Electrochemical Synthesis of Nanostructured Materials

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

“…The resulting anodic oxide film grown over the metal substrate can form a rigid compact layer or a nanostructured layer. The former case refers to barrier-type oxide films [ 2 ]. The latter case involves the formation of nanostructured oxide films with different morphologies, such as nanopores, nanotubes, nanowires, nanorods, nanopetals, and other nanogeometries [ 1 , 2 , 3 , 41 , 42 ].…”

“…The mechanisms of growth of anodic oxide nanostructures and the influences of anodizing conditions on the oxide film’s final properties are well-known in the scientific literature, with many papers devoted to these topics having been published in the last decades [ 1 , 2 , 3 , 43 , 44 , 45 ]. In general, to form a nanostructured morphology with a large surface area, the anodization must be performed in an electrolyte in which the formed oxide is partially soluble, for instance, oxalate media to produce nanoporous alumina [ 2 , 45 ] or fluoride ions to grown nanotubes of TiO 2 or ZrO 2 [ 1 , 46 , 47 ]. The pore or nanotube diameter can be controlled by the applied potential and temperature, whereas the oxide layer’s thickness can be tuned by the anodizing time [ 48 , 49 ].…”

“…The pore or nanotube diameter can be controlled by the applied potential and temperature, whereas the oxide layer’s thickness can be tuned by the anodizing time [ 48 , 49 ]. The anodizing time can vary from a few minutes to several hours depending on the layer’s desired thickness, usually obtained in the micrometer range [ 2 , 49 , 50 ]. Polishing procedures and the use of high-purity substrates tend to increase the orderly arrangement of the nanostructure.…”

“…The fabrication of anodic oxides from anodization of metallic substrates offers several advantages that can impact the technology economically in biological, environmental, and energy fields. The anodic oxidation is a facile, low-cost, and scalable method to obtain nanostructured porous oxide films with large surface areas by strict control of the morphological and structural properties, such as tube length, pore size, film thickness, and rigid adhesion to the substrate [ 1 , 2 , 3 ]. These features make the anodic films, such as the popular TiO 2 nanotubes (TiO 2 -NT) and anodic aluminum oxide (AAO), attractive for the development of a wide range of technologies, including drug delivery systems [ 4 ], implants [ 5 ], sensors [ 6 ], filtration membranes [ 7 ], photocatalysts for pollutant degradation [ 8 ], energy conversion [ 9 , 10 , 11 ] and energy-storage systems [ 12 , 13 ], as illustrated in Scheme 1 .…”

“…The use of copper oxides as photocathodes is emerging [ 23 , 24 ]. The utilization of AAO as a template or scaffold is also addressed [ 2 , 25 , 26 ].…”