Song Jin

University of Wisconsin–Madison, Madison, Wisconsin, United States

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Publications (82)738.5 Total impact

  • Matthew S. Faber, Song Jin
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    ABSTRACT: Electrocatalysis plays a key role in the energy conversion processes central to several renewable energy technologies that have been developed to lessen our reliance on fossil fuels. However, the best electrocatalysts for these processes—which include the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the redox reactions that enable regenerative liquid-junction photoelectrochemical solar cells—often contain scarce and expensive noble metals, substantially limiting the potential for these technologies to compete with fossil fuels. The considerable challenge is to develop robust electrocatalysts composed exclusively of low-cost, earth-abundant elements that exhibit activity comparable to that of the noble metals. In this review, we summarize recent progress in the development of such high-performance earth-abundant inorganic electrocatalysts (and nanostructures thereof), classifying these materials based on their elemental constituents. We then detail the most critical obstacles facing earth-abundant inorganic electrocatalysts and discuss various strategies for further improving their performance. Lastly, we offer our perspectives on the current directions of earth-abundant inorganic electrocatalyst development and suggest pathways toward achieving performance competitive with their noble metal-containing counterparts.
    Energy & Environmental Science 08/2014; · 11.65 Impact Factor
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    ABSTRACT: We report metallic WS2 nanosheets that display excellent catalytic activity for hydrogen evolution reaction (HER) that is the best reported for MX2 materials. They are chemically exfoliated from WS2 nanostructures synthesized by chemical vapour deposition, including by using a simple and fast microwave-assisted intercalation method. Structural and electrochemical studies confirm that the simultaneous conversion and exfoliation of semiconducting 2H-WS2 into nanosheets of its metallic 1T polymorph result in facile electrode kinetics, excellent electrical transport, and proliferation of catalytically active sites.
    Energy & Environmental Science 07/2014; 7(8). · 11.65 Impact Factor
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    ABSTRACT: The development of efficient and robust earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) is an ongoing challenge. We report metallic cobalt pyrite (cobalt disulfide, CoS2) as one such high-activity candidate material, and demonstrate that its specific morphology-film, microwire, or nanowire, made available through controlled synthesis-plays a crucial role in determining its overall catalytic efficacy. The increase in effective electrode surface area that accompanies CoS2 micro- and nanostructuring substantially boosts its performance, with CoS2 nanowire electrodes achieving geometric current densities of -10 mA cm(-2) at overpotentials as low as -145 mV vs. the reversible hydrogen electrode. Moreover, micro- and nanostructuring of the CoS2 material has the synergistic effect of increasing its operational stability, cyclability, and maximum achievable rate of hydrogen generation by promoting the release of evolved gas bubbles from the electrode surface. The benefits of catalyst micro- and nanostructuring are further demonstrated by the increased electrocatalytic activity of CoS2 nanowire electrodes over planar film electrodes toward polysulfide and triiodide reduction, which suggests a straightforward way to improve the performance of quantum dot- and dye-sensitized solar cells, respectively. Extension of this micro- and nanostructuring strategy to other earth-abundant materials could similarly enable inexpensive electrocatalysts that lack the high intrinsic activity of the noble metals.
    Journal of the American Chemical Society 06/2014; · 10.68 Impact Factor
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    ABSTRACT: We report the preparation and characterization of highly efficient and robust photocathodes based on heterostructures of chemically exfoliated metallic 1T-MoS2 and planar p-type Si for solar-driven hydrogen production. Photocurrents up to 17.6 mA/cm(2) at 0 V vs reversible hydrogen electrode were achieved under simulated 1 sun irradiation, and excellent stability was demonstrated over long-term operation. Electrochemical impedance spectroscopy revealed low charge-transfer resistances at the semiconductor/catalyst and catalyst/electrolyte interfaces, and surface photoresponse measurements also demonstrated slow carrier recombination dynamics and consequently efficient charge carrier separation, providing further evidence for the superior performance. Our results suggest that chemically exfoliated 1T-MoS2/Si heterostructures are promising earth-abundant alternatives to photocathodes based on noble metal catalysts for solar-driven hydrogen production.
