Hollow mesoporous carbon nanospheres space-confining ultrathin nanosheets superstructures for efficient capacitive deionization

In this work, we propose a novel strategy to fabricate nickel silicate nanoflakes inside hollow mesoporous carbon spheres (Ni₃Si₂O₅(OH)₄/C). Hollow mesoporous carbon spheres (HMCSs) can well regulate and limit the growth of Ni₃Si₂O₅(OH)₄ nanosheets, which obviously enhance the structural stability and conductivity of the composites. The core-shell Ni₃Si₂O₅(OH)₄/C superstructure has been proven to possess an extremely excellent electrosorption capacity of 28.7 mg g^-1 at 1.2 V under a NaCl concentration of 584 mg L^-1 for capacitive deionization (CDI). This outstanding property can be attributed to the core-shell superstructure with ultrathin Ni₃Si₂O₅(OH)₄ nanosheets as the stable core and mesoporous carbon as the conductive shell. This work will provide a direction for the application of core-shell superstructure carbon-based nanomaterials as high-performance electrode materials for CDI.

Template-free construction of hollow mesoporous carbon spheres from a covalent triazine framework for enhanced oxygen electroreduction

The construction of hollow mesoporous carbon nanospheres (HMCS) avoiding the use of traditional soft/hard templates is highly desired for nanoscience yet challenging. Herein, we report a simple and straightforward template-free strategy for preparing nitrogen, sulfur dual-doped HMCSs (N/S-HMCSs) as oxygen reduction reaction (ORR) electrocatalysts. The unique hollow spherical and mesoporous structure was in-situ formed via a thermally initiated hollowing pathway from an elaborately engineered covalent triazine framework. Regulation of pyrolysis temperatures contributed to precisely tailoring of the shell thickness of HMCSs. The resulting N/S-HMCS₉₀₀ (pyrolyzed at 900 °C) possessed high N and S contents, large specific surface areas, rich and uniform mesopores distribution. Consequently, as a metal-free ORR electrocatalyst, N/S-HMCS₉₀₀ exhibits a high half-wave potential, excellent methanol tolerance and great long-term durability. Additionally, density functional theory calculations demonstrate that N, S-dual dopant can create extra active sites with higher catalytic activity than the isolated N-dopant. This strategy provides new insights into the construction of hollow and mesoporous multi-heteroatom-doped carbon materials with tunable nanoarchitecture for various electrochemical applications.

MOF-Derived CoSe2@N-Doped Carbon Matrix Confined in Hollow Mesoporous Carbon Nanospheres as High-Performance Anodes for Potassium-Ion Batteries

In this work, a novel vacuum-assisted strategy is proposed to homogenously form Metal-organic frameworks within hollow mesoporous carbon nanospheres (HMCSs) via a solid-state reaction. The method is applied to synthesize an ultrafine CoSe2 nanocrystal@N-doped carbon matrix confined within HMCSs (denoted as CoSe2@NC/HMCS) for use as advanced anodes in high-performance potassium-ion batteries (KIBs). The approach involves a solvent-free thermal treatment to form a Co-based zeolitic imidazolate framework (ZIF-67) within the HMCS templates under vacuum conditions and the subsequent selenization. Thermal treatment under vacuum facilitates the infiltration of the cobalt precursor and organic linker into the HMCS and simultaneously transforms them into stable ZIF-67 particles without any solvents. During the subsequent selenization process, the "dual confinement system", composed of both the N-doped carbon matrix derived from the organic linker and the small-sized pores of HMCS, can effectively suppress the overgrowth of CoSe2 nanocrystals. Thus, the resulting uniquely structured composite exhibits a stable cycling performance (442 mAh g-1 at 0.1 A g-1 after 120 cycles) and excellent rate capability (263 mAh g-1 at 2.0 A g-1) as the anode material for KIBs.