Fabrication of Ti substrate grain dependent C/TiO₂ composites through carbothermal treatment of anodic TiO₂

Abstract

Composite materials of titania and graphitic carbon, and their optimized synthesis are highly interesting for application in sustainable energy conversion and storage. We report on planar C/TiO2 composite films that are prepared on a polycrystalline titanium substrate by carbothermal treatment of compact anodic TiO2 with acetylene. This thin film material allows for the study of functional properties of C/TiO2 as a function of chemical composition and structure. The chemical and structural properties of the composite on top of individual Ti substrate grains are examined by scanning photoelectron microscopy and micro-Raman spectroscopy. Through comparison of these data with electron backscatter diffraction, it is found that the amount of generated carbon and the grade of anodic film crystallinity correlate with the crystallographic orientation of the Ti substrate grains. On top of Ti grains with ∼(0001) orientations the anodic TiO2 exhibits the highest grade of crystallinity, and the composite contains the highest fraction of graphitic carbon compared to Ti grains with other orientations. This indirect effect of the Ti substrate grain orientation yields new insights into the activity of TiO2 towards the decomposition of carbon precursors.

Effect of Air‐Aging on the Electrochemical Characteristics of TiOxCy Films for Electrocatalysis Applications

“…When exposed to air, the carburized layer at the surface of TiOC 550 , and in particular the TiC species, are oxidized within a short time (Figure ), resulting in a C/TiO 2 composite film, with a thin layer of ( sp 2 and sp 3 ) carbon on a still slightly reduced, crystalline oxide. This statement could explain why no TiO x C y compound has been observed with XPS in Refs . and.…”

“…Apparently, the carbothermal treatment at 550 °C yields a superficial conversion of the compact anodic oxide film. While TiO x C y compounds are detected with XPS at the surface of pristine TiOC 550 (Figure ), the bulk of the TiOC 550 film is reported to consist of some reduced TiO x species in a mixed phase (anatase and rutile) crystalline TiO 2 matrix, which brings about a bluish optical appearance of TiOC 550 ,. When exposed to air, the carburized layer at the surface of TiOC 550 , and in particular the TiC species, are oxidized within a short time (Figure ), resulting in a C/TiO 2 composite film, with a thin layer of ( sp 2 and sp 3 ) carbon on a still slightly reduced, crystalline oxide.…”

“…It should be noted that XPS provides the average chemical surface composition of TiOC within a spot of a few mm diameter. Due to substrate grain effects, the chemical composition locally varies on a μm scale,, and it is likely that TiOC films on different substrate grains show a different aging behavior.…”

“…Figure shows the CVs of pristine and air aged TiOC together with CVs of as‐grown anodic TiO 2 and TiO 2‐x references. It has been shown that the as‐grown anodic TiO 2 film is amorphous, whereas the thermally treated TiO 2‐x film contains a considerable fraction of anatase TiO 2 . Titania is a wide bandgap n‐type semiconductor, where the electron donors are mainly oxygen vacancies.…”

“…The optimized carbothermal treatments of compact anodic TiO 2 with acetylene or ethylene as carbon source, can produce Ti−O−C films of different chemical composition and structure ,. Their simple morphology allows the use of scanning probe techniques as analysis tool, and facilitates the deposition of catalyst nanoparticles . The titanium substrate stabilizes the Ti−O−C film and provides the electrical contact, which is essential for electrochemical investigations.…”