N-doped Carbon Layer Research Articles

Enhanced conductivity and electrochemical performance of conformal mesoporous N/C co-decorated TiO2-RGO composites for lithium ion batteries

Abstract Conformal N/C co-decorated Titamum dioxide/reduced graphene oxide (NCTG) have been successfully synthesized through one-pot solvothermal process followed by the thermal nitriding treatment. After annealing of the Ti-complex/RGO hybrid nanocomposite in an NH3 gas flow, the TiO2 and RGO was effectively nitridated and the uniform mesoporous N-doped Carbon layer was decorated with the surface of TiO2 nanoparticles in order to further fortify the electronic conductivity of the nanocomposite. The results of our study demonstrate that NCTG exhibits higher rate capability and cycling performance. Remarkably, NCTG electrode exhibits a high reversible capacity of 164 mA h g−1 after 500 cycles at a current density of 800 mA g−1, which is much higher than those of carbon decorated Titamum dioxide/reduced graphene oxide nanosheets (HTCG) and carbon decorated TiO2 nanoflakes (TC). Moreover, a high capacity of 115 mAh g−1 can be retained at a high current density of 3000 mA g−1. Considering its simplicity and effectiveness, this strategy might be extended to other anode materials for enhanced lithium storage capability.

Highly selective hydrogenation of phenol to cyclohexanol over MOF-derived non-noble Co-Ni@NC catalysts

The selective hydrogenation of phenol is an attractive routine to produce cyclohexanol that is an important basic chemical raw in chemical industry, but the design of cost-efficient and highly selective catalysts remains a great challenge. Herein, we report the first example of non-noble bimetallic nanocatalysts for the selective hydrogenation of phenol with cyclohexanol as the sole product. These catalysts consisting of bimetallic Ni-Co alloy nanoparticles (NPs) encapsulated in N-doped carbon matrix were simply synthesized by using our previously developed MOF-templated strategy (Long et al., 2016). The sum of characterization results revealed that the Co and Ni elements were successfully alloyed in every individual NPs that were confined by N-doped carbon layers. Detailed catalytic test results suggested that both the pyrolysis temperature and the composition of these alloy NPs played the key roles in guiding their catalytic performance in the selective hydrogenation of phenol. It has been shown that Co-Ni@NC system was much more effective for hydrogenation of phenol than Cu@NC, Co-Cu@NC and Ni-Cu@NC systems. The optimal 1Co-1Ni@NC could completely catalyze the hydrogenation of phenol to >99.9% cyclohexanol with a TOF of 0.21h−1, which was approximately 2.8- and 4.3-fold higher than that of the Co@NC and Ni@NC respectively, underscoring a strong positive synergistic effect between Ni and Co for this reaction. The mechanism study revealed the cyclohexanol was formed directly by the one-step hydrogenation of phenol in our catalyst system. This one-step pathway could avoid the formation of other hydrogenated intermediate product thereby leading to >99.9% selectivity of cyclohexanol. Furthermore, this catalyst also showed good recyclability, magnetically reusability and general applicability for a wide range of phenol substrates, which together with the superior activity and selectivity make it a good potential for the industrial applications.

CoSb3 alloy nanoparticles wrapped with N-doped carbon layers as a highly active bifunctional electrocatalyst for zinc–air batteries

CoSb3 nanoparticles wrapped with N-doped carbon layers have been prepared and showed excellent catalytic activities both for ORR and OER. A real rechargeable zinc–air battery with CoSb3@NCL-30 catalyst as air cathode exhibited outstanding electrochemical properties.

Mesoporous TiO2@N-doped carbon composite nanospheres synthesized by the direct carbonization of surfactants after sol-gel process for superior lithium storage.

