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Developing metal‐free carbon catalysts with designable high nitrogen (N) content yet well‐organized N distribution within carbon at nanoscale is still one of the paramount challenges for electrochemical CO2 conversion. Herein, a gradient N doping enabled by the energetic microwave irradiation is realized along the radial direction of carbon nanotubes (CNTs), with an ultrahigh surface N content of 30.5 at%, beyond the upper limit of the tradition pyrolysis method. The unique time‐domain features of microwave heating presented as the sub‐minute residence time for precursors and relatively mild surface temperature on CNTs, contributing to the maximum reservation of the surface N species. The catalyst exhibits a prominent performance with great activity and selectivity for electrochemical CO2‐to‐CO conversion. Theoretical calculation confirmed the catalyst with high N‐doping level can promote the adsorption of CO2 molecule, with a low adsorption energy of −3.35 eV. This work provides a novel prototype to construct the distribution‐controlled and space‐intensive active sites over functional gradient metal‐free carbon materials. [ABSTRACT FROM AUTHOR]

Sodium metal, with a high theoretical specific capacity of 1165 mAh g−1, is the ultimate anode for sodium batteries, yet how to deal with the inhomogeneous and dendritic sodium deposition and the infinite relative dimension change of sodium metal anodes during sodium depositing/stripping is still challenging. Here, a facile fabricated sodiuphilic 2D N‐doped carbon nanosheets (N‐CSs) are proposed as sodium host material for sodium metal batteries (SMBs) to prevent dendrite formation and eliminate volume change during cycling. Revealing from combined in situ characterization analyses and theoretical simulations, the high nitrogen content and porous nanoscale interlayer gaps of the 2D N‐CSs can not only concede dendrite‐free sodium stripping/depositing but also accommodate the infinite relative dimension change. Furthermore, N‐CSs can be easily process into N‐CSs/Cu electrode via traditional commercial battery electrode coating equipment that pave the way for large‐scale industrial applications. On account of the abundant nucleation sites and sufficient deposition space, N‐CSs/Cu electrodes demonstrate a superior cycle stability of more than 1500 h at a current density of 2 mA cm−2 with a high coulomb efficiency of more than 99.9% and ultralow nucleation overpotential, which enable reversible and dendrites‐free SMBs and shed light on further development of SMBs with even higher performance. [ABSTRACT FROM AUTHOR]

Abstract Sodium metal, with a high theoretical specific capacity of 1165 mAh g−1, is the ultimate anode for sodium batteries, yet how to deal with the inhomogeneous and dendritic sodium deposition and the infinite relative dimension change of sodium metal anodes during sodium depositing/stripping is still challenging. Here, a facile fabricated sodiuphilic 2D N‐doped carbon nanosheets (N‐CSs) are proposed as sodium host material for sodium metal batteries (SMBs) to prevent dendrite formation and eliminate volume change during cycling. Revealing from combined in situ characterization analyses and theoretical simulations, the high nitrogen content and porous nanoscale interlayer gaps of the 2D N‐CSs can not only concede dendrite‐free sodium stripping/depositing but also accommodate the infinite relative dimension change. Furthermore, N‐CSs can be easily process into N‐CSs/Cu electrode via traditional commercial battery electrode coating equipment that pave the way for large‐scale industrial applications. On account of the abundant nucleation sites and sufficient deposition space, N‐CSs/Cu electrodes demonstrate a superior cycle stability of more than 1500 h at a current density of 2 mA cm−2 with a high coulomb efficiency of more than 99.9% and ultralow nucleation overpotential, which enable reversible and dendrites‐free SMBs and shed light on further development of SMBs with even higher performance.

An aqueous emulsion polymerization self‐assembly approach is demonstrated for the first time to synthesize ultrahigh nitrogen containing mesoporous polymer nanospheres, using melamine‐formaldehyde resin oligomers as precursors. In the synthesis, change from alkaline to acidic conditions is critical for the formation of monodisperse mesostructured polymer nanospheres. Owing to unique structure of triazine stabilized in the covalent polymeric networks during the pyrolysis process, the derived mesoporous carbon nanospheres possess an ultrahigh nitrogen content (up to 15.6 wt%) even after pyrolysis at 800 °C, which is the highest nitrogen content among mesoporous carbon nanospheres. Furthermore, these monodisperse mesoporous carbon nanospheres possess a high surface area (≈883 m2 g−1) and large pore size (≈8.1 nm). As an anode for sodium‐ion batteries, the ultrahigh nitrogen‐containing mesoporous carbon nanospheres exhibit superior rate capability (117 mAh g−1 at a high current density of 3 A g−1) and high reversible capacity (373 mAh g−1 at 0.06 A g−1), indicating a promising material for energy storage. [ABSTRACT FROM AUTHOR]

An efficient chemical synthesis route, with an aim of reaching an ultrahigh nitrogen (N)‐doping level in carbon materials can provide a platform where the type and amount of N dopant can be tuned over a wide range. We propose a C‐S‐C linkage‐triggered confined‐pyrolysis strategy for the high‐efficiency in situ N‐doping into carbon matrix and an ultrahigh doping level up to 13.5 at %, which is close to the theoretical upper limit (15.2 at %) is realized at a high carbonization temperature of 1000 °C. The pyridinic N is dominant with a maximum percent of 48.7 %. By using I3− reduction as an example, the resultant NCM‐5 exhibits the best activity with a power conversion efficiency of 8.77 %. A pyridinic N site‐dependent activity is demonstrated in which the amount of active sites increases with the increase of pyridinic N, and the carbon atom adjacent to electron‐withdrawing pyridinic N at the armchair edge acts as the most favorable site for the adsorption of I2. [ABSTRACT FROM AUTHOR]

To improve the electrochemical performance of carbonaceous anodes for lithium ion batteries (LIBs), the incorporation of both well-defined heteroatom species and the controllable 3D porous networks are urgently required. In this work, a novel N-enriched carbon/carbon nanotube composite (NEC/CNT) through a chemically induced precursor-controlled pyrolysis approach is developed. Instead of conventional N-containing sources or precursors, Schiff-base network (SNW-1) enables the desirable combination of a 3D polymer with intrinsic microporosity and ultrahigh N-content, which can significantly promote the fast transport of both Li + and electron. Significantly, the strong interaction between carbon skeleton and nitrogen atoms enables the retention of ultrahigh N-content up to 21 wt% in the resultant NEC/CNT, which exhibits a super-high capacity (1050 mAh g -1 ) for 1000 cycles and excellent rate performance (500 mAh g -1 at a current density of 5 A g -1 ) as the anode material for LIBs. The NEC/CNT composite affords a new model system as well as a totally different insight for deeply understanding the relationship between chemical structures and lithium ion storage properties, in which chemistry may play a more important role than previously expected., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)