Reduction of Ln2Ti2O7 Layered Perovskites: A Survey of the Anionic Lattice, Electronic Features, and Potentials

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• 作者：Tanguy Pussacq ; Houria Kabbour ; Silviu Colis ; Hervé VezinSébastien Saitzek ; Olivier Gardoll ; Cédric Tassel ; Hiroshi Kageyama ; Christel Laberty RobertOlivier Mentré
• 刊名：Chemistry of Materials
• 出版年：2017
• 出版时间：February 14, 2017
• 年：2017
• 卷：29
• 期：3
• 页码：1047-1057
• 全文大小：743K
• ISSN：1520-5002

文摘

The reduction of the layered perovskites Ln₂Ti₂O₇ (LnTO, with lanthanide Ln = La, Pr, or Nd) was studied with the aim of shifting the ultraviolet (UV) photocalytic activity for water splitting in the visible range by Ti³⁺ donor doping. For all phases, after reduction by CaH₂, the absorbance is extended beyond the UV–visible region, giving rise to a gaplike edge in the mid-infrared at ∼0.4 eV with a dark coloration of the samples. When the precursor with Ln = La was reduced under a high-temperature H₂ flow, we found a progressive nanotexturation down to 300 nm, which is responsible for a degree of Ti³⁺ segregation at the surface. Magnetic measurements, thermal analysis, and powder neutron diffraction reveal that the samples reduced by both routes have a similar amount of anion vacancy with δ = 0.27 (in La₂Ti₂O_7−δ). It represents a limited topotactic reduction stage, prior to the reconstructive reduction into La₅Ti^3.8+₅O₁₇ observed under more severe reducing conditions. For the sample reduced by CaH₂, a minor amount of hydride appears to be incorporated (∼0.02 H per FU), with Ti³⁺···H^– bonding observed by hyperfine sublevel correlation spectroscopy electron paramagnetic resonance and density functional theory calculations. Preliminary electrocatalysis tests show a promising anodic activity for water splitting hydrogen evolution with a voltage onset as low as 0.6 V versus the reversible hydrogen electrode.