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Enhancement in Oxygen Reduction Reaction Activity of Nitrogen‐Doped Carbon Nanostructures in Acidic Media through Chloride‐Ion Exposure
Author(s) -
Jain Deeksha,
Mamtani Kuldeep,
Gustin Vance,
Gunduz Seval,
Celik Gokhan,
Waluyo Iradwikanari,
Hunt Adrian,
Co Anne C.,
Ozkan Umit S.
Publication year - 2018
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.201800134
Subject(s) - chemistry , chlorine , inorganic chemistry , catalysis , chloride , x ray photoelectron spectroscopy , ionic bonding , electrochemistry , ion , organic chemistry , electrode , chemical engineering , engineering
Abstract Nitrogen‐doped carbon nanostructures (CN x ) are promising cathode materials as catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane (PEM) fuel cells. Incorporation of chlorine into CN x catalysts using a facile methodology can lead to a significant improvement in the ORR activity in acidic media, as confirmed by electrochemical half‐cell measurements. The chlorine‐containing CN x catalyst (CN x −Cl) is synthesized by soaking CN x powder in 0.3 M HCl. The analysis of near‐edge X‐ray absorption fine structure spectra collected in the C K‐edge region and Fourier‐transform infrared spectra confirm the formation of C−Cl bonds in CN x −Cl. X‐ray photoelectron spectroscopy (XPS) results reveal the presence of three distinct chlorine species in the CN x −Cl sample: (i) organic chlorine (C−Cl), (ii) anionic chloride in the positively charged environment of a pyridinium ring (N + Cl − ), and (iii) physisorbed ionic chloride. Results from temperature‐programmed desorption studies under inert atmosphere corroborate the conclusions from XPS depth profiling analysis. The improvement in ORR activity after exposure of the CN x catalyst to chloride anions can be attributed to the creation of C−Cl functionalities as additional active sites. The difference in the electronegativity of C and Cl atoms results in a net positive charge on adjacent carbon sites, leading to the side‐on adsorption of oxygen molecules and breakage of the O−O bond during ORR.