Cobalt Nitride Nanoparticles Encapsulated in N-Doped Carbon Nanotubes Modified Separator of Li-S Battery Achieving the Synergistic Effect of Restriction-Adsorption-Catalysis of Polysulfides.

Although lithium-sulfur (Li-S) batteries have broad market prospects due to their high theoretical energy density and potential cost-effectiveness, the practical applications still face serious shuttle effects of polysulfides (LiPSs) and slow redox reactions. Therefore, in this paper, cobalt nitride nanoparticles encapsulated in nitrogen-doped carbon nanotube (CoN@NCNT) are prepared as a functional layer for the separator of high-performance Li-S batteries. Carbon nanotubes with large specific surface areas not only promote the transport of ions and electrons but also weaken the migration of LiPSs and confine the dissolution of LiPSs in electrolytes. The lithiophilic heteroatom N adsorbs LiPSs by strong chemical adsorption, and the CoN particles with high catalytic activity greatly improve the kinetics of the conversion between LiPSs and Li2 S2 /Li2 S during the charge-discharge process. Due to these advantages, the battery with CoN@NCNT modified separator has superior rate performance (initial discharge capacity of 834.7 mAh g-1 after activation at 1 C) and excellent cycle performance (capacity remains 729.7 mAh g-1 after 200 cycles at 0.2 C). This work proposes a strategy that can give the separator a strong ability to confinement-adsorption-catalysis of LiPSs in order to provide more possibilities for the development of Li-S batteries.

Constructing CoNC coordination in Co9S8 embedded N,S-codoped carbon nanotube as an advanced electrode for supercapacitor and Na-ion battery.

Yolk-shell-structured transition metal sulfides (TMSs)/carbon nanocomposites are highly desirable in advanced energy storage system, such as sodium-ion batteries (SIBs) and supercapacitors (SCs). Nevertheless, practical applications are still prevented by the loose attachment of TMSs with carbon caused by conversion stress, the aggregation of TMSs nanoparticles and the sluggish ion transport caused by high crystallinity of carbon. Here, the disperse hollow Co9S8 nanoparticles encapsulated into N,S-codoped carbon nanotubes (CNTs) with poor crystallinity through CoNC bond was synthesized (CS-NSCNT) to overcome the above obstacles. The designed CS-NSCNT can provide the short diffusion path and prevent the huge volume expansion of conversion reaction. Moreover, the established CoNC bond endows the strong interaction and regulates the electronic structure thus promote the stability and rate performance effectively. The CS-NSCNT SCs's electrode delivers a high specific capacitance of 1150 F g-1 at 1 A g-1, with a high cycling life stability and rate performance. For SIBs, the CS-NSCNT cathode demonstrates an initial reversible capacity of 475 mAh g-1 at 0.1 A g-1 and an excellent rate performance with a capacity retention of 53 % at 10 A g-1. This work may satisfy the long-stability, high-capacitance/capacity, high-power/energy density application requirements of future applications.

Selection of oxygen reduction catalysts for secondary tri-electrode zinc-air batteries.

Oxygen reduction reaction (ORR) electrocatalysts, which are highly efficient, low-cost, yet durable, are important for secondary Zn-air cell applications. ORR activities of single and mixed metal oxide and carbon electrocatalysts were studied using rotating disc electrode (RDE) measurements, Tafel slope and Koutecky-Levich plots. It was found that MnOx combined with XC-72R demonstrated high ORR activity and good stability-up to 100 mA cm-2. The performance of the selected ORR electrode and a previously optimised oxygen evolution reaction (OER) electrode was thereafter tested in a custom-built secondary Zn-air cell in a tri-electrode configuration, and the effects of current density, electrolyte molarity, temperature, and oxygen purity on the performance of the ORR and OER electrode were investigated. Finally, the durability of the secondary Zn-air system was assessed, demonstrating energy efficiencies of 58-61% at 20 mA cm-2 over 40 h in 4 M NaOH + 0.3 M ZnO at 333 K.

Rational Design on Chemical Regulation of Interfacial Microstress Engineering by Matching Young's Modulus in a CsPbBr3 Perovskite Film with Mechanical Compatibility toward Enhanced Photoelectric Conversion Efficiency.

