Growth Model of the Tin Anodizing Process and the Capacitive Performance of Porous Tin Oxides

Nanoporous tin oxide layers were fabricated in NaOH during potentiostatic anodization at a low potential. With increasing potential, the nanochannel became fragmentized and a stacked morphology was formed. The total anodizing current was separated into ionic current and electronic current to explain the various morphologies of nanotubes. The ionic current determines ion migration and oxide growth. The electronic current determines oxygen evolution, porous structure formation, and oxide volume expansion. The continuous decline of the total current–time curve at 8 V was explained by a capacitor model. Through cyclic voltammetry, it was proposed that the stacked morphology exhibits a high specific capacitance (11.36 mF cm–²). Extending the annealing time can increase the crystallinity, thus improving the capacitive performance. The stacked morphology allows electrolytes to permeate the entire portion of the nanochannel more evenly, increasing the effective surface area of the electrode in the electrochemical process and thus improving the capacitive properties. The formation of a stacked morphology is related to the intense release of oxygen gas.