Enhanced N₂ Electroreduction over LaCoO₃ by Introducing Oxygen Vacancies

Abstract

Electroreduction of N2 into NH3 represents a promising method for N2 fixation. However, due to the inertness of NN covalent triple bonds, this process remains a huge challenge to achieve a high yield rate of NH3. In this work, we designed an effective approach to promoting N2 activation by introducing oxygen vacancies into LaCoO3. In N2 electroreduction, LaCoO3 with oxygen vacancies (denoted as V o-LaCoO3) exhibited a Faradaic efficiency of 7.6% for NH3 at −0.6 V versus the reversible hydrogen electrode (RHE). Notably, at −0.7 V versus RHE, the yield rate for NH3 of V o-LaCoO3 reached 182.2 μgNH3 mg–1 cat. h–1, which was 2.8 times higher than that (65.3 μgNH3 mg–1 h–1) of pristine LaCoO3. To the best of our knowledge, the yield rate for NH3 of V o-LaCoO3 approaches the activities of the state-of-the-art catalysts toward N2 electroreduction. Density functional theory calculations revealed that enhanced activation of N2 over V o-LaCoO3 originated from the increased charge density around the valence band edge via the introduction of oxygen vacancies. Furthermore, the analysis of the thermodynamic limiting potentials for N2 reduction and H2 evolution demonstrated the higher selectivity for N2 electroreduction over V o-LaCoO3 relative to pristine LaCoO3.

A General Strategy to Boost Electrocatalytic Nitrogen Reduction on Perovskite Oxides via the Oxygen Vacancies Derived from A‐Site Deficiency

“…In Table S5, Supporting Information, we also compared the NRR activities of all the samples in this work with those of other perovskite oxides in the literatures. [14][15][16][17][18][19] Our samples performed comparably to or better than those reported perovskite oxides except for LaCoO 3−δ that exhibited the highest NRR activities reported so far.…”

“…This reaction mechanism was consistent with several previous studies focused on metal oxide surfaces (e.g., TiO 2 (110) and LaCoO 3 (111)). [14,38] While the surface oxygen vacancy was introduced, the coordination environment as well as the electronic properties was changed, and the adsorption properties of the reaction species were also modulated. For the O v -LF(121), the N 2 molecule was also adsorbed on the top of Fe site instead of the vacancy site (Fe-Fe bridge site) over the surface.…”

“…[20][21][22][23][24][25][26] The main mechanism has been certified to be that B-site cations combining with their adjacent oxygen vacancies can serve as unsaturated active centers that strengthen the ability to adsorb/ activate N 2 molecule and thus lead NRR on the optimal reaction pathway. [14] Despite these efforts, their preparation methods involving special atmosphere (e.g., 5% H 2 /Ar) annealing had made it challenging to rationally tailor the oxygen vacancies, not mentioning the instability of most of the perovskite oxides under those conditions. [27][28][29] Such methods are not well-suited for the development of highly active perovskite oxides for NRR.…”

Surface Amorphization of Vanadium Dioxide (B) for K‐Ion Battery

“…[ 13 ] Moreover, oxygen vacancies on the surface of SA‐VO 2 could probably induce the formation of micropores causing the surface roughening of SA‐VO 2 nanorods, which effectively increase the N 2 adsorbing capacity and thus improve the surface area of SA‐VO 2 . [ 23 ] The enhanced specific surface area of SA‐VO 2 can increase the contact area between electrode/electrolyte and improve its reaction kinetics. [ 24 ]…”

Recent Progress of Vacancy Engineering for Electrochemical Energy Conversion Related Applications

“…[ 162,174 ] Among the developed strategies, the introduction of vacancies into nanomaterials is considered as an efficient strategy to improve electrocatalytic performance by facilitating the trapping of metastable electrons to activate N 2 molecules, tuning the electrochemical conductivity and enhance N 2 adsorption [ 55b,160,168,175 ] ( Table 3 ). For instance, Zeng and co‐workers [ 161 ] introduced oxygen vacancies into LaCoO 3 (Vo‐LaCoO 3 ) to accelerate N 2 activation. The Co atoms and adjacent oxygen vacancies can act as active centers to activate N 2 synergistically.…”