Wang, Haotian2023-08-092023-052023-04-21May 2023Xia, Yang. "A Combined Strategy of Catalyst Design and Cell Development for Efficient Electroreduction of O2 to H2O2." (2023) Diss., Rice University. <a href="https://hdl.handle.net/1911/115164">https://hdl.handle.net/1911/115164</a>.https://hdl.handle.net/1911/115164EMBARGO NOTE: This item is embargoed until 2025-05-01As the cost of renewable energy decreases in the past decades, it becomes increasingly attractive to utilize electric energy to produce fundamental chemical feedstocks or fuels. Hydrogen peroxide (H2O2), as an important chemical with a wide range of applications, is currently produced through the industrial anthraquinone process, which is energy and waste intensive. Electrocatalytic oxygen reduction reaction (ORR) towards H2O2 provides an alternative way to produce H2O2 in a green and delocalized H2O2 manner, with the need of only electricity, water, and air. The efficiency of this attractive alternative depends on the choices of cost-effective catalysts as well as well-designed reaction system. In the last decade, a rising number of catalysts have been reported showing promising ORR activity and selectivity. However, to make this green alternative as competitive as the current anthraquinone process in the industrial-relevant scale, there are still three major challenges. Firstly, there are still not many catalytic materials which can selectively and actively catalyze the 2e--ORR towards H2O2 instead of the commonly observed 4e- pathway towards H2O. Moreover, the as-generated H2O2 are typically in a mixture with liquid electrolytes in the traditional cell configurations, which needs further complicated separation process to obtain pure H2O2 solutions for real-world applications. Finally, the cell performance does not meet the requirement for industrial-level production needs, including low stability and low concentration. In this dissertation, we demonstrated a multi-approach solution, from catalyst design, reactor development and interfacial tuning to address the problems listed above. First, we report a direct electrosynthesis strategy combining a cost-effective oxidized carbon catalyst and a brand-new reactor design. The reaction system delivered separate hydrogen (H2)/water (H2O) and oxygen (O2) streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H+ and HO2– recombine to form pure aqueous H2O2 solutions. We achieved over 90% selectivity for pure H2O2 solutions with concentrations up to 20 weight %, and the catalyst retained activity and selectivity for 100 hours. This reactor design was set up as the optimal platform for our later studies (Chapter 3). To further boost the performance of the reaction system, especially under high-current regime, we developed a boron-doped carbon (B-C) catalyst by xxx. Unlike previously reported carbon-based catalyst, it can achieve high selectivity and activity simultaneously under industrial-relevant production rates. Compared to the state-of-the-art oxidized carbon catalyst, B-C catalyst presents enhanced activity (saving more than 210 mV overpotential) under industrial-relevant currents (up to 300 mA cm−2) while maintaining high H2O2 selectivity (Chapter 4). In addition to catalyst development, we tuned the reaction interfacial conditions to enhance the concentration of the H2O2 product that can be obtained in our reaction system and substantially enhanced the stability to a new level (over 1000 hours) (Chapter 5). Finally, the key strategies combining catalyst design, reactor development and interfacial tuning are summarized, and possible future directions are discussed (Chapter 6).application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Electrochemical synthesis of H2O2carbon-based catalystrenewable energyThesis2023-08-09