Here, we report mesoporous TiO2@N-doped carbon composite nanospheres synthesized via a double-surfactant-assisted assembly sol-gel process followed by sequential carbonization of surfactants under a N2 atmosphere. The resulting TiO2@N-doped C composite nanospheres are composed of uniformly distributed TiO2 nanocrystals with a diameter of ∼8 nm coated by a N-doped carbon layer that was formed by surfactants. Moreover, a large number of connected mesopores were observed in the nanospheres after high-temperature carbonization treatment. The synthesized nanospheres possess a large specific surface area (∼120 m2 g-1) and a large pore size (4-40 nm), with a well-defined spherical structure and a diameter in the nanoscale range. As an anode material for lithium-ion batteries (LIB), the mesoporous composite nanospheres delivered a reversible capacity of ∼117 mA h g-1 after 2000 cycles at a current rate as high as 10 C, as well as superior rate capability. The N-doped carbon layers greatly improved the overall electrical conductivity of the mesoporous TiO2 nanospheres. This study provides a remarkable synthetic route for the preparation of mesoporous TiO2-based N-doped carbon composite materials as high-performance anode materials in LIBs.

Na3V2(PO4)3 coated by N-doped carbon from ionic liquid as cathode materials for high rate and long-life Na-ion batteries.

A facile and simple hydrothermal assisted sol-gel route was developed to prepare nitrogen doped carbon coated Na3V2(PO4)3 nanocomposites (denoted as NVP@C-N) as cathodes for sodium ion batteries (NIBs). An ionic liquid (EMIm-dca) was used as the nitrogen doped carbon source. The optimized N-doped carbon coated Na3V2(PO4)3 (denoted as NVP@C-N150) displays a very thin and uniform N-doped carbon coating layer (thickness: ∼2 nm), showing an excellent sodium storage performance (85 mA h g-1 at 20 C after 5000 cycles) and high rate capability (71 mA h g-1 at 80 C). Such a superior sodium storage performance derives from the nitrogen doping carbon coating, triggering amounts of extrinsical defects and active sites in the N-doped amorphous carbon layer, which highly accelerates Na-ion and electron transport. This approach is simple, facile and shows easy scale-up. It could be extended to other materials for energy storage.

MOF-Derived Noble Metal Free Catalysts for Electrochemical Water Splitting.

Noble metal free electrocatalysts for water splitting are key to low-cost, sustainable hydrogen production. In this work, we demonstrate that metal-organic frameworks (MOFs) can be controllably converted into catalysts for the oxygen evolution reaction (OER) or the hydrogen evolution reaction (HER). The OER catalyst is composed of FeNi alloy nanoparticles encapsulated in N-doped carbon nanotubes, which is obtained by thermal decomposition of a trimetallic (Zn2+, Fe2+, and Ni2+) zeolitic imidazolate framework (ZIF). It reaches 10 mA cm-2 at the overpotential of 300 mV with a low Tafel slope of 47.7 mV dec-1. The HER catalyst consists of Ni nanoparticles coated with a thin layer of N-doped carbon. It is obtained by thermal decomposition of a Ni-MOF in NH3. It shows low overpotential of only 77 mV at 20 mA cm-2 with low Tafel slope of 68 mV dec-1. The above noble metal free OER and HER electrocatalysts are applied in an alkaline electrolyzer driven by a commercial polycrystalline solar cell. It achieves electrolysis efficiency of 64.4% at 65 mA cm-2 under sun irradiation of 50 mW cm-2. This practical application shows the promising prospect of low-cost and high-efficiency sustainable hydrogen production from combination of solar cells with high-performance noble metal free electrocatalysts.

Advanced LiTi2(PO4)3@N-doped carbon anode for aqueous lithium ion batteries

In this paper, LiTi2(PO4)3@N-doped carbon anode has been synthesized by in situ carbon coating approach. The well-proportioned N-doped carbon layer and loose nanoporous structure was obtained by using urea as nitrogen source and pore former. LiTi2(PO4)3@N-doped carbon as anode demonstrates much better rate capability than LiTi2(PO4)3@carbon in ALIBs. The optimized anode delivers the discharge capacity of 93.7mAhg−1 and 74.2mAhg−1 at rates of 10C and 20C, 22.5mAhg−1 and 50.0mAhg−1 larger than that of LiTi2(PO4)3@carbon. Moreover, LiTi2(PO4)3@N-doped carbon exhibits excellent cycling performance with capacity retention of 84.3% at 5C after 1000 cycles. As verified, the well-proportioned N-doped carbon layer could reduce charge transfer resistance and improve electrical conductivity. The loose nanoporous structure could shorten pathway and facilitate diffusion for Li ion. Therefore, LiTi2(PO4)3@N-doped carbon gets the superior electrochemical properties benefiting from those two characteristics.

