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J. B. Dawson - One of the best experts on this subject based on the ideXlab platform.
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a fertile harzburgite garnet lherzolite transition possible inferences for the roles of strain and metasomatism in upper mantle peridotites
Lithos, 2004Co-Authors: J. B. DawsonAbstract:Abstract Porphyroclastic enstatite in a garnet lherzolite xenolith from the Monastery Mine kimberlite, South Africa, has exsolved pyrope garnet, Cr-diopside and Al-chromite, and the specimen is interpreted as representing a transition from fertile harzburgite, (containing high Ca-Al-Cr enstatite) to granular garnet lherzolite. Although the exsolved phases occur in morphologically different forms (fine and coarse lamellae; equant, ripened grains), indicating textural disequilibrium, the exsolved grains are very constant in composition, indicating chemical equilibrium. Theoretically, the Exsolution could have been due to a fall in temperature, but the close association of Exsolution and deformation of the host enstatite suggests that Exsolution was also aided by straining of the enstatite lattice. The phase compositions can be broadly matched with those in other mantle peridotites, except that all phases are characterised by a virtual absence of Ti. In the garnet and diopside Ti, Co, Zr and most of the REE are lower than in published analyses of garnet and diopside in both granular and sheared garnet lherzolites from Southern African kimberlites, and diopside/garnet partitioning for Sr and the REE is higher. Comparison with the trace element chemistry of an enstatite from a fertile harzburgite indicates that, except for Nb, the trace element content and distribution found in the Monastery phases could arise by isochemical Exsolution from such an enstatite. On the assumption that (a) the Monastery specimen represents a transition from harzburgite to garnet lherzolite, and (b) many garnet lherzolites are of Exsolution origin (as suggested by their modal compositions), the inference is that most garnet lherzolites, and not just the sheared variety, have been subject to varying degrees of Ti, Zr, Sr and REE metasomatism.
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A fertile harzburgite–garnet lherzolite transition: possible inferences for the roles of strain and metasomatism in upper mantle peridotites
Lithos, 2004Co-Authors: J. B. DawsonAbstract:Abstract Porphyroclastic enstatite in a garnet lherzolite xenolith from the Monastery Mine kimberlite, South Africa, has exsolved pyrope garnet, Cr-diopside and Al-chromite, and the specimen is interpreted as representing a transition from fertile harzburgite, (containing high Ca-Al-Cr enstatite) to granular garnet lherzolite. Although the exsolved phases occur in morphologically different forms (fine and coarse lamellae; equant, ripened grains), indicating textural disequilibrium, the exsolved grains are very constant in composition, indicating chemical equilibrium. Theoretically, the Exsolution could have been due to a fall in temperature, but the close association of Exsolution and deformation of the host enstatite suggests that Exsolution was also aided by straining of the enstatite lattice. The phase compositions can be broadly matched with those in other mantle peridotites, except that all phases are characterised by a virtual absence of Ti. In the garnet and diopside Ti, Co, Zr and most of the REE are lower than in published analyses of garnet and diopside in both granular and sheared garnet lherzolites from Southern African kimberlites, and diopside/garnet partitioning for Sr and the REE is higher. Comparison with the trace element chemistry of an enstatite from a fertile harzburgite indicates that, except for Nb, the trace element content and distribution found in the Monastery phases could arise by isochemical Exsolution from such an enstatite. On the assumption that (a) the Monastery specimen represents a transition from harzburgite to garnet lherzolite, and (b) many garnet lherzolites are of Exsolution origin (as suggested by their modal compositions), the inference is that most garnet lherzolites, and not just the sheared variety, have been subject to varying degrees of Ti, Zr, Sr and REE metasomatism.
John T S Irvine - One of the best experts on this subject based on the ideXlab platform.
