Fabrication of high-pore volume carbon nanosheets with uniform arrangement of mesopores

Carbon nanosheets with a tunable mesopore size,large pore volume,and good electronic conductivity are synthesized via a solution-chemistry approach.In this synthesis,diaminohexane and graphene oxide (GO) are used as the structural directing agents,and a silica colloid is used as a mesopores template.Diaminohexane plays a crucial role in bridging silica colloid particles and GO,as well as initiating the polymerization of benzoxazine on the surfaces of both the GO and silica,resulting in the formation of a hybrid nanosheet polymer.The carbon nanosheets have graphene embedded in them and have several spherical mesopores with a pore volume up to 3.5 cm3·g-1 on their surfaces.These nuerous accessible mesopores in the carbon layers can act as reservoirs to host a high loading of active charge-storage materials with good dispersion and a uniform particle size.Compared with active materials with wide particle-size distributions,the unique proposed configuration with confined and uniform particles exhibits superior electrochemical performance during lithiation and delithiation,especially during long cycles and at high rates.     

炭气凝胶的制备、性能及应用

炭气凝胶是一种新型、轻质、纳米、多孔、非晶态炭材料,具有可在纳米尺度控制和剪裁的连续的三维网络结构,具有许多优异的性能和广阔的应用前景。通过结合所从事研究工作,综述了气凝胶的制备、性能及应用,分析了目前存在的问题和发展前景。     

Lysine-assisted rapid synthesis of crack-free hierarchical carbon monoliths with a hexagonal array of mesopores

The rapid and scalable synthesis of hierarchical carbon monoliths with an ordered mesostructure and fully interconnected macropores has been demonstrated. Resorcinol and formaldehyde based polymers were used as the carbon precursor, triblock copolymer Pluronic F127 as the structural directing agent, and organic base lysine as both the polymerization catalyst and mesostructure assembly promoter. In the presence of lysine, homogeneous and crack-free polymer monoliths can be obtained through rapid gelation in 15 min at 90 °C. The polymer monoliths have a robust framework, which can be directly dried at 50 °C in air and carbonized at high temperature under a nitrogen atmosphere. The carbon monoliths are crack-free and have an ordered mesostructure with fully interconnected macropores. The surface area and the macropore volume are high with values up to 600 m² g⁻¹ and 3.52 cm³ g⁻¹, respectively. Further steam activation of the carbon monolith can significantly improve the surface area to 2422 m² g⁻¹ while still maintaining the ordered mesostructure.     

Hard Carbon Nanosheets with Uniform Ultramicropores and Accessible Functional Groups Showing High Realistic Capacity and Superior Rate Performance for Sodium-Ion Storage

Hard carbon attracts considerable attention as an anode material for sodium-ion batteries; however, their poor rate capability and low realistic capacity have motivated intense research effort toward exploiting nanostructured carbons in order to boost their comprehensive performance. Ultramicropores are considered essential for attaining high-rate capacity as well as initial Coulombic efficiency by allowing the rapid diffusion of Na⁺ and inhibiting the contact of the electrolyte with the inner carbon surfaces. Herein, hard carbon nanosheets with centralized ultramicropores (≈0.5 nm) and easily accessible carbonyl groups (CO)/hydroxy groups (O H) are synthesized via interfacial assembly and carbonization strategies, delivering a large capacity (318 mA h g⁻¹ at 0.02 A g⁻¹), superior rate capability (145 mA h g⁻¹ at 5.00 A g⁻¹), and approximately 95% of reversible capacity below 1.00 V. Notably, a new charge model favoring fast capacitive sodium storage with dual potential plateaus is proposed. That is, the deintercalation of Na⁺ from graphitic layers is manifested as the low-potential plateau region (0.01−0.10 V), contributing to stable insertion capacity; meanwhile, the surface desodiation process of the CO and O H groups corresponds to the high-potential plateau region (0.40−0.70 V), contributing to a fast capacitive storage.     

Synthesis of nanocast ordered mesoporous carbons and their application as electrode materials for supercapacitor

Various nanocast ordered mesoporous carbons (OMCs) were synthesized using mesoporous silicas such as SBA-15, SBA-16, KIT-6, SBA-3 and MCM-48 as templates via nanocasting pathway. The structures of OMCs were analyzed by X-ray diffraction, transmission electron microscope and nitrogen sorption technique. These OMCs with well-defined pore structure were used as model electrode materials for investigating the influence of pore structure on their double layer capacitances. The cyclic voltammetry and galvanostatic charge/discharge measurements were conducted to estimate the capacitive behaviour of OMCs. The results show that the mesopore structures of OMCs play an important role in improving surface utilization for the formation of electrical double layer. OMCs synthesized from SBA-15 and SBA-16 show great advantage over others because their micropores are being easy accessible through the mesopores, thus allowing rapid electrolyte ion diffusion. To achieve a higher specific capacitance (μF cm⁻²), the optimized amount ratio between micropore and mesopore needs to be controlled. In addition, great impact of the electrode disc thickness on the capacitive performance was demonstrated by a series of careful measurements.     

