Exploring of catalytic oxygen reduction reaction activity of lattice
carbons of vanadium and niobium doped nitrogen codoped carbon nanotubes
by density functional theory
Abstract
The oxygen electroreduction mechanism on the V- and Nb-doped
nitrogen-codoped (6,6)armchair carbon nanotube with incorporated
MN4 fragment has been studied using the ωB97XD
and PBE density functional theory approaches. The metal center in
MN4 fragment and the adjacent NC=CN double bond
(C2 site) of the support have been revealed as
active centers. The metal active centers turned out to be irreversibly
oxidized at the first step of ORR affording stable O*, 2O*, or O*HO*
adsorbates depending on the applied electrode potential U, that
makes them no longer active in ORR. Therefore, the
C2 site comes at the forefront in ORR catalysis.
Among the metal oxidized forms M(O)N4–,
M(O)(O)N4– and M(O)(OH)N4–CNT, the
C2 site of the latter turned out to be most
active for 4e dissociative ORR. For both metals the last
protonation/electron transfer step, HO* + H* = H2O, is
the rate-limiting step. The alternative hydrogen peroxide formation is
not only thermodynamically less favorable but also kinetically slower
than the 4e dissociative ORR route on the
C2 site of model M(O)(OH)N4–CNT
catalyst.