Noncrystalline Titanium Oxide Catalysts for Electrochemical Oxygen Reduction Reactions

Abstract

Titanium oxides crystals are widely used in a variety of fields, but little has been reported on the functionalities of noncrystalline intermediates formed in their structural transformation. We measured the oxygen reduction reaction activity of titanium oxide nanoparticles heat-treated for a different time and found that the activity abruptly increased at a certain time of the treatment. We analyzed their structures by using X-ray pair distribution functions with the help of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy and ascertained that the abrupt increase in the activity corresponded to a structural transformation from a reduced lepidocrocite-type layered titanate to a disordered structure consisting of domains of brookite-like TiO 6 octahedral linkages. The further treatment transformed these brookite-like domains into another phase having more edge-sharing sites like the TiO-type cubic structure. This finding would position noncrystalline, disordered structure as a possible origin of the catalytic activity, though nanocrystalline rutile particles might be also considered as the origin.

Molecular‐Level Control of the Intersheet Distance and Electronic Coupling between 2D Semiconducting and Metallic Nanosheets: Establishing Design Rules for High‐Performance Hybrid Photocatalysts

“…The three intense FT peaks at ≈1.3, ≈2.2, and ≈2.7 Å are assigned as (TiO) and two different edge‐shared (TiTi) coordination shells, respectively (see Figure 2e). [ 23 ] All EXAFS data can be well reproduced considering a lepidocrocite‐type TiO 2 structure. According to the non‐linear curve fitting analysis, a shortening of the intersheet distance results in elongation of the (TiO) and (TiTi) bond distances (Table S2, Supporting Information), confirming an enhanced reduction of the Ti oxidation state.…”

Lepidocrocite-Type Titanate Formation from Isostructural Prestructures under Hydrothermal Reactions: Observation by Synchrotron X-ray Total Scattering Analyses

“…The lepidocrocite structure grown after the thermal treatment (e.g., “RT (cooled)” in Figure 4b) has a PDF peak assigned to Ti–Ti pairs in edge-shared TiO 6 octahedra around 3.0 Å and one assigned to Ti–Ti pairs in corner-shared TiO 6 octahedra around 3.5 Å. 3 Consistent with the crystalline product, the relative intensities of these peaks indicate the formation of lepidocrocite layers, which have more edge-sharing TiO 6 octahedra than anatase, brookite, and rutile. 3 The PDF peak around 1.4 Å is too short for Ti–O bonds 30 and is assigned to the C–N distance in TMAH and probably to a termination ripple.…”

Carbon Nanotube‐Based Non‐Precious Metal Electrode Catalysts for Fuel Cells, Water Splitting and Zinc‐Air Batteries

“…To increase in the density of the stabilized oxide vacancies by N‐doping, Ishihara et al. attempted to utilize TiOTPPz (oxy‐titanium tetrapyrazinoporphyrazine) as a new precursor instead of oxy‐metal phthalocyanine (MeOPc) because TiOTPPz has larger amount of N in the molecule than oxy‐titanium phthalocyanine (TiOPc) . The titanium oxide‐based catalyst prepared via a similar method shown in Figure using TiOTPPz had highest ORR activity among oxide‐based cathodes as expected.…”

“…The titanium oxide‐based catalyst prepared via a similar method shown in Figure using TiOTPPz had highest ORR activity among oxide‐based cathodes as expected. Figure shows the comparison of the Tafel plots of TaO x made from Ta 2 CN, designated as TaO x (Ta 2 CN), TaO x /MWNT made from TaOPc, TaO x /MWNT(TaOPc), ZrO x /MWNT made from ZrOP, ZrO x /MWNT(ZrOPc), TiO x /MWNT made from TiOTPPz, TiO x /MWNT(TiOTPPz), and Pt/C(TEC10E50E) in 0.1 M H 2 SO 4 at 30 °C. The ORR current was based on mass of oxides and Pt.…”