Temperature dependent performance and catalyst layer properties of PtRu supported on modified few-walled carbon nanotubes for the alkaline direct ethanol fuel cell

The performance of PtRu on three differently modified few-walled carbon nanotube (FWCNT) supports for ethanol electro-oxidation is evaluated in alkaline media both with rotating disc electrode (RDE) and direct ethanol fuel cell (DEFC) measurements at various temperatures (0–60°C). FWCNT are modified with oxidative treatment (O-FWCNT), aniline coating (A-FWCNT) and N-doped carbon layer (N-FWCNT). RDE testing shows that A-FWCNT/PtRu outperforms both O-FWCNT/PtRu and N-FWCNT/PtRu especially at high temperatures giving 1.5 times higher current at 60°C. The poisoning resistance of N-FWCNT/PtRu is high over the temperature range, while O-FWCNT/PtRu and A-FWCNT/PtRu become increasingly poisoned with increasing temperature. Alkaline DEFC testing at 30°C and 50°C indicates similar dependence to temperature as in RDE tests. However, only N-FWCNT/PtRu can sustain currents for longer than 20–30h during constant voltage measurement. SEM images of the catalyst layers reveal that both O-FWCNT/PtRu and A-FWCNT/PtRu form a dense structure with little pores for reactant and product transport explaining the quick performance loss, while large pores are formed with N-FWCNT/PtRu facilitating the transport. These results underline that the interactions between the catalyst support and the ionomer in the fuel cell catalyst layer are important in forming a suitable pore structure for efficient mass transfer.

Macroscale cobalt-MOFs derived metallic Co nanoparticles embedded in N-doped porous carbon layers as efficient oxygen electrocatalysts

Metal-organic frameworks (MOFs) materials have aroused great research interest in different areas owing to their unique properties, such as high surface area, various composition, well-organized framework and controllable porous structure. Controllable fabrication of MOFs materials at macro-scale may be more promising for their large-scale practical applications. Here we report the synthesis of macro-scale Co-MOFs crystals using 1,3,5-benzenetricarboxylic acid (H3BTC) linker in the presence of Co2+, triethylamine (TEA) and nonanoic acid by a facile solvothermal reaction. Further, the as-fabricated Co-MOFs as precursor was pyrolytically treated at different temperatures in N2 atmosphere to obtain metallic Co nanoparticles embedded in N-doped porous carbon layers (denoted as Co@NPC). The results demonstrate that the Co-MOFs derived sample obtained at 900°C (Co@NPC-900) shows a porous structure (including micropore and mesopore) with a surface area of 110.8m2g−1 and an N doping level of 1.62at.% resulted from TEA in the pyrolysis process. As electrocatalyst, the Co@NPC-900 exhibits bifunctional electrocatalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media which are key reactions in some renewable energy technologies such as fuel cells and rechargeable metal-air batteries. The results indicate that the Co@NPC-900 can afford an onset potential of 1.50V (vs. RHE) and a potential value of 1.61V (vs. RHE) at a current density of 10mAcm−2 for ORR and OER with high applicable stability, respectively. The efficient catalytic activity of Co@NPC-900 as bifunctional oxygen electrocatalyst can be ascribed to N doping and embedded metallic Co nanoparticles in carbon structure providing catalytic active sites and porous structure favourable for electrocatalysis-related mass transport.

Design of Metal Structure Encapsulated in N-Doped Carbon Layers As Tunable Catalyst for Electrochemical Applications

