Fabrication of low-Cost SnO2 anodes on silicon for the electrochemical degradation of organic pollutants in water

Abstract

Indirect anodic oxidation is a promising electrochemical advanced oxidation process (EAOP) that has demonstrated high efficiency in oxidating organic pollutants in water. The effectiveness of this process depends critically on anode’s ability to generate hydroxyl radicals while minimizing radical adsorption and resisting corrosion under high oxidative stress. Therefore, scaling up this technology demands electrode fabrication methods that are not only effective but also scalable, reproducible, and cost-effective. As an alternative to extrinsic dopants, depositing SnO2 films onto silicon substrates creates a p-n heterojunction that induces sufficient electronic conductivity and thus anodic activity without intentional doping. This work investigates two scalable manufacturing routes, reactive magnetron sputtering and ultrasonic spray pyrolysis to deposit SnO2 thin films on silicon, as well as the optimization of their performance as anodic oxidation electrodes. Comprehensive electrochemical characterizations including linear sweep voltammetry, cyclic voltammetry, and dye-removal assays are used to link each film’s electrochemical performance with its morphology and composition. Physicochemical analyses such as scanning electron microscopy (SEM) for surface morphology, atomic force microscopy (AFM) for topography and roughness, energy-dispersive X- ray spectroscopy (EDS) for elemental mapping, and X-ray diffraction (XRD) for phase identification are used to provide deeper insights into the impact of fabrication parameters on film structural properties and long-term stability. Magnetron sputtered films suffered from incomplete oxidation, revealing metallic Sn peaks, poor adhesion, and low corrosion resistance, highlighting reactor design limitations and indicating that, with the current reactor configuration, full SnO2 stoichiometry via PVD cannot be achieved without substrate pre-heating, cyclic voltammograms showed that these films had SnO2 like behavior but their reproducibility was compromised by its low mechanical stability during the electrochemical characterization. In contrast, films fabricated via ultrasonic spray pyrolysis formed rutile phase SnO2. The Si/SnO2 film exhibited an oxygen evolution potential of 1.93 V vs. Ag/AgCl, which increased to 2.21 V after annealing, and a significant decrease in their charge-transfer resistance. Both samples, with and without annealing, exhibited excellent methylene blue color removal (>95%), with the annealed samples demonstrating superior mechanical stability and corrosion resistance under electrooxidation stress. Finally, this thesis reviews the testing protocols implemented to refine both physicochemical and electrochemical characterizations, elucidating how each fabrication parameter impacts film properties and their subsequent performance in electrochemical evaluations, thus providing guidance for further optimization toward cost-effective, scalable manufacturing of SnO2 anodes for advanced water treatment applications.