Densely Branched Carbon Nanotubes for Boosting the Electrochemical Performance of Li-S Batteries.

To address the inherent limitations of conventional carbon nanotubes (CNTs), such as their tendency to agglomerate and scarcity of catalytic sites, the development of branched carbon nanotubes (BCNTs) with a unique hierarchical structure has emerged as a promising solution. Herein, gram scale quantities of densely branched and structurally consistent Ni-Fe decorated branched CNTs (Ni-Fe@BCNT) have been prepared. This uniform and densely branched architecture ensures excellent dispersibility and superior electrical conductivity. Additionally, each branched tip is equipped with Ni-Fe particles, thereby providing numerous catalytic sites which endow them with exceptional catalytic activity for the conversion of polysulfides. The polypropylene (PP) separator modified with Ni-Fe@BCNT interlayer is fabricated as a multifunctional barrier for Li-S batteries. The experimental results demonstrate that Ni-Fe@BCNT interlayer can effectively suppress the shuttle effect of polysulfides and enhance their redox kinetics. The outstanding catalytic ability of Ni-Fe@BCNT interlayer enables batteries with high specific capacities, outstanding rate performance, and remarkable cycling stability. This approach proposed in this work paves a new path for synthesizing BCNTs and shows great potential for scaling up the production of BCNTs to address more demanding applications.

Encasing Few-Layer MoS2 within 2D Ordered Cubic Graphitic Cages to Smooth Trapping-Conversion of Lithium Polysulfides for Dendrite-Free Lithium-Sulfur Batteries.

The industrialization of lithium-sulfur (Li-S) batteries faces challenges due to the shuttling effect of lithium polysulfides (LiPSs) and the growth of lithium dendrites. To address these issues, a simple and scalable method is proposed to synthesize 2D membranes comprising a single layer of cubic graphitic cages encased with few-layer, curved MoS2. The distinctive 2D architecture is achieved by confining the epitaxial growth of MoS2 within the open cages of a 2D-ordered mesoporous graphitic framework (MGF), resulting in MoS2@MGF heterostructures with abundant sulfur vacancies. The experimental and theoretical studies establish that these MoS2@MGF membranes can act as a multifunctional interlayer in Li-S batteries to boost their comprehensive performance. The inclusion of the MoS2@MGF interlayer facilitates the trapping and conversion kinetics of LiPSs, preventing their shuttling effect, while simultaneously promoting uniform lithium deposition to inhibit dendrite growth. As a result, Li-S batteries with the MoS2@MGF interlayer exhibit high electrochemical performance even under high sulfur loading and lean electrolyte conditions. This work highlights the potential of designing advanced MoS2-encased heterostructures as interlayers, offering a viable solution to the current limitations plaguing Li-S batteries.

Molecularly Confined Topochemical Transformation of MXene Enables Ultrathin Amorphous Metal-Oxide Nanosheets.

Two-dimensional (2D) amorphous nanosheets with ultrathin thicknesses have properties that differ from their crystalline counterparts. However, conventional methods for growing 2D materials often produce either crystalline flakes or amorphous nanosheets with an uncontrollable thickness. Here, we report that ultrathin amorphous metal-oxide nanosheets featuring superior flatness can be realized through the molecularly confined topochemical transformation of MXene. Using MXene Ti2CTx as an example, we show that surface modification of Ti2CTx nanosheets with molecular ligands, such as oleylamine (OAm) and oleic acid (OA), not only imparts notable colloidal dispersity to Ti2CTx nanosheets in nonpolar organic solvents but also confines their subsequent oxidation to in-plane configurations. We demonstrate that unlike the drastic oxidation conventionally observed for pristine MXene, hydrophobizing MXene with OAm and OA ligands enables individual Ti2CTx nanosheets to undergo independent oxidation in a nondestructive manner, resulting in amorphous titanium oxide (am-TiO2) nanosheets that faithfully retain the dimension and flatness of pristine MXene. These am-TiO2 nanosheets exhibit exceptional activity as substrates for surface-enhanced Raman scattering. Importantly, this molecular confinement strategy can be extended to other MXene materials, providing a versatile approach for synthesizing ultrathin amorphous metal-oxide nanosheets with tailored compositions and functionalities.

An elegant 3D-ordered hierarchically porous framework to anchor Pt nanocrystals for durable oxygen reduction reaction.

While Platinum (Pt)-based electrocatalysts have been extensively studied for the oxygen reduction reaction (ORR), improving their durability remains a challenge. One promising approach is to design structure-defined carbon supports that can uniformly immobilize Pt nanocrystals (NCs). In this study, we present an innovative strategy for constructing three-dimensional ordered, hierarchically porous carbon polyhedrons (3D-OHPCs) as an efficient support for immobilizing Pt NCs. We achieved this by template-confined pyrolysis of a zinc-based zeolite imidazolate framework (ZIF-8) grown within the voids of polystyrene templates, followed by carbonizing the native oleylamine ligands on Pt NCs to produce graphitic carbon shells. This hierarchical structure enables the uniform anchorage of Pt NCs, while enhancing facile mass transfer and local accessibility of active sites. The optimal material with graphitic carbon armor shells on the surface of Pt NCs (CA-Pt), named CA-Pt@3D-OHPCs-1600, shows comparable activities to commercial Pt/C catalysts. Furthermore, it can withstand over 30,000 cycles of accelerated durability tests, owing to the protective carbon shells and hierarchically ordered porous carbon supports. Our study presents a promising approach for designing highly efficient and durable electrocatalysts for energy-based applications and beyond.