Mechanisms of organic electrochemical reactions in electrosynthesis and batteries

Tana Siboonruang

doi:10.17918/00010887

Organic electrochemical reactions play a vital role in modern technology, enabling advances like lithium-ion batteries and nylon production. This doctoral thesis investigates the mechanisms of organic electrochemical reactions to advance their widespread adoption in energy storage and chemical manufacturing. Addressing the challenges posed by complex reaction schemes, short-lived intermediates, and sensitive reaction conditions, we employ a range of techniques to elucidate key mechanistic insights. To understand organic electrochemical transformations, we first explore the electrochemical oxidation of cyclohexane to KA oil, a key intermediate in nylon production, in nonaqueous media. Through chemical analysis of the electrolyte and electroanalysis, we demonstrate that O₂, rather than water, serves as the primary oxygen source, aligning with thermochemical oxidation pathways. Using isotopic labeling and concentration studies, we reveal that the reaction initiates via cyclohexyl or hydroxyl radicals, depending on electrode and electrolyte composition. Additionally, we highlight the impact of crossover effects in undivided cells, showing that cathodic reactions and reactor design can introduce potential artifacts affecting anodic activity and selectivity. To further probe reaction mechanisms, we apply in-situ x-ray absorption spectroscopy (XAS) to track Ni(OH)₂/NiOOH structure during the alkaline electrochemical alcohol/aldehyde oxidation (AOR), a potential alternative for the energy intensive oxygen evolution reaction (OER) in water electrolysis. Below OER potentials, both furfural and furfuryl alcohol follow a chemical oxidation mechanism, consistent with previous reports. However at OER potentials, furfural oxidation switches to a direct mechanism, whereas furfuryl alcohol follows the direct mechanism only at high concentrations and follows the chemical oxidation mechanism at low concentrations. Additionally, low conductivity of Ni(OH)₂ leads to catalyst film heterogeneity, highlighting key factors for rational design of Ni-based AOR catalysts. Lastly, we explore deconvoluting the effects of a complex reaction network in nonaqueous, Li-based batteries using physics-based modeling and novel reactor designs. Physics-based models help quantify lithium-generating versus lithium-trapping reactions and assess their contributions to capacity fade. However, these models require many inputs that require deconvolution of how crosstalk affects individual electrode processes. To address this, we develop a microfluidic flow cell to control transport between electrodes and an interdigitated electrode array for in-situ detection of side products. These advancements provide tools for transcending traditional coin cell testing and deconvoluting complex side reaction networks. Together, this thesis integrates electrochemical analysis, in-situ spectroscopy, kinetic modeling, and sensor development to provide a comprehensive understanding of organic electrochemical reaction mechanisms. These insights pave the way for optimizing electrochemical processes in energy storage, sustainable chemical synthesis, and beyond.

Mechanisms of organic electrochemical reactions in electrosynthesis and batteries

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Mechanisms of organic electrochemical reactions in electrosynthesis and batteries

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