Reactive Plasma N-Doping of Amorphous Carbon Electrodes: Decoupling Disorder and Chemical Effects on Capacitive and Electrocatalytic Performance
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2020Access:
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Hoque, M.K. and Behan, J.A. and Creel, J. and Lunney, J.G. and Perova, T.S. and Colavita, P.E., Reactive Plasma N-Doping of Amorphous Carbon Electrodes: Decoupling Disorder and Chemical Effects on Capacitive and Electrocatalytic Performance, Frontiers in Chemistry, 8, 2020Download Item:
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Abstract:
Nitrogen-free amorphous carbon thin films prepared via sputtering followed by graphitization, were used as precursor materials for the creation of N-doped carbon electrodes with varying degrees of amorphization. Incorporation of N-sites was achieved via nitrogen plasma treatments which resulted in both surface functionalization and amorphization of the carbon electrode materials. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to monitor composition and carbon organization: results indicate incorporation of predominantly pyrrolic-N sites after relatively short treatment cycles (5 min or less), accompanied by an initial etching of amorphous regions followed by a slower process of amorphization of graphitized clusters. By leveraging the difference in the rate of these two processes it was possible to investigate the effects of chemical N-sites and C-defect sites on their electrochemical response. The materials were tested as metal-free electrocatalysts in the oxygen reduction reaction (ORR) in alkaline conditions. We find that the introduction of predominantly pyrrolic-N sites via plasma modification results in improvements in selectivity in the ORR, relative to the nitrogen-free precursor material. Introduction of defects through prolonged plasma exposure has a more pronounced and beneficial effect on ORR descriptors than introduction of N-sites alone, leading to both increased onset potentials, and reduced hydroperoxide yields relative to the nitrogen-free carbon material. Our results suggest that increased structural disorder/heterogeneity results in the introduction of carbon sites that might either serve as main activity sites, or that enhance the effects of N-functionalities in the ORR via synergistic effects.
Sponsor
Grant Number
Irish Research Council (IRC)
GOIPG/2014/399.
Science Foundation Ireland (SFI)
13/CDA/2213.
Author's Homepage:
http://people.tcd.ie/jlunneyhttp://people.tcd.ie/perovat
http://people.tcd.ie/colavitp
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Frontiers in Chemistry8
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Full text availableKeywords:
ORR via synergistic effects, Nitrogen-free amorphous carbon thin films, graphitization, Amorphous Carbon (a-C), Carbon, Electrocatalysis and functionalized/modified electrodes, Metal-free, Nitrogen plasma (nitridation), Nitrogen plasma activationSubject (TCD):
Nanoscience & Materials , ElectrochemistryDOI:
http://dx.doi.org/10.3389/fchem.2020.593932Licences: