Understanding and Tuning Ionic Transport and Electrochemical Reactions on Air Electrodes of Solid Oxide Fuel Cells at the Nanoscale
In this dissertation, there are three topics including nanoscale engineering effects on cathodes for intermediate-temperature solid oxide fuel cells, effects of mechanical and electrical application on atomic force microscopy, and ionic diffusivity and mobility study of oxygen reduction/evolution reaction by nanoscale in situ characterization via atomic force microscopy. Their abstracts are listed below.
Topic I: The impact of various infiltrates on the kinetics and rate-limiting step of oxygen reduction reaction (ORR) is examined with LaNi0.6Fe0.4O3-δ (LNF) as the cathode backbone of solid oxide fuel cells (SOFC). Multiple materials were infiltrated on the backbone. The dependencies of electrode polarization resistance on the precursor concentration, temperature, and oxygen partial pressure are presented, and related discussions are made to interpret the differences in ORR kinetics and the rate-determining step for ORR.
Topic II: Conductive atomic force microscopy (CAFM) has been widely employed to study the localized electrical properties of a wide range of substrates in non-vacuum conditions by the use of noble metal-coated tips. In this topic, the impact of mechanical and electrical stimuli on the apex geometry of gold-coated tips and electrical conduction properties at the tip-substrate contact is discussed by choosing gold and highly-ordered pyrolytic graphite as the representative tip and substrate materials, respectively.
Topic III: The ionic transport in solid oxides after becoming thermally activated is understood as hopping to point defects (i.e. oxygen vacancies), and the kinetics behind it are highly dependent upon the bonding state of the ionic species with their surrounding lattice environment. In this study we report the findings of our recent efforts to directly observe ionic transport in SrTiO3 (STO) and Y2O3-stabilized ZrO2 (YSZ)–the most widely used cathode material in intermediate temperature SOFC–by use of Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM).