Nitrogen-doped Carbon Composites Research Articles

Pt Nanoparticles Supported on Nitrogen-Doped Carbon-TiO2 Composite as a High-Performance Electrocatalyst for Methanol Oxidation

Abstract Monodispersed Pt nanoparticles supported on a TiO2 and nitrogen-doped carbon composite (TiO2/NDC) were successfully synthesized via an efficient in situ self-assembly strategy and microwave-assisted polyol process. The Pt/TiO2/NDC catalyst exhibited superior electrocatalytic activity toward the methanol oxidation reaction (MOR). The electrochemically active surface area of the Pt/TiO2/NDC catalyst was twofold higher than that of the Pt/C/NDC catalyst. In addition, the Pt/TiO2/NDC catalyst revealed a better electrocatalytic activity and CO-tolerance as well as a stability toward the MOR. The combined characterization from Fourier transform infrared spectrum, Brunauer-Emmett-Teller surface area, scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometer, thermogravimetric analysis, inductively coupled plasma atomic emissions spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy analyses demonstrated that the superior catalytic performance and stability of the Pt/TiO2/NDC catalysts likely arose from the synergistic effect of their unique morphology and composition as well as the electronic effect between the TiO2/NDC and Pt. This electrocatalyst holds great promise for application in direct methanol fuel cells.

MOF-Derived Hybrid Hollow Submicrospheres of Nitrogen-Doped Carbon-Encapsulated Bimetallic Ni-Co-S Nanoparticles for Supercapacitors and Lithium Ion Batteries.

The development of bimetallic transition-metal sulfide and nitrogen-doped carbon composites with unique hollow structure is highly desirable for energy storage applications but is also challenging. In the present work, we demonstrate a facile metal-organic framework engaged strategy for synthesizing bimetallic nickel cobalt sulfide and nitrogen-doped carbon composites with hollow spherical structure (denoted as hollow Ni-Co-S- n/NC composites) and a Ni/Co molar ratio ( n value) that can be easily controlled. When evaluated as electrode materials for both supercapacitors and lithium ion batteries, it is found that the hollow Ni-Co-S-0.5/NC composite with a Ni/Co molar ratio of 0.5 exhibits optimal electrochemical performance. The hollow Ni-Co-S-0.5/NC composite exhibits a high specific capacity of 543.9 C g-1 at 1 A g-1 and maintains a capacity retention of 67.3% when the current density is increased to 20 A g-1. An asymmetric supercapacitor based on the hollow Ni-Co-S-0.5/NC composite is fabricated, which shows good electrochemical performance with a high energy density of 39.6 W h kg-1 at a power density of 808 W kg-1. For lithium storage, the hollow Ni-Co-S-0.5/NC composite manifests a high reversible discharge capacity of 755.0 mA h g-1 at 200 mA g-1 for 200 cycles as well as good rate capability. The excellent electrochemical performance could be attributed to the desirable structural, compositional, and component advantages. This work could offer new insight into the rational design and synthesis of highly efficient electrode materials for both supercapacitors and lithium ion batteries.

Stable Lithium Storage in Nitrogen-Doped Carbon-Coated Ferric Oxide Yolk-Shell Nanospindles with Preserved Hollow Space.

Iron oxide (Fe2 O3 ) is a promising anode material for next-generation high-energy lithium-ion batteries owing to its high theoretical specific capacity, but it suffers from unstable electrochemistry, as represented by a significant volume variation upon (de)lithiation and unstable solid-electrolyte interface. To target these issues, a double-coating synthetic route has been developed to prepare a yolk-shell-structured γ-Fe2 O3 /nitrogen-doped carbon composite, in which spindle-like γ-Fe2 O3 cores are encapsulated in the highly conductive carbon shell. Through precisely controlling the void space between the γ-Fe2 O3 core and the carbon shell, volume variation in γ-Fe2 O3 during (de)lithiation is well accommodated, while the composite maintains an intact and relatively dense structure, which stabilizes the solid-electrolyte interface and is beneficial for improving the practical energy density of the material. With a stabilized (de)lithiation electrochemistry and a synergistic storage effect between the two active components, the composite enables excellent lithium storage performance, in terms of reversible capacity, cycling ability, and rate capability.

Graphene-based metal and nitrogen-doped carbon composites as adsorbents for highly sensitive solid phase microextraction of polycyclic aromatic hydrocarbons.