Polymer electrolyte membrane fuel cells (PEMFCs) have been widely recognized as a promising energy conversion device owing to its high power density, environmentally clean products, low working temperature, and so on. On the other hand, the several issues such as a high material cost, a low activity, and a weak durability have impeded the commercialization of fuel cell applications. In general, these issues are directly correlated to the utilization of Pt catalyst, which is one of the noble metals and of the most broadly utilized catalyst. Hence, a number of studies of fuel cell catalysts have been concentrated on reducing the amount of Pt, for instance, by alloying with 3d-metals such as Pt-Co, Pt-Ni, and Pt-Cu. Stamenkovic et al. (1) and Doyle et al.(2) insisted, for example, that Pt3Ni (111) can improve its ORR activity about 10 times compared to pure Pt (111). To synthesize the Pt-alloy catalyst, however, an amount of expensive Pt metal in Pt-3d binary or ternary alloys is still consumed in spite of its high oxygen reduction reaction (ORR) activity. Recently, the studies on a non-precious catalyst increase rapidly due to its low material cost and a variety of applications such as oxygen reduction reaction (ORR) and metal-air batteries in cathode catalysts. Representatively, nitrogen doped graphene (N-Gr) has been considered as a proper candidate material to substitute Pt catalyst. Several researches have insisted that the performance of N-Gr is superior to that of single Pt catalyst in alkaline media (3). In addition, Zelenay et al. reported that the ORR activity of polyaniline-Fe carbon composite (PANI-Fe-C) is similar to that of Pt in acidic solution(4). Dodelet et al. insisted that the enhanced activity is based on the effect of 3d-metals (5). The commercialization of non-precious metal catalyst, however, is not enough to replace Pt-based catalysts due to its lack long-term stability and performance for ORR. Furthermore, a reaction mechanism or an active site of the catalyst has not been explained clearly until now. This study suggests that metal encapsulated in nitrogen doped carbon (M@N-C) catalyst could be a novel approach in acidic fuel cell by utilizing density functional theory (DFT) calculations and experimental results. As an important factor to tune the binding between a reaction intermediate and catalyst, the following three effects were mainly discussed: 1) nitrogen doped level (or position), 2) thickness effect of carbon layer and 3) alloying effects. The main purpose of this study is to provide the guideline for the design of N-doped carbon coated metal structure.

Azobenzene mesogens mediated preparation of SnS nanocrystals encapsulated with in-situ N-doped carbon and their enhanced electrochemical performance for lithium ion batteries application**Project supported by the National Natural Science Foundation of China (Grant No. 21574062) and the Huaian High-Technology Research Institute of Nanjing University, China (Grant No. 2011Q1).

In this work, azobenzene mesogen-containing tin thiolates have been synthesized, which possess ordered lamellar structures persistent to higher temperature and serve as liquid crystalline precursors. Based on the preorganized tin thiolate precursors, SnS nanocrystals encapsulated with in-situ N-doped carbon layer have been achieved through a simple solventless pyrolysis process with the azobenzene mesogenic thiolate precursor served as Sn, S, N, and C sources simultaneously. Thus prepared nanocomposite materials as anode of lithium ion batteries present a large specific capacity of 604.6 mAh·g−1 at a current density of 100 mA·g−1, keeping a high capacity retention up to 96% after 80 cycles, and display high rate capability due to the synergistic effect of well-dispersed SnS nanocrystals and N-doped carbon layer. Such encouraging results shed a light on the controlled preparation of advanced nanocomposites based on liquid crystalline metallomesogen precursors and may boost their novel intriguing applications.

N-doped carbon layer derived from polydopamine to improve the electrochemical performance of spray-dried Si/graphite composite anode material for lithium ion batteries

To improve the electrochemical performance of silicon-based anode, silicon/carbon (Si/C) material was synthesized via dopamine polymerization process and subsequent pyrolysis. The carbonized polydopamine (PDA-C) is N-doped, which improves the electronic conductivity of material and helps lithium ion transmission. The existence of polydopamine-derived carbon is evidenced by X-ray photoelectron spectroscopy and scanning electron microscopy. Electrochemical characterizations confirms that the composite with PDA-C layer exhibits initial reversible specific capacity of 741.2 mAh g−1 with an initial coulombic efficiency of 78.1% at current density of 300 mA g−1. A high capacity of 611.3 mAh g−1 can be delivered for composite with PDA-C layer after 100 cycles at a current density of 300 mA g−1. The rate capability is also enhanced, delivering reversible capacity of 704.3, 611.4, 529.3, 480.3 mAh g−1 at current densities of 1, 2, 3, 4 A g−1.

