Intensive research into the design of catalysts involved in energy conversion and fuel cell technologies has allowed great progress in the field. However, durable, efficient and selective electrocatalytic systems for the activation of fuel molecules at the lowest cost are still needed. The most developed strategies consist of tailoring the shape, size and composition of metallic nanomaterials. Yet, deliberate surface modification of the catalysts should be considered as a promising alternative approach. The functionalization of metallic catalysts with organic ligands has been recently demonstrated to promote high catalytic activity. This Review focuses on the functionalization of metallic or alloy catalysts with organic ligands, showing the impact of the surface modification for different materials and different reactions. Hybrid systems based on this alternative strategy could contribute to the elaboration of cutting‐edge systems for electrocatalysis.

Selective synthesis of n-propanol from electrocatalytic CO2/CO reduction on copper remains challenging and the impact of the local interfacial effects on the production of n-propanol is not yet fully understood. Here, we investigate the competition between CO and acetaldehyde adsorption and reduction on copper electrodes and how it affects the n-propanol formation. We show that n-propanol formation can be effectively enhanced by modulating the CO partial pressure or acetaldehyde concentration in solution. Upon successive additions of acetaldehyde in CO-saturated phosphate buffer electrolytes, n-propanol formation was increased. Oppositely, n-propanol formation was the most active at lower CO flow rates in a 50 mM acetaldehyde phosphate buffer electrolyte. In a conventional carbon monoxide reduction reaction (CORR) test in KOH, we show that, in the absence of acetaldehyde in solution, an optimum ratio of n-propanol/ethylene formation is found at intermediate CO partial pressure. From these observations, we can assume that the highest n-propanol formation rate from CO2RR is reached when a suitable ratio of CO and acetaldehyde intermediates is adsorbed. An optimum ratio was also found for n-propanol/ethanol formation but with a clear decrease in the formation rate for ethanol at this optimum, while the n-propanol formation rate was the highest. As this trend was not observed for ethylene formation, this finding suggests that adsorbed methylcarbonyl (adsorbed dehydrogenated acetaldehyde) is an intermediate for the formation of ethanol and n-propanol but not for ethylene. Finally, this work may explain why it is challenging to reach high faradaic efficiencies for n-propanol, as CO and the intermediates for n-propanol synthesis (like adsorbed methylcarbonyl) compete for active sites on the surface, where CO adsorption is favored.

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 AuS bonds, [15,16] more recently, AuC (carbene), [17] AuCC (acetylide), [18] or AuC (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...

The grafting of a polyfluorinated calix[4]arene-tetradiazonium derivative on various surfaces led to the formation of very robust and stable hydrophobic monolayers.