XPS Structural Studies of Nano-composite Non-platinum Electrocatalysts for Polymer Electrolyte Fuel Cells |
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Authors: | Kateryna Artyushkova Stephen Levendosky Plamen Atanassov Julia Fulghum |
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Affiliation: | (1) Chemical & Nuclear Engineering Department, University of New Mexico, Albuquerque, NM 87131, USA |
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Abstract: | The chemical structure of non-platinum electrocatalysts obtained from cobalt porphyrins (CoTMPP or CoTPP) by pyrolysis is
investigated by X-ray Photoelectron Spectroscopy (XPS). The catalysts represent highly dispersed, self-supported nano-composites
that demonstrate electrocatalytic performance for oxygen reduction and practically no activity in methanol electro-oxidation.
High-resolution Co2p, C1s, N1s and O1s XPS spectra acquired from precursors and electrocatalysts pyrolyzed at various experimental
conditions were curve-fit using (a) individual peaks of constrained width and shape as well as (b) experimentally obtained
photopeaks from the precursor with additional peaks required for a complete curve fit. Principal Component Analysis (PCA)
applied to quantitative results from the curve-fits of both types of spectra facilitates visualization and identification
of the chemical species that are formed or destroyed, and simplifies evaluation of critical correlations. As a result of these
studies it is established that the catalyst is a nano-composite of highly dispersed pyropolymer with some remaining N
x
-centers inserted into a graphite-like matrix. Approximately 50% of the metal is distributed as Co2+, associated with N4-centers. The remaining cobalt is present in crystallites of metallic Co. A thin layer of CoO coats these metallic cobalt
phases. The developed methodology, described herein, combines model curve-fits and principal component analysis (PCA), resulting
in a quantitative and unambiguous understanding of the chemical composition and structure of complex electrocatalysts. |
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Keywords: | Non-platinum electrocatalysts Structural studies XPS Multivariate analysis PCA |
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