An organic monolayer is obtained on Cu, Au, and SiH by electrografting 3,5-bis-tert-butyl benzenediazonium tetrafluoroborate, as evidenced by cyclic voltammetry, IR-ATR, and ellipsometry. This results from the bulky groups at the 3,5-positions that sterically hinder the growth of the layer.

It is possible to form micrometer thick polyphenylene (PP) films by electrochemical reduction of benzenediazonium tetrafluoroborate on metals in acetonitrile. The electrochemical behavior of the PP film is characterized by different electrochemical transient methods and is surprisingly different from that observed with other diazonium salts. The films are analyzed by IR and time-of-flight secondary ion mass spectroscopies; their thickness and conductivity are also characterized. Because they are conductive, these micrometer thick films can be further derivatized by electrochemical reduction of other diazonium salts, for example, nitrophenyl or bromophenyl diazonium salts. Copper can also be deposited on the top of the PP film. The behavior of redox probes on PP films is discussed as well as the origin of this increased conductivity. A simple model for the reaction kinetics of electrografting is presented.

The chemical grafting of iron surfaces at open-circuit potential by reduction of different aryldiazonium salts in aqueous acidic solution occurs spontaneously without the need of electrochemical assistance. X-ray photoelectron spectroscopy (XPS) and IR allowed to evidence the grafting of organic moieties without any adsorption of diazonium salts. The aryl groups are strongly bonded to the metal since they can withstand sonication in acetone. XPS measurements also show that spontaneous grafting in water is at least as efficient as electrochemical grafting and also indicate the presence of a multiphenyl layer coverage of the iron surface. The surface film of carboxyphenyl groups on iron was chemically derivatized further by octyltriethoxysilane. The anticorrosive effects of the different films were evaluated in 0.01 M H 2 SO 4 aqueous solution, by polarization and impedance measurements. Grafting of the diazonium salt results in an inhibition efficiency up to 73%, which can be slightly increased up to 85% by derivatization of the film by octyltriethoxysilane. The inhibition efficiency can be significantly improved up to 97% when the grafted metal is left in the corrosion medium in the presence of the diazonium salt.

Steric effects are investigated in the reaction of aryl radicals with surfaces. The electrochemical reduction of 2-, 3-, 4-methyl, 2-methoxy, 2-ethyl, 2,6-, 2,4-, and 3,5-dimethyl, 4-tert-butyl, 3,5-bis-tert-butyl benzenediazonium, 3,5-bis(trifluoromethyl), and pentafluoro benzenediazonium tetrafluoroborates is examined in acetonitrile solutions. It leads to the formation of grafted layers only if the steric hindrance at the 2- or 2,6-position(s) is small. When the 3,5-positions are crowded with tert-butyl groups, the growth of the organic layer is limited by steric effects and a monolayer is formed. The efficiency of the grafting process is assessed by cyclic voltammetry, X-ray photoelectron spectroscopy, infrared, and ellipsometry. These experiments, together with density functional computations of bonding energies of substituted phenyl groups on a copper surface, are discussed in terms of the reactivity of aryl radicals in the electrografting reaction and in the growth of the polyaryl layer.

Electrochemical (EC) impacts of single nanoparticles (NPs) on an ultramicroelectrode are coupled with optics to identify chemical processes at the level of individual NPs. While the EC signals characterize the charge transfer process, the optical monitoring gives a complementary picture of the transport and chemical transformation of the NPs. This is illustrated in the case of electrodissolution of Ag NPs. In the simplest case, the optically monitored dissolution of individual NPs is synchronized with individual EC spikes. Optics then validates in situ the concept of EC nanoimpacts for sizing and counting of NPs. Chemical complexity is introduced by using a precipitating agent, SCN(-), which tunes the overall electrodissolution kinetics. Particularly, the charge transfer and dissolution steps occur sequentially as the synchronicity between the EC and optical signals is lost. This demonstrates the level of complexity that can be revealed from such electrochemistry/optics coupling.

Grafting of aryl layers derived from aryl diazonium salts onto glassy carbon electrodes is observed by time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The grafting occurs spontaneously when a glassy carbon plate is immersed into a solution of aryl diazonium salt and can be enhanced by biasing the carbon plate at a potential a little more negative than the diazonium salt reduction. C-C and C-O covalent bonding are believed to be responsible for the strong attachment of these layers onto the carbon substrate. Fragments containing aryl dimers, trimers, or tetramers are also observed. A mechanism is proposed to account for the formation of these polymeric chains.

Polyoxometalates (POMs) are attractive candidates for the rational design of multi-level charge-storage materials because they display reversible multi-step reduction processes in a narrow range of potentials. The functionalization of POMs allows for their integration in hybrid complementary metal oxide semiconductor (CMOS)/molecular devices, provided that fine control of their immobilisation on various substrates can be achieved. Owing to the wide applicability of the diazonium route to surface modification, a functionalized Keggin-type POM [PW11 O39 {Ge(p-C6 H4 -CC-C6 H4 -${{\rm N}{{+\hfill \atop 2\hfill}}}$)}](3-) bearing a pending diazonium group was prepared and subsequently covalently anchored onto a glassy carbon electrode. Electron transfer with the immobilised POM was thoroughly investigated and compared to that of the free POM in solution.

While numerous efforts are produced towards the design of sustainable and efficient nano-catalysts of hydrogen evolution reaction (HER), there is a need for the operando observation and quantification of gas nanobubbles (NBs) formation involved in this electrochemical reaction. It is achieved herein through interference reflection microscopy (IRM) coupled to electrochemistry and optical modelling. Besides analyzing the geometry and growth rate of individual NBs at single nanocatalysts, the toolbox offered by super-localization and quantitative label-free optical microscopy allows analyzing the geometry (contact angle and footprint with surface) of individual NBs and their growth rate. It turns out that after few seconds, NBs are steadily growing while they are fully covering the Pt NPs that allowed their nucleation and their pinning on the electrode surface. It then raises relevant questions related to gas evolution catalysts as for example: does the evaluation of NB growth at single nano-catalyst really reflect its electrochemical activity? 2