Herein, a graphene-based metal and nitrogen-doped carbon (GNC-Co) composite, derived from zeolite imidazolate framework-67 (ZIF-67)-graphene oxide composites, was successfully developed and applied as an excellent fiber coating for solid phase microextraction (SPME) with enhanced performance. The fabricated carbon has a hierarchically micro/mesoporous structure with a high specific surface area of 123 m2 g-1. The study found that pyrolytic graphene (G) has good adsorption properties for anthracene, phenanthrene, fluoranthene and pyrene, while pyrolytic ZIF-67 (NC-Co) has good adsorption properties for naphthalene, acenaphthylene, acenaphthylene and fluorene. Combined with the advantage of G and NC-Co, the synthesized composite GNC-Co enabled the integration of the unique properties of these two fascinating materials and proved to show better performance in the extraction of all polycyclic aromatic hydrocarbons (PAHs). Compared to the commercial PDMS fiber, the self-made fiber achieved GC responses about 2-9 times as high as those obtained by the commercial 30 μm PDMS fiber. Furthermore, the self-made fiber obtained low detection limits in the range of 0.01-0.74 ng L-1 and wide linearity under the optimized extraction conditions. Finally, the GNC-Co coated fiber was successfully used for the detection of PAHs in real river water samples, which proved the applicability of the method.

Enhanced Electrochemical Performance of a Tin−antimony Alloy/N‐Doped Carbon Nanocomposite as a Sodium‐Ion Battery Anode

AbstractA simple one‐pot process for producing 3.5 nm diameter uniformly dispersed SnSb nanoparticles on a nitrogen‐doped carbon composite (NC) is reported. An ethanol slurry of SnCl4, SbCl3, and nitrilotriacetic acid (NTA) is heated in air to 300 °C to form the mixed metal oxide NTA complex; heating to 650 °C under argon yields the SnSb/NC nanocomposites, comprising 3.5 nm diameter SnSb nanocrystals uniformly distributed in the conductive N‐doped carbon. After 200 cycles at a specific current of 0.1 Ag−1, the SnSb/NC nanocomposite sodium‐ion anode retains a reversible capacity of 244 mAh g−1. The similarly prepared Sn/NC and Sb/NC anodes retain lower capacities of 88 and 188 mAh g−1, respectively. The improved performance of the SnSb/NC electrode might be ascribed to the stepwise sodiation/desodiation process of Sn and Sb species in the SnSb/NC electrode, which could act as an inert buffer matrix for each other, according to the potentials, slowing the capacity fading.

A Unique 3D Nitrogen-Doped Carbon Composite as High-Performance Oxygen Reduction Catalyst.

The synthesis and properties of an oxygen reduction catalyst based on a unique 3-dimensional (3D) nitrogen doped (N-doped) carbon composite are described. The composite material is synthesised via a two-step hydrothermal and pyrolysis method using bio-source low-cost materials of galactose and melamine. Firstly, the use of iron salts and galactose to hydrothermally produceiron oxide (Fe2O3) magnetic nanoparticle clusters embedded carbon spheres. Secondly, magnetic nanoparticles diffused out of the carbon sphere when pyrolysed in the presence of melamine as nitrogen precursor. Interestingly, many of these nanoparticles, as catalyst-grown carbon nanotubes (CNTs), resulted in the formation of N-doped CNTs and N-doped carbon spheres under the decomposition of carbon and a nitrogen environment. The composite material consists of integrated N-doped carbon microspheres and CNTs show high ORR activity through a predominantly four-electron pathway.

Nitrogen-doped carbon composites derived from 7,7,8,8-tetracyanoquinodimethane-based metal–organic frameworks for supercapacitors and lithium-ion batteries

N-doped carbon composites prepared by calcining TCNQ-based Sr-MOF, as supercapacitors electrode and LIBs anodes, they exhibited excellent specific capacitance and cycle durability.

Highly Active Non-PGM Catalysts Prepared from Metal Organic Frameworks

Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/Nx/C) prepared from iron doped zeolitic imidazolate frameworks (ZIFs) are among the most active ones in catalyzing the oxygen reduction reaction based on recent studies. In this report, we demonstrate that the catalytic activity of ZIF-based TM/Nx/C composites can be substantially improved through optimization of synthesis and post-treatment processing conditions. Ultimately, oxygen reduction reaction (ORR) electrocatalytic activity must be demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The process of preparing MEAs using ZIF-based non-PGM electrocatalysts involves many additional factors which may influence the overall catalytic activity at the fuel cell level. Evaluation of parameters such as catalyst loading and perfluorosulfonic acid ionomer to catalyst ratio were optimized. Our overall efforts to optimize both the catalyst and MEA construction process have yielded impressive ORR activity when tested in a fuel cell system.

