UC Riverside

The fast progress in renewable energy sources, emerging electronics, and electrical automobiles stimulate the development of next-generation energy storage devices. Among them, supercapacitors, possessing high power and high energy density, caught rabid attention worldwide. Theoretical studies on the electrode compositions, geometries, and interfaces delivered useful information on various material properties, which was essential for approaching high-performance supercapacitors. Recent computational screening techniques suggest potential electrode materials for future experimental designs and device fabrications. So far, transition metal oxides (TMO), carbon-based materials, and the newly discovered 2D MXenes, etc. were regarded as the promising supercapacitor electrodes due to their high theoretical capacitance, larger surface areas, and multiple constituents. In the first part of this dissertation, density functional theory (DFT) was employed to analyze the structure, energetics, and transport of hydrogen in 3d/4d transition metal perovskites (ABO3). The B-O bonding contributions before and after H absorption were unveiled. While simple chemical descriptors, allowing comprehensive searches for candidate proton-conductor perovskites with little computational cost, were provided. Likewise, the interfacial properties for the heterostructures MXene (Ti3C2Tx and Ti2CTx with T=-O, -OH, a mixture of -F and -O)/(pure or N-doped) anatase-TiO2 (101) were evaluated via DFT. We found that surface functional groups of MXene dramatically impacted the interface electronic charge transfers and interfacial configurations. In addition, the N-doped surface-O of TiO2 changed the electronic and geometric properties of these hybrid composites. Besides basic understandings of various material properties, perceiving energy storage mechanisms behind different types of supercapacitors is also a welcoming topic. In the second part of this dissertation, ab-initio molecular dynamics (AIMD) were utilized to study the proton transport performances at the mono water layer confined by Graphene-Ti3C2O2 (dissimilar interface) and Ti3C2O2-Ti3C2O2 (similar interface) with different intercalated-proton concentrations. The results showed that interfacial properties, as well as proton diffusion behavior, played a significant role in the faster proton surface-redox and transport process. Ultimately, this dissertation explores the fundamental knowledge of the recent sprout popular metal-oxides (perovskites), MXene-based composite electrode materials for supercapacitor applications. Meanwhile, we offered a theoretical interpretation of energy storage mechanisms for proton intercalated MXene-based layered interfaces.