Thermodynamically induced tensile stress in the perovskite film will lead to the formation of atomic vacancies, seriously destroying the photovoltaic efficiency stability of the perovskite solar cells (PSCs). Among them, cations and halide anions vacancies are unavoidable; these point vacancies are considered to be a major source of the ionic migration and perovskite degradation at the crystal boundary and surface of the perovskite films. Here, we use choline bromide to modify the perovskite film by occupying the atomic defects in the CsPbBr3 perovskite film. The results show that the zwitterion quaternary ammonium ions and bromide ions in choline bromide can simultaneously occupy the Cs+ cation and Br- anions vacancies in the perovskite film by the ionic bonding effect, for which the defect-state density on the surface of the perovskite film can be significantly reduced, leading to the effective enhancement of carrier lifetime. In addition, the residual stress at the crystal boundary can be effectively reduced by lowering the Young's modulus in the CsPbBr3 perovskite film. As a result, the optimized device achieves a photoelectric conversion efficiency (PCE) of 9.06% with an increase of 41.1% compared to the control device with a PCE of 6.42%. Most importantly, the newborn thermal stress due to thermal expansion during heat working conditions can be transferred from the polycrystalline perovskite to the carbon layer by the matched Young's modulus, thus resulting in improved stability perovskite film under environmental conditions. The work provides new insights for preparing high-quality perovskite films with low defect-state density and residual stress.

The cobalt atom protection layers in-situ anchored titanium carbide with controllable interlayer spacing towards stable and fast lithium ions storage.

MXenes are the typical ions insertion-type two-dimensional (2D) nanomaterials, have attracted extensive attention in the Li+ storage field. However, the self-stacking of layered structure and the consumption of electrolyte during the process of charge/discharge will limit the Li+ diffusion dynamics, rate capability and capacity of MXenes. Herein, a Co atom protection layers with electrochemical nonreactivity were anchored on/in the surface/interlayer of titanium carbide (Ti3C2) by in-situ thermal anchoring (x-Co/m-Ti3C2, x  = 45, 65 and 85), which can not only avoid the self-stacking and expand the interlayer spacing of Ti3C2 but also reduce the consumption of Li+ and electrolyte by forming the thin solid electrolyte interphase (SEI) film. The interlayer spacing of Ti3C2 can be expanded from 0.98 to 1.21, 1.36 and 1.33 nm when the anchoring temperatures are 45, 65 and 85 °C due to the pillaring effects of Co atom layers, in where the 65-Co/m-Ti3C2 can achieve the best specific capacity and rate capability attributed to its superior diffusion coefficient of 8.8 × 10-7 cm2 s-1 in Li+ storage process. Furthermore, the 45, 65 and 85-Co/m-Ti3C2 exhibit lower SEI resistances (RSEI) as 1.45 ± 0.01, 1.26 ± 0.01 and 1.83 ± 0.01 Ω compared with the RSEI of Ti3C2 (5.18 ± 0.01 Ω), suggesting the x-Co/m-Ti3C2 demonstrates a thin SEI film due to the protection of Co atom layers. The findings propose a Co atom protection layers with electrochemical nonreactivity, not only giving an approach to expand the interlayer spacing, but also providing a protection strategy for 2D nanomaterials.

A hybrid transition metal nanocrystal-embedded graphitic carbon nitride nanosheet system as a superior oxygen electrocatalyst for rechargeable Zn-air batteries.

In this study, we, for the first time, demonstrate a general solid-phase pyrolysis method to synthesize hybrid transition metal nanocrystal-embedded graphitic carbon nitride nanosheets, namely M-CNNs, as a highly efficient oxygen electrocatalyst for rechargeable Zn-air batteries (ZABs). The ratios between metallic acetylacetonates and the g-C3N4 precursor can be controlled where Fe-CNNs-0.7, Ni-CNNs-0.7 and Co-NNs-0.7 composites have been optimized to exhibit superior ORR/OER bifunctional electrocatalytic activities. Specifically, Co-CNNs-0.7 exhibited not only a comparable half-wave potential (0.803 V vs. RHE) to that of the commercial Pt/C catalyst (0.832 V) with a larger current density for the ORR but also a lower overpotential (440 mV) toward the OER compared with the commercial IrO2 catalyst (460 mV), revealing impressive application in rechargeable ZABs. As a result, ZABs using Co-CNNs-0.7 as the cathode exhibited an excellent peak power density of 85.3 mW cm-2 with a specific capacity of 675.7 mA h g-1 and remarkable cycling stability of 1000 cycles, outperforming the commercially available Pt/C + IrO2 catalysts. This study highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal-air cathode materials.

