## 3 Results and Discussion
### Fabrication and Characterization of Nanostructures  
For the fabrication of PdCo nanostructures, the membranes obtained in 0.4 M H\({}_{3}\)PO\({}_{4}\) and 160 C cm\({}^{-2}\) were used. Nanostructures were obtained in galvanostatic conditions, at \(-1\) mA cm\({}^{-2}\) and for a deposition time of 1 h. In addition to PdCo alloys, for comparison, also nanostructures of Pd and Co were prepared using the same conditions. Before the electrodeposition, a surface of PAA membrane was sputtered with a thin gold layer in order to make it conductive. To obtain the PdCo alloy with different compositions, different electrodeposition baths were used simply changing the Pd\({}^{2+}\)/Co\({}^{2+}\) ratio. Dilute solutions were also used in order to study the influence on nanostructure morphology and composition. All samples were characterized by FESEM, EDS and XRD and the results were summarized in Table 3.  
Figure 11: Pore mean diameter vs. charge density plots of PAA layers formed at 160 V and 0 \({}^{\circ}\)C in 0.4 M H\({}_{3}\)PO\({}_{4}\) aqueous solutions containing different amounts of Al(OH)\({}_{3}\).  
As concern the morphology, in concentrated solutions, the deposits consist of highly ordered and parallel NWs, perfectly replicating the structure of AAM, and thus with an average diameter of about 200 nm and a density of about \(10^{13}\) m\({}^{-2}\), coincident with that of the cylindrical channels. NWs length can be controlled by tuning the electrodeposition time. Indeed, we have verified that, after two hours of deposition, keeping all the other conditions the same, nanostructures have a mean height of about 100% higher than those obtained after 1h of deposition. In the case of diluted solution, arrays of NTs were formed. The NTs have an extremely thin wall, and in fact, appear almost transparent. We observed that the wall thickness can be controlled by increasing the concentration of Pd\({}^{2+}\) and Co\({}^{2+}\) in the deposition bath. This aspect is important because it allows for increasing the mechanical stability of the NTs, which, when they have a too-thin wall, tend to crumble during the dissolution of the alumina template. The elemental composition of the alloy was determined by EDS. In all spectra, apart from Pd and Co peaks, peaks of Al and O, coming from alumina template, and Au, due to the gold-sputtered layer, can be observed. The composition of the alloy clearly depends on the composition of the bath with a dependence that is roughly linear. Therefore, by simply controlling the Pd\({}^{2+}\)/Co\({}^{2+}\) ratio in solution, it is possible to obtain alloys rich in Pd in Co or with approximately similar content of the two metals. Using dilute solutions, but maintaining the same Pd/Co ratio, the composition of the nanostructures does not change.  
Interesting results were obtained from the XRD study. The crystallographic structure of nanostructures changes with their composition. In particular, pure Pd NWs are polycrystalline. The XRD pattern, apart from Au diffraction peaks, due to the gold-sputtered layer, shows the presence of all diffraction peaks of the face-centered cubic phase of Pd metal [84]. Co NWs are instead completely amorphous according to the data reported in [67]. Obviously, the tendency of cobalt to deposit amorphously affects the crystallinity of the alloy. In the case of alloys rich in Pd, the NWs are crystalline and practically have the same diffraction pattern as the pure Pd NWs. As the Co content increases, the crystallinity of the NWs decreases, and in fact, the intensity of the diffraction peaks of Pd decreases, which disappear completely in the alloy's rich in Co. In this case, the diffraction pattern is that typical of amorphous material and therefore completely similar to that of the NWs of pure Co. The dilution of the deposition solution has no effect on the crystallinity of the nanostructures, and in fact, keeping all the other deposition conditions the same, XRD patterns similar to those discussed so far are obtained.