N-doping Level Research Articles

Unraveling MOF growth in colloids with controllable dual-doping through ultrafast sintering for wide temperature range LIBs

Metal-organic frameworks (MOFs) offer versatile building blocks for high-performance materials across practical applications. Crystallization studies reveal MOF complex pathways crucial for biological and synthetic systems, yet understanding remains incomplete. Here, we employ in-situ liquid phase transmission electron microscopy (LPTEM) to scrutinize the growth dynamics of ZIF-8 in colloidal environments, aiming to deepen our comprehension of MOF crystallization. This study employs in-situ LPTEM to investigate ZIF-8 nanoparticle growth, revealing the combination of classical and non-classical nucleation processes in the same batch leading a challenge to control nanoparticle morphology and size, while heterogeneous nucleation is dominant giving monodispersed nanoparticle at the presence of ZIF-8 seeds in mother solution. Additionally, integrating MOF-derived carbon materials in lithium-ion batteries (LIBs) faces challenges in achieving high-performance, controllable N-doping and long-term stability. Ultrafast high-temperature sintering (UHS) is utilized to carbonize ZIF-8, regulating N-doping hard carbon with Zn single atoms doping. Results show optimal morphology at 800 °C for 20 s, yielding higher concentration of Zn-doping, higher N-doping levels, and good conductivity compared to conventional sintering in tube furnace. LIB tests demonstrate exceptional cycling performance and stability across wide temperatures. This UHS strategy for ZIF-8 contributes to establishing a balance between Zn-N-doping and the degree of graphitization, thus providing an interdisciplinary approach that offers efficient MOF derivative synthesis for promising wide temperature range applications of LIBs.

Role of Nitrogen-doping in porous carbon for enlarging working voltage window of aqueous supercapacitors in neutral electrolyte

The fundamental mechanism on enlarging working voltage window of carbon-based aqueous supercapacitors is still unclear owing to the indistinct principles in inhibiting water splitting occurred at the electrochemical interface. Herein, we design a set of N, O co-doped porous carbon (NOPC) free-standing electrodes with adjustable N-doping level, and establish that N-doping (N-content and specific N-configuration) governs neutral HER and OER. The NOPC electrode with a lower N-doping level can possess a wide working potential window of − 1–1 V, and thus the corresponding aqueous symmetric supercapacitors showcase a wide working voltage window of 2 V in LiCl aqueous solution. In situ spectroscopy evidences and theoretical simulation demonstrate that the low N-doping (N-content and percentage of pyrrolic nitrogen) level can weaken the interaction between the electrode and interfacial water molecules and suppress the formation of *OOH intermediate during the charge–discharge process, and thus significantly decreasing the HER and OER activities to inhibit water splitting. The finding can shed light on the fundamental understanding of mechanism on enlarging working voltage window of carbon-based aqueous supercapacitor.

Insight into the effect of N-doping level in N-doped carbons modified separator on improving the electrochemical performance of Li-S batteries

Carbon materials are widely applied in lithium-sulfur (Li-S) batteries due to their large specific surface area, high conductivity, and tunable properties. An appropriate heteroatom doping can enhance the adsorption ability and electrochemical activity toward lithium polysulfides, thus improving the overall performance of Li-S batteries. Herein, three nitrogen-doped carbons (NCs) with different nitrogen doping levels are firstly prepared and then used as the model materials to coat the common polypropylene (PP) separator, aiming to elaborate the effect of adsorption behavior from various N-doping level carbons surface toward lithium polysulfides on the subsequent catalytic conversion kinetics. The experimental data demonstrate that the NC800 with appropriate N-doped level shows the moderate adsorption of polysulfides as well as exhibits the best reaction kinetics on polysulfides conversion. In comparison, an assembled Li-S battery with NC800-PP separator delivers high capacity and good cycling stability, achieving an initial specific capacity of ∼ 1302.2 mAh g−1 at 0.2 C and a capacity fading rate of ∼ 0.061 % per cycle after 500 cycles at 1.0 C. Moreover, a Li-S battery using NC800-PP separator still delivers an initial specific capacity of ∼ 1147.6 mAh g−1 at 0.1 C and maintains a stable specific capacity of ∼ 833.5 mAh g−1 even with a sulfur loading of ∼ 3.9 mg cm−2. This study is believed to give better insight to reveal the internal correlation of adsorption and catalytic effect on polysulfides, as well as provide a guidance for rationally designing heteroatom doping carbon materials in Li-S batteries.

