Development ad characterisation of a carbon based electrode for water disinfection

Sustainable wastewater disinfection is a worldwide challenge since most proven processes are energy intensive and produce harmful by-products. H2O2 is a strong oxidizing agent capable of breaking down both organic pollutants and microorganisms in wastewaters. Moreover, its decomposition only results in harmless by-products. Unfortunately, the main production process for industrial H2O2 is the anthraquinone process, which is complex and unfeasible for distributed operation. Localised production of H2O2 represent a favourable, low energy alternative. Such process is electrochemically driven and its operation varies according to the working conditions (acidic or alkaline), the type of pollutant (bacteria, organic compounds…) and on the type of process: direct synthesis or Advance Oxidation Processes (AOP). Carbon based catalyst are a suitable, cheap and selective option for H2O2 direct synthesis, capable of working efficiently in various pH conditions. The purpose of this thesis is to characterise and assess the electrochemical properties of a Carbon Nano Onion (CNO) film deposited onto a glassy carbon (GC) substrate as an electrode for H2O2 production via Oxygen Reduction Reaction (ORR). The aim is to produce an electrode with the best possible performances in neutral medium to resemble a real case of wastewater disinfection scenario. The material was deposited thorough a novel technique known as NanoJeD developed at the Center for Nano Science and Technology (CNST-IIT@PoliMi), a Physically Enhanced Chemical Vapor Deposition (PECVD). Such electrode was then annealed to increase its electrical properties. The characterisation procedure was made thorough a Scanning Electron Microscope (SEM) and Raman spectroscopy (Raman) analysis. Different thicknesses of the film have been investigated in order to find the best compromise between productivity, efficiency and selectivity. To test these performances, different electrochemical tests and auxiliary procedures have been conducted in both a standard neutral medium (PBS) and in a modified medium to resemble the final working characteristics in the wastewater, made thorough a modified saline solution composed of M9 solution added of lactose. A Linear Sweep Voltammetry (LSV) involving a Rotating Ring and Disk Electrode (RRDE) has been performed to find the peak voltage for the H2O2 formation and has been correlated to the change in the reaction pathway thorough a Koutchey-Levich (KL) plot study to find the electron transfer number of the involved reaction (etn). The film has been subsequently tested through a Chronoamperometry at its peak voltage, to evaluate the absorbed current and subsequently relate it to the Faradaic Efficiency (FE) via a redox titration reaction. The film has been finally tested for longer periods of use to evaluate its stability and the physical characterisation has been repeated to check for variations. This sequence of tests has been also conducted for the same as deposited material annealed in air at lower temperature, to test the impact of the oxygen content into the film. Yet, the air annealed samples present clear signs of instability and poor electrochemical performances, concluding for the best configuration for the wastewater disinfection in a neutral, lactose rich environment is the 4 um vacuum annealed sample.