Nitrogen-doped Porous Hollow Carbon Research Articles

Metal-organic frameworks derived platinum-cobalt bimetallic nanoparticles in nitrogen-doped hollow porous carbon capsules as a highly active and durable catalyst for oxygen reduction reaction

Pt-based nanomaterials are regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, widespread adoption of PEMFCs requires solutions to major challenges encountered with ORR catalysts, namely high cost, sluggish kinetics, and low durability. Herein, a new efficient method utilizing Co-based metal-organic frameworks is developed to produce PtCo bimetallic nanoparticles embedded in unique nitrogen-doped hollow porous carbon capsules. The obtained catalyst demonstrates an outstanding ORR performance, with a mass activity that is 5.5 and 13.5 times greater than that of commercial Pt/C and Pt black, respectively. Most importantly, the product exhibits dramatically improved durability in terms of both electrochemically active surface area (ECAS) and mass activity compared to commercial Pt/C and Pt black catalysts. The remarkable ORR performance demonstrated here can be attributed to the structural features of the catalyst (its alloy structure, high dispersion and fine particle size) and the carbon support (its nitrogen dopant, large surface area and hollow porous structure).

Nitrogen-doped hollow porous carbon nanospheres coated with MnO2 nanosheets as excellent sulfur hosts for Li–S batteries

In this work, nitrogen-doped hollow porous carbon nanospheres coated with MnO2 nanosheets (NHPC@MnO2) were prepared as a novel sulfur host for the cathode of lithium–sulfur battery. N-doping of carbon and deposition of the inherently polar MnO2 promote chemical binding of the host with sulfur and its reduction products, known as polysulfides. Meanwhile, proper N-doping can improve the electron conductivity of carbon, and the nanosheet structure may help to guarantee facile electron- and lithium-ion transport through MnO2. Attributed to these advantages, the NHPC@MnO2/S cathode with a high sulfur content (70 wt% and 2.6 mg cm−2) exhibited an excellent cycle stability: its capacity retention was 93% within 100 cycles at 0.5 C. It also displayed a good rate capability: discharge capacities being ∼1130 mAh g−1 at 0.2 C, ∼1000 mAh g−1 at 0.5 C, ∼820 mAh g−1 at 1 C, and ∼630 mAh g−1 at 2 C. Our work demonstrates the synergistic effect of MnO2 nanostructure and N-doped carbon nanospheres for enhanced performance of lithium–sulfur battery cathodes.

Nitrogen-doped hollow carbon spheres derived from amination reaction of fullerene with alkyl diamines as a carbon catalyst for hydrogenation of aromatic nitro compounds

Hollow carbon nanospheres have received much interest by virtue of the special shape, low density and large interior void space, allowing their many potential applications. Here we report a template-free route to produce nitrogen-doped hollow porous carbon spheres (denoted as N-HPCSs) through amination reaction of C60 with alkyl diamines and subsequent carbonization. The size of wall thickness and cavity of hollow carbon spheres could be easily regulated by the chain length of alkyl diamines. After carbonization in Ar atmosphere, the obtained N-HPCSs exhibited excellent activity and recyclability for hydrogenation of aromatic nitro compounds with hydrazine hydrate. The facile approach presented in this work provides a new way for preparation of doped hollow porous carbon spheres.

Nitrogen-doped hollow porous carbon polyhedrons embedded with highly dispersed Pt nanoparticles as a highly efficient and stable hydrogen evolution electrocatalyst

The hydrogen evolution reaction (HER) is a promising alternative method of producing clean and renewable hydrogen resources. Although Pt-based nanomaterials are the most efficient catalysts for HER, their poor stability and durability strongly impede their practical application. In this study, we report a new, efficient strategy to fabricate highly dispersed Pt nanoparticles within unique nitrogen-doped hollow porous carbon polyhedrons (Pt@NHPCP) derived from polymer coated metal-organic frameworks. Pt@NHPCP displays enhanced HER activity compared to commercial Pt/C. Most importantly, Pt@NHPCP exhibits excellent stability and durability, showing no nanostructure change and negligible activity decrease after 5000 potential cycles. The outstanding HER performance of Pt@NHPCP can be attributed to its unique structural features including highly dispersed Pt, nitrogen-doping, large surface area, hollow nanostructure and hierarchical pore system.

