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

TL;DR

This study uses computational methods to analyze how transition-metal dopants in TiO$_2$ influence its ability to catalyze ammonia synthesis, revealing electronic structure trends and identifying promising dopants.

Contribution

It provides a systematic computational screening of transition-metal dopants in TiO$_2$, uncovering electronic factors affecting catalytic activity and predicting potential improvements.

Findings

Linear relationship between d-band center and dopant formation energy.

Strong correlation between N$_2$, N$_2$H, NH$_2$ binding energies and dopant cohesive energies.

Certain metals like Co, Mo, and V may enhance catalytic performance.

Abstract

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.