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electrical reduction of perovskite electrodes for accelerating Exsolution of nanoparticles
Electrochimica Acta, 2019Co-Authors: Merika Chanthanumataporn, Katsuyoshi Kakinuma, John T S Irvine, Katsunori HanamuraAbstract:Abstract Growth of finely dispersed nanocatalysts by Exsolution of metal nanoparticles from perovskite oxides under reducing conditions at elevated temperature is a promising approach of producing highly active catalytic materials. An alternative method of Exsolution using an applied potential has been recently shown to potentially accelerate the Exsolution process of nanoparticles that can be achieved in minutes rather than the hours required in chemical reduction. In the present study, we investigate Exsolution of nanoparticles from perovskite oxides of La0.43Ca0.37Ni0.06Ti0.94O3-γ (LCTNi) and La0.43Ca0.37Ni0.03Fe0.03Ti0.94O3-γ (LCTNi-Fe) under applied potentials in carbon dioxide atmosphere. The impedance spectra of single cells measured before and after electrochemical poling at varying voltages showed that the onset of Exsolution process occurred at 2 V of potential reduction. An average particle size of the exsolved nanoparticles observed after testing using a scanning electron microscopy was about 30–100 nm. The cells with the reduced electrodes exhibited desirable electrochemical performances not only in pure carbon dioxide (current density of 0.37 A cm−2 for LCTNi and 0.48 A cm−2 for LCTNi-Fe at 1.5 V) but also in dry hydrogen (0.36 W cm−2 for LCTNi and 0.43 W cm−2 for LCTNi-Fe).
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lattice strain enhanced Exsolution of nanoparticles in thin films
Nature Communications, 2019Co-Authors: Jucheol Park, Gyeong Man Choi, S S P Parkin, Hyun M Jang, John T S IrvineAbstract:Nanoparticles formed on oxide surfaces are of key importance in many fields such as catalysis and renewable energy. Here, we control B-site Exsolution via lattice strain to achieve a high degree of Exsolution of nanoparticles in perovskite thin films: more than 1100 particles μm−2 with a particle size as small as ~5 nm can be achieved via strain control. Compressive-strained films show a larger number of exsolved particles as compared with tensile-strained films. Moreover, the strain-enhanced in situ growth of nanoparticles offers high thermal stability and coking resistance, a low reduction temperature (550 °C), rapid release of particles, and wide tunability. The mechanism of lattice strain-enhanced Exsolution is illuminated by thermodynamic and kinetic aspects, emphasizing the unique role of the misfit-strain relaxation energy. This study provides critical insights not only into the design of new forms of nanostructures but also to applications ranging from catalysis, energy conversion/storage, nano-composites, nano-magnetism, to nano-optics. Dispersion of metallic nanoparticles is promising for energy conversion and storage, but gaining control of size and distribution is not trivial. Here the authors use lattice mismatch to manipulate Exsolution of nanoparticles, achieving a high population of small nanoparticles in perovskite thin films.
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nano socketed nickel particles with enhanced coking resistance grown in situ by redox Exsolution
Nature Communications, 2015Co-Authors: Dragos Neagu, Taesik Oh, David N Miller, Herve Menard, Syed Munawer Bukhari, Stephen Richard Gamble, Raymond J Gorte, John M Vohs, John T S IrvineAbstract:Metal particles supported on oxide surfaces are used as catalysts for a wide variety of processes in the chemical and energy conversion industries. For catalytic applications, metal particles are generally formed on an oxide support by physical or chemical deposition, or less commonly by Exsolution from it. Although fundamentally different, both methods might be assumed to produce morphologically and functionally similar particles. Here we show that unlike nickel particles deposited on perovskite oxides, exsolved analogues are socketed into the parent perovskite, leading to enhanced stability and a significant decrease in the propensity for hydrocarbon coking, indicative of a stronger metal–oxide interface. In addition, we reveal key surface effects and defect interactions critical for future design of Exsolution-based perovskite materials for catalytic and other functionalities. This study provides a new dimension for tailoring particle–substrate interactions in the context of increasing interest for emergent interfacial phenomena. Metal particles supported on oxide surfaces are widely used catalysts, and the composites are generally formed by deposition or Exsolution methods. Here, the authors show that nickel particles exsolved from the parent perovskite exhibit enhanced stability due to a stronger metal–oxide interface.
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step change in high temperature steam electrolysis performance of perovskite oxide cathodes with Exsolution of b site dopants
Energy and Environmental Science, 2013Co-Authors: George Tsekouras, Dragos Neagu, John T S IrvineAbstract:B-site doped, A-site deficient perovskite oxide titanates with formula La0.4Sr0.4Mn+xTi1−xO3−γ−δ (M = Fe3+ or Ni2+; x = 0.06; γ = (4 − n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis at 900 °C. A-site deficiency provided additional driving force for the Exsolution of a proportion of B-site dopants at the surface in the form of metallic nanoparticles under reducing SOEC cathode operating conditions. In the case of La0.4Sr0.4Fe0.06Ti0.94O2.97, this represents the first time that Fe0 has been exsolved from a perovskite in such a way. Exsolution was due in part to the inability of the host lattice to accommodate vacancies (introduced (δ) oxygen vacancies () and fixed A-site () and inherent (γ) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Fe0 or Ni0 nanoparticles and higher concentrations dramatically lowered the activation barrier to steam electrolysis compared to the parent material (x = 0). The use of defect chemistry to drive the Exsolution of less reducible dopant cations could conceivably be extended to produce new catalytically active perovskites with unique properties.
