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The copper and cobalt oxides composites coatings on aluminum substrates have been successfully synthesized via sol-gel method using nitrate-based sol precursors. The composites were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and UV-Vis-NIR spectrophotometry. The sol-gel reactions were discussed and Molecular Dynamics (MD) simulation was integrated into the study to predict molecules assembly properties. The XRD analyses revealed that the CuO and the Co3O4 composites were formed after the annealing process with the average difference of the calculated lattice parameters compared to ICDDs was 1.17%. The surface electronic structure was mainly consisted of tetrahedral Cu(I), octahedral Cu(II), tetrahedral Co(II), octahedral Co(III) as well as surface, sub-surface and lattice oxygen O−. The XRD, XPS and MD simulation results showed that there was minimal (or possibly non-existing) indication of copper-cobalt mixed phase oxides formations. FESEM and AFM surveys revealed that the coating had a porous surface composed of interlinked nanoparticles in the range of ~10 to ~40 nm. UV-Vis-NIR reflectance spectra showed that the sol precursors concentration and the dip-drying cycle significantly influenced the absorptance value with optimum absorptance (α) of 88.7% exhibited by coating synthesized using sol concentration of 0.1 M and 10 dip-drying cycles. High absorptance value and simplicity in the synthesis process render the coatings to be very promising candidates for solar selective absorber (SSA) applications.

Thin films of CoxCuyOz have been coated on aluminum substrates via sol–gel route using low concentration of copper and cobalt precursors at annealing temperatures in range of 500–650 °C. The coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis-NIR spectrophotometry, and nanoindentation. The XRD analysis in 2θ-range of 30°–42° revealed that the coatings exhibited low crystallinity of CoCu2O3, CoCuO2, and CuCoO2. The surface bonding structure analyzed using XPS indicated that the coating contained: Cu (tetrahedral Cu+ and octahedral Cu2+), Co (octahedral Co3+, tetrahedral Co2+, and mixed Co2+ and Co3+), and O (lattice, surface, and sub-surface oxygens). The optical properties characterized using UV-Vis-NIR showed that the reflectance spectra of coatings formed a spectrally solar selective absorber profile associated with the interference peaks and the absorption edges around wavelengths of below 1.2 μm. The maximum absorptance (α = 75.8%) was shown by coating synthesized at 500 °C. The mechanical properties of coatings showed that the increase of annealing temperature increased the coating's hardness (H) and the elastic modulus (E) due to the enhancement of the [CoCuO2/CuCoO2]:[CoCu2O3] oxide phases ratio, as the result, an excellent stability of the wear resistance (H/E) of around ∼0.035 was recorded.

Novel copper–cobalt oxide thin films with different copper/cobalt molar ratios, namely, [Cu]/[Co] = 0.5, 1, and 2, have been successfully coated on aluminum substrates via a simple and cost-effective sol–gel dip-coating method. Coatings were characterized using high resolution synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy, in combination with nanomechanical testing and field emission scanning electron microscopy (FESEM). The surfaces of both [Cu]/[Co] = 0.5 and 1 samples consisted primarily of fine granular nanoparticles, whereas the [Cu]/[Co] = 2 has a smoother surface. The analyses reveal that the increase of copper concentration in the synthesis process tends to promote the formation of octahedral Cu2+ which minimizes the development of octahedral Cu+, and these octahedral Cu2+ ions substitute the Co2+ site in cobalt structure host. The local coordinations of Co, Cu and O are not substantially influenced by the change...

Copper–cobalt oxides thin films had been successfully coated on reflective aluminium substrates via a facile sol–gel dip-coating method for solar absorptance study. The optimum absorptance in the range of solar radiation is needed for further optimum design of this material for selective solar absorber application. Field emission scanning electron microscopy was used to characterize the surface morphology of the coating whereby nano-size, grain-like morphology was observed. Synchrotron radiation X-ray photoelectron spectroscopy was employed to analyze the electronic structure of the coated surface showing that the (i) oxygen consisted of lattice, surface and subsurface oxygen, (ii) copper consisted of octahedral and tetrahedral Cu+, as well as octahedral and paramagnetic Cu2+ oxidation states, and (iii) cobalt consisted of tetrahedral and paramagnetic Co(II), octahedral Co(III) as well as mixed Co(II,III) oxidation states. In order to optimize the solar absorptance of the coatings, relevant parameters such as concentrations of cobalt and copper, copper/cobalt concentration ratios and dip-speed were investigated. The optimal coating with α = 83.4% was produced using 0.25 M copper acetate and 0.25 M cobalt chloride (Cu/Co ratio = 1) with dip-speed 120 mm/min (four cycles). The operational simplicity of the dip-coating system indicated that it could be extended for coating of other mixed metal oxides as well.