    Journal of the American Chemical Society 06/2014; · 10.68 Impact Factor
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    ABSTRACT: We report a facile chemical vapor deposition (CVD) growth of vertical heterostructures of layered metal dichalcogenides (MX2) enabled by van der Waals epitaxy. Few layers of MoS2, WS2, and WSe2 were grown uniformly onto microplates of SnS2 under mild CVD reaction conditions (< 500 °C) and the heteroepitaxy between them was confirmed using cross sectional transmission electron microscopy (TEM) and unequivocally characterized by resolving the large-area Moiré patterns appeared on the basal planes of microplates in conventional TEM (non-sectioned). Additional photoluminescence peaks were observed in heterostructures of MoS2-SnS2, which can be understood with electronic structure calculations to likely result from electronic coupling and charge separation between MoS2 and SnS2 layers. This work opens up the exploration of large-area heterostructures of diverse MX2 nanomaterials as the material platform for electronic structure engineering of atomically thin two-dimensional (2D) semiconducting heterostructures and device applications.
    Nano Letters 05/2014; · 13.03 Impact Factor
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    ABSTRACT: Higher manganese silicides (HMS) made of earth-abundant and non-toxic elements are regarded as promising p-type thermoelectric materials because their complex crystal structure results in low lattice thermal conductivity. It is shown here that the already low thermal conductivity of HMS can be reduced further to approach the minimum thermal conductivity via partial substitution of Mn with heavier rhenium (Re) to increase point defect scattering. The solubility limit of Re in the obtained RexMn1-xSi1.8 is determined to be about x = 0.18. Elemental inhomogeneity and the formation of ReSi1.75 inclusions with 50−200 nm size are found within the HMS matrix. It is found that the power factor does not change markedly at low Re content of x ≤ 0.04 before it drops considerably at higher Re contents. Compared to pure HMS, the reduced lattice thermal conductivity in RexMn1-xSi1.8 results in a 25% increase of the peak figure of merit ZT to reach 0.57 ± 0.08 at 800 K for x = 0.04. The suppressed thermal conductivity in the pure RexMn1-xSi1.8 can enable further investigations of the ZT limit of this system by exploring different impurity doping strategies to optimize the carrier concentration and power factor.
    Advanced Energy Materials 05/2014; · 10.04 Impact Factor
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    ABSTRACT: Topologically stable magnetic skyrmions realized in B20 metal silicide or germanide compounds with helimagnetic order are very promising for magnetic memory and logic devices. However, these applications are hindered because the skyrmions only survive in a small temperature-field (T-H) pocket near the critical temperature Tc in bulk materials. Here, we demonstrate that the skyrmion state in helimagnetic MnSi nanowires with varied sizes from 400 nm to 250 nm can exist in a substantially extended T-H region. Magnetoresistance measurements under a moderate external magnetic field along the long axis of the nanowires (H// ) show transitions corresponding to the skyrmion state from Tc ~32 K down to at least 3 K, the lowest temperature in our measurement. When the field is applied perpendicular to the wire axis (H⊥), the skyrmion state was not resolvable using the magnetoresistance measurements. Our analysis suggests that the shape-induced uniaxial anisotropy might be responsible for the stabilization of skyrmion state observed in nanowires.
    Nano Letters 03/2014; · 13.03 Impact Factor
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    ABSTRACT: Iron pyrite is an earth-abundant and inexpensive material that has long been interesting for electrochemical energy storage and solar energy conversion. A large-scale conversion synthesis of phase-pure pyrite nanowires has been developed for the first time. Nano-pyrite cathodes exhibited high Li-storage capacity and excellent capacity retention in Li/pyrite batteries using a liquid electrolyte, which retained a discharge capacity of 350 mAh g(-1) and a discharge energy density of 534 Wh kg(-1) after 50 cycles at 0.1 C rate.
    Nanoscale 01/2014; · 6.23 Impact Factor
  • Source
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    ABSTRACT: Effective control of phase growth under harsh conditions (such as high temperature, highly conductive liquids or high growth rate), where surfactants are unstable or ineffective, is still a long-standing challenge. Here we show a general approach for rapid control of diffusional growth through nanoparticle self-assembly on the fast-growing phase during cooling. After phase nucleation, the nanoparticles spontaneously assemble, within a few milliseconds, as a thin coating on the growing phase to block/limit diffusion, resulting in a uniformly dispersed phase orders of magnitude smaller than samples without nanoparticles. The effectiveness of this approach is demonstrated in both inorganic (immiscible alloy and eutectic alloy) and organic materials. Our approach overcomes the microstructure refinement limit set by the fast phase growth during cooling and breaks the inherent limitations of surfactants for growth control. Considering the growing availability of numerous types and sizes of nanoparticles, the nanoparticle-enabled growth control will find broad applications.
    Nature Communications 01/2014; 5:3879. · 10.02 Impact Factor
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    ABSTRACT: We report a novel synthesis of Ti5Si3 nanoparticles (NPs) via the magnesio-reduction of TiO2 NPs and SiO2 in eutectic LiCl-KCl molten salts at 700 °C. The Ti5Si3 particle size (∼25 nm) is confined to the nanoscale due to the partial dissolution of Mg and silica in the molten salts and a subsequent heterogeneous reduction on the surface of the TiO2 NPs.