Synthesis of uniform discrete cage-like nitrogen-doped hollow porous carbon spheres with tunable direct large mesoporous for ultrahigh supercapacitive performance

Uniform discrete cage-like nitrogen-doped hollow porous carbon spheres (CN-HPCS) with tunable direct large mesoporous (18–30nm) have been successfully synthesized for the first time by using the carboxylated polystyrene spheres and silica particles as a dual-template and dopamine as the carbon and nitrogen sources. When they are used as the electrode for supercapacitors, these CN-HPCS exhibit a high specific capacitance of 257Fg−1 at 1Ag−1 and 194Fg−1 at 10Ag−1 with excellent rate capability and cycling stability.

High capacity and high rate capability of nitrogen-doped porous hollow carbon spheres for capacitive deionization

In this work, nitrogen-doped porous hollow carbon spheres (N-PHCS) were well prepared by using polystyrene (PS) spheres as hard templates and dopamine hydrochloride as carbon and nitrogen sources. Field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate that the N-PHCS have a uniform, spherical and hollow structure. Nitrogen adsorption–desorption analysis shows that the N-PHCS have a high specific area of 512m2/g. X-ray photoelectron spectroscopy result reveals that the nitrogen doping amount is 2.92%. The hollow and porous structure and effective nitrogen doping can contribute to large accessible surface area, efficient ion transport and good conductivity. In the electrochemical tests, we can conclude that the N-PHCS have a high specific capacitance value, a good stability and low inner resistance. The N-PHCS electrodes present a high salt adsorption capacity of 12.95mg/g at a cell voltage of 1.4V with a flow rate of 40mL/min in a 500mg/L NaCl aqueous solution. Moreover, the N-PHCS electrodes show high salt adsorption rate and good regeneration performance in the CDI process. With high surface specific area and effective nitrogen doping, the N-PHCS is promising to the CDI and other electrochemical applications.

Nitrogen-doped porous hollow carbon sphere-decorated separators for advanced lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have a distinct advantage over other rechargeable battery systems since their high specific energy and low cost. However, the diffusion of polysulfides from cathode to anode leads to poor electrochemical stability of Li–S batteries, which is a main factor that restricts their further development. Herein, for the first time we present a separator with nitrogen-doped porous hollow carbon sphere (NHC) coating, with which Li–S cells enormously improve the utilization of active material and enhance excellent electrochemical performance. An initial discharge capacity of 1656 mAh g−1 (0.2 C) and a low fading rate of 0.11% per cycle within 500 cycles (1 C) are achieved, which ascribe to the chemical and physical adsorption properties of porous and nitrogen-doped NHCs. The NHC-decorated separator is of low cost and can effectively improve energy density of Li–S cells, exhibiting potential for further development of Li–S batteries.

Well-dispersed platinum nanoparticles supported on hierarchical nitrogen-doped porous hollow carbon spheres with enhanced activity and stability for methanol electrooxidation

Hierarchical nitrogen-doped porous hollow carbon spheres (HNPHCS) with porous-thin mesoporous shell and hollow macroporous core structure have been prepared via in-situ oxidation polymerization method using polyaniline as the precursor. After carbonization at 900 °C, the average diameter of HNPHCS is ca. 140 nm with shell thickness of ∼1 nm. Pt nanoparticles with high dispersion and small size have been successfully deposited on the HNPHCS by a microwave-assisted polyol process to synthesize Pt/HNPHCS catalyst. The obtained samples are characterized by physical characterization and electrochemical measurements. Electrochemical studies reveal that the prepared Pt/HNPHCS catalyst possesses notably higher catalytic activity and CO-tolerance, and better stability toward methanol electrooxidation in comparison with Pt/nitrogen-doped porous carbon and the commercial Pt/C catalysts. It is likely that enhanced catalytic properties of the Pt/HNPHCS could be due to the high dispersion of small Pt nanoparticles, the presence of nitrogen species, developed porous-thin mesoporous shell and hollow macroporous core structure of support HNPHCS. As a result, the as-developed Pt/HNPHCS present attractive advantages for the application in fuel cell electrocatalyst.