Time-resolved analysis of the FTO surface dynamics in aqueous solution

Fluorine-doped tin oxide (FTO) is a cornerstone transparent conducting oxide in electrochemistry and materials science, yet its stability is often assumed rather than verified. This work presents a time-resolved operando investigation into the degradation of the FTO electrode, quantitatively mapping its chemical and electrochemical stability in acidic (0.5 M H 2 SO 4 ), neutral (1.0 M KCl), and alkaline (1.0 M KOH) environments. By employing time-resolved electrochemical impedance analysis and cyclic voltammetry-coupled electrochemical impedance spectroscopy protocol, we simultaneously track changes in FTO resistance and double-layer capacitance to deconvolve distinct degradation mechanisms. Our findings reveal that FTO stability is highly conditional. Alkaline media are universally corrosive, causing severe surface roughening (capacitance increases >90 %) and conductivity loss even during simple chemical immersion. In contrast, under acidic and neutral conditions, cathodic cycling drives surface roughening, whereas anodic cycling leads to surface smoothing. Most notably, the impact on conductivity is potential-specific: anodic polarization improves conductivity in neutral KCl but is destructive in KOH, where stannate (SnO 3 2− ) formation causes the largest rise in resistance (+7.3 %). By correlating electrical parameters with specific redox processes, this study provides a quantitative framework for understanding FTO degradation and establishes critical operating windows to ensure FTO reliability in electrochemical applications.