Single-Molecule Spectroscopy of the Conjugated Polymer MEH-PPV

Single-Molecule Spectroscopy of the Conjugated Polymer MEH-PP

Ag-Ion Dynamics in the Low-Temperature Form of Ag₂S as Studied by Impedance Spectroscopy

In this study, Ag2S samples are characterized using X-ray diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry, and impedance spectroscopy. At 447 K, an AC conductivity jump of about two orders of magnitude is observed, and an endothermic peak is measured by differential scanning calorimetry, apparently resulting from the β-to-α phase transition, i.e., the order–disorder transition. A silver vacancy proportion of 2.2% is obtained by refinement of the X-ray diffraction profile. The dielectric loss peaks and analysis of the observed complex impedance peaks indicate four different relaxation processes, namely, P1, P2, P3, and P4, from low to high temperature. P1 and P2 are obviously the migration of silver ions from two types of lattice sites to their nonequivalent nearest-neighbor vacancies. P3 involves the migration of interstitial silver ions to adjacent interstitial sites. An Arrhenius-to-VFTH crossover of the P4 relaxation time is inferred to the hopping of the individual silver ion and then the cooperative jumps of several ions in the disordered region of the silver sublattice upon heating

Facile Synthesis of a “Two-in-One” Sulfur Host Featuring Metallic-Cobalt-Embedded N‑Doped Carbon Nanotubes for Efficient Lithium-Sulfur Batteries

The exploration of efficient host materials of sulfur is significant for the practical lithium-sulfur (Li-S) batteries, and the hosts are expected to be highly conductive for high sulfur utilization and exhibit strong interaction toward polysulfides to suppress the shuttle effect for long-lasting cycle stability. Herein, we propose a simple synthesis of metallic cobalt-embedded N-doping carbon nanotubes (Co@NCNT) as a “two-in-one” host of sulfur for efficient Li-S batteries. In the binary host, the N-doped CNTs, cooperating with metallic Co nanoparticles, can serve as 3D conductive networks for fast electron transportation, while the synergetic effect of metallic Co and doping N heteroatoms helps to chemically confine polysulfides, acting as active sites to accelerate electrochemical kinetics. With these advantages, the S/Co@NCNT composite delivers an excellent cycling stability with a capacity decay of 0.08% per cycle averaged within 500 cycles at a current density of 1 A g–1 and a high rate performance of 530 mA h g–1 at 5 A g–1. Further, the superior electrochemical performance of the S/Co@NCNT electrode can be maintained under a high sulfur loading up to 4 mg cm–2. Our work demonstrates a feasible strategy to design promising host materials simultaneously featuring high conductivity and strong confinement toward polysulfides for high-performance Li-S batteries

Manganese Monoxide/Biomass-Inherited Porous Carbon Nanostructure Composite Based on the High Water-Absorbent Agaric for Asymmetric Supercapacitor

Biomass-inherited metal oxide/carbon composites have been utilized as competitive materials of supercapacitor electrodes owing to the hierarchical structures, fast regeneration rate, and easy synthesis. However, the low content and agglomeration of metal oxides are the contradictory issues to be addressed for their practical applications. In this work, manganese monoxide/biomass-inherited porous carbon (MnO/BPC) nanostructure composites with high MnO content (∼75%) and uniform distribution have been prepared through a simple immersion-calcination process by high water-absorbent agaric. The superhigh Mn2+ solution absorption of agaric ensures the high MnO content in MnO/BPC composite, and the abundant internal chitin with hydrogel and hot-melting property enables the uniform dispersion of MnO in carbon matrix. The carbon nanostructure endows the composite with high specific surface area, efficient electron/ion transportation, and better electrolyte wettability. As expected, the MnO/BPC composite materials realizes high capacitance of ∼735 mF cm–2 (∼637 F g–1) at 3 mA cm–2, good rate performance (∼608 mF cm–2 at 10 mA cm–2), and excellent cycling performance (capacity retention of ∼91% at 10 mA cm–2, 5000 cycles). In addition, this work presents a facile and productive strategy to obtain metal-based composites with high metal-oxide content and homogeneous distribution by adopting the edible and worldwide abundant agaric

Efficient Polysulfide Redox Enabled by Lattice-Distorted Ni₃Fe Intermetallic Electrocatalyst-Modified Separator for Lithium–Sulfur Batteries

Exploring efficient electrocatalysts for lithium–sulfur (Li–S) batteries is of great significance for the sulfur/polysulfide/sulfide multiphase conversion. Herein, we report nickel–iron intermetallic (Ni3Fe) as a novel electrocatalyst to trigger the highly efficient polysulfide-involving surface reactions. The incorporation of iron into the cubic nickel phase can induce strong electronic interaction and lattice distortion, thereby activating the inferior Ni phase to catalytically active Ni3Fe phase. Kinetics investigations reveal that the Ni3Fe phase promotes the redox kinetics of the multiphase conversion of Li–S electrochemistry. As a result, the Li–S cells assembled with a 70 wt % sulfur cathode and a Ni3Fe-modified separator deliver initial capacities of 1310.3 mA h g–1 at 0.1 C and 598 mA h g–1 at 4 C with excellent rate capability and a long cycle life of 1000 cycles at 1 C with a low capacity fading rate of ∼0.034 per cycle. More impressively, the Ni3Fe-catalyzed cells exhibit outstanding performance even at harsh working conditions, such as high sulfur loading (7.7 mg cm–2) or lean electrolyte/sulfur ratio (∼6 μL mg–1). This work provides a new concept on exploring advanced intermetallic catalysts for high-rate and long-life Li–S batteries

Investigation on Relaxational Behavior of Alkylammonium Ions Intercalated in Graphite Oxide

