Theoretical Investigation of Photo-Electro-Catalysis Beyond Proton-Coupled Electron Transfer
Final Report Abstract
Photo- and electro-chemical processes play a central role in a diverse number of sectors, ranging from the sustainable conversion of solar to chemical energy to the storage of energy in batteries. In the past such processes had often been studies with simplified models and methods of potentially insufficient accuracy. In the research project “Theoretical Investigation of Photo-Electro-Catalysis Beyond Proton-Coupled Electron Transfer” we derived and improved a number of computational methods allowing us to study more complex influences on these reactions. We presented a highly efficient way to treat solvation effects in water and other solvents through so called implicit solvation models, where solvent regions are treated as a polarizable continuum. Together with our experimental partners we collected a database of reference solvation energies called SolvTUM which allowed us to demonstrate the efficacy of our methods. Along similar lines, we also significantly improved the method of solid-state embedding, where e.g. on a surface only parts of that surface are treated fully quantum mechanically, while other parts are simulated through less computationally demanding methods. We derived a new paradigm for the design of the shape of the quantum mechanically treated parts of the system, based on shape and symmetry of the chemically relevant edges of valence and conduction bands. We also conducted a detailed analysis of the highly popular DFT+U method, which—if used correctly—can give access to very accurate electronic structures of complex systems, yet at quite low computational costs. Surprisingly, we found the common of of this method as a kind of “black-box” approach, where one simply takes a value for the necessary parameter U from literature, to be far from the truth. This is due to the strong influence of the so called projector functions, which vary between implementation which turns out to make the U parameter not transferable between codes. This insight allowed us to improve the method by employing highly efficient numeric atomic orbitals as projector functions and use DFT+U to achieve a physically meaningful localization of charges in the studied oxide materials. Finally, based on our methodological advances, we were able to solve a heretofore not understood riddle of the popular battery material Lithium Titanium Oxide (LTO). We found that the increase of electronic conductivity observed on reduction of the material—i.e. introduction of Oxygen vacancies—is due to the formation of small polarons, electrons that are localized due to deformations of the surrounding lattice. We found these polarons to be quite mobile, especially near the vacancy sites, paving the way towards a possible defect nano-engineering of the material.
Publications
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“Efficient Implicit Solvation Method for Full Potential DFT ”, J. Chem. Theory Comput. 13, 5582 (2017)
M. Sinstein, C. Scheurer, S. Matera, V. Blum, K. Reuter, and H. Oberhofer
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“Generalized Molecular Solvation in Non-Aqueous Solutions by a Single Parameter Implicit Solvation Scheme”, J. Chem. Phys. 150, 041710 (2019)
C. Hille, S. Ringe, M. Deimel, C. Kunkel, W. E. Acree, K. Reuter, and H. Oberhofer
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“Intricacies of DFT+U, Not Only in a Numeric Atom Centered Orbital Framework ”, J. Chem. Theory Comput. 15, 1705 (2019)
M. Kick, K. Reuter, and H. Oberhofer
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“Towards a Transferable Design of Solid-state Embedding Models on the Example of a Rutile TiO2 (110) Surface”, J. Chem. Phys. 151, 184114 (2019)
M. Kick and H. Oberhofer
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“Electrocatalysis beyond the Computational Hydrogen Electrode”, in Handbook of Materials Modeling: Applications: Current and Emerging Materials (Springer, 2020), pp. 1–33
H. Oberhofer
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“Mobile Small Polarons Qualitatively Explain Conductivity in Lithium Titanium Oxide Battery Electrodes”, J. Phys. Chem. Lett., 2535 (2020)
M. Kick, C. Grosu, M. Schuderer, C. Scheurer, and H. Oberhofer
