Investigation of the Diffusion of Cr₂O₃ into Different Phases of TiO₂ upon Annealing

Abstract

Chromium oxide (Cr 2 O 3 ) can be used as a protective layer for photocatalysts to improve photocatalytic water splitting activity and is commonly photodeposited. However, it is not known how the conditions of the Cr 2 O 3 formation affect the formation of the protective layer and potential diffusion into the substrate onto which Cr 2 O 3 has been deposited. We have investigated the stability of Cr 2 O 3 photodeposited onto the surface of different crystal phases of TiO 2 with subsequent annealing at a range of temperatures up to 600 °C. X-ray photoelectron spectroscopy and synchrotron near-edge X-ray absorption fine structure were used to analyze the chemical composition of the sample, neutral impact collision ion scattering spectroscopy was used to study the concentration depth profile of the elements in the sample, and atomic force microscopy was used to investigate the morphology of the surface. Under annealing conditions, the Cr 2 O 3 layer diffuses into the amorphous and anatase phases of TiO 2 but remains at the surface of the rutile phase. This finding is attributed to differences in surface energy with Cr 2 O 3 being higher in surface energy than the amorphous and anatase phases of TiO 2 but lower in surface energy than the rutile phase of TiO 2 . Reduction of Cr 2 O 3 to Cr metal was observed after annealing with no observation of the formation of higher oxidized forms of chromium oxide like CrO 2 and CrO 3 . These findings are of general interest to researchers utilizing a protective overlayer to augment photocatalytic water splitting.

Nonadiabatic Small Polarons Produced by Ti Ions in Granular and Paramagnetic Cr1.8Ti0.2O3+z Particles

“…The Ti2p spectrum of TiO 2 is composed of two narrow peaks at 458.6 and 464.2 eV corresponding to the spin–orbit split 2p 3/2 and 2p 1/2 sublevels, respectively. These positions coincide with the reported BE’s for Ti 4+ . , In the spectrum of the CTO sample, the two peaks are considerably broader, but they appear practically in the same positions as in TiO 2 . The absence of any detectable shift or shoulder at the low-BE side indicates that the presence of Ti 3+ ions must be very small.…”

“…These positions coincide with the reported BE's for Ti 4+ . 45,46 In the spectrum of the CTO sample, the two peaks are considerably broader, but they appear practically in the same positions as in TiO 2 .…”

Suppression of phosphine-protected Au9 cluster agglomeration on SrTiO3 particles using a chromium hydroxide layer

“…In our previous work, the Cr 2p peak was described and fitted using a fixed relation between the intensity of the Ti 2p 3/2 and the Ti 2s loss peak. 59 The Cr 2p 3/2 peak is found at 577.4 AE 0.2 eV, which can be identified from literature reference data as being Cr(OH) 3 . 60 It should be noted that this is different to the binding energy of Cr 2 O 3 and will be discussed below (vide infra).…”

“…It was fitted by including the Ti 2s energy loss peak, which occurs in the same energy region. In our previous work, the Cr 2p peak was described and fitted using a fixed relation between the intensity of the Ti 2p 3/2 and the Ti 2s loss peak 59 . The Cr 2p 3/2 peak is found at 577.4 ± 0.2 eV, which can be identified from literature reference data as being Cr(OH) 3 60 .…”

Electrodeposited Nickel/Chromium(III) Oxide Nanostructure-Modified Pencil Graphite Electrode for Enhanced Electrocatalytic Hydrogen Evolution Reaction Activity

“…Chromium­(III) oxide (Cr 2 O 3 ), the most stable oxide of chromium, naturally occurs as eskolaite mineral . Cr 2 O 3 is a rigid and fragile material that has a hexagonal crystal structure, which has been used in many applications, such as lithium-ion batteries, supercapacitors, gas sensors, and magnetoelectric data storage. − Several studies have shown that Cr 2 O 3 exhibits high electrocatalytic activity and long-term stability for HER. − According to previous reports, nanostructured Cr 2 O 3 materials are prepared using various methods, such as chemical vapor deposition, the sol–gel method, physical vapor deposition, the microwave oven method, electrostatic spray deposition, and the precipitation technique. ,− The electrochemical technique, among other applications, is advantageous because it is inexpensive, straightforward, and applicable under ambient conditions. No studies have reported on the electrochemical synthesis of Cr 2 O 3 nanostructures directly on the electrode surface via potentiometric deposition using a three-electrode cell system.…”