Design and Synthesis of N-Doped Carbons as Efficient Metal-Free Catalysts in the Hydrogenation of 1-Chloro-4-Nitrobenzene.

Metal-free catalysts based on nitrogen-doped porous carbons were designed and synthesized from mixtures of melamine as nitrogen and carbon sources and calcium citrate as carbon source and porogen system. Considering the physicochemical and textural properties of the prepared carbons, a melamine/citrate ratio of 2:1 was selected to study the effect of the pyrolysis temperature. It was observed that a minimum pyrolysis temperature of 750 °C is required to obtain a carbonaceous structure. However, although there is a decrease in the nitrogen amount at higher pyrolysis temperatures, a gradual development of the porosity is produced from 750 °C to 850 °C. Above that temperature, a deterioration of the carbon porous structure is produced. All the prepared carbon materials, with no need for a further activation treatment, were active in the hydrogenation reaction of 1-chloro-4-nitrobenzene. A full degree of conversion was reached with the most active catalysts obtained from 2:1 melamine/citrate mixtures pyrolyzed at 850 °C and 900 °C, which exhibited a suitable compromise between the N-doping level and developed mesoporosity that facilitates the access of the reactants to the catalytic sites. What is more, all the materials showed 100% selectivity for the hydrogenation of the nitro group to form the corresponding chloro-aniline.

Magnetoresistance effect of nitrogen doped graphdiyne.

This investigation elucidates the influence of nitrogen doping (N-doping) on the magnetoresistance (MR) characteristics of graphdiyne (GDY) by methodically adjusting the levels of N-doping. Through exhaustive experimental analyses, encompassing SEM, XPS, and magneto-transport measurements, we demonstrate that N-doping markedly augments carrier concentration, thereby inducing distinct MR behaviors. Specifically, N30-GDY manifests negative magnetoresistance (NMR) attributable to weak localization phenomena, whereas N60-GDY and N90-GDY exhibit positive magnetoresistance (PMR) characterized by significant resistance enhancements. These results not only clarify the underlying mechanisms governing the MR properties of GDY but also introduce a novel strategy for optimizing MR performance via controlled heteroatom doping, thereby holding considerable implications for the advancement of carbon-based electronic devices.

Temperature-dependent photoconductivity in two-dimensional MoS2 transistors

The photoconductivity in monolayer MoS2 back-gate transistors is studied as a function of temperature and pressure. The photocurrent increases linearly with the light intensity up to a maximum responsivity of ∼30 A/W in air. Time-resolved photocurrent measurements confirm that the photoresponse is dominated by the photogating effect. The device shows slow photoresponse with two-time constants that are attributed to the photobolometric effect and the desorption of adsorbates, respectively. An enhancement of the photocurrent is observed above room temperature and below the atmospheric pressure, that is, when the photoinduced desorption of adsorbates such as O2 and H2O molecules is facilitated. Indeed, the light-induced removal of adsorbates from the surface of MoS2 enhances the n-doping level and the current of the channel. Moreover, at lower pressures, the reverse mechanism of re-adsorption in dark conditions is suppressed and results in a persistent photocurrent. The study clarifies the photocurrent relaxation dynamics and unveils the key role of surface adsorbates in the optoelectronic properties of monolayer MoS2 and other similar 2D materials.

Edge-nitrogen synergize with micropores to realize fast and durable potassium storage for carbon anode

Edge-N (pyridinic/pyrrolic-N) functionalized carbon is a promising anode for potassium-ion batteries, while micropores have been proven to be effective in increasing capacity and cyclability. However, the obtained carbon materials usually exhibit a low N-doping level and edge-N species based on the conventional pyrolysis method, and the exploration of the synergistic effect of edge-N doping and micropores on the potassium-storage performance is still lacking. Herein, a novel strategy is proposed to prepare edge-N doped carbon (ENC-850) by directly pyrolyzing supermolecule precursors self-assembled by terephthalic acid (BDC) and melamine (MA). Because the s-triazine structure in MA is more stable than BDC, which can easily ensure a higher N-doping content in carbon, and the decomposition of s-triazine structure is accompanied by the release of NCNH2 gas, which enables most doped N-atoms to be of edge-N configurations, favoring the adsorption storage of K-ions. Besides, the released small molecules can create numerous micropores, not only providing active sites, but accommodating volume fluctuation. Therefore, the optimized ENC-850 with the most suitable edge-N content of 60.6% (7.73 at% of total 11.71 at% N-doping) and micropores delivers a high capacity (280 mAh g−1 at 0.5 A g−1) and superior cycling stability (over 2000 cycles).

Layer-by-layer enriching active Ni-N3C sites in nickel-nitrogen-carbon electrocatalysts for enhanced CO2-to-CO reduction

Transition metal and nitrogen co-doped carbons (M-N-C) have proven to be promising catalysts for CO2 electroreduction into CO because of the high activity and selectivity. Effective enrichment of the active transition metal coordinated nitrogen sites is desirable but is challenging for a practical volumetric productivity. Herein, we report four kinds of model electrocatalysts to unveil this issue, which include the NC structures with surface N-functionalities, Ni-N-C_I with one layer of surface Ni-N3C sites, NC@Ni-N-C_I with surface N-functionalities and underneath Ni-N3C sites as well as Ni-N-C_II with doubled surface Ni-N3C sites. The X-ray absorption spectroscopy indicates the coordination configuration of Ni-N3C. For NC catalysts, when N-doping level increased from 3.5 at% to 8.4 at%, the CO partial current density increased from below 0.1 mA/cm2 to 3 mA/cm2. Introducing one layer of Ni-N3C onto the NC structures leads to a 54 times higher CO partial current density than that of NC, in the meantime the FECO is 66 times higher. Furthermore, doubling the density of surface Ni-N3C sites by a layer-by-layer method doubles the CO partial current density (jCO), indicating its potential to achieve a high density of active coordinated sites and current densities.

Energetic metal–organic frameworks derived porous nitrogen-doped carbon nanocages for highly efficient peroxymonosulfate activation

Porous nitrogen-doped carbon nanocages (PNCCs) are fabricated by one-step pyrolysis of energetic Zn-based MOF (MET-6) and employed as highly efficient PMS activator to decompose organic micropollutants. PNCCs-900 exhibits extraordinary catalytic activity for RhB degradation due to its high specific surface area (894.9 m2 g−1), N-doping level (13.1%), and optimum N configuration ratio. This work opens a new avenue for the development of efficient PMS activators for water remediation.

