Joakim Halldin Stenlid

Chemical bonding at metal surfaces is central to reactivity, but how does this concept evolve under realistic operating conditions? Surface reactivity is often rationalized using chemisorption models and electronic-structure descriptors, such as d-band theory, which implicitly assume well-defined interactions between adsorbates and electronically homogeneous surfaces. In this talk, I argue that such a picture is inherently incomplete and examine surface bonding from a spatially resolved perspective using the electrostatic potential, V(r), as a descriptor. The subatomic resolution of V(r) reveals that even ideal metal sites exhibit pronounced directionality, confinement, and local Lewis acidity and basicity, giving rise to weak interactions that blur the distinction between chemisorption and noncovalent bonding. Alloying, adsorbate-dependent interactions, and local coordination further challenge universal scaling relations, revealing surface bonding as intrinsically context-dependent. At the same time, these effects do not preclude the identification of useful descriptors but rather indicate that capturing reactivity requires sampling a broader configurational and environmental space and incorporating additional physical contributions into extended, yet still interpretable, descriptors. These effects are illustrated for reactions such as CO2 electroreduction, where interfacial structure and adsorbate environment critically influence reactivity. At electrified interfaces, this complexity becomes unavoidable: solvation, interfacial electric fields, and potential-controlled charge redistribution render bonding dynamic and environment-defined. Rather than replacing existing models, these observations invite us to reconsider how bonding concepts are applied across catalysis, electrochemistry, and functional materials under realistic conditions.