Poster NECS

Poster for NECS Fall 2017
Metal oxide defects of photocatalysts
Junbo Chen
12/08/2017

Transcript

1. Cu is stable at oxygen vacancy (Ov ) Photocatalyst surface defects, and why References Acknowledgement Conclusion Effect of Defects on Metal Cluster/Metal Oxide Photocatalysts for CO2 Photoreduction Junbo Chen, Satish Kumar Iyemperumal, N. Aaron Deskins Department of Chemical Engineering Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts, USA Oxygen vacancy (Ov ) further promotes bent CO2 formation Method: PBE+D3+U can correct electron delocalization by DFT e- (1) Liu, C.; Iyemperumal, S. K.; Deskins, N. A.; Li, G. Photocatalytic CO2 Reduction by Highly Dispersed Cu Sites on TiO2. Journal of Photonics for Energy 2016, 7 (1), 012004–012004. (2) He, H.; Zapol, P.; Curtiss, L. A. A Theoretical Study of CO2 Anions on Anatase (101) Surface. J. Phys. Chem. C 2010, 114 (49), 21474–21481. (3) Kumar Iyemperumal, S.; Aaron Deskins, N. Activation of CO 2 by Supported Cu Clusters. Physical Chemistry Chemical Physics 2017, 19 (42), 28788–28807. (4) Chang, X.; Wang, T.; Gong, J. CO2 Photo-Reduction: Insights into CO2 Activation and Reaction on Surfaces of Photocatalysts. Energy Environ. Sci. 2016, 9 (7), 2177–2196. (5) He, H.; Zapol, P.; Curtiss, L. A. Computational Screening of Dopants for Photocatalytic Two-Electron Reduction of CO2 on Anatase (101) Surfaces. Energy Environ. Sci. 2012, 5 (3), 6196–6205. • Activating CO2 to a bent structure is considered the first step in the CO2 reduction process.2 • We have shown both experimentally and computationally how small atoms or clusters of Cu on TiO2 may activate CO2 .3 • But surface defects have yet to be studied extensively. • Surface defects not only exist in experiments, but also alter the electronic properties in a different yet beneficial way, if we have a better understanding of the surface defects. • The calculations were performed for geometry optimization with periodic DFT code CP2K. • The bottom layer of the slab was freeze to mimic surface interaction, as agreed to the literature. • DFT-D3 was applied to account for vdW dispersion. • +U was examined to account for electron delocalization. • Cu at Ov exhibited stable adsorption to both stoichiometric and defective TiO2 . • Cu was negatively charged at defective surface, which allowed further charge transfer. • CO2 binded strongly to oxygen vacancy (Ov ) site. The most stable bent CO2 adsorbed in optimized geometry (e). • At stoichiometric surfaces (geometry a and c) CO2 was significantly less stable than CO2 interacting with Ov and Cu/Ov . Oxygen vacancy (Ov ) effectively converts CO2 from linear to bent form Photoexcited electron enhances the adsorption of bent CO2 Bent CO2 is more stable than linear CO2 in the presence of Ov . CO2 became negatively charged as surface charges transferred to form bent CO2 . The authors would like to thank WPI’s Academic and Research Computing (ARC) for providing generous CPU hours on Turing and Ace clusters; NSF’s XSEDE on TACC’s Stampede and Stampede2 for computing hours. Also special thanks to Dr. Spencer Pruitt for providing HPC supports. Linear CO2 optimized geometry, with Cu adsorbed near oxygen vacancy. * Density Derived Electrostatic and Chemical (DDEC), a method to partition and calculate net atomic charge (NAC). Hydrogen was placed far from the Ov site to avoid any interaction with the adsorbate. Hydrogen was only intended as an electron donor to the system.5 • Oxygen vacancy on TiO2 anatase (101) surface has shown significant improvement on bent CO2 formation. • This result aligns to the one e- charge transfer to CO2 that is critical to the activation of CO2 reduction process. • In the future we will investigate the dissociation/hydrogenation of CO2, thus might shed some light on the mechanisms of full CO2 photoreduction cycle. This TiO2 slab on the left we used in our calculations consists of a 4 x 2 unit cell in tri-layer, with a total number of 288 atoms in stoichiometric TiO2 , 287 in defective TiO2 .