Ultrafast GaAs MOVPE growth for power electronics

Schottky diodes designed with negative breakdown voltages of up to 400 V are used in applications like power supplies, motor drives, battery charging and server/data centers. GaAs is an ideal choice for such devices. Due to its high electron mobilities, lower series resistance and thus lower power consumptions in the “on” state than using Si, GaN or SiC can be achieved. Also GaAs wafers are available up to 8” with extremely high quality and low etch pit densities. To achieve breakdown voltages above 200 V in GaAs, typically doping levels below 1*1015 cm−3 and thicknesses in the range of tens of micrometers are needed. In order to achieve minimum turn-on losses, the thickness and doping has to be precisely controlled. For the epitaxy, the process time and group V precursor consumption due to typically high V/III ratios are the two largest cost factors. Recently, we have introduced MOVPE processes on a close coupled CRIUS showerhead reactor with growth rates up to 280 µm/h. Due to the extremely high growth rate, the loss of group-V material due to evaporation off the growth surface is minimized and even at V/III ratios below 15 a low C-background doping can be achieved. It is demonstrated that this low cost and ultrafast growth process is suitable for Schottky power diodes. 15 µm thick GaAs:Si Hall samples were grown at a growth rate of 100 µm/h. Controlled n-doping levels as low as 1.2*1014 cm−3 have been reached for a V/III ratio of 12. The room temperature mobilities were as high as 9*103 cm−3/Vs. Also, the electronic defect levels were analyzed by deep level transient spectroscopy. The EL2 (As anti-site) defect is found with a concentration 4.8*1014 cm−3. Nominally 20 µm and 30 µm thick layers were deposited on n-GaAs wafers for initial Schottky test diodes. The I-V curve in forward characteristics is characterized by an ideality factor of 1.2, a Schottky barrier height of 0.8 eV and a series resistance as low as 3.7 mΩcm2. Breakdown voltages above 370 V in reverse bias for doping levels of 2*1014 cm−3 were achieved proving the high potential of this approach.

Unravelling the Effect of Activators used in The Synthesis of Biomass-Derived Carbon Electrocatalysts on the Electrocatalytic Performance for CO2 Reduction.

N-doped carbon materials can be efficient and cost-effective catalysts for the electrochemical CO2 reduction reaction (CO2 RR). Activators are often used in the synthesis process to increase the specific surface area and porosity of these carbon materials. However, owing to the diversity of activators and the differences in physicochemical properties that these activators induce, the influence of activators used for the synthesis of N-doped carbon catalysts on their electrochemical performance is unclear. In this study, a series of bagasse-derived N-doped carbon catalysts is prepared with the assistance of different activators to understand the correlation between activators, physicochemical properties, and electrocatalytic performance for the CO2 RR. The properties of N-doped carbon catalysts, such as N-doping content, microstructure, and degree of graphitization, are found to be highly dependent on the type of activator applied in the synthesis procedure. Moreover, the overall CO2 RR performance of the synthesized electrocatalysts is not determined only by the N-doping level and the configuration of the N-dopant, but rather by the overall surface chemistry, where the porosity and the degree of graphitization are jointly responsible for significant differences in CO2 RR performance.

Highly efficient two-step nitrogen doping of graphene oxide-based materials in oxygen presence atmosphere for high-performance transistors and electrochemical applications

Nitrogen content in graphene influences application performance. Although many studies have been conducted on single-process nitrogen (N)-doping, dopant content is still quite low. Therefore, the objective of this study was to develop a novel two-step economical doping technique for improved nitrogen content and device performance. First, graphene oxide (GO) was hydrothermally nitrogen-doped. This nitrogen-doped reduced graphene oxide (NrGO) was then subjected to secondary plasma treatment. Two nitrogen(N)-doping mechanisms were observed depending on graphene’s oxygen functionalized group (OFG) content. OFG assisted N-doping mechanism was dominant if graphene had a high OFG content. Despite the presence of oxygen in plasma, significant OFG reduction and a higher degree of N-doping were observed. On the other hand, if graphene had a low OFG content, activated radicals in graphene structure by plasma ion bombardment mainly influenced secondary N-doping. Here, oxygen contaminants in the plasma stream showed dual effects. Low-power conditions showing no significant effect, whereas high-power plasma influenced re-oxidation and suppressed further N-doping. The maximum N/C ratio of 0.168 was observed in 5 W plasma-treated NrGO material which had nitrogen content over 40%. Compared to a single-step N-doping technique, this new technique can facilitate dominant n-type transistors with strong oxygen reduction characteristics. • The impact of oxygen in plasma depends on OFGs in graphene and plasma power. • Oxygen contaminants can suppress N-doping if graphene has low OFG content. • Oxidized nitrogen formation has no impact by oxygen contaminants in plasma. • Two-step N-doping can provide high N-doping level than single-step doping.

