Analysis of Photocatalytic Nitrogen Fixation on Rutile TiO$_2$(110)

TL;DR

This study uses computational methods to analyze photocatalytic nitrogen fixation on rutile TiO₂(110), revealing that the surface is unlikely to facilitate nitrogen reduction but may support oxidative pathways, challenging previous assumptions.

Contribution

First computational analysis of photocatalytic nitrogen fixation on rutile TiO₂(110), providing insights into its limited role in nitrogen reduction and potential oxidative pathways.

Findings

Nitrogen reduction on rutile (110) is thermodynamically unfavorable.

Oxidation pathways on rutile (110) are thermodynamically feasible.

Results challenge previous experimental hypotheses about rutile TiO₂'s role in nitrogen fixation.

Abstract

Photocatalytic nitrogen fixation provides a promising route to produce reactive nitrogen compounds at benign conditions. Titania has been reported as an active photocatalyst for reduction of dinitrogen to ammonia; however there is little fundamental understanding of how this process occurs. In this work the rutile (110) model surface is hypothesized to be the active site, and a computational model based on the Bayesian error estimation functional (BEEF-vdW) and computational hydrogen electrode is applied in order to analyze the expected dinitrogen coverage at the surface as well as the overpotentials for electrochemical reduction and oxidation. This is the first application of computational techniques to photocatalytic nitrogen fixation, and the results indicate that the thermodynamic limiting potential for nitrogen reduction on rutile (110) is considerably higher than the conduction band edge of rutile TiO$_2$, even at oxygen vacancies and iron substitutions. This work provides strong evidence against the most commonly reported experimental hypotheses, and indicates that rutile (110) is unlikely to be the relevant surface for nitrogen reduction. However, the limiting potential for nitrogen oxidation on rutile (110) is significantly lower, indicating that oxidative pathways may be relevant on rutile (110). These findings suggest that photocatalytic dinitrogen fixation may occur via a complex balance of oxidative and reductive processes.