    Chemical Communications 12/2013; · 6.38 Impact Factor
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    ABSTRACT: Stacking faults are an important class of crystal defects commonly observed in nanostructures of close packed crystal structures. They can bridge the transition between hexagonal wurtzite (WZ) and cubic zinc blende (ZB) phases, with the most known example represented by the "nanowire (NW) twinning superlattice". Understanding the formation mechanisms of stacking faults is crucial to better control them and thus enhance the capability of tailoring physical properties of nanomaterials through defect engineering. Here we provide a different perspective to the formation of stacking faults associated with the screw dislocation-driven growth mechanism of nanomaterials. With the use of NWs of WZ aluminum nitride (AlN) grown by a high-temperature nitridation method as the model system, dislocation-driven growth was first confirmed by transmission electron microscopy (TEM). Meanwhile numerous stacking faults and associated partial dislocations were also observed and identified to be the Type I stacking faults and the Frank partial dislocations, respectively, using high-resolution TEM. In contrast, AlN NWs obtained by rapid quenching after growth displayed no stacking faults or partial dislocations; instead many of them had voids that were associated with the dislocation-driven growth. On the basis of these observations, we suggest a formation mechanism of stacking faults that originate from dislocation voids during the cooling process in the syntheses. Similar stacking fault features were also observed in other NWs with WZ structure, such as cadmium sulfide (CdS) and zinc oxide (ZnO).
    ACS Nano 12/2013; · 12.03 Impact Factor
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    ABSTRACT: Organic ligands are widely used to enhance the ability of CdSe quantum dots (QDs) to resist photodegradation processes such as photo-oxidation. Because long alkyl chains may adversely affect the performance of QD devices that require fast and efficient charge transfer, shorter aromatic ligands are of increasing interest. In this work we characterize the formation of phenyl dithiocarbamate (DTC) adducts on CdSe surfaces and the relative effectiveness of different para -substituted phenyl dithiocarbamates to enhance the aqueous photostability of CdSe QDs on TiO2. Optical absorption and photoluminescence measurements show that phenyl DTC ligands can be highly effective at reducing QD photocorrosion in water, and that ligands bearing electron-donating substituents are the most effective. A comparison of the QD photostability resulting from use of ligands bearing DTC versus thiol surface-binding groups shows that the DTC group provides greater QD photostability. Density Functional calculations with Natural Bond Order analysis show that the effectiveness of substituted phenyl DTC results from the ability of these ligands to remove positive charge away from the CdSe and to delocalize positive charge on the ligand.
    ACS Applied Materials & Interfaces 11/2013; · 5.01 Impact Factor
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    ABSTRACT: Metal-matrix nanocomposites (MMNCs) have great potential for a wide range of applications. In order to provide high performance, effective nanoparticle (NP) dispersion in the liquid and NP capture within the metal grains during solidification is essential. In this work, we present the novel synthesis and structural characterization of surface-clean titanium diboride (TiB2) NPs with an average particle size of 20 nm, by ultrasonic-assisted reduction of fluorotitanate and fluoroboride salts in molten aluminum. The high-intensity ultrasonic field restricts NP growth. Using a master nanocomposite approach, the as-prepared TiB2 NPs are effectively incorporated into A206 alloys during solidification processing due to their clean surface, showing partial capture and significant grain refinement.
    ACS Applied Materials & Interfaces 08/2013; · 5.01 Impact Factor
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    ABSTRACT: We report a three-dimensional (3D) mesoscale heterostructure comprised of one-dimensional (1D) nanowire (NW) arrays epitaxially grown on two-dimensional (2D) nanoplates. Specifically, three facile syntheses are developed to assemble vertical ZnO NWs on CuGaO2 (CGO) nanoplates in mild aqueous solution conditions. The key to the successful 3D mesoscale integration is the preferential nucleation and heteroepitaxial growth of ZnO NWs on the CGO nanoplates. Using transmission electron microscopy, heteroepitaxy was found between the basal planes of CGO nanoplates and ZnO NWs, which are their respective (001) crystallographic planes, by the observation of a hexagonal Moiré fringes pattern resulting from the slight mismatch between the c planes of ZnO and CGO. Careful analysis shows that this pattern can be described by a hexagonal supercell with a lattice parameter of almost exactly 11 and 12 times the a lattice constants for ZnO and CGO, respectively. The electrical properties of the individual CGO-ZnO mesoscale heterostructures were measured using a current sensing atomic force microscopy setup to confirm the rectifying p-n diode behavior expected from the band alignment of p-type CGO and n-type ZnO wide band gap semiconductors. These 3D mesoscale heterostructures represent a new motif in nanoassembly for the integration of nanomaterials into functional devices with potential applications in electronics, photonics, and energy.
