Template-free synthesis of nitrogen-doped hierarchical porous carbons for CO2 adsorption and supercapacitor electrodes.

Nitrogen-doped hierarchical porous carbons (NHPCs) with controllable nitrogen content were prepared via a template-free method by direct carbonization of melamine-resorcinol-terephthaldehyde networks. The synthetic approach is facile and gentle, resulting in a hierarchical pore structure with modest micropores and well-developed meso-/macropores, and allowing the easy adjusting of the nitrogen content in the carbon framework. The micropore structure was generated within the highly cross-linked networks of polymer chains, while the mesopore and macropore structure were formed from the interconnected 3D gel network. The as-prepared NHPC has a large specific surface area of 1150m2·g-1, and a high nitrogen content of 14.5wt.%. CO2 adsorption performances were measured between 0°C and 75°C, and a high adsorption capacity of 3.96mmol·g-1 was achieved at 1bar and 0°C. Moreover, these nitrogen-doped hierarchical porous carbons exhibit a great potential to act as electrode materials for supercapacitors, which could deliver high specific capacitance of 214.0F·g-1 with an excellent rate capability of 74.7% from 0.1 to 10 A·g-1. The appropriate nitrogen doping and well-developed hierarchical porosity could accelerate the ion diffusion and the frequency response for excellent capacitive performance. This kind of new nitrogen-doped hierarchical porous carbons with controllable hierarchical porosity and chemical composition may have a good potential in the future applications.

Controllable Nitrogen Doping of High-Surface-Area Microporous Carbons Synthesized from an Organic-Inorganic Sol-Gel Approach for Li-S Cathodes.

High-surface-area microporous carbons with controllable nitrogen doping were prepared via a novel organic-inorganic sol-gel approach, using phenolic resol and hexamethoxymethyl melamine (HMMM) as carbon precursors, and partially hydrolyzed tetraethoxysilane as silica template. The pore structures of microporous carbons were completely replicated from a thin silica framework and could be tailored greatly by changing the organic/inorganic ratio. The nitrogen atoms doped into the carbon framework were issued from high-nitrogen-content HMMM precursors, and the nitrogen content could be adjusted in a wide range by changing the phenolic resol/HMMM ratio. Moreover, the porous structure and nitrogen content could be simultaneously controlled, allowing the preparation of a series of microporous carbons with almost the same microstructures (BET surface areas of ca.1900 m(2)·g(-1)and pore volumes of ca. 1.2 cm(3)·g(-1), and the same pore size distributions) but with different nitrogen contents (0-12 wt %). These results provided a general method to synthesize nitrogen-doped microporous carbons and allowed these materials to serve as a model system to illustrate the role of nitrogen content on the performance of the carbons. When used as the supports for sulfur cathodes, only an appropriate nitrogen content of ca. 6.3 wt % was found to effectively improve sulfur utilization and cycle life of the sulfur cathodes. The resulting sulfur cathodes could deliver an outstanding reversible discharge capacity of 1054 mAh·g(-1) at 0.5 C after 100 cycles.

Melamine-assisted one-pot synthesis of hierarchical nitrogen-doped carbon@MoS2 nanowalled core-shell microspheres and their enhanced Li-storage performances.

A facile and scalable one-pot approach has been developed to synthesize carbon@MoS2 core-shell microspheres by a hydrothermal method, which involves the fast formation of melamine-resorcinol-formaldehyde polymeric microspheres in situ, followed by direct growth of the MoS2 nanowalls on them. The results give unequivocal proof that melamine could be the key to forming the core-shell microspherical morphology, and the contents of MoS2 shells can be easily tuned by initial ratios of the precursors. After a simple heat treatment, the obtained carbon@MoS2 microspheres simultaneously integrate the nitrogen-doped carbon cores and the hierarchical shells which consist of few-layered MoS2 nanowalls with an expanded interlayer spacing. Their unique architectures are favourable for high electronic/ionic conductivity and accommodate volume strain during the electrochemical reaction of the MoS2 anodes in lithium-ion batteries. Thus, a very high reversibility capacity of 771 mA h g(-1) at 100 mA g(-1) after 100 cycles, and a rate capacity of 598 mA h g(-1) at 2000 mA g(-1) could be achieved for the carbon@MoS2 core-shell microspheres with the optimal composition. Furthermore, a thin carbon coating on the carbon@MoS2 microspheres could further increase the reversible capacity to 856 mA h g(-1) after 100 cycles at 100 mA g(-1). These encouraging results suggest that such a facile and efficient protocol can provide a new pathway to produce hierarchical core-shell microspheres which integrate the structural, morphological and compositional design rationales for advanced lithium-ion batteries.