Highly Active Non-PGM Catalysts Prepared from Metal-Organic Frameworks

Proton exchange membrane fuel cells (PEMFCs) represent the future powertrain for the automotive application due to their high efficiency, high power density, and emission of only water from the vehicle. Technology advancements are needed to enable the widespread commercialization of fuel cell-powered vehicles, including increased durability and decreased cost. Platinum is currently the electrocatalyst of choice for PEMFCs, contributing a significant fraction of the overall fuel cell stack cost [1]. There is an imperative need to develop inexpensive, non-platinum group metal (PGM) material as alternative catalysts. At Argonne National Laboratory, we are developing new methods of preparing non-PGM materials as potential substitutes for platinum cathode electrocatalysts for PEMFCs. Our approaches focus on transition metal and nitrogen-doped carbon composites prepared from highly porous organic precursors as electrocatalysts for the oxygen reduction reaction (ORR). One such method involves the use of metal-organic frameworks (MOFs) as sacrificial templates [2-4]. For example, we reported recently a one-pot solid-state synthesis technique to prepare Fe-doped zeolitic imidazolate frameworks (ZIFs), a sub-class of MOFs, which are subsequently pyrolyzed to yield highly-active ORR catalysts [4]. Although the one-pot synthesis method has been successfully demonstrated, we found that the catalyst activity could be substantially improved by optimizing the processing conditions of individual steps from synthesis, thermal activation, to post-treatment. For example, a major factor influencing catalytic activity are the heat treatment conditions. Optimizing pyrolysis time has proven to dramatically enhance ORR activity. Increased catalyst conductivity is another factor contributing to catalyst performance improvement. Furthermore, we also found that MOF synthesis conditions can significantly influence precursor structure and the resulting ORR activity of the catalyst. The improved catalyst activity has to be ultimately demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The engineering process of preparing MEAs using MOF-based non-PGM catalyst is, to certain degree, difference from that of conventional carbon-supported catalysts. Parameters such as the catalyst loading, perfluorosulfonic acid ionomer to catalyst ratio, affect the catalyst performance at the fuel cell level. In this presentation, we will also describe our effert in optimizing the MEA fabrication process. These improvements at both catalyst and MEA levels have yielded impressive ORR activity when tested in a fuel cell system, moving towards the performance targets set by U.S. DOE for the automotive application. The work performed at Argonne National Laboratory is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office.

Recent progress in nitrogen-doped carbon and its composites as electrocatalysts for fuel cell applications

The emergence of fuel cell technology has created a new tool for the generation of clean, high efficiency alternative energy for humans. The research and development of new catalysts to replace the expensive and rare platinum (Pt) to reduce the overall cost of fuel cells is ongoing in this area. Nitrogen-doped carbon and its composites possess great potential for fuel cell catalyst applications especially at the oxygen reduction cathode. It is proposed that the reaction mechanisms of nitrogen-doped carbon catalysts for oxygen reduction involve adsorption of oxygen at the partially polarised carbon atoms adjacent to the nitrogen dopants, different from the mechanism at platinum catalysts, which utilise d-bands filling at oxygen adsorption sites. Nitrogen doping in both carbon nanostructures and its composites with active metals or ceramics are reviewed. Nitrogen-doped carbon without composite metals, displays high catalytic activity in alkaline fuel cells and exhibits significant activity in proton exchange membrane fuel cells and direct methanol fuel cells. Pt-based catalysts with nitrogen-doped carbon supports show enhanced catalytic activity towards oxygen reduction, attributed to the enhanced anchoring of Pt to the support that results in better dispersion and stability of the electrodes. For nitrogen-doped carbon composites with non-noble metals (Fe, Co, etc), enhanced activity is seen in both proton exchange and alkaline fuel cells. There are many ongoing debates about the nature of nitrogen-carbon bond in catalysis. Pyrrole- and pyridinic-type nitrogen generally considered to be responsible for the catalytic sites in acidic and alkaline media, respectively. In recent years, significant efforts have been made towards increasing the stability of nitrogen-doped carbon catalysts in acidic media through the formation of composites with ceramic or metal oxide materials. This article reviews the progress in the area of this new class of catalysts and their composites for greater enhancement of oxygen reduction activity and stability in various fuel cell applications.

Coral-like α-MnS composites with N-doped carbon as anode materials for high-performance lithium-ion batteries

Coral-like α-MnS composites with nitrogen-doped carbon (NC) were designed as anode materials for lithium-ion batteries. A facile two-step method was developed to synthesize the composites. Hydrothermally obtained polyvinyl pyrrolidone (PVP) capped (NH4)2Mn2(SO4)3 was used as a precursor. The α-MnS–NC composites were attained by heating the precursor at different temperatures for an appropriate time in a N2 atmosphere. The microstructure and morphology were carefully investigated by means of field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). As anode materials, the α-MnS–NC composites exhibit large reversible capacity, excellent cyclic stability and high rate capability. At a current density of 500 mA g−1, the discharge capacity reaches as high as 878 mA h g−1 at the first cycle and remains at 699 mA h g−1 even after 400 cycles.