Jeeyoung Shin - One of the best experts on this subject based on the ideXlab platform.
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Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density
Nature Communications, 2019Co-Authors: Sangwook Joo, Kyeounghak Kim, Seona Kim, Hu Young Jeong, Jeong Woo Han, Sivaprakash Sengodan, Jeeyoung Shin, Hyunmin Kim, Ohhun Kwon, Guntae KimAbstract:Exsolution is attractive for the preparation of catalytically active metal nanoparticles, but versatility is limited. Here the authors report a technique for selective Exsolution through topotactic ion exchange, leading to an electrocatalyst for a solid oxide fuel cell with enhanced performance.AbstractExsolution has been intensively studied in the fields of energy conversion and storage as a method for the preparation of catalytically active and durable metal nanoparticles. Under typical conditions, however, only a limited number of nanoparticles can be exsolved from the host oxides. Herein, we report the preparation of catalytic nanoparticles by selective Exsolution through topotactic ion exchange, where deposited Fe guest cations can be exchanged with Co host cations in PrBaMn_1.7Co_0.3O_5+ δ . Interestingly, this phenomenon spontaneously yields the host PrBaMn_1.7Fe_0.3O_5+ δ , liberating all the Co cations from the host owing to the favorable incorporation energy of Fe into the lattice of the parent host (Δ E _incorporation = −0.41 eV) and the cation exchange energy (Δ E _exchange = −0.34 eV). Remarkably, the increase in the number of exsolved nanoparticles leads to their improved catalytic activity as a solid oxide fuel cell electrode and in the dry reforming of methane.
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self decorated mno nanoparticles on double perovskite solid oxide fuel cell anode by in situ Exsolution
ACS Sustainable Chemistry & Engineering, 2017Co-Authors: Sivaprakash Sengodan, Hu Young Jeong, Ohhun Kwon, Youngwan Ju, Tatsumi Ishihara, Jeeyoung ShinAbstract:Surface decorated electrocatalytic nanoparticles coupled with oxide materials can effectively improve the electrochemical catalytic properties in energy storage and conversion application, such as chemical processes, electrolysis, batteries, and fuel cells. Particularly, Mn rich simple perovskite-type R0.5Ba0.5MnO3-δ (R = Pr and Nd) undergoes a phase transition to layered perovskite RBaMn2O5+δ at high temperature reduced condition. During this phase transition, the Exsolution of MnO nanoparticles (MnO-NP) from the bulk layered perovskite NdBaMn2O5+δ is observed. For in-depth investigation on the Exsolution of MnO, a layered NdBaMn2O5+δ thin film is fabricated with pulsed laser deposition and characterized by transmission electron microscopy. For the first time, this paper reports clear evidence of self-decorated MnO nanoparticles on a layered NdBaMn2O5+δ matrix via Exsolution process and their electro catalytic effect in solid oxide fuel cells.
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Exsolution trends and co segregation aspects of self grown catalyst nanoparticles in perovskites
Nature Communications, 2017Co-Authors: Ohhun Kwon, Hu Young Jeong, Sivaprakash Sengodan, Jeeyoung Shin, Youngwan JuAbstract:In perovskites, Exsolution of transition metals has been proposed as a smart catalyst design for energy applications. Although there exist transition metals with superior catalytic activity, they are limited by their ability to exsolve under a reducing environment. When a doping element is present in the perovskite, it is often observed that the surface segregation of the doping element is changed by oxygen vacancies. However, the mechanism of co-segregation of doping element with oxygen vacancies is still an open question. Here we report trends in the Exsolution of transition metal (Mn, Co, Ni and Fe) on the PrBaMn2O5+δ layered perovskite oxide related to the co-segregation energy. Transmission electron microscopic observations show that easily reducible cations (Mn, Co and Ni) are exsolved from the perovskite depending on the transition metal-perovskite reducibility. In addition, using density functional calculations we reveal that co-segregation of B-site dopant and oxygen vacancies plays a central role in the Exsolution. Exsolution of transition metals from perovskites provides an effective route to useful catalysts, but the underlying factors governing Exsolution remain poorly understood. Here, the authors find trends in Exsolution in layered perovskites, showing that co-segregation of B-site dopant and oxygen vacancies plays a central role.
