Exploring new metal-free catalysts
with high activity for nitrogen
reduction reaction (NRR) is highly desirable but remains a big challenge.
Graphyne (GY) is a typical two-dimensional carbon material with many
excellent properties. However, the NRR has rarely been envisaged on
a GY-based metal-free catalyst up to now. Density functional theory
calculations reveal that although pristine GY is inactive for N2 reduction, boron modulation can endow it with efficient activity
toward NRR. Natural bond orbitals analysis, spin/charge density distributions,
and free energy change diagrams are performed and discussed. Three
boron doping formats including sp2-substituted, sp-substituted,
and adsorbed configuration are considered. The obtained data show
sp-substitution will induce local moderate spin and charge densities
at the boron site on the GY surface, which is convenient for N2 adsorption and activation, and conductive to N-related intermediates
formation and transformation. Moreover, the incorporated sp-hybridized
boron can provide one empty p orbital and one occupied p orbital around
itself, which plays a key role as an electron reservoir to accept
electrons from and donate electrons to the adsorbed N-related species,
and thus facilitate N2 reduction and ammonia synthesis.
Henceforth, it provides more opportunities for preparing GY and other
carbon materials as efficient catalysts toward renewable energy conversion
and storage.
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