Computational discovery of novel Ln 2 M 2 O 5 Ch 2 materials for photocatalytic water splitting Katarina Brlec 1,2 , Joe Willis 1,2 , David O Scanlon 1,2 1 Department of Chemistry, University College London, 20 Gordon Street, London, UK, 2 Thomas Young Centre, University College London, ower Street, London, UK Worldwide, 96% of all hydrogen is produced from fossil fuels in steam methane reforming or coal gasification processes, leading to large greenhouse gas emissions. [1] In addition to fossil fuels, another major source of hydrogen on Earth is water. Hydrogen can be sustainably produced using photocatalytic water splitting – a biomimicry of photosynthesis. TiO 2 and other d 0 oxides have been extensively studied over the last 50 years, however their electronic band structure with low-lying oxygen-dominated valence band prevents efficient hydrogen evolution photocatalysis. [2] Mixed anion systems (ON, OX, OCh systems) opened a new paradigm in the search for better photocatalysts, as the second anion can be engineered to have a higher-lying p orbital to optimise the band edge positions for water redox. A series of Ln 2 Ti 2 O 5 S 2 (Ln=Y, Sm, Gd, Tb) compounds exhibited visible-light photocatalytic water splitting, with Y 2 Ti 2 O 5 S 2 showing simultaneous oxygen and hydrogen evolution.[3,4] In this work we explore the 26 previously unknown members of the Ln 2 M 2 O 5 Ch 2 (Ln = Sc, Y, La; M = Ti, Zr, Hf; Ch = S, Se, Te) series using state-of-the-art density functional theory (DFT). In total, 289 competing phases of the entire Ln-M-O-Ch chemical space were evaluated at hybrid-DFT level to accurately determine the thermodynamic stability of the proposed materials. Phononic stability of the systems was confirmed using the supercell lattice dynamics approach, with any instabilities mapped out to obtain the true ground state structure. Finally, the relevant optoelectronic properties and bulk band alignments were calculated at hybrid-DFT level to assess the suitability of materials for photocatalytic applications. References 1. P. Nikolaidis and A. Poullikkas, Renewable and Sustainable Energy Reviews, 2017, 67, 597–611. 2. Z. Wang, C. Li and K. Domen Chem. Soc. Rev., 2019, 48, 2109 3. A. Ishikawa, T. Takata, T. Matsumura, J. N. Kondo, M. Hara, H. Kobayashi and K. Domen, The Journal of Physical Chemistry B, 2004, 108, 2637–2642. 4. Q. Wang, M. Nakabayashi, T. Hisatomi, S. Sun, S. Akiyama, Z. Wang, Z. Pan, X. Xiao, T. Watanabe, T. Yamada, N. Shibata, T. Takata and K. Domen, Nat. Mater., 2019, 18, 827–832.
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