## 3 Results and Discussion  
A separate study of nanostructured lead and lead oxide electrodes is reported in [4; 12]. The cell presented in this work consists of both nanostructured electrodes. In particular, the battery used for testing consists of a nanostructured PbO\({}_{2}\) electrode with a geometric area of about 1.1 cm\({}^{2}\), a nanostructured Pb electrode with a geometric area of about 7.1 cm\({}^{2}\), a commercial Absorptive Glass Mat separator (AGM) and a 5 M sulfuric acid aqueous solution as the electrolyte. Figure 3 shows a 3D scheme of the nanostructured battery. The nanostructured electrodes were assembled with zero gap configuration to simulate the similar condition of a commercial lead-acid battery, and tested at a C-rate from 1 to 30 C with a cut-off of 1.2 V. These are very stressing conditions in comparison to conventional working conditions of a commercial lead-acid battery. The lead oxide electrode was previously immersed in 5 M sulfuric acid before testing. This step is necessary to overcome its low wettability and avoid an initial high potential value that may result in electrode failure. The active mass of the nanowires used to evaluate the nominal capacity of the electrodes was evaluated by gravimetric measurements using a microbalance. Specifically, the electrochemical tests were based on the gravimetric capacitance of PbO\({}_{2}\) since the positive electrode was limiting compared to the negative Pb electrode due to the smaller size of the geometric surface area. Electrochemical tests were performed in two steps. First, conditioning of the nanostructured cells at 1 C was performed. After pre-soaking, the battery was subjected to an initial charge. This charge, which is conducted according to a previously predicted multi-step current procedure [4] which consists of a gradual increase in current from C/5 up to 1 C, plays a crucial role for the mechanical stability of the nanostructured electrodes. In fact, during this step, the cell voltage drops very slowly, avoiding the formation of hydrogen and oxygen that can damage the nanostructures. In particular, this procedure was optimized to keep the cell voltage below 3 V to avoid gas evolution, which would cause mechanical stress to the electrodes and the transportation of acidic drops to the metal parts, causing their corrosion. At the end of this charge, the nanostructured electrodes were cycled at 1 C for 100 cycles and at 25 \({}^{\circ}\)C. This is the conditioning phase of the nanostructured lead-acid electrodes and is necessary for electrode stabilization. The conditioning step was followed by an electron microscopic analysis using Scanning Electron Microscope to evaluate the change in electrode morphology. This analysis was performed because improved battery performance with nanostructured electrodes is associated with improved wettability of the porous mass of the nanostructured electrodes. This behavior is well-known as a peculiarity of lead-acid batteries [29; 30]. In Figure 3, we showed the morphology displayed by a PbO\({}_{2}\) electrode before and after the conditioning step. In detail, Figure 3a,c shows the initial top and cross-sectional view morphology of the lead oxide electrode, consisting of many nanowires that cover the overall surface of the electrode, and cavities that allow the electrolyte (H\({}_{2}\)SO\({}_{4}\) 5 M) to penetrate and encounter a larger active surface for the charge/discharge reactions of the battery. On the other hand, in Figure 3b,d, the micrographs shown are related to the morphology of the electrode after the conditioning phase, lasting 100 cycles. In particular, in Figure 3d, the cross-sectional view of the electrode was reported, which highlights both the top of the electrode, in which the nanowires are present, and the current collector. It is important to highlight that the collector appears perfectly intact, with an identical morphology to the as-prepared one, indicating that it does not fully participate in the charge and discharge reactions that only the nanowires undergo.