Enhancement of the SrTiO₃ Surface Reactivity by Exposure to Electric Fields

Abstract

In the present work the effect of electric field assisted treatments, i. e. flash sintering, on the physicochemical properties and surface reactivity of SrTiO3 nanoparticles is investigated. The materials were prepared by a hydrothermal approach and consolidated at high temperatures by conventional and electric field assisted procedures. The exposure to an electric field from 300 to 900 V/cm allowed rapid consolidation with progressive reduction of the grain growth and the shrinkage of the specific surface area to 22% and 43%, respectively. XPS analyses evidenced increasing Sr segregation at the surface if voltage was applied during the treatment. The corresponding presence of Sr vacancies in the perovskite lattice was demonstrated by ESR spectroscopy. Both techniques pointed out the appearance of highly oxidative O− species in all ceramics. The materials reactivity was investigated by methane oxidation, chosen as model high temperature catalytic reaction. With respect to conventionally treated SrTiO3, the surface area normalized reaction rate significantly improved for the ceramics exposed to electric field, until a maximum of three times for the material treated at 900 V/cm. Such enhanced properties were ascribed to the larger extent of Sr enrichment and in particular to the correlated field‐induced defect structure perturbation.

Photocatalytic Deacon Reaction over SrTiO3

“…The presence of a surface Sr species was reported before by Mascotto et al, [23,24] who describe the intrinsic segregation of Sr to the surface of SrTiO 3 which is supported by the Sr/Ti ratios > 1 (Table ST1) derived for all samples. From the chemical point of view, bulk Sr corresponds to SrTiO 3 , whereas surface Sr may be present as SrO, Sr(OH) 2 or undercoordinated Sr. [23] It is likely that these less coordinated and more easily accessible Sr surface species are converted to SrCl 2 more easily than SrTiO 3 . Similar to Sr, the O 1s signal was also deconvoluted into bulk O (Figure 5, right, red) and surface O (Figure 5, right, blue).…”

“…Carbonates, oxides, adsorbed water, OH groups or highly oxidizing species like O À or O 2 2À are conceivable O-containing surface species. [23] After reaction, less surface O is found (Figure 5, right, blue, Table ST1), probably due to a (partial) replacement by Cl À . XP spectra in the Cl 2p region (Figure 5, bottom) were recorded of the samples after reaction.…”

Understanding Oxygen Release from Nanoporous Perovskite Oxides and Its Effect on the Catalytic Oxidation of CH4 and CO

“…The signals at 529 eV and 531 eV belong to the lattice oxygen and to hydroxides/chemisorbed oxygen, respectively 29 . A contribution at 533 eV is characteristic for physically adsorbed oxygenated species 36,37 (e.g. water) and was detected only in GLY-STF35.…”

“…Also, we found that the concentration of surface oxygen vacancies plays a significant role. From the analysis of the reaction rate (Figure 4d), HD-STF35 and GLY-STF35 possess higher turnover, which is ascribed to their higher concentration of surface oxygen defects, which are well-known to promote the dehydrogenation of methane 36,37,50 . These results are in very good agreement with our recent findings 16 , indicating that the reaction rate of methane oxidation on perovskite of similar composition is determined by a cooperative action of both surface and lattice oxygen species.…”

Flash Sintering Research Perspective: A Bibliometric Analysis

“…An inner working atmosphere is not a prerequisite either, but indeed it is possible to tune it to study its effect over the final properties of the material [14,19,20]. Moreover, some flashsintered materials have been granted special properties [21,22] and it has been shown that it is possible to sinter unstable oxides with volatile components and complex composition while preserving their stoichiometry and properties [23][24][25][26]. Very recently, in 2018, it was reported that sintering and synthesis can be merged into a single step, giving rise to what has been named Reaction or Reactive Flash Sintering (RFS) and constitutes [27], by itself, another important branch of research.…”