Quasi-Zero Volume Strain Cathode Materials for Sodium Ion Battery through Synergetic Substitution Effect of Li and Mg

P2-type layered oxide material Na_2/3Ni_1/3Mn_2/3O₂ is a competitive candidate for sodium-ion batteries (SIBs). Nevertheless, it suffers from the strong P2–O2 phase transition during charging to the high voltage regime, rendering drastic volume variations and poor cycling performance. Here, a Quasi-zero strain P2-Na_0.75Li_0.15Mg_0.05Ni_0.1Mn_0.7O₂ cathode is synthesized, which reflects the vanishing P2–O2 transition with a volume change as low as 0.49%, thus resulting in the material an excellent cycling performance (83.9% capacity retention after 500 cycles at 5 C). The low-volume strain can be attributed to two aspects: (1) the Mg²⁺ riveted in the Na layer can act as a “pillar” to stabilize the crystal structure under the condition of sodium removal, thus restricting the structural changes under high voltage. (2) The entry of Li⁺ into the transition metal (TM) layer can mitigate the electron localization in the highly desodiation state and can effectively immobilize the coordination oxygen atoms, thus suppressing the slip of P2–O2 transition. This study not only provides a new insight of Li and Mg synergetic substitution effect on the structural stability of P2-type cathode, but also an efficient avenue for developing cathode materials of SIBs with ultralow bulk strain.     

Dual functions of activated carbon in a positive electrode for MnO2-based hybrid supercapacitor

Utilizing the dual functions of activated carbon (AC) both as a conductive agent and an active substance of a positive electrode, a hybrid supercapacitor (AC-MnO₂&AC) with a composite of manganese dioxide (MnO₂) and activated carbon as the positive electrode (MnO₂&AC) and AC as the negative electrode is fabricated, which integrates approximate symmetric and asymmetric behaviors in the distinct parts of 2 V operating windows. MnO₂ in the positive electrode and AC in the negative electrode together form a pure asymmetric structure, which extends the operating voltage to 2 V due to the compensatory effect of opposite over-potentials. In the range of 0-1.1 V, both AC in the positive and negative electrode assemble as a symmetric structure via a parallel connection which offers more capacitance and less internal resistance. The optimal mass proportions of electrodes are calculated though a mathematical process. In a stable operating window of 2 V, the capacitance of AC-MnO₂&AC can reach 33.2 F g⁻¹. After 2500 cycles, maximum energy density is 18.2 Wh kg⁻¹ with a 4% loss compared to the initial cycle. The power density is 10.1 kW kg⁻¹ with an 8% loss.     

Template synthesis of large pore ordered mesoporous carbon

Nanocast carbon (NCC-1) with large pores and ordered structure was synthesized via a nanocasting process using aluminum-containing SBA-15 as template and furfuryl alcohol (FA) as carbon precursor. This carbon has several interesting features, such as two steps with distinguished hystereses in the nitrogen sorption isotherm, high surface area of 2000 m²/g and large pore volumes of 3.0 cm³/g. It was found that the key factors in the synthesis of such carbons are the aging temperature of the SBA-15 template, the concentration of furfuryl alcohol (dissolved in trimethylbenzene), and the carbonization temperature. The optimal conditions for materials with high surface area and pore volumes are SBA-15 starting materials aged at 140 °C, 25 vol% of FA solution and 850–1100 °C carbonization temperatures. Moreover, it has been demonstrated that such nanocast carbon can be synthesized in a more facile way than previously reported. Purely siliceous SBA-15 without the need of Al³⁺-incorporation can be directly used as template. In this case, the polymerization catalyst—oxalic acid and FA were simultaneously introduced into the pore space of SBA-15.     

Comparison of gold supported catalysts obtained by using different allotropic forms of titanium dioxide

Gold catalysts were prepared on different allotropic phases of TiO₂ using the colloidal deposition method. The supports were chosen in order to study the influence of the support structure on the catalytic activity of the final material. Furthermore, for the same allotropic modification of titania, materials with a different particle size distributions have been used to study the influence of the grain size of the support on the deposition of the colloid. Our results indicate that the activity of the final catalyst is not much affected by the variation of the titania structure, though the situation becomes different when the catalyst is calcined at different temperatures. In this case, pure anatase and rutile supported catalysts showed a lower thermostability than the one prepared using P25 titanium oxide (Degussa). Concerning the colloid immobilization on the support it was found that the most important parameter is the grain size of the support. In particular, the deposition of the colloidal gold particles is greatly enhanced in the case of supports composed of particles of few nanometers in size.     

Gold nanoparticles stabilized by a flake-like Al2O3 support

A flake-like alumina with rough surface and small mesopores has been prepared by a hydrothermal method. Remarkably, such alumina was able to stabilize Au nanoparticles, predominantly ∼2.2 nm in size, even up to an annealing temperature of 700°C. The catalytic activity was tested using the CO oxidation model reaction where a complete conversion of 1% CO in air at 30°C was obtained.