PEM fuel cells are susceptible to airborne sulfur contaminants that cause catalyst degradation, disrupting the oxygen reduction reaction (ORR) and producing hydrogen peroxide (H2O2) as an undesired intermediate product within the membrane electrode assembly (MEA). Sulfur adsorbs onto the surface of the platinum/carbon catalyst, blocking active platinum sites and changing the reaction mechanism from a 4e- pathway producing water, to a 2e- pathway producing H2O2. Today, 95% of commercially available H2O2 is made from an expensive, energy-intensive, and environmentally harmful anthraquinone oxidation process. This thesis seeks to take advantage of the described MEA vulnerability and intentionally modifies the catalyst for cogeneration of H2O2 and electricity using ex-situ rotating ring-disk electrode (RRDE) methodology. Mechanisms behind this electrochemical process could provide a scalable, environmentally friendly, and more cost-effective production method of H2O2.

In this work, a catalyst modification process is developed and for the first time, the stability of the modified catalyst and H2O2 production is tested over long periods of time and under potential control. Cyclic voltammetry confirmed the stability of the modified catalyst for a minimum of 24 hours. The ORR activity after catalyst modification is measured under polarization (0 V→1V), as well as potentiostatic control at 0.1 V, 0.2 V, 0.3 V, and 0.4 V over time; results show that activity is decreased after catalyst modification. The fraction of H2O2 produced can theoretically be deduced from disk and ring currents during the ORR and are quantified in this study. While existing studies rely on this method of H2O2 quantification, the production of H2O2 is physically confirmed via a dual traditional-potentiometric titration in the bulk solution after long term stability testing of 24 hours. Experiments reveal a rearrangement of adsorbed sulfur and a previously unknown change to the surface due to difficulties in controlling rapid changes in operating conditions during testing in an RRDE setup (liquid phase environment). In-situ testing in PEM fuel cells would be more appropriate because such a design is a closer representation of the application and control of the operating conditions would be simplified (gas phase environment).

Alexandra M. Fernandez received her B.S. degree in Chemical Engineering from Arizona State University in May 2021. She joined the Hawai‘i Natural Energy Institute in August 2021 as a Graduate Assistant pursuing her M.S. degree in Electrical Engineering. Her current research involves the PEM fuel cell modification for electrochemical production of hydrogen peroxide. Her other research interests include PEM fuel cell optimization and implementation for sustainable grid energy.