Ceria (CeO2) and titanium oxide (TiO2) are two prominent compounds used in the splitting of hydrogen gas for catalysis or producing hydrogen fuel. This ability is dependent on surface termination, whose electrostatic potential might orient the molecules towards reactive sites determining their reactivity. The goal is to characterize optimal geometries and the position and strength of prospective reaction points (maxima/minima of the electrostatic potential above the surface) to ultimately identify sites for hydrogen dissociation. In this study, five ceria terminations, eight titanium oxide terminations from anatase and rutile, and three titanium clusters have been investigated. To do this, VASP was used to determine the electrostatic potential and charge density for the geometry optimized substrate (slab or cluster), and VESTA was employed as a visualization tool, that combined both values from VASP to map an accurate and proportional electrostatic potential for the different surfaces. Both ceria {110} and the n=6 cluster of titanium had notably high electropositive and electronegative values across the surface, indicating a potential ability to attract and dissociate hydrogen. However, several of the rutile titanium oxide surfaces showed very low values despite their prominent oxygen atoms across and within the upper surface layers. Furthermore, titanium was found to be more electropositive than cerium, counter to what was expected based on their electronic configurations. More calculations taking other variables into account (such as orbital interactions), energetics of adsorption, and experimental data are needed to answer the unknowns about titanium oxide and confirm the results.

Using theoretical electrostatic potentials in CeO2 and TiO2 to predict reactivity for molecular adsorption

ACS Spring 2022

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