Synthesis of N-doped SiC nano-powders with effective microwave absorption and enhanced photoluminescence

Although their preparation remains challenging, N-doped SiC nanostructures have received much attention due to their high performance characteristics compared to pure Si3N4 and SiC phases. In this study, N-doped SiC nano-powders were synthesized in one step through hexamethyldisilane pyrolysis in Ar/N2 plasma atmosphere. The results show that the undoped products included β-SiC nanoparticles sized in the range of 5–20 nm and carbon layers with 1–10 layers, while N-doped SiC nano-powders were mainly amorphous Si3N4/SiCN aggregates sized in the range of 30–200 nm with some β-SiC nanoparticles attached. The increased N2 flow rate and arc currents favored nitrogen doping and carbon removal. In addition, according to the X-ray photoelectron spectroscopy, the highest N-doping level approached 20% (atomic ratio). Nitrogen doping can effectively adjust the dielectric properties and affect the microwave absorption ability. The optimal reflection loss reached −56.2 dB at 8.9 GHz under an absorber thickness of 3.1 mm when the N-doping level was 12.1%. Moreover, due to the defect states, the N-doped SiC nano-powders exhibited good photoluminescence performance in the blue-green emission region. Therefore, the synthesized N-doped SiC nano-powders developed herein present potential applicability as microwave absorbers and light-emitting sources.

Edge-Nitrogen Enriched Porous Carbon Nanosheets Anodes with Enlarged Interlayer Distance for Fast Charging Sodium-Ion Batteries.

The application of nitrogen-doped porous carbon for sodium-ion batteries (SIBs) has attracted tremendous attention. Herein, a series of edge-nitrogen enriched porous carbon nanosheets (ENPCNs) are synthesized by annealing g-C3 N4 and glucose in a sealed graphite crucible at different temperatures (T= 700, 800, and 900 °C). Surprisingly, under the closed thermal treatment condition, the ENPCNs-T possess a high N-doping level (>12.62 at%) and different carbon interlayer distance ranging from 0.429 to 0.487nm. By correlating the carbon interlayer distance with the N configurations of ENPCNs-T materials, a reasonable perception of the important influence of pyrrolic N on the increase of carbon interlayer distance is proposed. When applied as anode materials for SIBs, the ENPCNs-800 exhibits a remarkable capacity (294.1 mAh g-1 at 0.1 A g-1 ), excellent rate performance (132.8 mAh g-1 at 10 A g-1 ), and outstanding cycle life (180.6 mAh g-1 at 1 A g-1 after 1000 cycles with a capacity retention of 104.7%). Meanwhile, the characterizations of cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy demonstrate that the edge-nitrogen doping and enlarged carbon interlayer distance improve the capacity and fast charging performance of ENPCNs-800. Considering the detailed investigation of the Na+ storage mechanism and excellent electrochemical performance of ENPCNs-800, this work can pave a new avenue for the research of SIBs.

Highly N-doped and flexible carbon nanofiber membrane as cathode host for Li-Se batteries

Se as an active material attracts tremendous attention because of its high volumetric capacity and better conductivity than S for rechargeable batteries. Herein, a carbon nanofiber membrane (PM-CNF) is designed and prepared as free-standing Se host by electrospinning the solution of polyacrylonitrile (PAN) and poly(styrenesulfonic acid)-melamine salt, followed by carbonization and activation process. PM-CNF shows super flexibility and high N-doping level of 8.92 % (pyrrolic-N: 2.15 % and pyridinic-N: 3.07 %), which is beneficial for ions diffusion and electrons transformation. The free-standing PM-CNF/Se cathode delivers a high reversible capacity of 570 mAh g−1 at 0.5 C, superior rate capacity of 375 mAh g−1 at 8 C, and stabile cycling over 1800 cycles. The excellent electrochemical performance can be ascribed to high Li-ion diffusion coefficient (2.99 × 10−9 cm2 s−1) and capacitance-contributed ratio (77.1 % at 0.1 mV s−1). The analysis of the charge/discharge process reveals that no polyselenide intermediates are observed during the first cycling process and thus the inhibited shuttle effect of polyselenides over cycling, which primarily contributes to the long cycling stability.

