blocking an important proportion of their active sites and deactivating the catalysts. The removal of ligands from the nanoparticles surface without altering the specific structure that rules their catalytic function, is a major challenge. [5-7] Interestingly, organic ligands are commonly designed and employed in homogeneous catalysis to steer the activity and selectivity of metal centers. [8,9] The presence of organic ligands allows better control of selectivity. In line with this concept, the chemical surface modification of metallic nanostructures has just emerged as a promising strategy to increase their catalytic performances as recently reviewed. [10] Recent reports have highlighted that organic functionalization of metallic nanoparticles can boost their electrocatalytic properties through local interfacial steric or electronic effects. [11,12] Far from having a detrimental impact, the ligands are found to have a beneficial role. The nature of the ligands, [13] and/or the interfacial bonding, [14] promote high electrocatalytic activity, selectivity, and durability. [10] The immobilization of organic molecules to metallic surfaces includes the chemisorption of monomers, polymers or surfactants, the self-assembly, the covalent grafting or the electrostatic adsorption of charged molecules (e.g., citrates, polyelectrolytes). The strength of interaction between surface and ligands depends on the employed procedures. Whereas thiol molecules are known for decades to efficiently bind gold nanoparticles (AuNPs) via AuS bonds, [15,16] more recently, AuC (carbene), [17] AuCC (acetylide), [18] or AuC (through aryl diazonium salts reduction), [19] provide robust interfacial bonds with strong metal-ligands interactions. The aryldiazonium reduction leads to strong interaction between the metallic surfaces and the aryl moieties, with adsorption energies over 200 kJ mol −1. [20] In contrast, electrostatic adsorption, involved for instance in citrate-stabilized gold nanoparticles corresponds to a weaker interaction with binding energy lower than 85 kJ mol −1. [21] We have recently developed a unique strategy to prepare dense and compact monolayers on a wide range of materials including nanomaterials thanks to the reductive grafting of calix[4]arene-tetradiazonium salts. [22,23] The calix[4]arene-tetradiazonium cation exhibits a cone-constrained structure made up of four aromatic units linked by methylene bridges, allowing The deliberate surface modification of nanocatalysts with organic ligands has recently emerged as a promising strategy to boost their efficiency, durability, and/or selectivity in key electrocatalytic processes. The interface between the metallic interface and the immobilized ligands promotes high electrocatalytic activity. Herein, the oxygen reduction reaction activity of gold nanoparticles functionalized with a covalently bound monolayer of calix[4]arenes is compared with commercially available gold nanoparticles, classically stabilized through electrostatic adsorption of citrates onto the gold surfa...