Improvement of Interfacial Charge Transport Kinetics for Efficient Electrochemical Systems

Abstract

Understanding of the charge transport and reaction kinetics through the heterogeneous interfaces of electrochemical system is crucial in enhancing its performance. In this regard, the precise analysis of the charge transport and reaction kinetics at interfaces and corresponding development of the efficient system are key points for improving their sustainable and efficient operation. This dissertation is composed of 6 chapters. Chapter 1 is Introduction, where the fundamentals and basics for energy conversion system including the reaction kinetics and charge transport in the interface of the system are briefly described. Furthermore, the concept on electrochemical impedance spectroscopy (EIS) of two energy conversion systems (bipolar membrane for water splitting and perovskite solar cells) is also introduced. In Chapters 2 and 3, electrochemical analysis in the junction of bipolar membrane is discussed. In particular, roles of water dissociation catalysts affecting interfacial hydrogen bond network and their effects on both water dissociation and ion transport are emphasized. In Chapter 2, electrochemical impedance spectroscopic studies through bipolar membrane junctions containing three layers revealed that both dissociation rate constant and ion transport resistance influenced on the performance of bipolar membrane. In Chapter 3, roles of water dissociation catalyst in bipolar membrane will be discussed. The hematite nanoparticle catalyst was growth on the graphene oxide (GO) surface. The strong Lewis acidity of Fe atoms in hematite surface triggers the formation of partially dissociated bound waters (PDBWs) on the Fe atom. The PDBWs induced strong hydrogen bond network of surface water having weak intramolecular O-H bond, which leads the fast water dissociation. Furthermore, analysis on water morphology by nuclear magnetic resonance, infrared spectroscopy, and small angle X-ray scattering technique reveals that new distinct water clusters having ice like clusters were developed on the surface of catalyst, which facilitates the ion transport. As a result, the fast dissociation and ion transport caused high performance of bipolar membrane. Discussion on the interface charge transport and recombination kinetics in another energy conversion system is proceeded in Chapter 4. Perovskite solar cells receiving great attention due to their high efficiency have been studied for last 10 years. It has been known that it is strongly recommended to construct a highly crystalline perovskite layer to improve solar cell performance. Furthermore, charge transport and recombination kinetics is also strongly influenced by the crystallinity of perovskite layers. In this chapter, the effects of charge transport and recombination on performance of perovskite solar cells will be discussed. In conclusions, efficient charge transport and fast reaction kinetics in the heterogeneous interface are key points for reducing loss in energy conversion systems. In this context, electrochemical impedance spectroscopy is utilized to understand of interfacial charge transport and reaction kinetics of energy conversion systems especially for bipolar membrane in water splitting and perovskite solar cells.