Electrochemical Engineering for Critical Elements Recovery and Utilization

Today, non-renewable energy sources are still dominating the world's energy consumption. Carbon dioxide emitted from the combustion of fossil fuels has caused the greenhouse effect and raised serious concerns about the inevitable consequences to the atmosphere, ocean, and all living creatures. Transportation counts as one of the largest sectors of carbon emissions; therefore, finding an alternative solution to replace the current internal combustion engine has become imperative for a sustainable future. Electrochemical energy conversion devices such as Lithium-ion batteries and fuel cells are the most promising options. However, their massive application was hindered by the high cost and resource limitations of several critical elements, for example, lithium in LIB and platinum for PEMFC. This dissertation aims to investigate the electrochemical systems that potentially improve the recovery and utilization of these critical elements. An electrochemical system employing a solid-state electrolyte membrane was investigated for continuous lithium extraction from brine and seawater. The system exhibited 95.7% total energy efficiency and nearly 100% selectivity to extract over 200 μg·cm-2h-1 lithium from artificial brines or seawater from the Inner Habor of Baltimore. The system also demonstrates good profitability; when operating at 0.25 mA·cm-2, the average price of produced LiOH is estimated to be $19.8/kg. Additionally, two kinds of nanomaterials with carefully designed compositions, morphologies, and structures were developed for the fuel cell's cathode reaction, oxygen reduction reaction (ORR). Core-shell electrocatalysts with low platinum-group metal content and tunable surface strains were investigated; a platinum-based multi-principal element alloy (MPEA) electrocatalyst was also developed. Both catalysts exhibited significant enhancement of ORR activity compared to commercial Pt catalysts. The design and synthetic approach of these two kinds of nanostructures as electrocatalysts for ORR reveal their structure-property-performance relationships that can be used to guide the improvement and optimization of the activity and stability of electrocatalysts in the future