Wong, Michael S2023-08-092023-08-092023-052023-03-30May 2023Conrad, Chris Leif. "Oxygenation Catalysis to Enable Sustainable Chemical Production and Wastewater Treatment." (2023) Diss., Rice University. <a href="https://hdl.handle.net/1911/115095">https://hdl.handle.net/1911/115095</a>.https://hdl.handle.net/1911/115095Modern efforts to mitigate CO2 emissions, meet rising energy demands, and source sustainable feedstocks has highlighted the value of (photo)electrochemical ((P)EC) technologies. This vision relies on numerous half-cell reduction reactions such as H2 from H2O, C-feedstocks from CO2, H2O2 from O2, and NH4+ from N2 or NO2-/NO3-. Critically, these reactions all require coupling to the anodic oxygen evolution reaction (OER) to supply protons and balance charge. In addition to enabling sustainable production, anodic oxidation can also provide an efficient means of treating the associated wastewaters (e.g., EC advanced oxidation processes) through the generation of reactive oxygen species and/or other in-situ biocides and oxidative species. This work leverages a materials design approach to engineer solutions within this water-energy nexus. Specifically, we develop synthesis methods amenable to industrial scale-up (i.e., robust, reproducible, rapid) for key catalytic materials: Ir/Ru-based catalysts for acidic OER, and TiO2 electrodes for water treatment applications. Commercially, H2 production via proton exchange membrane (PEM) electrolyzers is positioned to be the cornerstone of our technology transition in the immediate future. However, reliance on expensive and scarce Ir catalysts for the OER presents an immediate bottleneck risk for deployment. Although numerous catalysts report improved activity (i.e., Ir utilization), their complex synthesis routes can be time-consuming, unwieldy, and impractical. Here, we report a one-pot borohydride reduction synthesis to quickly yield >100 mg of aggregated Ir, Ru, and IrRu nanoparticles with outstanding inter-batch consistency. We further demonstrate this method’s versatility by supporting all three particles onto earth-abundant yttrium oxide, resulting in improved precious metal utilization during OER. However, meeting the aggressive (i.e., 2050, 2070) net-zero proposals will require a rapid diversification of sustainable technologies. For H2 generation, integrated PEC and photovoltaic-EC (PV-EC) devices present the most promising avenues towards highly efficient (i.e., >20%) solar-to-hydrogen technologies. We investigated an array of low-Ir catalysts synthesized through the aforementioned method which exhibit an intrinsic activity of >400 A g-1Ir at 1.55 V vs. RHE in acidic conditions. Crucially, a remarkable stability of 10 days of H2 generation in a prototype solar cell architecture is demonstrated for Ir0.5Ru0.5Ox during liquid flow cell electrolysis at a commercially sustainable loading of only 0.1 mgIr cm-2 (0.1 M HClO4, 1.65 VCell). These results represent one of the first demonstrations of PEC-derived H2 at practical loadings. To highlight other opportunities for EC technologies during this energy transition, a case study in the Oil & Gas industry is performed. Hydraulic fracturing (HF) requires >4 million gal. of water be pumped underground per well to stimulate the release of entrapped hydrocarbons. The associated produced water (PW) volumes exceed 150 billion gallons/year and are projected to grow for at least another two decades. Concerns over the potential environmental impact, along with evolving regulatory and economic drivers, has spurred interest in technological innovation. Here, we suggest “fit-for-purpose treatment” to enhance cost-effective regulatory compliance, water recovery/reuse, and resource valorization. We highlight emerging technologies that may enhance cost-effective PW management as HF activities evolve. Based on this analysis, we further sought to improve the synthesis of one of the most promising materials for EC advanced oxidation: TiO2 nanotube arrays (NTAs). Owning to its simplicity, Ti anodization stands as the prevailing NTA synthesis method. However, this approach is marred by sluggish, inconsistent growth rates (ca. 10 nm/min). Here, we determined a broad set of conditions (at 60V) that allow quick NTA fabrication. By modulating conductivity through bulk electrolyte temperature and the addition of several hydroxy acid species, we achieve consistent growth up to 10× faster than traditional methods. We find that regulating the solution conductivity within a desired region (e.g., ~800 – 1000 µS cm-1) enabled the fabrication of double-sided NTA layers of ~10 µm and ~90 µm NTA in 10 and 180 min, respectively.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.ElectrocatalysisWater TreatmentOERMaterials SynthesisThesis2023-08-09