Graphite oxide (GO) nanocomposites have been synthesized to contain various concentrations of intercalated alkylammonium ions and characterized with X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and differential scanning calorimetry. Depending on their concentration, the alkyl chains may lie parallel to the GO plane one or two layers thick or they form two columns inclined at an angle ∼37° to the plane. Dielectric spectroscopy reveals a relaxation process far below room temperature, attributed to small-angle wobbling around the long molecular axis. The activation energy of this relaxation increases as the intercalate changes from one to two layers, and to dual columns, with increasing interactions among the intercalated molecules. An additional phase transition occurs in composites with high concentrations of intercalate between a rotator-type solid phase to a disordered phase for the confined alkyl chains

In Situ Constructing a Stable Solid Electrolyte Interface by Multifunctional Electrolyte Additive to Stabilize Lithium Metal Anodes for Li–S Batteries

Lithium (Li) metal is considered to be the most promising anode due to the ultrahigh capacity and extremely low electrochemical potential. The tricky thing is that the growth of dendritic Li brings huge safety hazards to Li metal batteries. Herein, we demonstrate cerium nitrate as a multifunctional electrolyte additive to form a stable solid electrolyte interface on the metallic Li anode surface for durable Li–S batteries. The presence of Ce3+ helps to modulate the electroplating/stripping of Li and inhibits the growth of dendritic Li. An excellent cycle life exceeding 1400 h at the current density of 1 mA cm–2 can be realized in symmetric Li||Li cells. In addition, the in situ formed robust solid–electrolyte interface (SEI) layer containing cerium sulfide on the Li anode surface conduces to weaken the reducibility of Li and regulate the electrochemical dissolution/deposition reaction on the Li anode. Surprisingly, by virtue of cerium nitrate additive with a low concentration of 0.03 M, the Li–S batteries can afford a capacity of 553 mA h g–1 at 5 C and a long cycle life at 1 C with a high capacity retention of 70.4%. Therefore, this study provides a novel idea to realize a uniform and dendrite-free Li anode for practical Li–S batteries

Defect-Rich W/Mo-Doped V₂O₅ Microspheres as a Catalytic Host To Boost Sulfur Redox Kinetics for Lithium–Sulfur Batteries

It is very important to develop ideal electrocatalysts to accelerate the sulfur redox kinetics in both the discharging and charging processes for high-performance lithium–sulfur batteries. Herein, defect-rich cation-doped V2O5 yolk–shell microspheres are reported as a catalytic host of sulfur. The doping of W or Mo cations induces no impurities, broadens the lattice spacing of V2O5, and enriches the oxygen vacancy defects. Thus, the doped V2O5 host affords sufficient active sites for chemically anchoring polysulfides and promising catalytic effect on the mutual conversion between different sulfur intermediates. As a result, the S/W–V2O5 cathode delivers a discharging capacity of 1143.3 mA g–1 at an initial rate of 0.3 C and 681.8 mA g–1 at 5 C. Even under a sulfur loading of up to 5.5 mg cm–2 and a minimal electrolyte/sulfur ratio of 6 μL mg–1, the S/W–V2O5 cathode could still achieve good sulfur utilization and dependable cycle stability. Thus, this work offers an electrocatalytic host based on the cation doping strategy to greatly enhance the sulfur redox kinetics for high-performance Li–S batteries

ZnS/SnS₂ Heterostructures Encapsulated in N‑Doped Carbon Nanofibers for High-Performance Alkali Metal-Ion Batteries

Heterogeneous composite ZnS/SnS2 is designed to meet various requirements for alkali metal-ion batteries. The composite is prepared using an electrostatic spinning method and encapsulated in N-doped carbon fibers after high-temperature vulcanization. The special structure of the composite provides a dependable interconnection and fast conductive network for alkali metal ions. The conductive carbon network shortens the diffusion path and greatly improves the migration efficiency of the alkali metal ions in the electrode. As expected, when the current density is 0.1 A g–1, the ZnS/SnS2@NCNFs maintain a high discharge capacity of more than 1437.5, 1321.2, and 861.6 mA h g–1 for lithium-ion, sodium-ion, and potassium-ion batteries, respectively. What is more, a full cell using a prelithiated composite anode and a LiFePO4 cathode is tested and shows excellent electrochemical performance. This work provides new perspectives for the development of novel anodes that can efficiently store alkali metal ions, as well as for the fine-structure design of materials

Two for One: A Biomass Strategy for Simultaneous Synthesis of MnO₂ Microcubes and Porous Carbon Microcubes for High Performance Asymmetric Supercapacitors

The capacitive properties of asymmetric supercapacitors (ASCs) are inseparable from the development of anode and cathode materials, which usually require high accessible surface area and uniform porous distribution. Herein, a simple and economical “two for one” strategy is introduced for the simultaneous synthesis of microscale porous MnO2 microcubes (PMMs) and porous carbon microcubes (PCMs) derived from a single precursor cubic MnCO3/biocarbon (CM) which are prepared by natural agaric. Benefiting from a high specific surface area, delicate construction, and adequate mesoporous distribution, PCMs and PMMs could help to realize fast ion diffusion and easy ion accessibility. As expected, microscale PCM anode and PMM cathode materials exhibit superior capacitive performances, including high specific capacitance and impressive rate performance in a three-electrode system, respectively. Moreover, the assembled ASCs physical device PCM//PMM presents a high energy density (46.1 Wh kg–1 at 1.0 kW kg–1) and an excellent long-term cyclability (91% capacitance retention after 10 000 cycles at 1.0 A g–1). Therefore, the two-for-one strategy not only provided a simple and effective method to prepare high-performance electrode materials for ASCs, but also it is of great significance for natural biomass to achieve multidirectional applications and effectively replace commercial carbon sources from fossil fuels