Showing papers by "Song Jin published in 2014"
TL;DR: In this article, the authors report metallic cobalt pyrite (cobalt disulfide, CoS2) as one such high-activity candidate material and demonstrate that its specific morphology plays a crucial role in determining its overall catalytic efficacy.
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 HER catalytic 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 ca...
1,135 citations
TL;DR: In this article, the authors summarize recent progress in the development of high-performance earth-abundant inorganic electrocatalysts (and nanostructures thereof), classifying these materials based on their elemental constituents.
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.
1,088 citations
TL;DR: In this paper, the authors report metallic WS2 nanosheets that display excellent catalytic activity for hydrogen evolution reaction (HER) that is the best reported for MX2 materials.
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.
638 citations
TL;DR: Thick films of the earth-abundant pyrite-phase transition metal disulfides are investigated as promising alternative electrocatalysts for both the HER and polysulfide reduction and structural disorder introduced by alloying different transition metal pyrites could increase their areal density of active sites for catalysis, leading to enhanced performance.
Abstract: Many materials have been explored as potential hydrogen evolution reaction (HER) electrocatalysts to generate clean hydrogen fuel via water electrolysis, but none so far compete with the highly efficient and stable (but cost prohibitive) noble metals. Similarly, noble metals often excel as electrocatalytic counter electrode materials in regenerative liquid-junction photoelectrochemical solar cells, such as quantum dot-sensitized solar cells (QDSSCs) that employ the sulfide/polysulfide redox electrolyte as the hole mediator. Here, we systematically investigate thin films of the earth-abundant pyrite-phase transition metal disulfides (FeS2, CoS2, NiS2, and their alloys) as promising alternative electrocatalysts for both the HER and polysulfide reduction. Their electrocatalytic activity toward the HER is correlated to their composition and morphology. The emergent trends in their performance suggest that cobalt plays an important role in facilitating the HER, with CoS2 exhibiting highest overall performance....
528 citations
TL;DR: The 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.
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.
367 citations
TL;DR: A facile chemical vapor deposition (CVD) growth of vertical heterostructures of layered metal dichalcogenides (MX2) enabled by van der Waals epitaxy is reported, which opens up the exploration of large-area heteroststructures of diverse MX2 nanomaterials as the material platform for electronic structure engineering of atomically thin two-dimensional (2D) semiconducting heterostructure and device applications.
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 Moire patterns that appeared on the basal planes of microplates in conventional TEM (nonsectioned). 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 heterostructu...
144 citations
TL;DR: This work shows a general approach for rapid control of diffusional growth through nanoparticle self-assembly on the fast-growing phase during cooling that overcomes the microstructure refinement limit set by the fast phase growth during cooling and breaks the inherent limitations of surfactants for growth control.
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.
144 citations
TL;DR: A large-scale conversion synthesis of phase-pure pyrite nanowires has been developed for the first time, which exhibited high Li-storage capacity and excellent capacity retention in Li/pyrite batteries using a liquid electrolyte.
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.
140 citations
TL;DR: It is demonstrated that the skyrmion state in helimagnetic MnSi nanowires with varied sizes from 400 to 250 nm can exist in a substantially extended T-H region and suggested that the shape-induced uniaxial anisotropy might be responsible for the stabilization of skyrMion state observed in Nanowires.
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 applic...
96 citations
TL;DR: A comprehensive investigation on {100}-faceted n-type iron pyrite single crystals to understand its puzzling low VOC revealed that the high-density of intrinsic surface states cannot satisfactorily explain the low photovoltage; instead, the ionization of high- density bulk deep donor states creates a nonconstant charge distribution and a very narrow surface space charge region that limits the total barrier height.
Abstract: Iron pyrite (FeS2) is considered a promising earth-abundant semiconductor for solar energy conversion with the potential to achieve terawatt-scale deployment. However, despite extensive efforts and progress, the solar conversion efficiency of iron pyrite remains below 3%, primarily due to a low open circuit voltage (VOC). Here we report a comprehensive investigation on {100}-faceted n-type iron pyrite single crystals to understand its puzzling low VOC. We utilized electrical transport, optical spectroscopy, surface photovoltage, photoelectrochemical measurements in aqueous and acetonitrile electrolytes, UV and X-ray photoelectron spectroscopy, and Kelvin force microscopy to characterize the bulk and surface defect states and their influence on the semiconducting properties and solar conversion efficiency of iron pyrite single crystals. These insights were used to develop a circuit model analysis for the electrochemical impedance spectroscopy that allowed a complete characterization of the bulk and surface...
95 citations
TL;DR: In this paper, it is shown that the already low thermal conductivity of manganese silicides can be reduced further to approach the minimum thermal conductivities via partial substitution of Mn with heavier rhenium (Re) to increase point defect scattering.
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.
TL;DR: This study has identified ammonium tartrate as a MS-compatible salt for HIC with comparable separation performance as the conventionally used ammonium sulfate and found that the selectivity obtained with ammonium Tartrate in the HIC mobile phases is orthogonal to that of reverse phase chromatography (RPC).
