Alternative Mechanistic Considerations: Charactering Multiple Reaction Pathways for the Oxygen Evolution Reaction

Abstract

H2 remains an important chemical precursor in processes such as the Haber-Bosch process to synthesize ammonia and hydrocracking for refining of hydrocarbons and also exists as an alternative fuel for transportation. Currently, 95% of H2 is produced by steam methane reforming, whose byproduct is pollutant CO. Electrolysis is a clean, efficient method run at room temperature to split water into H2and O2. However, electrolysis is not cost-competitive with steam methane reforming, utilizing large amounts of platinum group materials. Computational chemistry can give atomic and electronic levels of understanding of a material by identifying highly active facets of a known material or predicting the catalytic potential of unknown materials. We will model catalysts used in the oxygen evolution reaction, the half-cell reaction requiring the most catalyst and occurring many orders of magnitude slower than the hydrogen evolution reaction. We will focus on the effect of the ensemble: modeling different facets of iridium oxide, characterizing all possible configurations of key reaction intermediates, and incorporating explicit solvation to fully understand the nuances of optimizing a premier catalyst such as IrO2. In particular, we will focus our calculations on two facets: (110), the more thermodynamically stable facet and (001), a potentially more active facet due to the presence of undercoordinated, surface Ir sites. We will compare the reaction profile of the ensemble of key reaction intermediates on the (110) versus the (001) facet and in vacuum versus with solvation. The ensemble of intermediates allows us to explore multiple reaction pathways on the surface that have not been characterized.Figure 1. A schematic summarizing the different isomers found at each reaction step (TOP) and the reaction profile of the oxygen evolution reaction on the (110) facet of iridium oxide (BOTTOM). Figure 1