Promoted Hydride/Oxide Exchange in SrTiO₃ by Introduction of Anion Vacancy via Aliovalent Cation Substitution

Abstract

We investigated topochemical anion exchange reactions for a Sc-substituted SrTiO perovskite, Sr(TiSc)O□ (y ≤ 0.1), using CaH. It was found that the initial introduction of a small amount of anion vacancies (y/2) is crucial to enhance the anion (H/O) exchangeability. For example, hydride reduction of Sr(TiSc)O yielded the oxyhydride SrTiScOH in which the hydride concentration is increased by 33% with respect to pristine SrTiO (leading to SrTiOH). This observation highlights the importance of anion vacancies to improve anion (H/O) diffusion, which is a well-known strategy for improving oxide anion conductivity, and suggests that such a vacancy-assisted reaction could be applied to other anion exchange reactions (e.g., F/O and N/O) to extend the solubility range.

Neutron Scattering Investigations of Hydride Species in Heterogeneous Catalysis

“…Because IR spectroscopy has been successfully utilized to study hydride species over ZnO and ZrO 2 , in this section we focus on neutron investigations into H 2 interactions with CeO 2 ‐based oxides, for which traditional spectroscopy fails to detect the hydride species. There are recent neutron studies, including ND and neutron scattering, of transition‐metal oxyhydrides, which are emerging materials with intriguing physicochemical properties, such as excellent anion and electronic conductivity. Herein, we highlight findings about these materials as they relate to heterogeneous catalysis.…”

“…The presenceo ft he MÀHv ibrational bands is diagnostic of heterolytic dissociation on oxide surfaces, and can be furtherc onfirmed from the isotopic shift from D 2 adsorption.M etal hydrides were experimentally observedo nm any oxide surfaces, including MgO, SiO 2 ,A l 2 O 3 , Ga 2 O 3 ,Z nO, and ZrO 2 ,m ostlyt hrough IR spectroscopy,a ss ummarized by Coperet et al [1] Amongm any oxides, only af ew, such as ZnO, ZrO 2 ,a nd CeO 2 ,a re able to activateH 2 for hydrogenationr eactions. [68] Because IR spectroscopy has been successfully utilized to study hydride species over ZnO and ZrO 2 , in this sectionwefocus on neutroninvestigationsinto H 2 interactions with CeO 2 -based oxides, for which traditional spectroscopy fails to detect the hydrides pecies.T here are recent neutron studies, includingN Da nd neutrons cattering, of transi-tion-metal oxyhydrides, [11,[69][70][71][72][73] which are emerging materials with intriguing physicochemical properties, such as excellent anion and electronic conductivity.Herein, we highlight findings about thesem aterials as they relate to heterogeneousc atalysis.…”

Direct synthesis of barium titanium oxyhydride promising for electrode material with hydrogen permeability

“…It is because that not only thermodynamic but also kinetic factor, such as anion diffusivity in the lattice, should be considered. 12,13 For example, BaTiO3-xHx in single phase was obtained from the precursors of nano size (~ 170 nm) particles, while the multi-phases with different hydrogen concentrations generated from those of larger particles (10-30 µm). 10 In addition, the long reaction period for a week and washing process to remove the residual CaH2 and the byproduct CaO are inevitable.…”

Direct synthesis of barium titanium oxyhydride promising for electrode material with hydrogen permeability

“…It is because that not only thermodynamic but also kinetic factor, such as anion diffusivity in the lattice, should be considered. 12,13 For example, BaTiO3-xHx in single phase was obtained from the precursors of nano size (~ 170 nm) particles, while the multi-phases wherein hydrogen concentration differs generated from those of larger particles (10-30 mm). 10 In addition, the long reaction period for a week and washing process to remove the residual CaH2 and the byproduct CaO are inevitable in topochemical reactions.…”