Sivaprakash Sengodan - One of the best experts on this subject based on the ideXlab platform.
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Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density
Nature Communications, 2019Co-Authors: Sangwook Joo, Kyeounghak Kim, Seona Kim, Hu Young Jeong, Jeong Woo Han, Sivaprakash Sengodan, Jeeyoung Shin, Hyunmin Kim, Ohhun Kwon, Guntae KimAbstract:Exsolution is attractive for the preparation of catalytically active metal nanoparticles, but versatility is limited. Here the authors report a technique for selective Exsolution through topotactic ion exchange, leading to an electrocatalyst for a solid oxide fuel cell with enhanced performance.AbstractExsolution has been intensively studied in the fields of energy conversion and storage as a method for the preparation of catalytically active and durable metal nanoparticles. Under typical conditions, however, only a limited number of nanoparticles can be exsolved from the host oxides. Herein, we report the preparation of catalytic nanoparticles by selective Exsolution through topotactic ion exchange, where deposited Fe guest cations can be exchanged with Co host cations in PrBaMn_1.7Co_0.3O_5+ δ . Interestingly, this phenomenon spontaneously yields the host PrBaMn_1.7Fe_0.3O_5+ δ , liberating all the Co cations from the host owing to the favorable incorporation energy of Fe into the lattice of the parent host (Δ E _incorporation = −0.41 eV) and the cation exchange energy (Δ E _exchange = −0.34 eV). Remarkably, the increase in the number of exsolved nanoparticles leads to their improved catalytic activity as a solid oxide fuel cell electrode and in the dry reforming of methane.
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self decorated mno nanoparticles on double perovskite solid oxide fuel cell anode by in situ Exsolution
ACS Sustainable Chemistry & Engineering, 2017Co-Authors: Sivaprakash Sengodan, Hu Young Jeong, Ohhun Kwon, Youngwan Ju, Tatsumi Ishihara, Jeeyoung ShinAbstract:Surface decorated electrocatalytic nanoparticles coupled with oxide materials can effectively improve the electrochemical catalytic properties in energy storage and conversion application, such as chemical processes, electrolysis, batteries, and fuel cells. Particularly, Mn rich simple perovskite-type R0.5Ba0.5MnO3-δ (R = Pr and Nd) undergoes a phase transition to layered perovskite RBaMn2O5+δ at high temperature reduced condition. During this phase transition, the Exsolution of MnO nanoparticles (MnO-NP) from the bulk layered perovskite NdBaMn2O5+δ is observed. For in-depth investigation on the Exsolution of MnO, a layered NdBaMn2O5+δ thin film is fabricated with pulsed laser deposition and characterized by transmission electron microscopy. For the first time, this paper reports clear evidence of self-decorated MnO nanoparticles on a layered NdBaMn2O5+δ matrix via Exsolution process and their electro catalytic effect in solid oxide fuel cells.
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Exsolution trends and co segregation aspects of self grown catalyst nanoparticles in perovskites
Nature Communications, 2017Co-Authors: Ohhun Kwon, Hu Young Jeong, Sivaprakash Sengodan, Jeeyoung Shin, Youngwan JuAbstract:In perovskites, Exsolution of transition metals has been proposed as a smart catalyst design for energy applications. Although there exist transition metals with superior catalytic activity, they are limited by their ability to exsolve under a reducing environment. When a doping element is present in the perovskite, it is often observed that the surface segregation of the doping element is changed by oxygen vacancies. However, the mechanism of co-segregation of doping element with oxygen vacancies is still an open question. Here we report trends in the Exsolution of transition metal (Mn, Co, Ni and Fe) on the PrBaMn2O5+δ layered perovskite oxide related to the co-segregation energy. Transmission electron microscopic observations show that easily reducible cations (Mn, Co and Ni) are exsolved from the perovskite depending on the transition metal-perovskite reducibility. In addition, using density functional calculations we reveal that co-segregation of B-site dopant and oxygen vacancies plays a central role in the Exsolution. Exsolution of transition metals from perovskites provides an effective route to useful catalysts, but the underlying factors governing Exsolution remain poorly understood. Here, the authors find trends in Exsolution in layered perovskites, showing that co-segregation of B-site dopant and oxygen vacancies plays a central role.
