(697d) Elucidating the Mechanisms of Electrochemical Nitrogen Oxidation Reactions (NORs) on Metal Oxides

The electrocatalytic conversion of dinitrogen (N2) has potential as a promising approach for the
sustainable production of ammonia and nitrates, which are widely used in fertilizers and
explosives. However, breaking the strong N≡N bond is thermodynamically unfavorable and poses
a significant challenge for the practical realization of the N2 oxidation reaction (NOR).
Consequently, the development of efficient electrocatalysts for the NOR and the identification of
reaction pathways that can overcome the kinetic barriers associated with N2 activation are crucial
for the advancement of sustainable nitrate production. In this work, we employ a combination of
density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations to
systematically investigate the NOR pathway on metal oxide surfaces. In particular, we analyze the
thermodynamics and kinetics of breaking the N-N bond in N2 and N2O and propose that water
adsorbates on coordinatively unsaturated (cus) adsorption sites (*OxHy,cus) and lattice oxygen (Olat)
play a crucial role in the N-N bond breaking and stabilization of NOx species. Furthermore, we
show that N-N bond breaking in N2O is more favorable than in N2 from both thermodynamic and
kinetic standpoints, suggesting that nitrogen oxidation to N2O is a rate limiting step. Our findings
provide valuable insight into the behavior of N2 and N2O on metal oxide surfaces and serve as a
stepping stone for future studies on the mechanisms of NOR electrocatalysts.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344.