(472b) The Adsorption of CO2 On Anatase TiO2(101) Surfaces in the Presence of Subnano Ag and Pt Clusters: Implications for Promising Photocatalysis

The broad objective of this research is to address two significant challenges facing the planet: reducing Green House Gas emission and the production of sustainable fuels by harnessing solar energy. Photocatalysis is an possible way to use solar energy to convert CO2 to fuels[1]. CO2 to form CO2 anion  is commonly considered as the first and key step of the CO2 photoreduction mechanism, followed by interactions of CO2 anion and H · to form hydrocarbons[1, 2].  Due to the highest reduction potential (vs. NHE) of this step compared to the others[1], the study of it benefit the feasibility of successive steps, improving the generation of clean energy from sunlight. 

The electronic structure of the catalyst surface governs the easiness of the formation of the CO2 anion from CO2; this formation relies on the adsorbed forms of CO2 on the catalyst surface. The angle of the bend form of the adsorbed CO2 determines the barrier to the transfer of photoexcited electrons to CO2 to form  CO2 anion [3-5]. This is attributed to the changing of CO2 LUMO energy as O-C-O bond angle varies[6]. Many researchers have studied the adsorbed forms of CO2 on different TiO2 surfaces and other semiconductor along with the anticipated electron transfers [3, 5, 7, 8]. In recent years, due to the experimental capability, subnano clusters of several atoms are reported to possess dynamic structural fluxionality[9] and a large fraction of under-coordinated surface atoms[10], which grants the reaction enhanced reactivity. To the best of our knowledge, the first principle study of photoreduction considering the incorporation of subnano metal clusters on TiO2 surfaces is lacking. Therefore, one goal of this work is to study the effects of ultrasmall clusters of Ag, Pt deposited on TiO2 on the first and key step of the CO2 photoreduction. Another goal is the understanding of the sub-bandgap introduced by these clusters, which make possible the efficient utilization of the sunlight[11]. Perfect anatase TiO2(101) surface as well as the existence of the oxygen vacancy are studied along with the Ag and Pt octamers. Vienna Ab Initio Simulation package (VASP) is used to investigate the various adsorbed forms of CO2 on the model surfaces. In comparison of with the literature results, the electronic understandings of CO2 at the interface composed of subnano clusters and the conventional photocatalyst, TiO2, are believed to contribute the CO2 photoreduction to shed some light on these new class photocatalysts in the CO2 photoreduction.

The interplay of the electronic structures of the subnano clusters deposited on the anatase TiO2(101) and the CO2 is the focus of this study. We demonstrate how the presence of the subnano clusters on the anatase TiO2(101) influences the CO2 adsorption as well as the density of states of such model. The altered properties of the adsorbed CO2, and new CO2 adsorption sites on the surface of clusters and at interfaces are expected to be found.  These findings give valuable information for the design of more efficient photocatalysts for CO2 photoreduction to generate light hydrocarbon fuels.

References

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