Nitrogen-Doped Carbon

Yu Li2012.10.10

Visualizing Individual Nitrogen Dopants in Monolayer Graphene

Liuyan Zhao et al.Science 333, 999 (2011); DOI: 10.1126/science.1208759

Introduction

In monolayer graphene, substitutional doping during growth can be used

to alter its electronic properties. Several characterization techniques

including x-ray photoemission , Raman spectroscopy and transmission

electron microscopy have been used to analyze the effect of the doping

process in graphene. However, a microscopic understanding of the atomic

and low-energy electronic structure induced by the substitutional doping

process in monolayer graphene is lacking.

We used scanning tunneling microscopy, Raman spectroscopy, x-ray

spectroscopy, and first principles calculations to characterize individual

nitrogen dopants in monolayer graphene grown on a copper substrate.

Raman, XPS, STM of N-doped graphene

Raman spectra taken at pristine and N-doped graphene on a SiO2/Si substrate showing systematic changes in the spectra as a function of doping. N-doping results in a new peak in the spectrum at 400.7 eV dueto graphitic N. XAS, x-ray absorption spectroscopy. XPS data showed a higher–binding energy component. STM image shows the presence of numerous pointlike dopants and occasional clusters of dopants.

STM measurements

the graphene-coated substrates were transferred in ambient atmosphere after preparation into an ultra-high–vacuum (UHV), low-temperature instrument that is capable of picometer resolution. The treated copper substrates were degassed in UHV at 350°C.

Local electronic structure effect

The local electronic structure around a N dopant also affects the electronic nature of the doped graphene film. The result indicates that the electronic perturbationcaused by a nitrogen dopant is localized near the dopant atom, which is confirmed in large-area dI/dV maps.

Spectroscopic mapping around a single N dopant

Conclusions

Individual nitrogen atoms were incorporated as graphitic dopants, and a

fraction of the extra electron on each nitrogen atom was delocalized into

the graphene lattice. The electronic structure of nitrogen-doped graphene

was strongly modified only within a few lattice spacings of the site of the

nitrogen dopant. These findings show that chemical doping is a promising

route to achieving high-quality graphene films with a large carrier

concentration.

N-doped carbon prepared by pyrolysis of dicyandiamide with various MeCl2·xH2O (Me = Co, Fe, and Ni) composites: Effect of type and amount of metal seed on oxygen reduction reactions

Chang Hyuck Choia, Sung Hyeon Parka, Seong Ihl Wooa,b,∗Applied Catalysis B: Environmental 119– 120 (2012) 123– 131

Introduction

Nitrogen doping into carbon alters structural, mechanical, and electrical properties of carbon. In particular, nitrogen doping causes structural deformation of carbon and it increases the n-type conductivity by acting as an electron donor. Although transition metals such as Co and Fe used for synthesizing N-doped carbon do not act as active sites after pyrolysis, they play important roles in the carbonization of feed chemicals or the doping structure of nitrogen into carbon. The roles of metal seeds and characteristics of N-doped carbon grown on the seeds are discussed. N-doped carbons synthesized from pyrolysis of DCDA with various metal types (MeCl2·xH2O, Me = Co, Fe and Ni) and amounts were characterized to clarify the effects of seed metal on the catalysts used for oxygen reduction reactions.

Experimental

N-doped carbons were obtained through pyrolysis of homogeneous

mixtures of DCDA and metal precursors

300 mL of ethanol,5 g of DCDA and 1 g of MeCl2·xH2O (Me = Co,

Fe,and Ni and x = 6, 4, and 6, respectively;) were mixed

stirring, vaporizing, drying the mixtures of

DCDA with CoCl2, FeCl2, and NiCl2

Me-DCDA-BA Me-DCDA-AA

Characterization---TGA 、 XRD 、 TEM 、

XPSEA 、 Raman 、 BET

Calculation---H2O2(%)=200*(IR/N)/(IR/

N+ID)

Effects of metal types for N-doped carbon

Raman spectroscopy analysisXPS-C1s results of (a) Co-DCDA-AA, (b) Fe DCDA-AA, and (c) Ni-DCDA-AA. Dotted line at

284.5 eV indicates C-C bonding of the catalysts. ID/IG values from Raman spectroscopy and intensities of C-C bonding from XPS-C1s show that sp2-bonding structure in carbon is improved. Co is the most effective metal for constructing ordered carbon structure among Co, Fe and Ni.

Effects of metal types for N-doped carbon

Effects of metal types for N-doped carbon

TGA results of the Me-DCDA-AA (Me = Co, Fe and Ni)

H2O2 production yields of the prepared catalysts during ORRs

Effects of metal amount for N-doped carbon

Conclusions

Properties of N-doped carbon including physical and electrochemicalcharacteristics are varied by used seed metal type and amount. It is revealed that degree of sp2-carbon structure is affected by the type of seed metal (Co > Fe > Ni), and it determines ORR activity of N-doped carbon. The amount of metal seed does not change the electrochemical properties significantly including capacitance, ORR activity, and H2O2 production yield, but it was related with the yield of carbonization of DCDA during the pyrolysis.