Preparation of amide-enriched micro-mesoporous carbons from bayberry core via prepolymerization and ammonization co-treatment for high-performance supercapacitors

The rational design and synthesis of environmental, low-cost and eco-friendly renewable biomass-based carbons are highly desired for the development of high-performance supercapacitors. Herein, a novel amide-enriched synthesis strategy for biomass-based carbon from bayberry core (BC) by in-situ melamine-BC prepolymerization and subsequent NH3 ammonization. The synthesized biomass-based BC carbons were characterized by N2 adsorption/desorption, scanning electron microscope, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that the BC carbons by melamine and ammonization co-treatment had both much higher N-doping level (up to 6.43%) and surface area (up to 960 m2 g−1) than the N-free doped carbon. The doped N functional group was mainly dominated by the form of amide-N rather than pyridine-N or quaternary-N. More excitingly, the amide-N content increased with the extension of ammonization time while pyridine-N and quaternary-N went down. The prepared amide-enriched BC carbon via 20 g melamine pre-polymerization and 3 h ammonization treatment delivered an excellent specific capacitance of 259 F g−1, which was 35–72 F g−1 higher than the samples by 1h and 2h NH3 treatment though the latter two had much higher surface area, pyridine and quaternary-N content. The results indicated that the amide-N on the N-doped biomass-based carbon made a great role for enhancing the capacitance, and its promotion to electric double layer capacitance and pseudo-capacitance exceeded that of pyridine and quaternary-N.

Enriched nitrogen-doped carbon derived from expired drug with dual active sites as effective peroxymonosulfate activator: Ultra-fast sulfamethoxazole degradation and mechanism insight

It’s a win–win strategy to treat organic wastewater by activating peroxymonosulfate (PMS) with nitrogen-doped carbocatalysts derived from solid waste. However, the preparation of carbocatalysts with a high nitrogen content is still tricky. Herein, enriched nitrogen-doped carbon (NDC20) with dual active sites derived from expired drugs (999 cold medicine) was developed to improve PMS activation and ultra-fast sulfamethoxazole (SMX) degradation. NDC20 with high N-doping level (23.26 at %) adjusted the charge distribution of the catalyst surface, resulting in an excellent catalytic activation of PMS. Remarkably, the NDC20/PMS system fully eliminated SMX within 2 min (kobs = 4.912 min−1), which was higher than all previously reported N-doped carbon catalysts. Quenching and electron paramagnetic resonance (EPR) experiments verified that the main mechanism involved a dual nonradical pathway involving singlet oxygen (1O2) and direct electron transfer (DET). Combined with theoretical calculations and in situ FTIR spectra, the exclusive role of dual active sites (pyridinic N/pyrrolic N and electron-deficient carbon atoms) was identified. An unanticipated generation pathway of 1O2 involving electrons acquisition by dissolved oxygen to form a superoxide radical (O2·-) and PMS oxidation over electron-deficient carbon atoms was revealed. Moreover, the possible pathways of SMX degradation were proposed, and the toxicity of the intermediates was anticipated. Finally, the practical application experiments demonstrated the sustainability of the catalytic activity of NDC20, which completely removed SMX after 100 h. This work provides a neoteric idea for synthesizing high-level N-doped carbocatalysts and solid waste treatment, and deepens the mechanistic understanding of PMS activation over high-level N-doped carbocatalysts.

Synergistic catalytic enhancement of metal-organic framework derived nanoarchitectures decorated on graphene as a high-efficiency bifunctional electrocatalyst for methanol oxidation and oxygen reduction