Interface Engineered Binary Platinum Free Alloy-based Counter Electrodes with Improved Performance in Dye-Sensitized Solar Cells.

The high cost and platinum dissolution issues of counter electrodes (CEs) are two core problems for the development of dye-sensitized solar cells (DSSCs). In this work, different CEs based on binary alloy Ru81.09Co18.91, Ru80.55Se19.45 and Co20.85Se79.15 nanostructures for DSSCs were successfully synthesized and investigated by a facile and environmentally friendly approach. Here, we found that the Co20.85Se79.15 alloy CE-based device yields the higher photoelectric conversion efficiency of 7.08% compared with that (5.80%) of the DSSC using a pure Pt CE because of the larger number of active sites with improved charge transferability and reduced interface resistance by matching work function with the I3‒/I‒ redox electrolyte. The inexpensive synthesis method, cost-effectiveness and superior catalytic activity of the Co20.85Se79.15 alloy may open up a new avenue for the development of CEs for DSSCs in the near future.

3D Hierarchically Structured CoS Nanosheets: Li+ Storage Mechanism and Application of the High-Performance Lithium-Ion Capacitors.

Lithium-ion capacitors possess excellent power and energy densities, and they can combine both of those advantages from supercapacitors and lithium-ion batteries, leading to novel generation hybrid devices for storing energy. This study synthesized one three-dimensional (3D) hierarchical structure, self-assembled from CoS nanosheets, according to a simple and efficient manner, and can be used as an anode for lithium ion capacitors. This CoS anode, based on a conversion-type Li+ storage mechanism dominated by diffusion control, showed a large reversible capacity, together with excellent stability for cycling. The CoS shows a discharge capacity ≈434 mA h/g at 0.1 A/g. The hybrid lithium-ion capacitor, which had the CoS anode as well as the biochar cathode, exhibits excellent electrochemical performance with ultrahigh energy and power densities of 125.2 Wh/kg and 6400 W/kg, respectively, and an extended cycling life of 81.75% retention after 40 000 cycles. The CoS with self-assembled 3D hierarchical structure in combination with a carbon cathode offers a versatile device for future applications in energy storage.

Experimental and Theoretical Investigation of the Effect of Oxygen Vacancies on the Electronic Structure and Pseudocapacitance of MnO2.

Defect engineering is an effective way to modulate the intrinsic physicochemical properties of materials. In this work, δ-MnO2 with oxygen vacancies is fabricated by a simple oxidation or reduction process, and the relationship between the electronic structure and pseudocapacitance is systematically studied through experimental analysis and theoretical calculations. The peaks in the Raman spectra of the as-prepared samples are shifted compared with those of pure MnO2 and the Mn3+ /Mn4+ ratio and O species content also change after the introduction of oxygen vacancies. The optimized samples exhibit a better specific capacitance of 207 F g-1 after the oxidation process and 181.4 F g-1 after the reduction treatment compared with only 143.9 F g-1 for the pure MnO2 . The samples obtained through the oxidation or reduction process also retain 93.3 or 86.4 % of the initial capacity after 5000 cycles. The excellent properties are attributed to the enhanced conductivity and increased surface reactivity or electrochemically active sites. Theoretical calculations demonstrate that the presence of oxygen vacancies leads to an increase in the density of states, which improves the redox reaction of MnO2 . This study will provide a reference for exploring and designing highperformance pseudocapacitive materials.

Electrostatically Charged MoS2/Graphene Oxide Hybrid Composites for Excellent Electrochemical Energy Storage Devices.

