Fig. 2 shows the XRD characteristic

Fig. 2 shows the XRD characteristics of SS/Sn0.8Pd0.2 electrodes prepared at different N values and deposition steps. In all cases, major diffraction peaks located at 2θ = 38.1, 44.4, and 64.6 (excluding SS peaks) were observed, indicating the presence of Sn3Pd alloy with major crystal phases (214), (131), and (420), respectively [39]. XRD data in Fig. 2 showed relative peak intensity changes, which indicated changes in crystal facet distribution and potential complex formation between Sn and Pd metals among SS/Sn0.8Pd0.2 electrodes. The HRSEM images in Fig. 3 revealed clear influences by N and mode of metal electrodeposition on the surface morphologies. The electrode surface appeared to be composed of multiple nanoparticles at N = 1, N = 2 and N = 14; whereas the degree of surface roughness for electrodes with N = 3, 4, and 5 likely was relatively lower than that of N = 1. Fig. S6 shows the typical AFM image of electrode surface and Fig. S7 shows the relationship between surface roughness, ε (nm), and N value. Generally, results demonstrated a decrease in surface roughness (ε) with N increase from 1 to 5, then increase to a constant value around 150 nm at N > 6. The formation of metallic particles on the SS surface was a combination of several pertinent steps, including surface diffusion of metal ions, electron transfer converting the metal ions to elemental metallic particles, nucleation and coalescence of metal clusters [40]. Bordo and Rubahn studied the effect of deposition rate on structure and structure morphology of thin evaporated Al films on dielectrics and reported dependence of grain size on deposition rate [41]. Jeon et al. studied the effect of electro-deposition potential on the morphology and substrate of iron-based films on carbon steel substrate in alkaline solution and observed ion diffusion played a role on the grain sizes [42].