Unifying the Nitrogen Reduction Activity of Anatase and Rutile TiO₂ Surfaces

Abstract

TiO 2 is a model transition metal oxide that has been applied frequently in both photocatalytic and electrocatalytic nitrogen reduction reactions (NRR). However, the phase which is more NRR active still remains a puzzle. This work presents a theoretical study on the NRR activity of the ( 001), ( 100), (101), and (110) surfaces of both anatase and rutile TiO 2 . We found that perfect surfaces are not active for NRR, while the oxygen vacancy can promote the reaction by providing excess electrons and low-coordinated Ti atoms that enhance the binding of the key intermediate (HNN*). The NRR activity of the eight facets can be unified into a single scaling line. The anatase TiO 2 (101) and rutile TiO 2 (101) surfaces were found to be the most and the second most active surfaces with a limiting potential of À 0.91 V and À 0.95 V respectively, suggesting that the TiO 2 NRR activity is not very phase-sensitive. For photocatalytic NRR, the results suggest that the anatase TiO 2 (101) surface is still the most active facet. We further found that the binding strength of key intermediates scale well with the formation energy of oxygen vacancy, which is determined by the oxygen coordination number and the degree of relaxation of the surface after the creation of oxygen vacancy. This work provides a comprehensive understanding of the activity of TiO 2 surfaces. The results should be helpful for the design of more efficient TiO 2 -based NRR catalysts.

ZrN6‐Doped Graphene for Ammonia Synthesis: A Density Functional Theory Study

“…*NH 3 ). [42][43][44] Herein, the filtering thresholds of G ads (*N 2 ) and ΔΔG ads are zero since the negative values indicate the exothermic adsorption of nitrogen molecule and the energetically favored nitrogen adsorption in comparison with hydrogen adsorption, respectively. Meanwhile, we artificially set the filtering thresholds of ΔG(*N 2 !…”

Screening and Discovery of Metal Compound Active Sites for Strong and Selective Adsorption of N2 in Air

“…The high thermodynamic barrier for N 2 H hydrogenation on the trigonal TiO 2 (001) active site is due to very stable adsorption of the *N 2 H intermediate state, which is in contrast to the VBO 4 and rutile (110) surfaces, where formation of N 2 H is one of the most endergonic steps. Indeed, N 2 H formation has been identified as the likely rate‐limiting step for numerous NRR catalysts in the literature, [18,92,93] indicating that the trigonal TiO 2 (001) exhibits notable stabilization of N 2 H. The fact that N 2 H formation is exergonic compared to the initial state suggests that under reaction conditions the N 2 H coverage will likely increase, effectively increasing the free energy of the state due to configurational entropy and thus lowering the barrier for N 2 H formation and providing a possible route for experimental validation via spectroscopic studies. In the limit that adsorbed N 2 H is in equilibrium with the initial state (causing the free energies to be identical by definition) the barrier to N 2 H 2 formation would decrease to ∼1 eV, bringing it close to the ∼0.75 eV limit needed for an active NRR catalyst [19] .…”

Graph neural network with classification accelerating the discovery of Heusler catalysts for nitrogen reduction reaction

“…Additionally, we exclude where ∆Gr of N2 and NNH are more positive that of H to ensure that reactants in NRR can effectively occupy active sites. Finally, we introduce a desorption criterion to limit the ∆Gr(*NH2), ensuring the effective desorption of NH3(g) 47 . We also include an uncertainty threshold (T) to narrow down the screening space, guaranteeing that selected alloys are more likely to meet the above criteria.…”