Carbon nanofibers as nanoreactors in the construction of PtCo alloy carbon core-shell structures for highly efficient and stable water splitting

Carbon nanofibers served as nanoreactors for the design and construction of PtCo alloy carbon core-shell nanostructures with nitrogen doping (PtCo/NCNF) through a combination of electrospinning and nitrogen doping treatments. The PtCo/NCNF hybrid consists of PtCo alloy nanoparticles surrounded by a few of N-doped carbon layers, demonstrating a typical core-shell structures. The PtCo/NCNF hybrid can both served as electrode materials for electrocatalytic water splitting including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For the HER performance, the PtCo/NCNF exhibits very small onset potential of 20mV, an overpotential of 50mV at a j (vs RHE)=10mAcm−2 and Tafel slope of 30mVdec−1. The PtCo/NCNF hybrid also exhibits high OER activity with an onset potential of 310mV, an overpotential of 400mV at a j of 10mAcm−2 and a small Tafel slope of 76mVdec−1. The high catalytic activities of PtCo alloy for HER and OER originate from the 3D hierarchical structures, well-dispersed PtCo alloy, high conductivity of NCNF, protection from the carbon-encapsulated structure, and the introduction of nitrogen.

Nitrogen-Doped Carbon Embedded MoS2 Microspheres as Advanced Anodes for Lithium- and Sodium-Ion Batteries.

Rational design and synthesis of advanced anode materials are extremely important for high-performance lithium-ion and sodium-ion batteries. Herein, a simple one-step hydrothermal method is developed for fabrication of N-C@MoS2 microspheres with the help of polyurethane as carbon and nitrogen sources. The MoS2 microspheres are composed of MoS2 nanoflakes, which are wrapped by an N-doped carbon layer. Owing to its unique structural features, the N-C@MoS2 microspheres exhibit greatly enhanced lithium- and sodium-storage performances including a high specific capacity, high rate capability, and excellent capacity retention. Additionally, the developed polyurethane-assisted hydrothermal method could be useful for the construction of many other high-capacity metal oxide/sulfide composite electrode materials for energy storage.

Facile conductive surface modification of Si nanoparticle with nitrogen-doped carbon layers for lithium-ion batteries

Modified Si nanoparticles were investigated as an anode material for lithium-ion batteries. The Si nanoparticle surfaces were modified with conductive, N-doped carbon layers and prepared by a simple pyrolysis process using an ionic liquid that contained nitrogen. After the heat treatment, the N-doped carbon layers were uniformly coated onto the Si nanoparticles. The smooth carbon layers connected the Si nanoparticles without any morphological changes. Si nanoparticles containing 34 wt.% N-doped carbon exhibited the best electrochemical performance with a capacity of ∼1145 mAh g−1 and excellent capacity retention over 100 cycles. The high electrochemical performance was attributed to the N-doped carbon layers that improved the electrical conductivity and minimized the volume expansion associated with the alloy during cycling.

Cycle Stability of Silicon Nanoparticles Coated with Nitrogen-Doped Carbon Layer for Lithium Ion Battery Anode

Silicon is one of the promising candidate materials for lithium ion anode. This anode has a theoretical specific capacity of 4200 mAh/g which is about 10 times higher than the commercial graphite anode. However, Si anode has a short cycle life during the lithiation-delithiation process because of its volume expansion of up to 400%. In this study, to improve the cycle stability of Si anode through the control of volume expansion, we fabricated the single crystal Si nanoparticles (dia. ~50 nm) by using laser photo-pyrolysis technique and then the nitrogen-doped carbon layer was coated on them by using FeCl3 source. The electrochemical performance of samples according to the amount of FeCl3(0.3-2g) was investigated. The capacity retention of the Si nanoparticle with N-doped carbon layer (Si@NC) sample was approximately 74.9% at 1C after 300 cycles. Surface chemical states for elements of the anode materials according to the thickness of nitrogen-dpoed carbon layer are mentioned in detail. The effect of the coating layer is very strong to prevent Si volume change, so our experimental result for cycling test could be expected.

