Partitioning adsorption energy: An electronegativity-based descriptor for hydrogen adsorption on group IV and III-V...

Understanding and predicting hydrogen adsorption energy is key to designing effective electrocatalysts. In this study, we develop a physically interpretable descriptor within a framework that decomposes atomic hydrogen adsorption energy into intuitive contributions, applied to 22 group IV and III-V 2D honeycomb materials. The density functional theory (DFT) calculated adsorption energy is decomposed into two components: bond energy, approximated by the integrated crystal orbital Hamilton population (ICOHP), and the energy cost of forming the additional bond, termed distortion energy Ed. This decomposition facilitates analysis of adsorption trends beyond treating adsorption energy as a single quantity. We find that ICOHP correlates strongly with the adsorption site electronegativity (R2 = 0.86), improving to R2 = 0.91 when electronegativity differences and structural parameters are included. Ed shows moderate correlation with the unrelaxed vacancy energy Evac (R2 = 0.60) and can be accurately modeled (R2 = 0.92) using similar dependences on electronegativity and structural parameters. Notably, Evac can be expressed in terms of the sum of electronegativities, enabling a DFT-free formulation. Combining both components into an Eads descriptor, we achieve an R2 score of 0.82 across both group IV and III-V systems. Further analysis reveals that increasing the adsorption site electronegativity weakens adsorption unless the lattice constant is sufficiently large. In addition, we identify a linear relationship between ICOHP and the zero-point energy change, allowing the descriptor to be extended to the free energy of hydrogen adsorption, a key indicator of hydrogen evolution reaction activity.