Core Level Shifts of Hydrogenated Pyridinic and Pyrrolic Nitrogen in the Nitrogen-Containing Graphene-Based Electrocatalysts: In-Plane vs Edge Defects

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• 作者：Ivana Matanovic ; Kateryna Artyushkova ; Matthew B. StrandMichael J. Dzara ; Svitlana Pylypenko ; Plamen Atanassov
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：December 29, 2016
• 年：2016
• 卷：120
• 期：51
• 页码：29225-29232
• 全文大小：431K
• ISSN：1932-7455

文摘

A combination of N 1s X-ray photoelectron spectroscopy (XPS) and first principles calculations of nitrogen-containing model electrocatalysts was used to elucidate the nature of the nitrogen defects that contribute to the binding energy (BE) range of the N 1s XPS spectra of these materials above ∼400 eV. Experimental core level shifts were obtained for a set of model materials, namely N-doped carbon nanospheres, Fe–N–carbon nanospheres, polypyrrole, polypyridine, and pyridinium chloride, and were compared to the shifts calculated using density functional theory. The results confirm that the broad peak positioned at ∼400.7 eV in the N 1s XPS spectra of N-containing catalysts, which is typically assigned to pyrrolic nitrogen, contains contributions from other hydrogenated nitrogen species such as hydrogenated pyridinic functionalities. Namely, N 1s BEs of hydrogenated pyridinic-N and pyrrolic-N were calculated as 400.6 and 400.7 eV, respectively, using the Perdew–Burke–Ernzerhof exchange-correlation functional. A special emphasis was placed on the study of the differences in the XPS imprint of N-containing defects that are situated in the plane and on the edges of the graphene sheet. Density functional theory calculations for BEs of the N 1s of in-plane and edge defects show that hydrogenated N defects are more sensitive to the change in the chemical environment in the carbon matrix than the non-hydrogenated N defects. Calculations also show that edge-hydrogenated pyridinic-N and pyrrolic-N defects only contribute to the N 1s XPS peak located at ∼400.7 eV if the graphene edges are oxygenated or terminated with bare carbon atoms.