Song Jin

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

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Publications (129)1378.8 Total impact

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    ABSTRACT: Metal fluoride and oxides can store multiple lithium-ions through conversion chemistry to enable high energy-density lithium-ion batteries. However, their practical applications have been hindered by an unusually large voltage hysteresis between charge and discharge voltage-profiles and the consequent low energy efficiency (< 80%). The physical origins of such hysteresis are rarely studied and poorly understood. Here we employ in situ X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM), density-functional-theory (DFT) calculations, and galvanostatic intermittent titration technique (GITT) to first correlate the voltage profile of iron fluoride (FeF3), a representative conversion electrode material, with evolution and spatial distribution of intermediate phases in the electrode. The results reveal that, contrary to conventional belief, the phase evolution in the electrode is symmetrical during discharge and charge. However, the spatial evolution of the electrochemically active phases, which is controlled by reaction kinetics, is different. We further propose that the voltage hysteresis in the FeF3 electrode is kinetic in nature. It is the result of Ohmic voltage drop, reaction overpotential, and different spatial distributions of electrochemically-active phases (i.e. compositional inhomogeneity). Therefore, the large hysteresis can be expected to be mitigated by rational design and optimization of material microstructure and electrode architecture to improve the energy efficiency of lithium-ion batteries based on conversion chemistry.
    No preview · Article · Feb 2016 · Journal of the American Chemical Society
  • Dong Liang · Matthew J. Stolt · Song Jin

