A first principles computational study of ZnO/PbTiO₃ as a tunable catalyst for CO₂ conversion

Abstract

Due to its role in climate change, there is great interest in finding ways to take advantage of the vast amount of waste CO₂ we produce by its conversion to useful substances. This approach is currently impractical due to the high temperatures and pressures generally required for the synthesis of compounds using CO₂ as a precursor. To make direct CO₂ capture and conversion economically viable, new materials able to catalyze the conversion reactions at significantly milder conditions will be essential. In this thesis, we use DFT computations to begin the design of a dynamically tunable ferroelectric oxide-supported thin film catalyst that can capture CO₂ directly from the emission stream and convert it into methanol or cyclic carbonates. Promising candidates for a dynamically tunable catalyst of this type are the different combinations of ZnO directions grown on the perovskite PbTiO₃. For the non-polar ZnO(112̄0) grown on the perovskite, we demonstrate that the surface chemistry is dependent on both the polarization direction of the PbTiO₃ substrate and on the number of ZnO(112̄0) layers n. Growing the ZnO in the (0001) direction on the perovskite showed even more interesting results. We found that this process is sufficient to obtain a ZnO ferroelectric and is superior to previous attempts to make ferroelectric phase changes possible in the oxide, namely Li-doping. We demonstrate that switching the polarization direction of the perovskite substrate is sufficient to switch the polarity at the ZnO surface. This is an excellent basis for a dynamically tunable catalyst.