Dual CoxSy-Modified Tungsten Disulfide Double-Heterojunction Electrocatalyst for Efficient Hydrogen Evolution in All-pH Media.

The rational design and preparation of a heterogeneous electrocatalyst for hydrogen evolution reaction (HER) has become a research hotspot, while applicable and pH-universal tungsten disulfide (WS2)-based hybrid composites are rarely reported. Herein, we propose a novel hybrid catalyst (WS2/Co9S8/Co4S3) comprising two heterojunctions of WS2/Co4S3 and WS2/Co9S8, which grow on the porous skeleton of Co, N-codoped carbon (Co/NC) flexibly applicable to all-pH electrolytes. The effect of double heterogeneous coupling on HER activity is explored as the highly flexible heterojunction is conducive to tune the activity of the catalyst, and the synergistic interaction of the double heterojunctions is maximized by adjusting the proportion of heterojunction components. Theoretical calculations show that both WS2/Co9S8 and WS2/Co4S3 heterojunctions have a Gibbs free energy of H reaction (|ΔGH*|) close to 0.0 eV and a facile decomposition water barrier. As collective synergy of dual CoxSy-modified WS2 double heterojunction, WS2/Co9S8/Co4S3 greatly enhances HER activity compared to bare Co9S8/Co4S3 or single heterojunction (WS2/Co9S8) in all-pH media. Besides, we have elucidated the unique HER mechanism of the double heterojunction to decompose H2O and confirm its excellent activity under alkaline and neutral conditions. Thus, this work provides new insights into WS2-based hybrid materials potentially applied to sustainable energy.

Studies on Kinetics, Isotherms, Thermodynamics and Adsorption Mechanism of Methylene Blue by N and S Co-Doped Porous Carbon Spheres.

Heteroatom-doped carbon is widely used in the fields of adsorbents, electrode materials and catalysts due to its excellent physicochemical properties. N and S co-doped porous carbon spheres (N,S-PCSs) were synthesized using glucose and L-cysteine as carbon and heteroatom sources using a combined hydrothermal and KOH activation process. The physicochemical structures and single-factor methylene blue (MB) adsorption properties of the N,S-PCSs were then studied. The optimized N,S-PCSs-1 possessed a perfect spherical morphology with a 2-8-µm diameter and a large specific area of 1769.41 m2 g-1, in which the N and S contents were 2.97 at% and 0.88 at%, respectively. In the single-factor adsorption experiment for MB, the MB adsorption rate increased with an increase in carbon dosage and MB initial concentration, and the adsorption reached equilibrium within 2-3 h. The pseudo-second-order kinetic model could excellently fit the experimental data with a high R2 (0.9999). The Langmuir isothermal adsorption equation fitted well with the experimental results with an R2 value of 0.9618, and the MB maximum adsorption quantity was 909.10 mg g-1. The adsorption of MB by N,S-PCSs-1 was a spontaneous, endothermic, and random process based on the thermodynamics analyses. The adsorption mechanism mainly involved Van der Waals force adsorption, π-π stacking, hydrogen bonds and Lewis acid-base interactions.

Boron-Doped Spherical Hollow-Porous Silicon Local Lattice Expansion toward a High-Performance Lithium-Ion-Battery Anode.

Silicon (Si) attracts extensive attention as the advanced anode material for lithium (Li)-ion batteries (LIBs) because of its ultrahigh Li storage capacity and suitable voltage plateau. Hollow porous structure and dopant-induced lattice expansion can enhance the cycling stability and transporting kinetics of Li ions. However, it is still difficult to synthesize the Si anode possessing these structures simultaneously by a facile method. Herein, the lightly boron (B)-doped spherical hollow-porous Si (B-HPSi) anode material for LIBs is synthesized by a facile magnesiothermic reduction from B-doped silica. B-HPSi exhibits local lattice expansion located on boundaries of refined subgrains. B atoms in Si contribute to the increase of the conductivity and the expansion of lattices. On the basis of the first-principles calculations, the B dopants induce the conductivity increase and local lattice expansion. As a result, B-HPSi electrodes exhibit a high specific capacity of ∼1500 mAh g-1 at 0.84 A g-1 and maintains 93% after 150 cycles. The reversible capacities of ∼1250, ∼1000, and ∼800 mAh g-1 can be delivered at 2.1, 4.2, and 8.4 A g-1, respectively.