Abstract: One of the challenges in proteomics is the proteome’s complexity, which necessitates the fractionation of proteins prior to the mass spectrometry (MS) analysis. Despite recent advances in top-down proteomics, separation of intact proteins remains challenging. Hydrophobic interaction chromatography (HIC) appears to be a promising method that provides high-resolution separation of intact proteins, but unfortunately the salts conventionally used for HIC are incompatible with MS. In this study, we have identified ammonium tartrate as a MS-compatible salt for HIC with comparable separation performance as the conventionally used ammonium sulfate. Furthermore, we found that the selectivity obtained with ammonium tartrate in the HIC mobile phases is orthogonal to that of reverse phase chromatography (RPC). By coupling HIC and RPC as a novel two-dimensional chromatographic method, we have achieved effective high-resolution intact protein separation as demonstrated with standard protein mixtures and a complex cell ...
TL;DR: In this article, the synthesis of high-purity MnSi-free single crystals of HMS by chemical vapor transport and the thermoelectric properties of consolidated HMS samples prepared by spark plasma sintering (SPS) were verified by scanning and transmission electron microscopy, electron diffraction, and synchrotron high-resolution X-ray diffraction.
Abstract: Semiconducting higher manganese silicides (HMS), with a nominal composition of MnSi1.73, are particularly promising thermoelectric materials because of their elemental abundance, nontoxicity, and reported ZT of around 0.4 at 800 K for undoped samples. However, embedded MnSi impurities naturally form during the melt growth of HMS materials. The influences of such naturally occurring MnSi impurities within bulk HMS have yet to be carefully studied. Herein, we report the synthesis of high-purity MnSi-free single crystals of HMS by chemical vapor transport and the thermoelectric properties of consolidated HMS samples prepared by spark plasma sintering (SPS). The high purity of the HMS crystals is verified by scanning and transmission electron microscopy, electron diffraction, and synchrotron high-resolution X-ray diffraction. Despite successfully growing high purity HMS single crystals, we find that MnSi will nevertheless precipitate from HMS after SPS processing. In-situ sychrotron high-resolution X-ray diff...
TL;DR: This work presents a general methodology for using transport measurements of nanostructures to study both bulk and surface transport properties of semiconductors and suggests that high-density of surface states are present on surface of pyrite, which partially explains the universal p-type conductivity and lack of photovoltage in polycrystalline pyrites.
Abstract: Understanding semiconductor surface states is critical for their applications, but fully characterizing surface electrical properties is challenging. Such a challenge is especially crippling for semiconducting iron pyrite (FeS2), whose potential for solar energy conversion has been suggested to be held back by rich surface states. Here, by taking advantage of the high surface-to-bulk ratio in nanostructures and effective electrolyte gating, we develop a general method to fully characterize both the surface inversion and bulk electrical transport properties for the first time through electrolyte-gated Hall measurements of pyrite nanoplate devices. Our study shows that pyrite is n-type in the bulk and p-type near the surface due to strong inversion and yields the concentrations and mobilities of both bulk electrons and surface holes. Further, solutions of the Poisson equation reveal a high-density of surface holes accumulated in a 1.3 nm thick strong inversion layer and an upward band bending of 0.9-1.0 eV. This work presents a general methodology for using transport measurements of nanostructures to study both bulk and surface transport properties of semiconductors. It also suggests that high-density of surface states are present on surface of pyrite, which partially explains the universal p-type conductivity and lack of photovoltage in polycrystalline pyrite.
TL;DR: 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 is reported.
02 Dec 2014
TL;DR: In this article, the authors review the various strategies currently used to directly grow free-standing silicide nanomaterials, discuss the challenges in understanding the nucleation and growth of silicide nano-nodes, and present the intriguing physical properties and emerging applications of one-dimensional (1D) silicide micro-nomoms in spintronic and renewable energy.
Abstract: Metal silicides comprise a large family of refractory intermetallic materials that have diverse physical properties and many applications, including complementary metal-oxide-semiconductor (CMOS) devices, thin film coatings, bulk structural components, electrical heating elements, thermoelectric, and solar energy conversion. One-dimensional (1D) silicide nanomaterials, such as nanowires (NWs), are currently being investigated for potential enhancement of these applications and realizing potential new applications such as the use of magnetic skyrmion domains in spintronic device applications. However, the growth of silicide NWs is challenging due to the complex phase behaviors between metals and Si and the many stoichiometries and structures of the resulting compounds. Several synthetic approaches have been developed to overcome this challenge, as evidenced by the increasing literature reports of silicide NWs in the last decade. In this chapter, we review the various strategies currently used to directly grow free-standing silicide NWs, discuss the challenges in understanding the nucleation and growth of silicide NWs, and present the intriguing physical properties and emerging applications of silicide NWs in spintronic and renewable energy. Emphasis will be given to the physics of the recently discovered magnetic skyrmions and the recent study of magnetic B20 monosilcide NWs towards the goals of realizing their spintronics and magnetic information storage applications.
TL;DR: In this paper, the title nanoparticles were synthesized from TiO2 and SiO2 nanoparticles in a LiCl/KCl eutectic mixture in the presence of Mg powder (autoclave, 700 °C, 2 h; 73% yield).
Abstract: The title nanoparticles are synthesized from TiO2 and SiO2 nanoparticles in a LiCl/KCl eutectic mixture in the presence of Mg powder (autoclave, 700 °C, 2 h; 73% yield).