Optical and Physical Properties of Cobalt Oxide Films Electrogenerated in Bicarbonate Aqueous Media

Abstract

For the first time, cobalt oxide films that are highly protective against localized corrosion and depicting a wide variety of bright and uniform colors due to light interference, have been successfully electrogenerated on polycrystalline cobalt disk electrodes under potentiostatic polarization in a mild aqueous bicarbonate medium. Open circuit potential measurements have shown the formation of a film with a bilayered structure, organized as a thin Co 3 O 4 outer layer and a thick CoO inner layer. The existence of Co 3 O 4 as a thin outer layer, previously postulated from galvanostatic reduction experiments, has been confirmed from XPS analysis. Raman spectroscopy, performed using a very low laser intensity, has shown that the films are mainly composed of CoO. The broadness of the Raman bands observed is associated to the amorphous character of the film, a result that has been confirmed by spectroscopic ellipsometry and X-ray diffraction analysis. Overall film thicknesses, well controlled by the anodization duration, were determined and correlated using mechanical (atomic force microscopy and profilometry) and spectroscopic (specular UV-vis-NIR reflectance and ellipsometry) techniques. Spectroscopic ellipsometry, using a simple amorphous dispersion model, has proved efficient for measuring thicknesses of films ranging from 31 to 290 nm with very low standard deviations. The real part of the complex refractive indices of these films, ranging from 1.8 to 2.2 (at λ ) 632.8 nm) depending on the anodization duration, is in good agreement with values reported in the literature for CoO. The film with the highest refractive index, and consequently the more densely packed structure, was obtained following a 30-minute anodization period.

Gold-supported two-dimensional cobalt oxyhydroxide (CoOOH) and multilayer cobalt oxide islands

“…The features of a broadening of the main component and a shake-up satellite are indicative of high-spin Co 2+ species in the bilayer structure [16][17][18] (as also predicted by DFT calculations 11 ). On the other hand, low-spin Co 3+ compounds exhibit almost no satellite structure 19 .…”

Absence of ferromagnetic order in high quality bulk Co-doped ZnO samples

“…30,31 CoO presents two sharp lines at 484 ͑weak͒ and 691 ͑strong͒ cm −1 associated to the A g and E g modes and a broad band between 500 to 600 cm −1 attributed to anharmonic interactions. 32 ͑F 2g ͒, 485 ͑E g ͒, 523 ͑F 2g ͒, 624 ͑F 2g ͒, and 693 ͑A 1g ͒. 32 For both materials the peak at ϳ690 cm −1 is always the strongest one.…”

“…32 ͑F 2g ͒, 485 ͑E g ͒, 523 ͑F 2g ͒, 624 ͑F 2g ͒, and 693 ͑A 1g ͒. 32 For both materials the peak at ϳ690 cm −1 is always the strongest one. We do not observe, however, any indication of a peak at this frequency for our set of samples.…”

Pulsed laser deposition of porous N-carbon supported cobalt (oxide) thin films for highly efficient oxygen evolution

“…Hence, the deposition of small cobalt nanoclusters may result in a better interconnection of cobalt with C-N species with an improved electrical conductivity. 16 Moreover, the lower cobalt (oxide) peak intensity at Co(Ox) 50 @PNC compared to that of Co(Ox) 50 @PC (with equal cobalt concentration) indicates that cobalt oxides are partially surrounded by some graphitic carbon layers, which is favourable for electrocatalyst stability. 17 As the nitrogen atoms (structural defects) are an important component of Co(Ox) 50 @PNC, the nitrogen bonding configurations were further studied by XPS spectrum.…”