Methanol oxidation on Pt/CeO2@C–N electrocatalysts prepared by the in-situ carbonization of polyvinylpyrrolidone

This research is aimed to improve the poor electron conductivity of CeO2 as the catalyst support for methanol oxidation. Pt/CeO2 catalyst coated with nitrogen-doped carbon layer has been prepared through a combined microwave-assisted polyol with in-situ carbonization of nitrogen-doped carbon-coating process using polyvinylpyrrolidone as the nitrogen-doped carbon precursor. Electrochemical results show that Pt/CeO2 catalyst coated with nitrogen-doped carbon layer has higher activity than the uncoated Pt/CeO2 catalyst due to more uniform dispersion, electron-donating effects, and the superior electrical conductivity of the CeO2 support enhanced by the nitrogen-doped carbon layer. Further, electrochemical results show that the optimal doped amount of polyvinylpyrrolidone is 20 wt%. The physical characteristics such as high-resolution transmission electron microscopy and X-ray photoelectron spectrometer have confirmed the existence of the nitrogen-doped carbon layer on CeO2. A novel Pt/CeO2 catalyst coated with N-doped carbon layer has been successfully prepared through a combined microwave-assisted polyol with in-situ carbonization of N-doped carbon-coating process using polyvinylpyrrolidone (PVP) as the N-doped carbon precursor. The greatly improved activity and durability of Pt/CeO2@C–N catalyst is mainly a consequence of more uniform dispersion, smaller size of Pt nanoparticles, and the superior electrical conductivity of the CeO2 support enhanced by the N-doped carbon layer.

Iron-rich nanoparticle encapsulated, nitrogen doped porous carbon materials as efficient cathode electrocatalyst for microbial fuel cells

Developing efficient, readily available, and sustainable electrocatalysts for oxygen reduction reaction (ORR) in neutral medium is of great importance to practical applications of microbial fuel cells (MFCs). Herein, a porous nitrogen-doped carbon material with encapsulated Fe-based nanoparticles (Fe-Nx/C) has been developed and utilized as an efficient ORR catalyst in MFCs. The material was obtained through pyrolysis of a highly porous organic polymer containing iron(II) porphyrins. The characterizations of morphology, crystalline structure and elemental composition reveal that Fe-Nx/C consists of well-dispersed Fe-based nanoparticles coated by N-doped graphitic carbon layer. ORR catalytic performance of Fe-Nx/C has been evaluated through cyclic voltammetry and rotating ring-disk electrode measurements, and its application as a cathode electrocatalyst in an air-cathode single-chamber MFC has been investigated. Fe-Nx/C exhibits comparable or better performance in MFCs than 20% Pt/C, displaying higher cell voltage (601 mV vs. 591 mV), maximum power density (1227 mW m−2 vs. 1031 mW m−2) and Coulombic efficiency (50% vs. 31%). These findings indicate that Fe-Nx/C is more tolerant and durable than Pt/C in a system with bacteria metabolism and thus holds great potential for practical MFC applications.

Graphene coated with controllable N-doped carbon layer by molecular layer deposition as electrode materials for supercapacitors

In this work, graphene is coated with nitrogen-doped carbon layer, which is produced by a carbonization process of aromatic polyimide (PI) films deposited on the surfaces of graphene by molecular layer deposition (MLD). The utilization of MLD not only allows uniform coating of PI layers on the surfaces of pristine graphene without any surface treatment, but also enables homogenous dispersion of doped nitrogen atoms in the carbonized products. The as-prepared N-doped carbon layer coated graphene (NC-G) exhibited remarkable capacitance performance as electrode materials for supercapacitor, showing a high specific capacitance of 290.2 F g−1 at current density of 1 A g−1 in 6 M KOH aqueous electrolyte, meanwhile maintaining good rate performance and stable cycle capability. The NC-G synthesized by this way represents an alternative promising candidate as electrode material for supercapacitors.

ZIF-67-derived Co-NC@CoP-NC nanopolyhedra as an efficient bifunctional oxygen electrocatalyst

Co/CoP embedded-N-doped carbon (Co-NC@CoP-NC) nanopolyhedra have been prepared through pyrolysis of ZIF-67 under an Ar atmosphere followed by subsequent phosphorization. The nanopolyhedra show excellent activity and stability for both the OER and ORR, which are attributed to the production of highly stable active CoP, and the intact protection of the Co by the N-doped carbon layers.