    No preview · Article · Jan 2016 · Nature Physics
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    ABSTRACT: The excellent intrinsic optoelectronic properties of methylammonium lead halide perovskites (MAPbX3, X=Br, I) - such as high photoluminescence quantum efficiency, long carrier lifetime and high gain - coupled with the facile solution growth of nanowires make them promising new materials for ultralow-threshold nanowire lasers. However their photo- and thermal stabilities need to be improved for practical applications. Herein, we report a low-temperature solution growth of single crystal nanowires of formamidinium lead halide perovskites (FAPbX3) that feature red-shifted emission and better thermal stability compared to MAPbX3. We demonstrate optically-pumped room-temperature near-infrared (~820 nm) and green lasing (~560 nm) from FAPbI3 (and MABr-stabilized FAPbI3) and FAPbBr3 nanowires with low lasing thresholds of several µJ cm-2 and high quality factors of about 1500-2300. More remarkably, the FAPbI3 and MABr-stabilized FAPbI3 nanowires display durable room-temperature lasing under ~108 shots of sustained illumination of 402 nm pulsed laser excitation (150 fs, 250 kHz), substantially exceeding the stability of MAPbI3 (~107 laser shots). We further demonstrate tunable nanowire lasers in wider wavelength region from FA-based lead halide perovskite alloys (FA,MA)PbI3 and (FA,MA)Pb(I,Br)3 through cation and anion substitutions. The results suggest that formamidinium lead halide perovskite nanostructures could be more promising and stable materials for the development of light emitting diodes and continuous-wave lasers.
    Preview · Article · Jan 2016 · Nano Letters
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    ABSTRACT: Nickel-iron oxides/hydroxides are among the most active electrocatalysts for the oxygen evolution reaction. In an effort to gain insight into the role of Fe in these catalysts, we have performed operando Mössbauer spectroscopic studies of a 3:1 Ni:Fe layered hydroxide and a hydrous Fe oxide electrocatalyst. The catalysts were prepared by a hydrothermal precipitation method that enabled catalyst growth directly on carbon paper electrodes. Fe(4+) species were detected in the NiFe hydroxide catalyst during steady-state water oxidation, accounting for up to 21% of the total Fe. In contrast, no Fe(4+) was detected in the Fe oxide catalyst. The observed Fe(4+) species are not kinetically competent to serve as the active site in water oxidation; however, their presence has important implications for the role of Fe in NiFe oxide electrocatalysts.
    Full-text · Article · Nov 2015 · Journal of the American Chemical Society
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    ABSTRACT: We report metallic cobalt pyrite (CoS2) nanowires (NWs) prepared directly on current collecting electrodes, e.g., carbon cloth or graphite disc, for high-performance supercapacitors. These CoS2 NWs have a variety of advantages for supercapacitor applications. Because the metallic CoS2 NWs are synthesized directly on the current collector, the good electrical connection enables efficient charge transfer between the active CoS2 materials and the current collector. In addition, the open spaces between the sea urchin structure NWs lead to a large accessible surface area and afford rapid mass transport. Moreover, the robust CoS2 NW structure results in high stability of the active materials during long-term operation. Electrochemical characterization reveals that the CoS2 NWs enable large specific capacitance (828.2 F g(-1) at a scan rate of 0.01 V s(-1)) and excellent long term cycling stability (0-2.5% capacity loss after 4250 cycles at 5 A g(-1)) for pseudocapacitors. This example of metallic CoS2 NWs for supercapacitor applications expands the opportunities for transition metal sulfide-based nanostructures in emerging energy storage applications.
    Full-text · Article · Nov 2015 · Nanotechnology
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    ABSTRACT: We report the first coherent multidimensional spectroscopy study of a MoS2 film. A four-layer sample of MoS2 was synthesized on a silica substrate by a simplified sulfidation reaction and characterized by absorption and Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. State-selective coherent multidimensional spectroscopy (CMDS) on the as-prepared MoS2 film resolved the dynamics of a series of diagonal and cross-peak features involving the spin-orbit split A and B excitonic states and continuum states. The spectra are characterized by striped features that are similar to those observed in CMDS studies of quantum wells where the continuum states contribute strongly to the initial excitation of both the diagonal and cross-peak features, while the A and B excitonic states contributed strongly to the final output signal. The strong contribution from the continuum states to the initial excitation shows that the continuum states are coupled to the A and B excitonic states and that fast intraband relaxation is occurring on a sub-70 fs time scale. A comparison of the CMDS excitation signal and the absorption spectrum shows that the relative importance of the continuum states is determined primarily by their absorption strength. Diagonal and cross-peak features decay with a 680 fs time constant characteristic of exciton recombination and/or trapping. The short time dynamics are complicated by coherent and partially coherent pathways that become important when the excitation pulses are temporally overlapped. In this region, the coherent dynamics create diagonal features involving both the excitonic states and continuum states, while the partially coherent pathways contribute to cross-peak features.
    No preview · Article · Nov 2015 · ACS Nano
  • Ankit Pokhrel · Leith Samad · Fei Meng · Song Jin
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    ABSTRACT: In order to utilize nanostructured materials for potential solar and other energy-harvesting applications, scalable synthetic techniques for these materials must be developed. Herein we use a vapor phase conversion approach to synthesize nanowire (NW) arrays of semiconducting barium silicide (BaSi2) in high yield for the first time for potential solar applications. Dense arrays of silicon NWs obtained by metal-assisted chemical etching were converted to single-crystalline BaSi2 NW arrays by reacting with Ba vapor at about 930 °C. Structural characterization by X-ray diffraction and high-resolution transmission electron microscopy confirm that the converted NWs are single-crystalline BaSi2. The optimal conversion reaction conditions allow the phase-pure synthesis of BaSi2 NWs that maintain the original NW morphology, and tuning the reaction parameters led to a controllable synthesis of BaSi2 films on silicon substrates. The optical bandgap and electrochemical measurements of these BaSi2 NWs reveal a bandgap and carrier concentrations comparable to previously reported values for BaSi2 thin films.
