This dissertation presents chemical sensors that are based on an emerging optical fiber sensing technology for the determination of the presence and concentration of hydrogen peroxide (H2O2) at low concentrations. The motivation to determine hydrogen peroxide lies on the fact that this chemical species is generated as a by-product of the operation of hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs), and the presence and formation of this peroxide has been associated with the chemical degradation that results in low durability of PEMFCs. Currently, there are no techniques that allow the hydrogen peroxide to be determined in situ in PEMFCs in a reliable manner, since the only report of this type of measurement was performed using electrochemical techniques, which can be affected by the environmental conditions and that can alter the proper operation of the PEMFCs. The sensors presented in this dissertation are designed to detect the presence and quantify hydrogen peroxide in solution at the conditions at which PEMFCs operate. Since they are made using fused silica optical fibers and are based on a spectroscopic technique to perform the detection of H2O2 , they are not affected by the electromagnetic fields or the harsh chemical environment inside PEMFCs. In addition, they are able to still detect the presence of H2O2 at the operating temperatures. The construction of the sensing film on the tip of an optical fiber and its small size (125 µm diameter), make the sensors here developed an ideal solution for being deployed in situ in PEMFCs, ensuring that they would be minimally invasive and that the operation of the fuel cell would not be compromised by the presence of the sensor. The sensors developed in this dissertation not only present design characteristics that are applicable to PEMFCs, they are also suitable for applications in other fields such as environmental, defense, and biological processes. / Graduate / 0548 / 0756 / 0791 / jfbotero@gmail.com

This dissertation presents chemical sensors that are based on an emerging optical fiber sensing technology for the determination of the presence and concentration of hydrogen peroxide (H2O2) at low concentrations. The motivation to determine hydrogen peroxide lies on the fact that this chemical species is generated as a by-product of the operation of hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs), and the presence and formation of this peroxide has been associated with the chemical degradation that results in low durability of PEMFCs. Currently, there are no techniques that allow the hydrogen peroxide to be determined in situ in PEMFCs in a reliable manner, since the only report of this type of measurement was performed using electrochemical techniques, which can be affected by the environmental conditions and that can alter the proper operation of the PEMFCs. The sensors presented in this dissertation are designed to detect the presence and quantify hydrogen peroxide in solution at the conditions at which PEMFCs operate. Since they are made using fused silica optical fibers and are based on a spectroscopic technique to perform the detection of H2O2 , they are not affected by the electromagnetic fields or the harsh chemical environment inside PEMFCs. In addition, they are able to still detect the presence of H2O2 at the operating temperatures. The construction of the sensing film on the tip of an optical fiber and its small size (125 µm diameter), make the sensors here developed an ideal solution for being deployed in situ in PEMFCs, ensuring that they would be minimally invasive and that the operation of the fuel cell would not be compromised by the presence of the sensor. The sensors developed in this dissertation not only present design characteristics that are applicable to PEMFCs, they are also suitable for applications in other fields such as environmental, defense, and biological processes. / Graduate / 0548 / 0756 / 0791 / jfbotero@gmail.com

Hydrogen peroxide (H2O2) is extensively used in a broad range of industrial and medical applications, such as aseptic processing of food and pharmaceuticals, disinfection, water treatment plants, and decontamination of industrial effluents. H2O2 is believed to be responsible for chemical degradation of polymer membranes in Polymer-Electrolyte-Membrane (PEM) fuel cells. Therefore, a versatile H2O2 sensor that functions in different environments with different conditions is of practical importance in various fields. This dissertation presents the fabrication of a fiber-optic H2O2 sensing probe (optrode) and its H2O2 sensing behavior in different conditions. An H2O2 optrode is fabricated using chemical deposition of Prussian blue (PB) onto the tip of a multimode optical fiber. Sensing tests are performed in aqueous solutions at a constant pH and different concentrations of H2O2. Sensing features of the optrode (i.e. repeatability, durability, and reproducibility) are assessed by performing multiple sensing tests with several optrodes. The results show the prepared optrode is able to detect concentrations of H2O2 in aqueous solutions at a constant pH of 4 and the optrode features a repeatable and durable response at this condition. The functionality of optrodes at different pH values is further investigated by performing additional sensing experiments. These experiments are carried out in aqueous solutions with different concentrations of H2O2 at different pH values (i.e. pH 2-7). The sensor detects the presence of H2O2 at a range of pH values. Sensing behavior of optrodes toward detection and measurement of H2O2 concentrations is studied at the pH value corresponding to an operating PEM fuel cell (i.e. pH 2). The optrode is able to detect concentrations of H2O2 at this condition with a repeatable and durable response. The stability of PB films, prepared through different conditions, is investigated to address the stability of optrodes at elevated temperatures. PB films are first deposited onto the glass slides through three different chemical processes, and then at different synthesis temperatures. The PB films are left in Phosphate-Buffer-Solutions (PBS) with pH 2 and at elevated temperatures for a day. Finally, PB films are characterized using Fourier transform infrared spectroscopy (FTIR) to analyze their stability following PBS processing at operating temperatures and pH value corresponding to an operating PEM fuel cell (i.e. 80 °C and pH 2). The results of these experiments illustrate the PB films prepared through the single-source precursor (SSP) technique and at synthesis temperatures above 60 °C remain stable after the PBS processing. The proposed optrode shows reliable sensing behavior toward detection and measurement of H2O2 concentrations in aqueous solutions at different conditions. The prepared optrode has the potential for being developed and used in different industrial and medical fields, as well as an operating PEM fuel cell, to detect and measure H2O2 concentrations. / Graduate / 0794 / 0548 / 0485 / hakbarik@uvic.ca