Electrosynthesis of nanocomposite thin films at immiscible liquid|liquid interfaces

Moshrefi, Reza (2023) Electrosynthesis of nanocomposite thin films at immiscible liquid|liquid interfaces. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Contemporary research on conductive thin film materials has expanded beyond its applications in solar cells, semiconductor devices, and optical coatings to include the development of biocompatible electrode materials and organic thin film transistors. This study focuses on the use of immiscible micro liquid|liquid interfaces between water|oil (w|o) or water|ionic liquid (w|IL) to generate free-standing thin films that incorporate metal nanoparticles (NPs) electrogenerated in situ by reducing a metal salt in the aqueous phase and a hydrophobic electron donor dissolved in the organic/ionic liquid phase. Following an exploration of recent advancements in electropolymerization at an electrified interface, which encompassed the synthesis of polymeric base networks, metal nanoparticles, and nanocomposite film formation, as well as the electrochemical processes at the interface between immiscible electrolyte solutions, four electron donors were examined: ferrocene, IL-modified ferrocene, 2,2′:5′,2′′-terthiophene (TT), and a specialized dithiafulvenyl-substituted pyrene (bis(dithiafulvenyl)pyrene). The research first focused on TT polymerization and the reduction of AuCl₄σ¯ to Au NPs to generate a flexible electrocatalytic composite thin film. The results showed that high aqueous phase pH facilitated the polymerization reaction and the half-wave potential of the electron transfer wave shifted to lower potentials, indicating improved thermodynamics. Furthermore, the study found that the capacitive nature of the interface increased, and the resistance towards simple ion transfer increased with increasing [TT], pH, and potential cycling. Later the metal salt was replaced with copper sulfate to study the formation of Cu NP/poly-TT nanocomposite thin films at different interfacial sizes. The data revealed that the film formed quickly, but the interfacial reaction did not proceed without an applied potential. Preliminary electrocatalysis results showed that the nanocomposite-modified large glassy carbon electrode had a >2× increase in CO₂ reduction currents compared to an unmodified electrode. Finally, the electropolymerization of bis(dithiafulvenyl)pyrene with KAuCl₄(aq) was studied. The study found that miniaturization of the immiscible micro liquid|liquid interface facilitated external potential control and limited the reaction pathway to heterogeneous electron transfer across the interface. This method of nanocomposite film generation provides a low overpotential, controlled alternative to large-scale film generation, making it an attractive option for materials chemistry, electrocatalysis, and as soft electrodes for bioimplantation. The chapter dedicated to conclusions and future work provides a comprehensive analysis of the findings and identifies potential avenues for future research in this field.

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