Computational Study of Transition-Metal Substitutions in Rutile TiO\(_2\) (110) for Photoelectrocatalytic Ammonia Synthesis

• Published in: arXiv.org 2019-12
• Main Authors: Comer, Benjamin M, Lenk, Max H, Rajanala, Aradhya P, Flynn, Emma L, Medford, Andrew J
• Format: Article
• Language: English
• Subjects: Ammonia; Catalysis; Catalysts; Chemical synthesis; Dopants; Electrocatalysts; Electronic structure; Free energy; Heat of formation; Metals; Nitrogen; Stability analysis; Surface stability; Transition metals; Trends
• ISSN: 2331-8422

Synthesis of ammonia through photo- and electrocatalysis is a rapidly growing field. Titania-based catalysts are widely reported for photocatalytic ammonia synthesis and have also been suggested as electrocatalysts. The addition of transition-metal dopants is one strategy for improving the performance of titania-based catalysts. In this work, we screen d-block transition-metal dopants for surface site stability and evaluate trends in their performance as the active site for the reduction of nitrogen to ammonia on TiO\(_2\). We find a linear relationship between the d-band center and formation energy of the dopant site, while the binding energies of N\(_2\), N\(_2\)H, and NH\(_2\) all are strongly correlated with the cohesive energies of the dopant metals. The activity of the metal-doped systems shows a volcano type relationship with the NH\(_2\) and N\(_2\)H energies as descriptors. Some metals such as Co, Mo, and V are predicted to slightly improve photo- and electrocatalytic performance, but most metals inhibit the ammonia synthesis reaction. The results provide insight into the role of transition-metal dopants for promoting ammonia synthesis, and the trends are based on unexpected electronic structure factors that may have broader implications for single-atom catalysis and doped oxides.