Herein, a 3D hierarchical structure is constructed by growing NiCo₂O₄ nanowires on few-layer Ti₃C₂ nanosheets using Ni foam (NF) as substrate via simple vacuum filtration and solvothermal treatment. Ti₃C₂ nanosheets are directly anchored on NF surface without binders or surfactants, and NiCo₂O₄ nanowires composed of about 15 nm nanoparticles uniformly grow on Ti₃C₂/NF skeleton, which can provide abundant active sites and ion diffusion pathways for enhancing electrochemical performance. Benefiting from the unique structure feature and the synergistic effects of active materials, NiCo₂O₄/Ti₃C₂ exhibits a high specific capacitance of 2468 F g⁻¹ at a current density of 0.5 A g⁻¹ and a good rate performance. Based on this, an asymmetric supercapacitor (ASC) based on NiCo₂O₄/Ti₃C₂ as positive electrode and activated carbon (AC)/NF as negative electrode is assembled. The ASC achieves a high specific capacitance of 253 F g⁻¹ at 1 A g⁻¹ along with 91.5% retention over 10,000 cycles at 15 A g⁻¹. Furthermore, the ACS presents an outstanding energy density of 90 Wh kg⁻¹ at the power density of 2880 W kg⁻¹. This work provides promising guidance for the fabrication of binder-free, free-standing and hierarchical composites for energy storage application.

As a graphene-like material, h-BN has stimulated great research interest recently due to its potential application for next-generation electronic devices. Herein, a systematic theoretical investigation of electronic structures and optical properties of C-doped and Cu-Al co-doped h-BN is carried out by the first-principles calculations. Firstly, two different C-doped h-BN structures for the para-position and ortho-position are constructed. The results show that the C ortho-doped h-BN (BCN) structure with a band gap of 3.05 eV is relatively stable, which is selected as a substate to achieve the Cu-Al co-doped h-BN. Based on this, the effect of the concentration of C atom doping on the electronic and optical properties of Cu-Al co-doped BC_xN (x = 0, 11.1% and 22.2%) is investigated. The results demonstrate that the band gap of Cu-Al co-doped BC_xN decreases and the optical properties improve with the increase in C atom concentration. The band gap and static dielectric constant of Cu-Al co-doped BC₀N, BC₁N and BC₂N are 0.98 eV, 0.87 eV and 0.23 eV and 2.34, 3.03 and 3.77, respectively. As for all Cu-Al co-doped BC_xN systems, the adsorption peak is red-shifted, and the peak intensity obviously decreases compared to the undoped h-BN. Additionally, the Cu-Al co-doped BC₂N exhibits the best response to visible light. This work will provide valuable guidance for designing and developing h-BN-based doping systems with good performance in the field of optical and photocatalysis.

Hexagonal boron nitride (h-BN) nanoparticles have attracted increasing attention due to their unique structure and properties. However, it is difficult to synthesize h-BN nanoparticles with uniform spherical morphology due to their crystal characteristic. The morphology control by tuning their precursor synthesis is a promising and effective strategy to solve this problem. Especially, the treatment temperature of precursors plays an important role in the morphology and surface area of h-BN nanoparticles. Herein, h-BN nanoparticles with different morphologies were synthesized via regulating the treatment temperature of precursors. The result shows that treatment temperature will affect the microstructure and state of precursor and further influence the morphology of h-BN products. Benefiting from the unique structure, the h-BN obtained using 250 °C precursors shows higher specific surface area (61.1 m² g⁻¹) than that of 85 °C (36.5 m² g⁻¹) and 145 °C (27.9 m² g⁻¹). h-BN products obtained using 250 °C precursors show higher specific surface area than that of 85 °C and 145 °C. The optimal condition for obtaining high-quality spherical h-BN is the pretreatment temperature of 250 °C and sintering temperature of 1300 °C. Importantly, compared with commercial h-BN nanoparticles, the synthesized h-BN nanoparticles show more uniform structure and larger specific surface area, indicating that sintering activity will be greatly improved. Furthermore, the reaction pathway and formation mechanism of h-BN was revealed by DFT calculations. The result shows that the five stationary states and five transition states exist in the reaction pathway, and the energy barrier can be overcome at high temperatures to form a ring h-BN. In view of its simplicity and efficiency, this work is promising for designing and guiding the synthesis of h-BN nanoparticles with uniform morphology.

High-performance ceramics, especially h-BN-based ceramics, are widely used in the metallurgical field. The interface state of h-BN-based ceramic composites, including chemical reactions, molecular diffusion, and interface structure changes, will greatly affect the properties of composite materials. Herein, taking Si ₃ N ₄ /BN composites as a representative case, their interfacial interactions were investigated by first-principles calculations. First, the structural and electronic properties and elastic modulus of bulk Si ₃ N ₄ and h-BN were calculated. Then, the interface mismatch relationship and interface models of Si ₃ N ₄ /BN were studied and established. Finally, the interface bond structure of Si ₃ N ₄ /BN was analyzed by charge density and state density calculations. The results showed that the band gap of bulk Si ₃ N ₄ and h-BN was 4.18 and 4.24 eV, respectively. Besides, bulk h-BN exhibited better compression performance and resistance to deformation than Si ₃ N ₄ based on elastic modulus calculation. Therefore, h-BN was used as a substrate, and when interface mismatch is 1.3%, good matching and bonding at the interface layer can be obtained. Based on this, two interface models of Si ₃ N ₄ (100)/BN(002) were established, which were named the B-N _Si interface and Si-N _B interface. The BN/Si ₃ N₄ interface exhibited strong van der Waals interactions, and the charge transfer from Si ₃ N ₄ to h-BN was observed, which indicate that the weak covalent bond also exists in the BN/Si ₃ N ₄ interface. The low interface energy indicates that the formed interface is relatively stable, which is beneficial for applications requiring high thermal and mechanical stability. This work provides valuable insights into the interfacial interaction between h-BN and Si ₃ N ₄ and will give a promising theoretical guidance for designing and optimizing h-BN-based ceramic composites.