    ACS Nano 08/2013; · 12.03 Impact Factor
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    ABSTRACT: We report here the real-space observation of skyrmions and helical magnetic domains in a MnSi nanowire (NW) using Lorentz transmission electron microscopy (LTEM). The MnSi NW was thinned to a rectangular cross-section by focused-ion beam milling to reduce obstructive Fresnel fringes. Helimagnetic domains, imaged as alternating bright and dark contrast stripes with an 18 nm period were observed to be the spontaneous magnetic ground state at 6 K, while the hexagonal skyrmion lattice (SkX) with a domain diameter of 18 nm was observed under a normal magnetic field of 210 mT. Temperature dependent measurements reveal that the SkX is stable over a larger range in this NW system (6 K - 35 K) compared to the narrow temperature regime of skyrmion phase in bulk MnSi (26 - 30 K) and thin films of MnSi (5 - 23 K).
    Nano Letters 07/2013; · 13.03 Impact Factor
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    ABSTRACT: Promising catalytic activity from molybdenum disulfide (MoS2) in the hydrogen evolution reaction (HER) is attributed to active sites located along the edges of its two-dimensional layered crystal structure, but its performance is currently limited by the density and reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst. Here we report dramatically enhanced HER catalysis (an electrocatalytic current density of 10 mA/cm(2) at a low overpotential of ‒187 mV vs. RHE and a Tafel slope of 43 mV/decade) from metallic nanosheets of 1T-MoS2 chemically exfoliated via lithium intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Structural characterization and electrochemical studies confirm that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics, low-loss electrical transport, and possess a proliferated density of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make these metallic nanosheets a highly competitive earth-abundant HER catalyst.
    Journal of the American Chemical Society 06/2013; · 10.68 Impact Factor
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    ABSTRACT: Nanoscience and nanotechnology impact our lives in many ways, from electronic and photonic devices to biosensors. They also hold the promise of tackling the renewable energy challenges facing us. However, one limiting scientific challenge is the effective and efficient bottom-up synthesis of nanomaterials. We can approach this core challenge in nanoscience and nanotechnology from two perspectives: (a) how to controllably grow high-quality nanomaterials with desired dimensions, morphologies, and material compositions and (b) how to produce them in a large quantity at reasonable cost. Because many chemical and physical properties of nanomaterials are size- and shape-dependent, rational syntheses of nanomaterials to achieve desirable dimensionalities and morphologies are essential to exploit their utilities. In this Account, we show that the dislocation-driven growth mechanism, where screw dislocation defects provide self-perpetuating growth steps to enable the anisotropic growth of various nanomaterials at low supersaturation, can be a powerful and versatile synthetic method for a wide variety of nanomaterials. Despite significant progress in the last two decades, nanomaterial synthesis has often remained an "art", and except for a few well-studied model systems, the growth mechanisms of many anisotropic nanostructures remain poorly understood. We strive to go beyond the empirical science ("cook-and-look") and adopt a fundamental and mechanistic perspective to the anisotropic growth of nanomaterials by first understanding the kinetics of the crystal growth process. Since most functional nanomaterials are in single-crystal form, insights from the classical crystal growth theories are crucial. We pay attention to how screw dislocations impact the growth kinetics along different crystallographic directions and how the strain energy of defected crystals influences their equilibrium shapes. Furthermore, such inquiries are supported by detailed structural investigation to identify the evidence of dislocations. The dislocation-driven growth mechanism not only can unify the various explanations behind a wide variety of exotic nanoscale morphologies but also allows the rational design of catalyst-free solution-phase syntheses that could enable the scalable and low cost production of nanomaterials necessary for large scale applications, such as solar and thermoelectric energy conversions, energy storage, and nanocomposites. In this Account, we discuss the fundamental theories of the screw dislocation driven growth of various nanostructures including one-dimensional nanowires and nanotubes, two-dimensional nanoplates, and three-dimensional hierarchical tree-like nanostructures. We then introduce the transmission electron microscopy (TEM) techniques to structurally characterize the dislocation-driven nanomaterials for future searching and identifying purposes. We summarize the guidelines for rationally designing the dislocation-driven growth and discuss specific examples to illustrate how to implement the guidelines. By highlighting our recent discoveries in the last five years, we show that dislocation growth is a general and versatile mechanism that can be used to grow a variety of nanomaterials via distinct reaction chemistry and synthetic methods. These discoveries are complemented by selected examples of anisotropic crystal growth from other researchers. The fundamental investigation and development of dislocation-driven growth of nanomaterials will create a new dimension to the rational design and synthesis of increasingly complex nanomaterials.