Si nanoflake-assembled blocks towards high initial coulombic efficiency anodes for lithium-ion batteries.

Assisted by artificial amorphous copper silicate, Si with a flake-like structure was obtained through a facile magnesiothermic reduction. The Si anodes exhibit excellent cyclic performance and rate performance. Particularly, a high initial coulombic efficiency of 85%-89% was obtained due to their greatly reduced surface and internal defects.

Sn-Co Nanoalloys Encapsulated in N-Doped Carbon Hollow Cubes as a High-Performance Anode Material for Lithium-Ion Batteries.

To address the huge volumetric change and unstable solid electrolyte interphase (SEI) issues of Sn-based anodes, this paper proposes a Sn-Co-C ternary composite with a cubic yolk-shell structure. The proposed Sn-Co nanoalloys encapsulated in N-doped carbon hollow cubes (Sn-Co@C) are simply synthesized by the conformal polydopamine coating of home-made CoSn(OH)6 hollow nanocubes subsequent with hydrogen reduction. The cubic Sn-Co@C yolk-shell structure possessing an optimized carbon shell thickness displays excellent cyclic performance and superior rate capability when utilized as an anode for lithium-ion batteries. The composite shows an initial discharge capacity of 885 mA h g-1 at 200 mA g-1 with a high capacity retention of ∼91.2% after 180 cycles. It can still deliver a considerable capacity of 560 mA h g-1 at a high current density of 1 A g-1 after 200 cycles. This attractive electrochemical characteristic can be ascribed to the distinct cubic yolk-shell architecture, in which the inner inactive Co can buffer the volumetric expansion of Sn, the void can provide external space for the volumetric change of Sn, and the outer carbon shell can effectively prevent the agglomeration of Sn-Co nanoalloys and maintain the stability of SEI films.

Metal-Organic Frameworks Derived Okra-like SnO2 Encapsulated in Nitrogen-Doped Graphene for Lithium Ion Battery.

A facile process is developed to prepare SnO2-based composites through using metal-organic frameworks (MOFs) as precursors. The nitrogen-doped graphene wrapped okra-like SnO2 composites (SnO2@N-RGO) are successfully synthesized for the first time by using Sn-based metal-organic frameworks (Sn-MOF) as precursors. When utilized as an anode material for lithium-ion batteries, the SnO2@N-RGO composites possess a remarkably superior reversible capacity of 1041 mA h g-1 at a constant current of 200 mA g-1 after 180 charge-discharge processes and excellent rate capability. The excellent performance can be primarily ascribed to the unique structure of 1D okra-like SnO2 in SnO2@N-RGO which are actually composed of a great number of SnO2 primary crystallites and numerous well-defined internal voids, can effectively alleviate the huge volume change of SnO2, and facilitate the transport and storage of lithium ions. Besides, the structural stability acquires further improvement when the okra-like SnO2 are wrapped by N-doped graphene. Similarly, this synthetic strategy can be employed to synthesize other high-capacity metal-oxide-based composites starting from various metal-organic frameworks, exhibiting promising application in novel electrode material field of lithium-ion batteries.

Enhanced Electrochemical Performance of Heterogeneous Si/MoSi2 Anodes Prepared by a Magnesiothermic Reduction.

This work explores facile synthesis of heterogeneous Si/MoSi2 nanocomposites via a one-step magnesiothermic reduction. MoSi2 serves as a highly electrically conductive nanoparticle that has several advantages of electrochemical properties, which is formed through the absorption of local heat accumulation generated by magnesiothermic reduction. As a result, the Si/MoSi2 nanocomposites exhibit excellent electrochemical performance, showing initial charge capacity of 1933.9 mA h g(-1) at a rate of 0.2 C and retaining 85.2% after 150 cycles. This work using local heat accumulation generated by magnesiothermic reduction demonstrates a large-scale method for producing high-performance Si-based anode materials, which could provide referential significances for other materials.