Recently, commercial graphite and other carbon-based materials have shown promising properties as the anode for potassium-ion batteries. A fundamental problem related to those carbon electrodes, significant volume expansion, and structural instability/collapsing caused by cyclic K-ion intercalation, remains unsolved and severely limits further development and applications of K-ion batteries. Here, a multiwalled hierarchical carbon nanotube (HCNT) is reported to address the issue, and a reversible specific capacity of 232 mAh g , excellent rate capability, and cycling stability for 500 cycles are achieved. The key structure of the HCNTs consists of an inner CNT with dense-stacked graphitic walls and a loose-stacked outer CNT with more disordered walls, and individual HCNTs are further interconnected into a hyperporous bulk sponge with huge macropore volume, high conductivity, and tunable modulus. It is discovered that the inner dense-CNT serves as a robust skeleton, and collectively, the outer loose-CNT is beneficial for K-ion accommodation; meanwhile the hyperporous sponge facilitates reaction kinetics and offers stable surface capacitive behavior. The hierarchical carbon nanotube structure has great potential in developing high-performance and stable-structure electrodes for next generation K and other metal-ion batteries.

attention because of its low cost and abundant supply of sodium. [1][2][3] However, because of its narrow interlayer spacing ≈0.34 nm, the larger size of Na + compared to Li + makes it difficult if not unsuitable for intercalation in graphite, which is commercially employed for LIB. [4][5][6] Further, the large radius of Na + in SIB electrodes produces sluggish electrochemical kinetics, provides higher diffusion barriers, and causes large volume expansion which leads to low rate capability and poor cyclic stability. [7,8] The ionization potential of Na + is also lower than Li + which results in a lower operating voltage and consequently, a lower energy density. [9] A lot of efforts in the development of advanced anode materials for SIBs have been proposed to address these issues.Recently, 2D transition metal dichalcogenides (TMDCs) have received considerable attention in electrochemical energy storage and conversion devices due to their layered structure, and the favorable electronic, chemical, and mechanical properties and stability. [10][11][12] TMDCs such as MoS 2 are often considered a promising anode candidate for LIBs. [13] However, when MoS 2 is employed in SIBs, it displays a lower capacity and a poor cyclic stability as a result of the low intrinsic conductivity and the small interlayer distance (≈0.62 nm). [14] In contrast, MoSe 2 possesses a slightly larger interlayer distance (≈0.64 nm) and better electrical conductivity due to small bandgap (≈1.1 eV). Moreover, it possesses higher theoretical capacity (≈422 mAh g −1 ) [10,15] than graphite (≈35 mAh g −1 ) [6] which makes it one of the most promising TMDC candidates for SIBs. However, the practical applications of MoSe 2 as an anode is limited by capacity fading due to the large volume expansion during long charging/discharging processes and the poor rate capability due to the low intrinsic electrical conductivity. [10] Modifying the nanostructure of the SIB electrodes can often solve some of these problems. For example, expanding the interlayer distance of MoSe 2 can lead to an improvement of the Na + storage and reducing the Na + diffusion barrier energy can enhance the reaction kinetics for the Na + intercalation/deintercalation. [16] Due to the high surface energy and weak van der Waal interactions between layers, Freestanding composite structures with embedded transition metal dichalcogenides (TMDCs) as the active material are highly attractive in the development of advanced electrodes for energy storage devices. Most 3D electrodes consist of a bilayer design involving a core-shell combination. To further enhance the gravimetric and areal capacities, a 3D trilayer design is proposed that has MoSe 2 as the TMDC sandwiched in-between an inner carbon nanotube (CNT) core and an outer carbon layer to form a CNT/ MoSe 2 /C framework. The CNT core creates interconnected pathways for the e − /Na + conduction, while the conductive inert carbon layer not only protects the corrosive environment between the electrolyte and MoSe 2 but also is fully tunable fo...

Tailoring the interfaces between active metal centers and supporting materials is an efficient strategy to obtain a superior catalyst for a certain reaction. Herein, an active interface between Ru and CeO2 was identified and constructed by adjusting the morphology of CeO2 support, such as rods (R), cubes (C), and octahedra (O), to optimize both the activity and the stability of Ru/CeO2 catalyst for propane combustion. We found that the morphology of CeO2 support does not significantly affect the chemical states of Ru species but controls the interaction between the Ru and CeO2, leading to the tuning of oxygen vacancy in the CeO2 surface around the Ru–CeO2 interface. The Ru/CeO2 catalyst possesses more oxygen vacancy when CeO2-R with predominantly exposed CeO2{110} surface facets is used, providing a higher ability to adsorb and activate oxygen and propane. As a result, the Ru/CeO2-R catalyst exhibits higher catalytic activity and stability for propane combustion compared with the Ru/CeO2-C and Ru/CeO2-O catalysts. This work highlights a new strategy for the design of efficient metal/CeO2 catalysts by engineering morphology and associated surface facet of CeO2 support for the elimination of light alkane pollutants and other volatile organic compounds.

Metal‐organic frameworks (MOFs) hybridized with a conductive matrix could potentially serve as a sulfur host for lithium‐sulfur (Li‐S) battery electrodes; so far most of the previously studied hybrid structures are in the powder form or thin compact films. This study reports 3D porous MOF@carbon nanotube (CNT) networks by grafting MOFs with tailored particle size uniformly throughout a CNT sponge skeleton. Growing larger‐size MOF particles to entrap the conductive CNT network yields a mutually embedded structure with high stability, and after sulfur encapsulation, it shows an initial discharge capacity of ≈1380 mA h g−1 (at 0.1 C) and excellent cycling stability with a very low fading rate. Furthermore, owing to the 3D porous network that is suitable for enhanced sulfur loading, a remarkable areal capacity of ≈11 mA h cm−2 (at 0.1 C) is obtained, which is much higher than other MOF‐based hybrid electrodes. The mutually embedded MOF@CNTs with simultaneously high specific capacity, areal capacity, and cycling stability represent an advanced candidate for developing high‐performance Li‐S batteries and other energy storage systems.

Heterogeneous inorganic nanotube structures consisting of multiwalled carbon nanotubes coated by long, continuous MoS sheets with tunable sheet number are synthesized using a carbon-nanotube sponge as a template. The resulting 3D porous hybrid sponges have potential applications as high-performance freestanding anodes for Li-ion batteries with excellent specific capacity and cycling stability.