Unveiling the key factor for the phase reconstruction and exsolved metallic particle distribution in perovskites

Abstract

To significantly increase the amount of exsolved particles, the complete phase reconstruction from simple perovskite to Ruddlesden-Popper (R-P) perovskite is greatly desirable. However, a comprehensive understanding of key parameters affecting the phase reconstruction to R-P perovskite is still unexplored. Herein, we propose the Gibbs free energy for oxygen vacancy formation in Pr0.5(Ba/Sr)0.5TO3-δ (T = Mn, Fe, Co, and Ni) as the important factor in determining the type of phase reconstruction. Furthermore, using in-situ temperature & environment-controlled X-ray diffraction measurements, we report the phase diagram and optimum ‘x’ range required for the complete phase reconstruction to R-P perovskite in Pr0.5Ba0.5-xSrxFeO3-δ system. Among the Pr0.5Ba0.5-xSrxFeO3-δ, (Pr0.5Ba0.2Sr0.3)2FeO4+δ – Fe metal demonstrates the smallest size of exsolved Fe metal particles when the phase reconstruction occurs under reducing condition. The exsolved nano-Fe metal particles exhibit high particle density and are well-distributed on the perovskite surface, showing great catalytic activity in fuel cell and syngas production.

Fast Surface Oxygen Release Kinetics Accelerate Nanoparticle Exsolution in Perovskite Oxides

“…While exsolution is powering a revolution in nanoengineering, the underlying reactions controlling it remain poorly understood. To date, the mechanistic understanding of exsolution is mostly gained from equilibrium thermodynamics, with key parameters such as cation segregation energies , and point defect formation energies. , Although these thermodynamic descriptors can provide valuable insights, they fail to capture the kinetic processes in exsolution, such as cation diffusion , and nanoparticle nucleation. ,,, On the other hand, a fundamental understanding of the exsolution kinetics is crucial to realize judicious control over particle size and density, and hence the materials’ catalytic activities . To bridge this gap, Jo et al and Neagu et al have used in situ transmission electron microscopy (TEM) to study the growth kinetics of individual particles during exsolution.…”

“…To date, the mechanistic understanding of exsolution is mostly gained from equilibrium thermodynamics, with key parameters such as cation segregation energies 19,20 and point defect formation energies. 21,22 Although these thermodynamic descriptors can provide valuable insights, they fail to capture the kinetic processes in exsolution, such as cation diffusion 14,18 and nanoparticle nucleation. 15,21,23,24 On the other hand, a fundamental understanding of the exsolution kinetics is crucial to realize judicious control over particle size and density, 25 and hence the materials' catalytic activities.…”

Oxygen Vacancy‐Rich La0.5Sr1.5Ni0.9Cu0.1O4–δ as a High‐Performance Bifunctional Catalyst for Symmetric Ammonia Electrolyzer

“…In RP oxides, it is generally recognized that oxygen vacancies are responsible for phase reconstruction and the exsolved phases tend to favor the reactions. [ 44 ] In addition, Ni‐based AOR catalysts always tend to transfom to metal hydroxide or oxyhydroxide during the ammonia oxidation process where these materials are the true active sites for AOR. [ 7b,24,35,45 ] In order to maintain electrical neutrality of the oxides, some A‐site cations separated from the lattice and formed SrCO 3 in the LSNC‐Ar anode after the electrolysis test (marked by LSNC‐Ar anode).…”

Exsolution on perovskite oxides: morphology and anchorage of nanoparticles

“…Another way of classifying the publications review for this article is to distinguish between exsolution triggered during a pre-treatment before further tests or applications (for instance electrochemical measurements 65 or NH 3 sensing 95 ) and in situ exsolution, i.e. nanoparticles are exsolve during tests, applications, or chemical reactions (like the aforementioned methane 13,17,23, Fe-Ni, 35,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] Co-Ni, 65 Cu-Ni, 66 Fe-Ni-Re, 49 Fe-Ni-Mo 58 Fe 41 Fe, 13,24,[67][68][69][70][71][72][73][74] Fe-Ni, 35,[48][49][50][51][52][53][54][55][56][57][58]…”

“….). For instance, the sizes described for Fe nanoparticles (across 7 publications 24,[67][68][69]71,73,74 ) span a range from 14 nm up to 600 nm. That is, of course, not surprising given the fact that in those cases 6 different reducing gas atmospheres were used, temperatures between 625 1C and 850 1C were applied and the duration of the reducing treatment varied from 30 minutes to 60 hours.…”