Untangling cooperative effects of pyridinic and graphitic nitrogen sites at metal-free N-doped carbon electrocatalysts for the oxygen reduction reaction
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2019Access:
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Behan, J. A.; Mates-Torres, E.; Stamatin, S. N.; Domínguez, C.; Iannaci, A.; Fleischer, K.; Hoque, Md. K.; Perova, T. S.; García-Melchor, M.; Colavita, P. E., Untangling cooperative effects of pyridinic and graphitic nitrogen sites at metal-free N-doped carbon electrocatalysts for the oxygen reduction reaction, Small, 15, 2019, 1902081-Abstract:
Metal-free carbon electrodes with well-defined composition and smooth topography were prepared via sputter deposition followed by thermal treatment with inert and reactive gases. XPS and Raman spectroscopies show that three carbons of similar N/C content that differ in N-site composition were thus prepared: an electrode consisting of almost exclusively graphitic-N (NG), an electrode with predominantly pyridinic-N (NP) and one with ca. 1:1 NG:NP composition. These materials were used as model systems to investigate activity of N-doped carbons in the oxygen reduction reaction (ORR) using voltammetry. Results show that selectivity towards 4e-reduction of O2 is strongly influenced by the NG/NP site composition, with the material possessing nearly uniform NG/NP composition being the only one yielding a 4e-reduction. Computational studies on model graphene clusters were carried out to elucidate the effect of N-site homogeneity on the reaction pathway. Calculations show that for pure NG-doping or NP-doping of model graphene clusters, adsorption of hydroperoxide and hydroperoxyl radical intermediates, respectively, is weak thus favoring desorption prior to complete 4e-reduction to hydroxide. Clusters with mixed NG/NP sites display synergistic effects, suggesting that co-presence of these sites improves activity and selectivity by achieving high theoretical reduction potentials while facilitating retention of intermediates.
Sponsor
Grant Number
Irish Research Council (IRC)
GOIPG/2014/399
Marie Curie
748968 (FREMAB) and 799175 (HiBriCarbon)
Science Foundation Ireland (SFI)
13/CDA/2213
Author's Homepage:
http://people.tcd.ie/garciammhttp://people.tcd.ie/perovat
http://people.tcd.ie/colavitp
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Small15
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N-doped carbon, Oxygen reduction reaction, Electrocatalysis, Density functional theory, SynergisticSubject (TCD):
Nanoscience & Materials , Smart & Sustainable PlanetDOI:
https://doi.org/10.1002/smll.201902081Metadata
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