    No preview · Article · Oct 2015 · Nanoscale
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    ABSTRACT: Silicon micropyramids with n(+) pp(+) junctions are demonstrated to be efficient absorbers for integrated solar-driven hydrogen production systems enabling significant improvements in both photocurrent and onset potential. When conformally coated with MoSx Cly , a catalyst that has excellent catalytic activity and high optical transparency, the highest photocurrent density for Si-based photocathodes with earth-abundant catalysts is achieved.
    No preview · Article · Sep 2015 · Advanced Materials
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    ABSTRACT: The study of efficient, robust, and earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) is essential for hydrogen-based energy technologies. Previous works have demonstrated that pyrite-structure materials (e.g., CoS2, NiSe2) are efficient HER catalysts. Here, we first systematically investigate the nanostructure synthesis of a series of pyrite-phase nickel phosphoselenide materials—NiP2, Se-doped NiP2 (NiP1.93Se0.07), P-doped NiSe2 (NiP0.09Se1.91), and NiSe2—through a facile thermal conversion of Ni(OH)2 nanoflakes. The similar nanostructures enable a systematic and fair comparison of their structural properties and catalytic activities for HER. We found that NiP1.93Se0.07 shows the best HER performance, followed by NiP2, NiP0.09Se1.91, and NiSe2. Se-doped NiP2 grown on carbon fiber paper can achieve an electrocatalytic current density of 10 mA cm–2 at an overpotential as low as 84 mV and a small Tafel slope of 41 mV decade–1. This study not only estabilishes Se-doped NiP2 as a competitive HER catalyst, but also demonstrates that doping or alloying of developed catalysts (especially doping with anions from another group; e.g., selenium to phosphorus) can improve the HER catalytic activity, which provides a general strategy to improve catalytic efficiencies of existing electrocatalysts for HER.
    Full-text · Article · Sep 2015 · ACS Catalysis
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    ABSTRACT: The scalable and sustainable production of hydrogen fuel through water splitting demands efficient and robust Earth-abundant catalysts for the hydrogen evolution reaction (HER). Building on promising metal compounds with high HER catalytic activity, such as pyrite structure cobalt disulphide (CoS2), and substituting non-metal elements to tune the hydrogen adsorption free energy could lead to further improvements in catalytic activity. Here we present a combined theoretical and experimental study to establish ternary pyrite-type cobalt phosphosulphide (CoPS) as a high-performance Earth-abundant catalyst for electrochemical and photoelectrochemical hydrogen production. Nanostructured CoPS electrodes achieved a geometrical catalytic current density of 10 mA cm(-2) at overpotentials as low as 48 mV, with outstanding long-term operational stability. Integrated photocathodes of CoPS on n(+)-p-p(+) silicon micropyramids achieved photocurrents up to 35 mA cm(-2) at 0 V versus the reversible hydrogen electrode (RHE), onset photovoltages as high as 450 mV versus RHE, and the most efficient solar-driven hydrogen generation from Earth-abundant systems.
    No preview · Article · Sep 2015 · Nature Materials
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    ABSTRACT: Porous materials are of particular interest due to their high surface area and rich edge sites, which are favorable for applications such as catalysis. Although there are well-established strategies for synthesizing porous metal oxides (e.g., by annealing the corresponding metal hydroxides), facile and scalable routes to porous metal hydroxides and metal chalcogenides are lacking. Here, we report a simple and general strategy to synthesize porous nanosheets of metal hydroxides by selectively etching layered double hydroxide (LDH) nanoplate precursors that contain amphoteric metal and to further convert them into porous metal chalcogenides by a solution method. Using NiGa LDH as an example, we show that the thin nanoplates with high surface accessibility facilitate the topotactic conversion of NiGa LDH to β-Ni(OH)2 and further to NiSe2 with porous texture while preserving the sheet-like morphology. The converted β-Ni(OH)2 and NiSe2 are highly active for electrocatalytic oxygen evolution reaction and hydrogen evolution reaction (HER), respectively, which demonstrates the applications of such high surface area porous nanostructures with rich edge sites. Particularly, the porous NiSe2 nanosheets exhibited excellent catalytic activity toward HER with low onset overpotential, small Tafel slope, and good stability under both acidic and alkaline conditions. Overall electrochemical water splitting experiments using these porous β-Ni(OH)2 and NiSe2 nanosheets were further demonstrated. Our work presents a new strategy to prepare porous nanomaterials and to further enhance their catalytic and other applications. (Figure Presented).
    Full-text · Article · Sep 2015 · Chemistry of Materials
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    ABSTRACT: Supplementary information available for this article at http://www.nature.com/ncomms/2015/150420/ncomms7883/suppinfo/ncomms7883_S1.html
    No preview · Article · Apr 2015
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    ABSTRACT: In situ techniques with high temporal, spatial and chemical resolution are key to understand ubiquitous solid-state phase transformations, which are crucial to many technological applications. Hard X-ray spectro-imaging can visualize electrochemically driven phase transformations but demands considerably large samples with strong absorption signal so far. Here we show a conceptually new data analysis method to enable operando visualization of mechanistically relevant weakly absorbing samples at the nanoscale and study electrochemical reaction dynamics of iron fluoride, a promising high-capacity conversion cathode material. In two specially designed samples with distinctive microstructure and porosity, we observe homogeneous phase transformations during both discharge and charge, faster and more complete Li-storage occurring in porous polycrystalline iron fluoride, and further, incomplete charge reaction following a pathway different from conventional belief. These mechanistic insights provide guidelines for designing better conversion cathode materials to realize the promise of high-capacity lithium-ion batteries.
    Preview · Article · Apr 2015 · Nature Communications

  • No preview · Article · Apr 2015 · Nature Communications
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    ABSTRACT: Supplementary information available for this article at http://www.nature.com/ncomms/2015/150420/ncomms7883/suppinfo/ncomms7883_S1.html
    No preview · Article · Apr 2015
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    ABSTRACT: Magnetic skyrmions are topologically stable whirlpool-like spin textures that offer great promise as information carriers for future ultra-dense memory and logic devices1-4. To enable such applications, particular attention has been focused on the skyrmions properties in highly confined geometry such as one dimensional nanowires5-8. Hitherto it is still experimentally unclear what happens when the width of the nanowire is comparable to that of a single skyrmion. Here we report the experimental demonstration of such scheme, where magnetic field-driven skyrmion cluster (SC) states with small numbers of skyrmions were demonstrated to exist on the cross-sections of ultra-narrow single-crystal MnSi nanowires (NWs) with diameters, comparable to the skyrmion lattice constant (18 nm). In contrast to the skyrmion lattice in bulk MnSi samples, the skyrmion clusters lead to anomalous magnetoresistance (MR) behavior measured under magnetic field parallel to the NW long axis, where quantized jumps in MR are observed and directly associated with the change of the skyrmion number in the cluster, which is supported by Monte Carlo simulations. These jumps show the key difference between the clustering and crystalline states of skyrmions, and lay a solid foundation to realize skyrmion-based memory devices that the number of skyrmions can be counted via conventional electrical measurements.
    Full-text · Article · Apr 2015 · Nature Communications
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    ABSTRACT: A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain the low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.
    No preview · Article · Apr 2015 · Nature Communications
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    ABSTRACT: Understanding crystal growth and improving material quality is important for improving semiconductors for electronic, optoelectronic, and photovoltaic applications. Amidst the surging interest in solar cells based on hybrid organic-inorganic lead halide perovskites and the exciting progress in device performance, improved understanding and better control of the crystal growth of these perovskites could further boost their optoelectronic and photovoltaic performance. Here, we report new insights on the crystal growth of the perovskite materials, especially crystalline nanostructures. Specifically, single crystal nanowires, nanorods, and nanoplates of methylammonium lead halide perovskites (CH3NH3PbI3 and CH3NH3PbBr3) are successfully grown via a dissolution-recrystallization pathway in a solution synthesis from lead iodide (or lead acetate) films coated on substrates. These single crystal nanostructures display strong room-temperature photoluminescence and long carrier lifetime. We also report that a solid-liquid interfacial conversion reaction can create a highly crystalline, nanostructured MAPbI3 film with micrometer grain size and high surface coverage which enables photovoltaic devices with a power conversion efficiency of 10.6%. These results suggest that single-crystal perovskite nanostructures provide improved photophysical properties that are important for fundamental studies and future applications in nanoscale optoelectronic and photonic devices.
    No preview · Article · Apr 2015 · Journal of the American Chemical Society
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    ABSTRACT: Layered double hydroxides (LDHs) are a family of two-dimensional (2D) materials with layered crystal structures that have found many applications. Common strategies to synthesize LDHs lead to a wide variety of morphologies, from discrete 2D nanosheets to nanoflowers. Here we report a study of carefully controlled LDH nanoplate syntheses using zinc aluminum (ZnAl) and cobalt aluminum (CoAl) LDHs as examples, and reveal their crystal growth to be driven by screw dislocations. By controlling and maintaining a low precursor supersaturation using a continuous flow reactor, individual LDH nanoplates with well-defined morphologies were synthesized on alumina-coated substrates, instead of the nanoflowers that result from uncontrolled overgrowth. The dislocation-driven growth was further established for LDH nanoplates directly synthesized using the respective metal salt precursors. Atomic force microscopy revealed screw dislocation growth spirals, and under transmission electron microscopy thin CoAl LDH nanoplates displayed complex contrast contours indicative of strong lattice strain caused by dislocations. These results suggest the dislocation-driven mechanism is generally responsible for the growth of 2D LDH nanostructures, and likely other materials with layered crystal structures, which could help the rational synthesis of well-defined 2D nanomaterials with improved properties.
    Full-text · Article · Apr 2015 · Nano Letters
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    ABSTRACT: The remarkable performance of lead halide perovskites in solar cells can be attributed to the long carrier lifetimes and low non-radiative recombination rates, the same physical properties that are ideal for semiconductor lasers. Here, we show room-temperature and wavelength-tunable lasing from single-crystal lead halide perovskite nanowires with very low lasing thresholds (220 nJ cm(-2)) and high quality factors (Q ∼ 3,600). The lasing threshold corresponds to a charge carrier density as low as 1.5 × 10(16) cm(-3). Kinetic analysis based on time-resolved fluorescence reveals little charge carrier trapping in these single-crystal nanowires and gives estimated lasing quantum yields approaching 100%. Such lasing performance, coupled with the facile solution growth of single-crystal nanowires and the broad stoichiometry-dependent tunability of emission colour, makes lead halide perovskites ideal materials for the development of nanophotonics, in parallel with the rapid development in photovoltaics from the same materials.
    Full-text · Article · Apr 2015 · Nature Materials

Publication Stats

5k Citations
1,378.80 Total Impact Points

Institutions

  • 2006-2016
    • University of Wisconsin–Madison
      • Department of Chemistry
      Madison, Wisconsin, United States
  • 1999-2010
    • Cornell University
      • Department of Chemistry and Chemical Biology
      Итак, New York, United States