semiconductor heterostructures can be efficiently optimized by adjusting the electron transfer through the interface structure control.