A Study of Energy Materials via Transmission Electron Microscopy

This work recognizes the imperative need for green energy solutions in order to secure a clean and safe future for the planet. Transition from greenhouse producing fossil fuels can’t happen overnight, as green energy technologies will have to be introduced into the global infrastructure in tiers according to their economic feasibility. Intermittent renewable sources like solar and wind are in need of a storable, transportable, and clean energy carrier to expand their contribution to the global energy supply. Hydrogen gas is the most promising candidate to play this role, as H2 production and usage is as clean as the renewable sources themselves. Generation of H2 and O2 from water, or electrolysis, on industrial scales will require water-splitting catalysts to perform as efficiently as possible, so the design of novel materials to serve as these catalysts is an important field of research. Three interesting electrocatalysts are investigated via transmission electron microscopy to gain insights on their properties through their structure and composition. One involves a facile, ultrafast, and energy-inexpensive synthesis method to directly grow the active species on the substrate. Another uses a low-energy synthesis technique to modify and improve the layered double hydroxide structure, which is one of the more promising structures in the field. The last involves a core-shell structure that shows excellent potential especially in seawater splitting. On a smaller tier, thermoelectric generators are more immediately assessable and can improve the energy efficiency of existing technologies by converting waste heat into useable electricity. Some of the most promising candidate materials are Mg3Sb2-based compounds. Understanding of charge carrier mobility is critical toward improving the power factor, which is needed to increase the output power density of devices. A precise understanding of the thermally activated mobility seen in these materials has not been achieved. This work investigates this phenomena via a microstructural comparison between samples with variation in their room-temperature conductivities. Interesting results are found involving crystalline bismuth segregations in Mg3.2Sb1.5Bi0.5Te0.01 samples that involve lower temperature synthesis conditions. This result could lead to a better understanding of low temperature mobility in this as well as other similar material systems.