## 4 Conclusions  
The fabrication of PAA to be used as a template for the synthesis of nanostructured materials was studied. Particular attention has been devoted to evidence the morphological features of PAA when aluminum is anodized in 0.4 M H\({}_{3}\)PO\({}_{4}\) added with various amounts of Al(OH)\({}_{3}\). For a more complete elucidation of the PAA fabrication process, the kinetic behavior of aluminum anodizing in the pure and mixed electrolyte has been considered. The role of both Al(OH)\({}_{3}\) concentration and electrical charge on PAA growth can be explained on the basis of the extent of oxide dissolution into the electrolyte, over anodizing, so that it appears as a key parameter in controlling both the growth kinetics and morphology of PAA. As the Al(OH)\({}_{3}\) increased, more structured porous layers were formed that could be further modified by changing the anodizing electric charge. In particular, the increase in the electric charge implies a longer exposure time of the outer oxide surface to the electrolyte with consequent enhancement of chemical dissolution.  
The Al(OH)\({}_{3}\) concentration also controls the development of secondary pore, i.e., pores generated at the oxide/electrolyte interface after the complete development of the PAA layer. Their growth is due almost exclusively to oxide chemical dissolution with minor contribution by an electric field because its strength is diminishing as the PAA thickness is increasing. As a consequence, the growth of these pores stops after partial penetration into the PAA layer. This can be due to the saturation of the electrolyte contacting the base of the growing channel because the onset and propagation of the secondary pores are controlledby chemical dissolution. The secondary pores greatly contribute to the PAA disorder, which can be eliminated by re-anodizing the scalloped aluminum surface obtained after removing the disordered oxide layer formed by first anodizing.  
In conclusion, it can be said that aluminum anodizing in mixed Al(OH)\({}_{3}\) and 0.4 M H\({}_{3}\)PO\({}_{4}\) suggests another cheap and easy way for fabricating PAA that can be used as a template when a high level of order is not required. The flexibility of the procedure, in terms of aspect ratio values that can be accomplished, is very high, so that tailoring of PAA for each specific application is possible.  
PAA obtained in 0.4 M of H\({}_{3}\)PO\({}_{4}\) was used as a template for fabrication of nanostructured arrays of Pd, Co and PdCo alloys. Pd NWs have a polycrystalline nature while Co NWs present a completely amorphous structure. The composition of the alloy was controlled by adjusting the electrolyte composition. The content of Co influences the crystallinity of the NWs. In fact, polycrystalline NWs following the diffraction peaks of Pd were obtained in the case of a low Co content, while a practically amorphous alloy was obtained in the case of a high Co content. Very dilute solutions lead to the formation of an alloy with crystallinity and composition similar to the concentrated solution which has a completely different morphology formed by an array of nanotubes.  
Conceptualization, B.P. and R.I.; methodology, R.I. and B.P.; validation, R.I. and B.P.; investigation, R.I. and B.P.; data curation, R.I. and B.P.; writing--original draft preparation, C.S. and R.I.; writing--review and editing, R.I., and B.P.; supervision, S.P., C.S. and R.I. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data is contained within the article.  
The authors declare no conflict of interest.