Understanding the Enhancement Mechanism of A-Site-Deficient La_xNiO₃ as an Oxygen Redox Catalyst

Abstract

Lanthanide perovskite oxides have attracted much attention as an oxygen reduction and evolution catalyst because of their high chemical stability and composition adjustability. A defect strategy has been applied to enhance their electrocatalytic activity with the modulation of the crystal/electronic structure. However, the intrinsic roles of the defects, particularly A-site vacancies, are poorly understood. Herein, we prepare La x NiO 3 with various ratios of A-site vacancies by a facile nonstoichiometric strategy, which has boosted the dual-function catalytic activity of LaNiO 3 . More importantly, the enhancement mechanism of A-site-deficient La x NiO 3 as an oxygen redox catalyst has been unveiled. Induced vacancy defects on the A sites raise a compression strain in the NiO 6 octahedron, exerting a positive enhancement on Ni−O covalency. Furthermore, the e g electron filling in the active cation Ni and the overlapping state of Ni 3d−O 2p hybridization have also been optimized, in which renovation will further boost the catalytic ability of oxygen redox processes. This work not only clarifies the intrinsic roles of A-site deficiency in the structure and electrocatalytic activities of perovskite oxides but also presents some insights into the design and exploration of high-activity catalysts by cation defect modulation.

Addressing voltage decay in Li-rich cathodes by broadening the gap between metallic and anionic bands

“…A cutoff energy of 500 eV was adopted for the simulation. Structure relaxation proceeded until all forces on atoms were less than 1 meV Å −1 and the total stress tensor was within 0.01 GPa of the target value, as in a previous study 50 . In order to accurately describe the electronic structure of the transition metal, the DFT + U approach was used, assuming U values for Mn- 3d , Ni- 3d , and Zr- 4d of 6.0, 7.4, and 4.0 eV, respectively.…”

In Situ Modulation of A‐Site Vacancies in LaMnO3.15 Perovskite for Surface Lattice Oxygen Activation and Boosted Redox Reactions

“…What is more, to verify the effect of V La caused by urea addition on performance improvement, we designed several comparison experiments. It was found that only by reducing the dosage of La 3+ in preparation may result in the formation of oxygen vacancies as well as unstable LMO structure [9–12] . More importantly, the activity improvement in model toluene oxidation of such approach is very limited as shown in Figure S32.…”

“…It is well known that the introduction of A‐site deficiencies into the lattice structure of perovskites can significantly alter the catalytic performance in oxygen‐related reactions [8] . For example, A‐site defects generated by nonstoichiometric strategy could boost the catalytic activity of LaFeO 3 , [9] (BS) 1− x CF, [10] double perovskites PrBa 1− x Co 2 O 5+ δ [11] and La x NiO 3 [12] in oxygen reduction reaction (ORR), and the phenomena were attributed to the creation of surface oxygen vacancies ( V O ). Moreover, the preferential generation of cation vacancies on SnCoFe perovskite by Ar plasma treatment resulted in high exposure of B‐site metal and improved catalytic activity for OER [13] .…”

Perovskite Oxides for Cathodic Electrocatalysis of Energy‐Related Gases: From O2 to CO2 and N2

“…Besides the stoichiometric A‐site substitution, the A‐site nonstoichiometry, in either A‐site deficient or A‐site excessive materials, can also effectively tune the catalytic performance of perovskite oxides. [ 74 ] For example, the A‐site deficient La 1−x FeO 3− δ presented excellent ORR activity at x = 0.05, which mainly followed the 4‐electron transfer process. It was proposed to be attributed to the increased content of oxygen vacancies and the formation of Fe 4+ /Fe 3+ couple.…”