Charge Separation in Graded Metal Oxide Nanocomposites

Converting light into chemical and electrical energy offers the opportunity to effectively harvest incoming solar radiation. The photoconversion of CO 2 into technologically relevant short molecules is particularly attractive to recycle the large amounts of CO2 released by our societies. Unfortunately, current materials systems for such photoconversion processes have severe efficiency and selectivity limitations. To develop these concepts into real-world technologies, new materials systems need to be developed. This research program focusses on the synthesis and characterization of a new class of nanocomposites involving chemically reactive alkaline earth oxides (barium oxide and strontium oxide) and titanium dioxide, a well-established photocatalyst. Upon thermal annealing, such composites can transform at least partially into ferroelectric perovskites that are expected to promote charge separation in the presence of light. Fundamental light-induced processes will be investigated to explore ferroelectric contributions to enhance charge separation and photoconversion efficiencies. Two model systems will be studied: (i) Layered nanohole films with controlled porosity, composition, and doping, supported on 2- dimensional substrates - an ideal model system, well-suited for fundamental studies; (ii) Nanoparticle powders with high specific surface areas and tunable densities - a real-life system, quite representative of what the industry could mass-produce. The influence of spontaneous polarization on the surface chemistry and separation of photogenerated charge carriers will be investigated in the metal oxide grains and on the compositionally graded interface layers. We will explore size effects on structure, strain and ferroelectric properties and use microscopy, X- ray diffraction and spectroscopic techniques. Figures of merit for the materials photoactivities will be provided by using complementary test assays. The knowledge acquired during this project will be used to improve the CO2 conversion into added-value chemicals, which is a particularly timely endeavor that could provide a new path to mitigate global warming. This project will contribute to the rational development of photoactive materials for energy conversion and photocatalysis. Moreover, we believe that this work will be highly influential for materials science activities that focus on sensors, piezoelectric energy harvesters and for light induced processes in functional electroceramics.