Designing highly efficient, long-lasting, and cost-effective cathodic and anodic functional materials as a bifunctional electrocatalyst is essential for overcoming the bottleneck in fuel cell development. Herein, a novel two-step synthesis strategy is developed to synthesize metal-organic framework (MOF) derived nitrogen-doped carbon (NC) with improved spatial isolation and a higher loading amount of cobalt (Co) and nickel carbide (Ni3C) nanocrystal decorated on graphene (denoted as Co@NC-Ni3C/G). Benefiting from multiple active sites of high N-doping level, uniform dispersion of Co and Ni3C nanocrystals, and a large active area of graphene, the Co@NC-Ni3C/G hybrids exhibit excellent methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) efficiency in an alkaline environment. For MOR, the optimized Co@NC-Ni3C/G-350 catalyst achieved a current density of 44.8 mA cm−2 at an applied potential of 1.47 V (V vs. RHE), which is significantly higher than Co@NC-Ni3C (42.07 mA cm−2) and Co@NC (24.1 mA cm−2) in 0.5 M methanol + 1.0 M KOH solutions. In addition, during the CO retention test, the Co@NC-Ni3C/G-350 catalyst exhibits excellent CO tolerance capacity. Excitingly, the as-prepared Co@NC-Ni3C/G-350 hybrid exhibits significantly improved ORR catalytic efficiency in terms of positive onset and half-wave potential (Eonset = 0.90 V, E1/2 = 0.830 V vs. RHE), small Tafel slope (34 mV dec−1) and excellent durability (only reduced 0.016 V after 5000 s test). This work provides new insights into MOF-derived functional nanomaterials for anode and cathode co-catalysts for methanol fuel cells.

Ultra-high N-doped open hollow carbon nano-cage with excellent Na+ and K+ storage performances

The sodium and potassium ion batteries develop rapidly with the aid of abundant resources and similar electrochemistry with lithium ion batteries, being the promising candidates for the next-generation energy storage devices. Nevertheless, the limited storage capacity of Na+/K+ and poor structural stability become the challenging obstructions for the development of carbon anodes. Herein, we creatively prepared the ultra-high N-doping carbons with open carbon nano-cages morphology. Thanks to the adjustable carbonization conditions, the N-doping level can be precisely controlled. This process leads to abundant defective carbons (HNC-550) with a high N-doping level of 17.03 at%, an edge-N–doped ratio of 92.17 at% and an open hollow structure. As for anodes for sodium ion batteries, the optimized HNC-550 demonstrates a high rate performance of 352.2 mAh/g of 100 mA/g. Based on the cross-linked open channel and outstanding structural stability, the sodium ion batteries also exhibit a superior capacity of 97.5 mAh/g after 2000 cycles at an extremely high current density of 10 A/g. Additionally, potassium ion batteries coupled with HNC-550 deliver excellent K+ storage performance of 293.3 mAh/g under 100 mA/g and unprecedented cyclic stability (merely 0.0068% capacity decay per cycle).

Controlled n-Doping of Naphthalene-Diimide-Based 2D Polymers.

2D polymers (2DPs) are promising as structurally well-defined, permanently porous, organic semiconductors. However, 2DPs are nearly always isolated as closed shell organic species with limited charge carriers, which leads to low bulk conductivities. Here, the bulk conductivity of two naphthalene diimide (NDI)-containing 2DP semiconductors is enhanced by controllably n-doping the NDI units using cobaltocene (CoCp2 ). Optical and transient microwave spectroscopy reveal that both as-prepared NDI-containing 2DPs are semiconducting with sub-2eV optical bandgaps and photoexcited charge-carrier lifetimes of tens of nanoseconds. Following reduction with CoCp2 , both 2DPs largely retain their periodic structures and exhibit optical and electron-spin resonance spectroscopic features consistent with the presence of NDI-radical anions. While the native NDI-based 2DPs are electronically insulating, maximum bulk conductivities of >10-4 Scm-1 are achieved by substoichiometric levels of n-doping. Density functional theory calculations show that the strongest electronic couplings in these 2DPs exist in the out-of-plane (π-stacking) crystallographic directions, which indicates that cross-plane electronic transport through NDI stacks is primarily responsible for the observed electronic conductivity. Taken together, the controlled molecular doping is a useful approach to access structurally well-defined, paramagnetic, 2DP n-type semiconductors with measurable bulk electronic conductivities of interest for electronic or spintronic devices.