The ABC of Generalized Coordination Numbers and Their Use as a Descriptor in Electrocatalysis

Abstract

The quest for enhanced electrocatalysts can be boosted by descriptor-based analyses. Because adsorption energies are the most common descriptors, electrocatalyst design is largely based on brute-force routines that comb materials databases until an energetic criterion is verified. In this review, it is shown that an alternative is provided by generalized coordination numbers (denoted by $\overline{\mathrm{CN}}$ or GCN), an inexpensive geometric descriptor for strained and unstrained transition metals and some alloys. $\overline{\mathrm{CN}}$ captures trends in adsorption energies on both extended surfaces and nanoparticles and is used to elaborate structure-sensitive electrocatalytic activity plots and selectivity maps. Importantly, $\overline{\mathrm{CN}}$ outlines the geometric configuration of the active sites, thereby enabling an atom-by-atom design, which is not possible using energetic descriptors. Specific examples for various adsorbates (e.g., *OH, *OOH, *CO, and *H), metals (e.g., Pt and Cu), and electrocatalytic reactions (e.g., O₂ reduction, H₂ evolution, CO oxidation, and reduction) are presented, and comparisons are made against other descriptors.

Keywords: computational electrocatalysis; coordination numbers; coordination-activity plots; descriptor-based analysis; selectivity maps; structural sensitivity.