Hematite photoelectrodes grown on porous CuO–Sb₂O₅–SnO₂ ceramics for photoelectrochemical water splitting

Photoelectrodes capable of cost-effective hydrogen production on a large scale, via photoelectrochemical water splitting under solar light, could offer an elegant solution to many current problems of humankind caused by over-reliance on fossil fuels and the resulting environmental pollution. The search and design of low-cost photoelectrode materials and substrates for practical applications are required. In this work, unmodified hematite photoanodes grown by metal-organic chemical vapor deposition (MO-CVD) onto CuO–Sb2O5–SnO2 ceramic substrates are reported. The deposition time of hematite precursor varied between 10 min, 60 min, and 90 min. The photoanode grown for 60 min exhibits the highest photocurrent density recorded at 1.23 V vs RHE (reversible hydrogen electrode): 4.79 mA/cm2 under blue light of Thorlabs LED M455L2 (455 nm), 0.41 mA/cm2 under the radiation of the real sun in Mexico, and 0.38 mA/cm2 under AM1.5G solar simulator conditions. The high porosity of CuO–Sb2O5–SnO2 ceramics permits the permeation of the hematite precursor into the substrate bulk, which results in 3D-growth of a thin Fe2O3-coating (50 nm or less) on conductive SnO2-grains in the ceramics to a depth of ca. 5 μm. The thick photocatalytic layer (SnO2-grains coated by hematite) of several micrometers assures a good light harvesting by the photoelectrode, while the nano-sized Fe2O3-films on conductive SnO2-grains is favorable for charge diffusion. This architecture of the photoelectrode results in good photoelectrochemical characteristics and is promising for further development.</p

Corrosion Behavior of AA2055 Aluminum-Lithium Alloys Anodized in the Presence of Sulfuric Acid Solution

The aim of this work was to evaluate the corrosion behavior of the AA2055 Aluminum-lithium alloy anodized in a sulfuric acid (H2SO4) bath, varying the current density of 0.19 and 1 A·cm−2 and why the sealing solution was water (H2O) and sodium dichromate (Na2Cr2O7). Anodized samples were exposed to a 10 vol.% H2SO4 solution and the electrochemical technique used was electrochemical impedance spectroscopy. Scanning electron microscopy and X-ray photoelectron spectroscopy were employed to characterization of the anodizing layer, determinate morphology and thickness of coatings. The Na2Cr2O7 sealing solution tends to increase the charge transfer resistance and produces a more homogeneous and compact passive oxide layer, and imparts a corrosion inhibition protection to the AA2055. SEM observations indicated that the morphology and thickness of the anodic films formed on AA2055 aluminum-lithium alloy anodized have the best results for both current densities

Effect of sealing treatment on the corrosion behavior of anodized AA2099 aluminum-lithium alloy

The corrosion behavior of the sulphuric-anodized AA2099 using two different current densities, 0.19 or 1.0 A·cm−2, with two different sealing treatments in H2O and 6 wt.% Na2Cr2O7 at 95 °C was studied in 3.5 wt.% NaCl and 10 vol.% H2SO4 solutions. The AA2099 is widely used in aeronautical applications, thus it is essential to present good corrosion performance in chloride and acid rain environments. The surface morphology of the anodized film was characterized by scanning electron microscopy (SEM), the electrochemical corrosion behavior was studied using electrochemical impedance (EIS), and finally characterization of the surface chemical composition was revealed by X-ray photoelectron spectroscopy (XPS). It was found the 6 wt.% Na2Cr2O7 sealing treatment imparts a more homogeneous and compact passive layer, and tends to increase the charge transfer resistance, thus improving the corrosion behavior of the anodized AA2099