We demonstrate, for the first time, a new method of fabricating hybrid MoS2/poly(ethyleneimine)-modified graphene oxide (PEI-GO) composites assembled through electrostatically charged interaction between the negatively charged MoS2 nanosheets and positively charged PEI-GO in an aqueous solution. The GO can not only improve the electronic conductivity of the MoS2/PEI-GO composites, leading to an excellent charge-transfer network, but also hamper the restacking of MoS2 nanosheets. The composition ratios between MoS2 and PEI-GO were also optimized with the highest specific capacitance of 153.9 F g-1 where 96.0% of the initial specific capacitance remains after 6800 cycles. The specific capacitance of only 117.5 F g-1 was observed for the pure MoS2 nanosheets, and 68.2% of the initial specific capacitance was achieved after 5000 cycles. The excellent electrochemical performance of the hybrid MoS2/PEI-GO composites was demonstrated by establishing an asymmetric supercapacitor with a MoS2/PEI-GO-based negative electrode and an activated-carbon positive electrode. The asymmetric supercapacitor provided a maximum capacitance of 42.9 F g-1, and 93.1% of the initial capacitance was maintained after 8000 cycles. Furthermore, a MoS2/PEI-GO//activated-carbon asymmetric supercapacitor delivered an energy density of 19.3 W h kg-1 and a power density of 4500 W kg-1, indicating the potential of the hybrid MoS2/PEI-GO composites in electrochemical energy storage applications.

A Facile Strategy for the Preparation of MoS3 and its Application as a Negative Electrode for Supercapacitors.

Owing to their graphene-like structure and available oxidation valence states, transition metal sulfides are promising candidates for supercapacitors. Herein, we report the application of MoS3 as a new negative electrode for supercapacitors. MoS3 was fabricated by the facile thermal decomposition of a (NH4 )2 MoS4 precursor. For comparison, samples of MoS3 &MoS2 and MoS2 were also synthesized by using the same method. Moreover, this is the first report of the application of MoS3 as a negative electrode for supercapacitors. MoS3 displayed a high specific capacitance of 455.6 F g(-1) at a current density of 0.5 A g(-1) . The capacitance retention of the MoS3 electrode was 92 % after 1500 cycles, and even 71 % after 5000 cycles. In addition, an asymmetric supercapacitor assembly of MoS3 as the negative electrode demonstrated a high energy density at a high potential of 2.0 V in aqueous electrolyte. These notable results show that MoS3 has significant potential in energy-storage devices.

An Approach to Preparing Ni-P with Different Phases for Use as Supercapacitor Electrode Materials.

Herein, we describe a simple two-step approach to prepare nickel phosphide with different phases, such as Ni2 P and Ni5 P4 , to explain the influence of material microstructure and electrical conductivity on electrochemical performance. In this approach, we first prepared a Ni-P precursor through a ball milling process, then controlled the synthesis of either Ni2 P or Ni5 P4 by the annealing method. The as-prepared Ni2 P and Ni5 P4 are investigated as supercapacitor electrode materials for potential energy storage applications. The Ni2 P exhibits a high specific capacitance of 843.25 F g(-1) , whereas the specific capacitance of Ni5 P4 is 801.5 F g(-1) . Ni2 P possesses better cycle stability and rate capability than Ni5 P4 . In addition, the Fe2 O3 //Ni2 P supercapacitor displays a high energy density of 35.5 Wh kg(-1) at a power density of 400 W kg(-1) and long cycle stability with a specific capacitance retention rate of 96 % after 1000 cycles, whereas the Fe2 O3 //Ni5 P4 supercapacitor exhibits a high energy density of 29.8 Wh kg(-1) at a power density of 400 W kg(-1) and a specific capacitance retention rate of 86 % after 1000 cycles.

A sol-gel process for fabrication of NiO/NiCo2O4/Co3O4 composite with improved electrochemical behavior for electrochemical capacitors.

Transition metal oxides possess multiple oxidation states that enable rich redox reactions for pseudo capacitanc. They have been investigated as promising electrode materials to achieve high energy density. In this study, NiO/NiCo(2)O(4)/Co(3)O(4) composite with high specific surface and mesoporous structure is fabricated by a sol-gel process then calcined at 250 °C. Benefits from the improved electron conductivity and effective mesoporous structure, the fabricated composite exhibits high specific capacitance (1717 F g(-1)), enhanced rate capability, and excellent electrochemical stability (94.9% retention after 1000 cycles). Interestingly, the specific capacitance of the composite is higher than that of NiO, NiCo(2)O(4), and Co(3)O(4), which indicates a synergistic effect of the composite on improvement of electrochemical performance. The findings demonstrate the importance and great potential of NiO/NiCo(2)O(4)/Co(3)O(4) composite in development of high-performance energy-storage systems.