Activation of Graphenic Carbon Due to Substitutional Doping by Nitrogen: Mechanistic Understanding from First Principles.
Nitrogen-doped graphene and carbon nanotubes are popularly in focus as metal-free electrocatalysts for oxygen reduction reactions (ORR) central to fuel cells. N-doped CNTs have been also reported to chemisorb mutually, promising a route to their robust predetermined assembly into devices and mechanical reinforcements. We propose from first principles a common mechanistic understanding of these two aspects pointing further to a generic chemical activation of carbon atoms due to substitution by nitrogen in experimentally observed configurations. Wannier-function based orbital resolved study of mechanisms suggests increase in C-N bond-orders in attempt to retain π-conjugation among carbon atoms, causing mechanical stress and loss of charge neutrality of nitrogen and carbon atoms, which remedially facilitate chemical activation of N-coordinated C atoms, enhancing sharply with increasing coordination to N and proximity to zigzag edges. Activated C atoms facilitate covalent adsorption of radicals in general, diradicals like O2 relevant to ORR, and also other similarly activated C atoms, leading to self-assembly of graphenic nanostructures while remaining inert to ordinary graphenic C atoms.
School of Physical Sciences, National Institute of Science Education and Research, IOP campus, Sachivalay Marg, Bhubaneswar 751005, India.
Joydeep
J
Bhattacharjee
Wannier function; activated carbon; nitrogen-doped graphene; oxygen reduction; radical adsorption; self-assembly of nanotubes