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

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 [Formula: see text] or GCN), an inexpensive geometric descriptor for strained and unstrained transition metals and some alloys. [Formula: see text] 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, [Formula: see text] 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., O(2) reduction, H(2) evolution, CO oxidation, and reduction) are presented, and comparisons are made against other descriptors.