Establishing new reactivity map descriptor of TOF–SD for PGM-free Fe–N–C catalysts ORR activity.

International audienc

Electrochemical experiments at individual metal nanoparticles (NPs) can provide new insights into their electrocatalytic behavior. In this Communication, we report the preparation of nanometer-sized carbon electrodes and their use as substrates for the immobilization of single gold NPs (AuNPs). In addition to its very small size, the surface of a carbon nanoelectrode is catalytically inert, which makes it an excellent substrate for studying electrocatalytic reactions. The activity of single AuNPs towards the hydrogen evolution reaction was investigated and compared to that of low-atomicity gold clusters. Three approaches to attaching AuNPs to either chemically modified or bare carbon nanoelectrodes, and the effects of immobilization on hydrogen adsorption and catalytic behavior of AuNPs are discussed. The developed methodology should be useful for studying the effects of NP size, geometry, and surface attachment on the electrocatalytic activity.Metal nanoparticles (NPs) have attracted a great deal of research interest because of their unique physical and chemical properties. They are extensively utilized as catalysts, owing to their high surface-area-to-mass ratio. Understanding the relationship between the size and structure of a NP and its catalytic activity is essential for fundamental advances in electrocatalysis and technological applications. [1][2][3][4][5][6][7] In most published stud-ies, the use of a large ensemble of particles obscures the effects of variations in NP size, shape, orientation, and local environment on the catalytic activity.Different electrochemical strategies have been proposed to perform experiments at single NPs, [3c] most of which focus on monitoring current transients produced by collisions of a metal particle with a micrometer-sized electrode. [8, 9] Xiao and Bard were the first to detect the landing of catalytic NPs on the microelectrode surface. [8a] Compton and co-workers used the particle collision method to determine the size distribution and concentration of NPs by measuring the charge transferred in the current transient. [10] Such experiments provided information about transport processes and collision dynamics rather than electron transfer (ET) or catalytic reactions.To access chemical information at a single metal NP, one can attach it to the surface of a nanometer-sized electrode, which has to be sufficiently small to eliminate the possibility of multi-NP binding. [11] In this way, Zhang and co-workers probed the oxygen reduction reaction and the underpotential deposition of Cu at a gold NP (AuNP) attached to the Pt nanoelectrode. [12] This work also showed the importance of using catalytically inert substrate materials in single NP experiments; although well-shaped steady-state voltammograms and chronoamperometric transients were obtained, it was difficult to differentiate between the currents flowing at the AuNP and the underlying Pt surface.We have previously studied AuNPs attached to glass [13a] and carbon nanopipettes, [13b] but no isolated single particles at...

Electroreduction of diazonium salts is a widely used technique for grafting organic films on various surfaces. In this paper, scanning electrochemical microscopy (SECM) was used for high-resolution characterization of a thiolated aryl multilayer film obtained by electrografting of thiophenol diazonium on highly ordered pyrolytic graphite (HOPG). The blocking properties of the film were evaluated, and the origins of incomplete surface passivation were elucidated by comparing current-distance curves and surface reactivity maps obtained with nanometer- and micrometer-sized tips. In this way, one can distinguish between different pathways of charge transport in the film, e.g., pinhole defects versus rate-limiting charge transfer through the film. Pd nanocubes were anchored to the film by thiol groups and imaged by SECM. The applicability of SECM to in situ visualization of the geometry of non-spherical nanoparticles has been demonstrated.