Ohhun Kwon - One of the best experts on this subject based on the ideXlab platform.
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Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density
Nature Communications, 2019Co-Authors: Sangwook Joo, Kyeounghak Kim, Seona Kim, Hu Young Jeong, Jeong Woo Han, Sivaprakash Sengodan, Jeeyoung Shin, Hyunmin Kim, Ohhun Kwon, Guntae KimAbstract:Exsolution is attractive for the preparation of catalytically active metal nanoparticles, but versatility is limited. Here the authors report a technique for selective Exsolution through topotactic ion exchange, leading to an electrocatalyst for a solid oxide fuel cell with enhanced performance.AbstractExsolution has been intensively studied in the fields of energy conversion and storage as a method for the preparation of catalytically active and durable metal nanoparticles. Under typical conditions, however, only a limited number of nanoparticles can be exsolved from the host oxides. Herein, we report the preparation of catalytic nanoparticles by selective Exsolution through topotactic ion exchange, where deposited Fe guest cations can be exchanged with Co host cations in PrBaMn_1.7Co_0.3O_5+ δ . Interestingly, this phenomenon spontaneously yields the host PrBaMn_1.7Fe_0.3O_5+ δ , liberating all the Co cations from the host owing to the favorable incorporation energy of Fe into the lattice of the parent host (Δ E _incorporation = −0.41 eV) and the cation exchange energy (Δ E _exchange = −0.34 eV). Remarkably, the increase in the number of exsolved nanoparticles leads to their improved catalytic activity as a solid oxide fuel cell electrode and in the dry reforming of methane.
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self decorated mno nanoparticles on double perovskite solid oxide fuel cell anode by in situ Exsolution
ACS Sustainable Chemistry & Engineering, 2017Co-Authors: Sivaprakash Sengodan, Hu Young Jeong, Ohhun Kwon, Youngwan Ju, Tatsumi Ishihara, Jeeyoung ShinAbstract:Surface decorated electrocatalytic nanoparticles coupled with oxide materials can effectively improve the electrochemical catalytic properties in energy storage and conversion application, such as chemical processes, electrolysis, batteries, and fuel cells. Particularly, Mn rich simple perovskite-type R0.5Ba0.5MnO3-δ (R = Pr and Nd) undergoes a phase transition to layered perovskite RBaMn2O5+δ at high temperature reduced condition. During this phase transition, the Exsolution of MnO nanoparticles (MnO-NP) from the bulk layered perovskite NdBaMn2O5+δ is observed. For in-depth investigation on the Exsolution of MnO, a layered NdBaMn2O5+δ thin film is fabricated with pulsed laser deposition and characterized by transmission electron microscopy. For the first time, this paper reports clear evidence of self-decorated MnO nanoparticles on a layered NdBaMn2O5+δ matrix via Exsolution process and their electro catalytic effect in solid oxide fuel cells.
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Exsolution trends and co segregation aspects of self grown catalyst nanoparticles in perovskites
Nature Communications, 2017Co-Authors: Ohhun Kwon, Hu Young Jeong, Sivaprakash Sengodan, Jeeyoung Shin, Youngwan JuAbstract:In perovskites, Exsolution of transition metals has been proposed as a smart catalyst design for energy applications. Although there exist transition metals with superior catalytic activity, they are limited by their ability to exsolve under a reducing environment. When a doping element is present in the perovskite, it is often observed that the surface segregation of the doping element is changed by oxygen vacancies. However, the mechanism of co-segregation of doping element with oxygen vacancies is still an open question. Here we report trends in the Exsolution of transition metal (Mn, Co, Ni and Fe) on the PrBaMn2O5+δ layered perovskite oxide related to the co-segregation energy. Transmission electron microscopic observations show that easily reducible cations (Mn, Co and Ni) are exsolved from the perovskite depending on the transition metal-perovskite reducibility. In addition, using density functional calculations we reveal that co-segregation of B-site dopant and oxygen vacancies plays a central role in the Exsolution. Exsolution of transition metals from perovskites provides an effective route to useful catalysts, but the underlying factors governing Exsolution remain poorly understood. Here, the authors find trends in Exsolution in layered perovskites, showing that co-segregation of B-site dopant and oxygen vacancies plays a central role.
