Fig. 3: Electrochemical and morphological investigations of the two different zinc metal electrodes.

a A schematic of the three-electrode cell for the in situ optical microscopy. b Galvanostatic curves of the NP Zn and the Zn powder electrodes during discharging and charging at 20 mA/cm². c Photographic pictures of the NP Zn anode captured at five different stages: pristine, 20% discharged, 40% discharged, 20% recharged, and fully recharged, from left to right respectively. The states are estimated based on the theoretical capacities of the electrode. The white dashed lines, whose distance stays the same for all five photographic pictures, correspond to the approximate boundaries of the pristine electrode. d SEM of the NP Zn anode harvested from the cell at the same states as the photographic pictures in c. e Photographic pictures of the Zn powder anode captured at nominally the same states as the NP Zn anode in c, where the red arrows highlight locations of morphology changes and the exposure of the Cu substrate. The scale bars are 1 mm in the photos and 1 µm in the SEM images.