The development of sodium-ion batteries for large-scale applications requires the synthesis of electrode materials with high capacity, high initial Coulombic efficiency (ICE), high rate performance, long cycle life, and low cost. A rational design of freestanding anode materials is reported for sodium-ion batteries, consisting of molybdenum disulfide (MoS2) nanosheets aligned vertically on carbon paper derived from paper towel. The hierarchical structure enables sufficient electrode/electrolyte interaction and fast electron transportation. Meanwhile, the unique architecture can minimize the excessive interface between carbon and electrolyte, enabling high ICE. The as-prepared MoS2@carbon paper composites as freestanding electrodes for sodium-ion batteries can liberate the traditional electrode manufacturing procedure, thereby reducing the cost of sodium-ion batteries. The freestanding MoS2@carbon paper electrode exhibits a high reversible capacity, high ICE, good cycling performance, and excellent rate capability. By exploiting in situ Raman spectroscopy, the reversibility of the phase transition from 2H-MoS2 to 1T-MoS2 is observed during the sodium-ion intercalation/deintercalation process. This work is expected to inspire the development of advanced electrode materials for high-performance sodium-ion batteries.

MoS2 Nanosheets Vertically Aligned on Carbon Paper: A Freestanding Electrode for Highly Reversible Sodium Ion Batteries

Molybdenum disulfide (MoS2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS2 nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS2 always outperforms the corresponding 2H phase MoS2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS2 or other layered materials with enhanced HER performance.

(Invited) Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Strategies to improve electrocatalytic and photocatalytic performance of two-dimensional materials for hydrogen evolution reaction

2D Material-Based Heterostructures for Rechargeable Batteries

Enhancing catalytic properties of noble metal@MoS2/WS2 heterojunction for the hydrogen evolution reaction

The thermodynamically stable phase of molybdenum disulfide (MoS2) is evaluated as a promising and durable nonprecious-metal electrocatalyst toward the hydrogen evolution reaction (HER); however, its actual catalytic activity is restricted by an inert basal plane, low electronic conductivity, low density, and using efficiency of edged atoms. Moreover, 2D/2D van der Waals (vdws) heterostructures (HSs) with face-to-face contact can construct a highly coupled interface and are demonstrated to have immense potential for catalytic applications. In the present work, a 2D/2D hetero-layered architecture of an electrocatalyst, based on the alternate arrangement of ultrasmall monolayer MoS2 nanosheets (approximately 5-10 nm) and ultrathin graphene (G) sheets, is prepared by a facilely chemical process, which is named as MoS2/G HS. The unique structural characteristic of MoS2/G HS is in favor of accommodating more active sites as the centers of ad/desorption hydrogen and transferring and separating the charges at a coupled interface to improve the electronic conductivity and durability. The density functional theory calculation results further confirm that the alternately arranged G layers and MoS2 monolayers, as well as the expanded interplanar distance of 1.104 nm for MoS2/G HS, can exhibit a superior HER performance in both 0.5 M H2SO4 and 1.0 M KOH.

Design of MoS2/Graphene van der Waals Heterostructure as Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution in Acidic and Alkaline Media.

MoS2/graphene heterostructure with facilitated Mg-diffusion kinetics for high-performance rechargeable magnesium batteries

A MoS2 and Graphene Alternately Stacking van der Waals Heterostructure for Li+/Mg2+ Co-Intercalation

Hybrid Mg2+/Li+ batteries (MLIBs) are attractive energy storage devices that combine the advantages of Mg- and Li-rechargeable batteries. Recently, conversion-type transition metal sulfides (CTMS) have received growing attention as MLIB cathodes due to their large theoretical capacity, but these cathodes experience huge volumetric changes and dissolution of polysulfide intermediates during cycling, which cause the exfoliation of active materials and the deterioration of lifespan. Herein, self-supported PPy-encapsulated CoS2 nanosheets anchored on the TiO2−x nanorod array support by Ti–S bonds (TiO2−x@CoS2@PPy) were prepared for the MLIB cathode. The Ti–S bonds and TiO2−x support effectively suppress the exfoliation of active material CoS2 and dissolution of polysulfide intermediates, leading to remarkable stability of the electrode during long cycles. Theoretical calculations demonstrate that TiO2−x possesses stronger chemical interaction with polysulfide intermediates, CoS2 and corresponding discharge products than pristine TiO2. Additionally, the nanorod array structure and the outer PPy coating layer can provide a superior conductive network, buffer volumetric changes, and further prevent the APC electrolyte from reacting with polysulfide intermediates upon cycling. Therefore, the prepared electrodes exhibit impressive cycle stability (81.1% capacity retention at 5 A g−1 after 5000 cycles), high specific capacity (720.4 mA h g−1), superior energy density (416.5 W h kg−1), and good rate capability.

Self-supported PPy-encapsulated CoS2 nanosheets anchored on the TiO2−x nanorod array support by Ti–S bonds for ultra-long life hybrid Mg2+/Li+ batteries

Combining the high operational security of magnesium-ion batteries (MIBs) and the fast Li intercalation mechanism of lithium-ion batteries (LIBs), Li+/Mg2+ hybrid-ion batteries (LMIBs) have been developed and are regarded as a promising source of stored power for applications However, pristine MoS2 with an interplanar distance of 062 nm only allows Li+ intercalation, leading to limited energy densities and mediocre electrochemical performance Herein, we designed and prepared a material consisting of hierarchical interlayer-expanded MoS2 nanosheets/hollow N-doped carbon nanofibers (O–MoS2/HN-CNFs) with interplanar expanded O–MoS2 (094 nm) HN-CNFs adequately conduct electrons, and the expanded interlayer spacing of O–MoS2 ensures that Mg2+ and Li+ simultaneously intercalate into the host, even at 1000 mA g−1 Additionally, O–MoS2/HN-CNFs can significantly reduce the ion diffusion barrier and increase the number of intercalated active sites As a result, O–MoS2/HN-CNFs exhibited superior rate capabilities, good cycling performance, and long-term cycling stability, with a reversible capacity of 1344 mA h g−1 at 1000 mA g−1 after 2000 cycles

Xianbo Yu

Papers

Design of MoS2/Graphene van der Waals Heterostructure as Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution in Acidic and Alkaline Media.

MoS2/graphene heterostructure with facilitated Mg-diffusion kinetics for high-performance rechargeable magnesium batteries

A MoS2 and Graphene Alternately Stacking van der Waals Heterostructure for Li+/Mg2+ Co-Intercalation

Self-supported PPy-encapsulated CoS2 nanosheets anchored on the TiO2−x nanorod array support by Ti–S bonds for ultra-long life hybrid Mg2+/Li+ batteries

A material of hierarchical interlayer-expanded MoS2 nanosheets/hollow N-doped carbon nanofibers as a promising Li+/Mg2+ co-intercalation host