Effect Of Heteroatom Doping Research Articles

Enhancing the Electrocatalytic Activity of Graphitic Carbon Nitride Towards Oxygen Reduction Reaction Via Heteroatom Doping: A DFT Approach

With the continued depletion of conventional fuel sources, the search for alternative fuel becomes increasingly important. Low temperature fuel cells such as PEMFCs and AFCs have attracted significant attention as a power generation technology. However, the cost of noble metals—which are important in speeding up the sluggish oxygen reduction reaction—remains an impediment in the commercialization of this technology. Metal-free catalysts are now being seen as possible alternatives to these noble metals. Among these metal-free catalysts is the graphitic carbon nitride. Graphitic carbon nitride, g-C3N4, is a polymeric material consisting of C, N, and some impurity H, connected via tris-triazine-based patterns. Due to its unique electronic structure, g-C3N4 and other graphene analogs have garnered interest in the material science community. While previous studies have been able to show experimentally the activity of g-C3N4 towards ORR, ab initio studies to explain and generalize the findings of the experiments remain scarce. Here we explain from the standpoint of density functional theory (DFT) calculations the effect of heteroatom doping (e.g., phosphorus, boron, sulfur) in further altering the material’s electronic structure in an effort to render g-C3N4 more active towards oxygen reduction reaction. The trends exhibited by graphitic carbon nitrides in our DFT computations indicate that this emerging class of material can pave the way for the rational design of fuel cell catalysts.

Effect of Heteroatoms in Ordered Microporous Carbons on Their Electrochemical Capacitance.

Micropores play a more important role in enhancing the electrochemical capacitance than mesopores and macropores; therefore, the effect of heteroatom doping into micropores on the electrochemical behavior is interesting. However, heteroatom doping into porous carbon materials would potentially change their pore structures and pore sizes, which also affect their electrochemical capacitive behaviors. To gain insight into the intrinsic effects of heteroatoms on the electrochemical capacitive behaviors, zeolite-templated carbon (ZTC) may be the most suitable candidate. ZTC is an ordered microporous carbon with a uniform micropore size of 1.2 nm, a high surface area, and a large micropore volume. In this work, a series of ZTCs containing oxygen, nitrogen, or boron as heteroatoms, with an ordered pore structure and the same pore size, are prepared. By examining their electrochemical capacitive behaviors in an organic electrolyte, the effect of heteroatom doping can be isolated and discussed without considering the effects of pore structure and pore size. Acid anhydride groups are found to generate pseudocapacitance in two potential ranges, -1.0 to -0.3 V (vs Ag/AgClO4) and -0.2 to 0.4 V. B is introduced into the ZTC framework solely as -B(OH)2, which is found to be an electrochemically inert species. N is introduced as pyridine (3.0%), pyridone/pyrrole (23.8%), quaternary (66.6%), and oxidized N (6.6%), and these species exhibit noticeable pseudocapacitance in the microporous carbon.

High-Level Doping of Nitrogen, Phosphorus, and Sulfur into Activated Carbon Monoliths and Their Electrochemical Capacitances

The present report demonstrates a new technique for doping heteroatoms (nitrogen, phosphorus, and sulfur) into carbon materials via a versatile post-treatment. The heat-treatment of carbon materials with a reagent, which is stable at ambient temperatures and evolves reactive gases on heating, in a vacuum-closed tube allows the introduction of various heteroatom-containing functional groups into a carbon matrix. In addition, the sequential doping reactions give rise to dual- and triple-heteroatom-doped carbons. The pore properties of the precursor carbon materials are preserved through each heteroatom doping process, which indicates that independent tuning of heteroatom doping and nanostructural morphology can be achieved in various carbon materials. The electrochemical investigation on the undoped and doped carbon monolithic electrodes applied to supercapacitors provides insights into the effects of heteroatom doping on electrochemical capacitance.

Albumen-Derived Hierarchical Porous N- and O-Enriched Carbon towards High-Performance Electrochemical Capacitors

In the work, we developed a facile yet scalable fabrication of N- and O-enriched carbon with hierarchical micro-/mesopores from common agricultural-derived chicken albumen. The albumen-derived hierarchical micro-/mesoporous carbon (AHMC) was endowed with large specific surface area (SSA, 1227 m2 g−1), hierarchical porosity with high microporosity of ∼50.7%, and high content of heteroatom functionalities (∼2.7 at% N and ∼20 at% O). Thanks to hierarchical micro-/mesoporosity, large effective SSA, and remarkable heteroatom (N, O) doping effects, i.e., the prominent synergy of the structural and compositional advantages, the resultant AHMC delivered a high specific capacitance (SC) of 329 F g−1 at 0.2 A g−1, and even 175 F g−1 at large current rate of 10 A g−1. The high SC retention of ∼93.3% over continuous 5000 cycles further highlighted promising advantages of the AHMC for long-term ECs. More remarkably, a striking energy density of ∼6.1 Wh kg−1 was obtained for the AHMC-based aqueous symmetric device with 1 M H2SO4 electrolyte.

Hierarchical porous and N-doped carbon nanotubes derived from polyaniline for electrode materials in supercapacitors

Open carbon nanotube materials with hierarchical porosity and N-doping are prepared from polyaniline nanotubes via a combination method of pre-carbonization and post-KOH activation. The morphology, pore texture and surface properties of the carbon materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The prepared carbon materials have a typical hierarchical pore texture and very high specific surface area up to 3253 m2 g−1. The electrochemical capacitive performance of the prepared carbons was systematically investigated in the 6 M KOH electrolyte. HPCT-4 exhibits high charge storage capacity with a specific capacitance of 365.9 F g−1 at a current density of 0.1 A g−1, good rate capability of 60% in the range of 0.1–10 A g−1, and excellent stability over 10 000 cycles. The high capacitive performance could be due to the hierarchical porosity combined with high effective surface area and heteroatom doping effects, resulting in both electrochemical double layer and Faradaic capacitance contributions.

