Selective and efficient electrocatalysts are imperative for the successful deployment of electrochemistry toward synthetic applications. In this study, we used galvanic replacement reactions to synthesize iridium-decorated manganese oxide nanoparticles, which showed a cyclooctene epoxidation partial current density of 10.5 ± 2.8 mA/cm2 and a Faradaic efficiency of 46 ± 4%. Results from operando X-ray absorption spectroscopy suggest that manganese leaching from the nanoparticles during galvanic replacement introduces lattice vacancies that make the nanoparticles more susceptible to metal oxidation and catalyst reconstruction under an applied anodic potential. This results in an increased presence of electrophilic oxygen atoms on the catalyst surface during reaction conditions, which may contribute to the enhanced electrocatalytic activity toward cyclooctene epoxidation.
The use of a liquid electrolyte is nearly ubiquitous in electrosynthetic systems and can have a significant impact on the selectivity and efficiency of electrochemical reactions. Solvent selection is thus a key step during optimization, yet this selection process usually involves trial-and-error. As a step toward more rational solvent selection, this work examines how the electrolyte solvent impacts the selectivity of electrocarboxylation of organic halides. For the carboxylation of a model alkyl bromide, hydrogenolysis is the primary side reaction. Isotope-labeling studies indicate the hydrogen atom in the hydrogenolysis product comes solely from the aprotic electrolyte solvent. Further mechanistic studies reveal that under synthetically relevant electrocarboxylation conditions, the hydrogenolysis product is formed via deprotonation of the solvent. Guided by these mechanistic findings, a simple computational descriptor based on the free energy to deprotonate a solvent molecule was shown to correlate strongly with carboxylation selectivity, overcoming limitations of traditional solvent descriptors such as pK a . Through careful mechanistic analysis surrounding the role of the solvent, this work furthers the development of selective electrocarboxylation systems and more broadly highlights the benefits of such analysis to electrosynthetic reactions.
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