Electrochemical Investigation Of Oxygen Reduction Reactions At Liquid/Liquid Interfaces

The oxygen reduction reaction (ORR) is a key step of the respiratory chain of aerobic organisms. In nature, ORR occurs at soft interfaces, namely biomembranes, that provide both a physical separation of the reactants and products and an electrochemical driving force resulting from the membrane electrical potential difference.Liquid/liquid interfaces (L/L interfaces), also named the interface between two immiscible electrolyte solutions (ITIES). Indeed, ITIES also provide a physical separation of the reactants and products and the polarization of this soft interface provides an electrochemical driving force to ORR. In comparison with the conventional solid/liquid interfaces, not only electron transfer reaction but also ion transfer reaction can be studied at L/L interfaces. Therefore, L/L interfaces have been considered as the simple model of biological membranes.ORR at L/L interfaces has been studied by using various lipophilic electron donors, ferrocene (Fc) and its derivative(DFc, DMFc), tetrachlorohydroquinone (CQH2), fullerene monoanion (C60-) and tetrathiafulvalene (TTF). Recently, many lipophilic complexes of transition metals with macrocyclic ligands like porphyrins and phthalocyanines have been widely studied instead of expensive metal nanoparticles to catalyze ORR at L/L interfaces. Therefore, developing cheap, efficient and good bio-compatible catalyst to ORR at liquid/liquid interface is still active.This thesis has been devided into three parts.Chapter1briefly summarized the development of electrochemistry at the L/L interfaces. The basic theory of electrochemistry at L/L interfaces and its application in electrocatalysis was also introduced. Finally, a prospect to application of electrochemistry at L/L interfaces was given. In addition, the principles of electrocatalytic ORR at L/L interfaces and the experimental methods of four-electrode experiment were also described. In Chapter2, four-electrode system was used to study the catalysis of lipophilic metal-free porphyrin, H2TPP, to ORR by TTF at the water/DCE interfaces. Experiments which were conducted by electrochemical cyclic voltammetric and UV-visible spectroscopy, proved the protonated H2TPP could catalyze ORR by TTF to generate H2O2mainly via two-electron reduction mechanism.In Chapter3, the protonation of H2(TMPyP[4]) under different pH values was studied by using UV-visible spectroscopy and the phase transfer of H2(TMPyP[4]) through water/DCE interfaces was proved by both UV-visible spectroscopy and electrochemical cyclic voltammetric. The phase transfer catalysis of H2(TMPyP[4]) to ORR by DMFc at the water/DCE interface was also studied by using UV-visible spectroscopy. The results proved the protonated H2(TMPyP[4]) could take place phase transfer and catalyze ORR by DMFc to generate H2O2mainly via two-electron reduction mechanism.