Human hair-derived carbon flakes for electrochemical supercapacitors

Heteroatom doped porous carbon flakes were prepared via carbonization of Chinese human hair fibers and employed for high-performance supercapacitor electrode materials. The morphology and chemical composition of the resultant carbon materials were characterized by electron microscopy (EM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) measurements. Human hair carbonized at 800 °C exhibited high charge storage capacity with a specific capacitance of 340 F g−1 in 6 M KOH at a current density of 1 A g−1 and good stability over 20 000 cycles. The specific capacitance of 126 F g−1 is also verified in a 1 M LiPF6 ethylene carbonate/diethyl carbonate (EC/DEC) organic electrolyte at a current density of 1 A g−1. The high supercapacitor performance could be due to the micro/mesoporosity combined with high effective surface area and heteroatom doping effects, combining double layer and Faradaic contributions.

安定かつ高機能なナノ物質の創製を目指して：魔法数金クラスターの高機能化

Nanomaterials which exhibit both stability and functionality are currently considered to hold the most promise as components of nanotechnology devices. Thiolate (RS)-protected gold nanoclusters (Aun(SR)m) have attracted significant attention in this regard and, among these, the magic clusters are believed to be the best candidates since they are the most stable. We have investigated the effects of heteroatom doping, protection by selenolate ligands and protection by photoresponsive thiolates on the stability and physical/chemical properties of these clusters. Through such studies, we have attempted to establish methods of modifying magic Aun(SR)m clusters as a means of creating metal clusters that are both robust and functional. This paper summarizes our studies towards this goal and the obtained results.

Toward the creation of stable, functionalized metal clusters

Nanomaterials which exhibit both stability and functionality are currently considered to hold the most promise as components of nanotechnology devices. Thiolate (RS)-protected gold nanoclusters (Aun(SR)m) have attracted significant attention in this regard and, among these, the magic clusters are believed to be the best candidates since they are the most stable. We have investigated the effects of heteroatom doping, protection by selenolate ligands and protection by photoresponsive thiolates on the stability and physical/chemical properties of these clusters. Through such studies, we have attempted to establish methods of modifying magic Aun(SR)m clusters as a means of creating metal clusters that are both robust and functional. This paper summarizes our studies towards this goal and the obtained results.

The Effects of Heteroatom-Doping in Stone-Wales Defects on the Electronic Properties of Graphene Nanoribbons

The effects of boron(nitrogen/silicon)-dopant in Stone-Wales defects on electronic properties of graphene nanoribbons are investigated by using density functional theory. It is shown that the geometry structures and band structures have changed distinctly for these complex configurations. Interestingly for the dopant site 1, the distortions of boron/silicon-doping configurations are larger than that of the nitrogen-doping configurations, which affects the band structures of these configurations. The theoretical results may be valuable for the design of electronic devices.

Effect of heteroatom doping on surface acidity and hydrophilicity of Al, Ti, Zr-doped mesoporous SBA-15

Syntheses for achieving Al, Ti, or Zr-doped mesoporous SBA-15 under strongly acidic conditions optimised by using additional hydrothermal treatment have been repeated so as to get at least 20 g of each material and the impact of doping procedure on surface acidity and hydrophilicity of the resulting samples has been studied, paying special attention to the use of interfacial phenomena in flow regimes. The textural parameters of the calcined materials were inferred from nitrogen adsorption–desorption isotherms at 77 K and powder X-ray diffraction patterns. The energy-dispersive X-ray spectroscopy was used to determine the molar ratio of silicon to heteroatom in the final product. These results gave indications for increasing heterogeneity of mesopore distribution with the heteroatom incorporation, especially for Al and Ti-doped materials. Stoichiometric heteroatom insertion was possible for zirconium and titanium. Surface acidity and hydrophilic character of the materials were evaluated by means of two-cycle gaseous ammonia adsorption at 373 K, gas flow-calorimetry measurements of ammonia adsorption at 353 K, liquid-flow-calorimetry measurements of the competitive adsorption of butan-1-ol from a 2 g L −1 solution in n-heptane, as well as potentiometric titration of powdered samples suspended in a 10 −1 mol L −1 NaNO 3 aqueous solution. Doping procedure enhanced both surface acidity and hydrophilicity, although the two aspects of surface activity did not necessarily follow the same tendency for the various samples. A large increase in the two parameters was observed only for Al-SBA-15. The particular behaviour of these samples could be explained based on the LUMO energy-levels evaluated using DFT modelling.

Isomerism and aromaticity of heterofullerene C70-nPn (n=2-10).

A systematic investigation on possible structures of heterofullerenes C70-nPn (n=2-10) has been performed employing semiempirical MNDO and ab initio methods. The stabilities decrease with increasing number of heteroatoms. The structures whose carbon atoms are substituted in the para pattern across the equatorial hexagons correspond to the most stable isomers. The isomeric pattern of P-doped C70 systems follows our previously proposed correlation between the isomerism of the fullerene adducts C60Xn/C70Xn and those of the heterofullerenes C60-nNn or C60-nBn /C70-nNn or C70-nBn. The aromaticity of the most stable structures of heterofullerenes is studied to investigate the heteroatom doping effect on the electron delocalization of the fullerene cage.