Selective Adsorption and Electrocatalysis of Polysulfides through Hexatomic Nickel Clusters Embedded in N-Doped Graphene toward High-Performance Li-S Batteries

Advanced Nanostructured MXene-Based Materials for High Energy Density Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are one of the most promising candidates for next-generation high-energy-density energy storage systems, but their commercialization is hindered by the poor cycling stability due to the insulativity of sulfur and the reaction end products, and the migration of lithium polysulfide. MXenes are a type of emerging two-dimensional material and have shown excellent electrochemical properties in LSBs due to their high conductivity and large specific surface area. Herein, several synthetic strategies developed for MXenes since their discovery are summarized alongside discussion of the excellent properties of MXenes for LSBs. Recent advances in MXene-based materials as cathodes for LSBs as well as interlayers are also reviewed. Finally, the future development strategy and prospect of MXene-based materials in high-energy-density LSBs are put forward.

Structural and Surfacial Modification of Carbon Nanofoam as an Interlayer for Electrochemically Stable Lithium-Sulfur Cells

Electrochemical lithium-sulfur batteries engage the attention of researchers due to their high-capacity sulfur cathodes, which meet the increasing energy-density needs of next-generation energy-storage systems. We present here the design, modification, and investigation of a carbon nanofoam as the interlayer in a lithium-sulfur cell to enable its high-loading sulfur cathode to attain high electrochemical utilization, efficiency, and stability. The carbon-nanofoam interlayer features a porous and tortuous carbon network that accelerates the charge transfer while decelerating the polysulfide diffusion. The improved cell demonstrates a high electrochemical utilization of over 80% and an enhanced stability of 200 cycles. With such a high-performance cell configuration, we investigate how the battery chemistry is affected by an additional polysulfide-trapping MoS2 layer and an additional electron-transferring graphene layer on the interlayer. Our results confirm that the cell-configuration modification brings major benefits to the development of a high-loading sulfur cathode for excellent electrochemical performances. We further demonstrate a high-loading cathode with the carbon-nanofoam interlayer, which attains a high sulfur loading of 8 mg cm-2, an excellent areal capacity of 8.7 mAh cm-2, and a superior energy density of 18.7 mWh cm-2 at a low electrolyte-to-sulfur ratio of 10 µL mg-1.

Basal-Plane-Activated Molybdenum Sulfide Nanosheets with Suitable Orbital Orientation as Efficient Electrocatalysts for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are one of the most promising candidates for next-generation energy storage systems because of their high theoretical energy density. However, the shuttling behavior and sluggish conversion kinetics of lithium polysulfides (LiPSs) limit their practical application. Herein, B-doped MoS₂ nanosheets are synthesized on carbon nanotubes (denoted as CNT@MoS₂-B) to function as catalysts to boost the performance of Li-S batteries. The poor catalytic performance of the pristine MoS₂ is revealed to be the result of unsuitable orbital orientation of the basal plane, which hinders the orbital overlap with sulfur species. B in CNT@MoS₂-B is sp³ hybridized, and it has a vacant σ orbital perpendicular to the basal plane, which can maximize the head-on orbital overlap with S. The incorporation of B significantly increases the reactivity of MoS₂ basal plane, which can facilitate the kinetics of Li₂S formation and dissolution. With these merits, the S/CNT@MoS₂-B cathodes deliver high rate capability and outstanding cycling stability, holding great promise for both scientific research and practical application. This work affords fresh insights for developing effective catalysts to accelerate LiPS conversion.

A review of size engineering-enabled electrocatalysts for Li-S chemistry

Li-S batteries (LSBs) have received extensive attention owing to their remarkable theoretical capacity (1672 mA h g^-1) and high energy density (2600 W h kg^-1), which are far beyond those of the state-of-the-art Li-ion batteries (LIBs). However, the retarded sulfur reaction kinetics and fatal shuttle effect have hindered the practical implementations of LSBs. In response, constructing electrocatalysts for Li-S systems has been considered an effective strategy to date. Particularly, size engineering-enabled electrocatalysts show high activity in the sulfur redox reaction, considerably contributing to the latest advances in Li-S system research. In this tutorial review, we provide a systematic summary of nano- to atomic-scale electrocatalysts employed in Li-S chemistry, aiming at figuring out the working mechanism of size engineering-enabled electrocatalysts in the sulfur redox reaction and guiding the rational construction of advanced LSBs toward practically viable applications.

Graphene-Based Nanomaterials as the Cathode for Lithium-Sulfur Batteries

The global energy crisis and environmental problems are becoming increasingly serious. It is now urgent to vigorously develop an efficient energy storage system. Lithium-sulfur batteries (LSBs) are considered to be one of the most promising candidates for next-generation energy storage systems due to their high energy density. Sulfur is abundant on Earth, low-cost, and environmentally friendly, which is consistent with the characteristics of new clean energy. Although LSBs possess numerous advantages, they still suffer from numerous problems such as the dissolution and diffusion of sulfur intermediate products during the discharge process, the expansion of the electrode volume, and so on, which severely limit their further development. Graphene is a two-dimensional crystal material with a single atomic layer thickness and honeycomb bonding structure formed by sp2 hybridization of carbon atoms. Since its discovery in 2004, graphene has attracted worldwide attention due to its excellent physical and chemical properties. Herein, this review summarizes the latest developments in graphene frameworks, heteroatom-modified graphene, and graphene composite frameworks in sulfur cathodes. Moreover, the challenges and future development of graphene-based sulfur cathodes are also discussed.

Platinum Atomic Clusters Embedded in Defects of Anatase/Graphene for Efficient Electro- and Photocatalytic Hydrogen Evolution

Electro- and photocatalytic hydrogen evolution reaction (e-HER and p-HER) are two promising strategies to produce green hydrogen fuel from water. High intrinsic activity, sufficient active sites, fast charge-transfer capacity, and good optoelectronic properties must be taken into consideration simultaneously in pursuit of an ideal bifunctional catalyst. Here, platinum atomic clusters embedded in defects of TiO₂ nanocrystals/graphene nanosheets (Pt-T/G) are reported as a bifunctional catalyst for electro- and photocatalytic hydrogen evolution reaction (e-HER and p-HER). High activity is delivered due to the charge transfer from the other part of the catalyst to the active center (Pt₂-O₄-Ti_x), decreasing the activation energy of the rate-limiting step, which is revealed by synchrotron X-ray absorption spectroscopy, photoelectrochemical measurements, and simulated calculations. In regard to e-HER, it outperforms the commercial 20 wt % Pt/C catalyst by a factor of 17.5 on Pt mass basis, allowing for a 93% reduction in Pt loadings. In regard to p-HER, it achieves photocatalytic efficiency (686.8 μmol h^-1) without any attenuation in 9 h.