Understanding intermediates adsorption in oxygen reduction/evolution reactions from the local aromaticities of catalyst sites

Abstract

The adsorption behaviors of active sites for various adsorbates in reactions determine the performance of a catalyst, and different surface positions usually exhibit diverse adsorption strengths for the same species. Herein, density functional theory calculations were conducted to study the adsorptions of all oxygen-containing intermediates in oxygen reduction/evolution reactions (ORR/OER) on the surfaces of various graphene-based electrocatalysts with varied heteroatoms and coordination environments. By using the local aromaticity concept, we found a direct correlation between the adsorption strength of a metal/nonmetal site and its NICS(1)ZZ (perpendicular tensor of the nucleus-independent chemical shift at 1 Å above plane) value: positive (antiaromatic) and negative (aromatic) values basically correspond to stronger and weaker adsorptions, respectively. Consistently, the linear relationship between aromatic characteristics and adsorption behavior can be obtained from the magnetic induced ring currents at the surface sites as well. The stronger adsorptions at the antiaromatic sites may because these catalysts always tend to maximumly preserve their global aromaticities and structural stabilities. Our work not only demonstrates that local aromaticity can serve as a useful indicator for predicting/evaluating the adsorption abilities of various catalyst sites, but also provides a novel understanding of the complex heterocatalytic process from the magnetic response properties of catalysts.