    Accounts of Chemical Research 06/2013; · 20.83 Impact Factor
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    ABSTRACT: We present a general methodology for measuring the Hall effect on nanostructures with one-dimensional (1D) nanowire morphology. Relying only on typical e-beam lithography, the methodology developed herein utilizes an angled electrode evaporation technique so that the nanowire itself is a shadow mask and an intimate sidewall contact can be formed for the Hall electrodes. A six-contact electrode scheme with offset transverse contacts is utilized that allows monitoring of both the longitudinal resistivity and the Hall resistivity which is extracted from the raw voltage from the transverse electrodes using an antisymmetrization procedure. Our method does not require the use of a highly engineered lithographic process to produce directly opposing Hall electrodes with a very small gap. Hall effect measurements on semiconducting iron pyrite (FeS2) nanowire devices are validated by comparing to Hall effect measurements in the conventional Hall geometry using FeS2 plate devices. This Hall effect measurement is further extended to MnSi nanowires, and the distinct anomalous Hall effect signature is identified for the first time in chiral magnetic MnSi nanowires, a significant step towards identifying the topological Hall effect due to skyrmions in chiral magnetic nanowires.
    Nano Letters 05/2013; · 13.03 Impact Factor
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    ABSTRACT: We report a cobalt pyrite (cobalt disulfide, CoS2) thin film on glass as a robust, high-performance, low-cost, earth-abundant counter electrode for liquid-junction quantum dot-sensitized solar cells (QDSSCs) that employ the aqueous sulfide/polysulfide (S2–/Sn2–) redox electrolyte as the hole-transporting medium. The metallic CoS2 thin film electrode is prepared via thermal sulfidation of a cobalt film deposited on glass and has been characterized by powder X-ray diffraction and electron microscopy. Using the CoS2 counter electrode, CdS/CdSe-sensitized QDSSCs display improved short-circuit photocurrent density and fill factor, achieving solar light-to-electricity conversion efficiencies as high as 4.16%, with an average efficiency improvement of 54 (±14)% over equivalent devices assembled with a traditional platinum counter electrode. Electrochemical measurements verify that CoS2 shows high electrocatalytic activity toward polysulfide reduction, rationalizing the improved QDSSC performance. CoS2 is also less susceptible to poisoning by the sulfide/polysulfide electrolyte, a problem that plagues platinum electrodes in this application; furthermore, CoS2 exhibits excellent stability in sulfide/polysulfide electrolyte, resulting in highly reproducible performance.
    Journal of Physical Chemistry Letters 05/2013; 4(11):1843–1849. · 6.59 Impact Factor
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    ABSTRACT: If nanostructured thermoelectric materials are to be used for future energy harvesting and power generation applications, scalable production of thermoelectric nanostructures must be developed. Herein we report a vapor phase conversion method to synthesize nanowire (NW) arrays of semiconducting higher manganese silicides (HMS, or MnSi1.75) for enhanced thermoelectric applications. Dense arrays of silicon NWs obtained by metal-assisted chemical etching were converted to single-crystalline HMS NW arrays with the original nanoscale morphology preserved by reacting with Mn vapor in a sealed stainless steel reactor at 950 °C. Structural characterization by X-ray and electron diffraction and high-resolution transmission electron microscopy confirm that the converted NWs are single-crystalline NWs of HMS phases such as Mn7Si12, Mn27Si47, and Mn39Si68. Investigations of the conversion process using in situ high resolution powder X-ray diffraction (HRPXRD) and mechanistic experiments reveal that the presence of excess Si substrate underneath the Si NWs, careful control of Mn precursor, and high reaction temperature are crucial to the selective formation of HMS phase. The electrical resistivity of these HMS NWs are similar to that of the bulk HMS.
    Chemistry of Materials. 02/2013; 25(4):632–638.

Publication Stats

741 Citations
738.50 Total Impact Points

Institutions

  • 2006–2014
    • University of Wisconsin–Madison
      • Department of Chemistry
      Madison, Wisconsin, United States
  • 2011
    • Nanyang Technological University
      • School of Materials Science and Engineering
      Singapore, Singapore
  • 2007
    • University of Texas at Austin
      • Department of Materials Science and Engineering
      Austin, TX, United States