Electrowetting on conductors: Anatomy of the phenomenon

We have recently reported that reversible electrowetting can be observed on the basal plane of graphite, without the presence of a dielectric layer, in both liquid/air and liquid/liquid configurations. The influence of carbon structure on the wetting phenomenon is investigated in more detail here. Specifically, it is shown that the adsorption of adventitious impurities on the graphite surface markedly suppresses the electrowetting response. Similarly, the use of pyrolysed carbon films, although exhibiting a roughness below the threshold previously identified as the barrier to wetting on basal plane graphite, does not give a noticeable electrowetting response, which leads us to conclude that specific interactions at the water–graphite interface as well as graphite crystallinity are responsible for the reversible response seen in the latter case. Preliminary experiments on mechanically exfoliated and chemical vapour deposition grown graphene are also reported.</p

Boron-doped diamond dual-plate deep-microtrench device for generator-collector sulfide sensing

International audienceA BDD-BDD dual-plate microtrench electrode with 6 μm inter-electrode spacing is investigated using generator-collector electrochemistry and shown to give microtrench depth-dependent sulfide detection down to the μM levels. The effect of the microtrench depth is compared for a “shallow” 44 μm and a “deep” 180 μm microtrench and linked to the reduction of oxygen to hydrogen peroxide which interferes with sulfide redox cycling. With a deeper microtrench and a fixed collector potential at −1.4 V vs. SCE, two distinct redox cycling potential domains are observed at 0.0 V vs. SCE (2-electron) and at 1.1 V vs. SCE (6-electron)

Oxidative IR Spectroelectrochemistry of Copper in Methanol Containing Carbon Monoxide

IR spectroelectrochemistry was used to examine the electro-oxidation behavior of carbon monoxide in methanol at a polycrystalline copper electrode. Under such neutral conditions copper electrodes are coated with ill-defined copper oxides and hydroxides and at the oxidative potentials can be expected to generate soluble copper species. The electrochemistry displayed complex behavior suggesting that methanol oxidation was one prominent reaction. However, the spectroscopy revealed that very little methanol oxidation had occurred and that carbon monoxide was not adsorbed to the copper electrode. Instead, the electro-oxidation generated an intense IR band at 2107 cm^–1 that was attributed to a soluble [Cu­(I)­CO]⁺ species

Electrografting of 4-Nitrobenzenediazonium Ion at Carbon Electrodes: Catalyzed and Uncatalyzed Reduction Processes

International audienceCyclic voltammograms for the reduction of aryldiazonium ions at glassy carbon electrodes are often, but not always, reported to show two peaks. The origin of this intriguing behavior remains controversial. Using 4-nitrobenzenediazonium ion (NBD), the most widely studied aryldiazonium salt, we make a detailed examination of the electroreduction processes in acetonitrile solution. We confirm that deposition of film can occur during both reduction processes. Film thickness measurements using atomic force microscopy reveal that multilayer films of very similar thickness are formed when reduction is carried out at either peak, even though the film formed at the more negative potential is significantly more blocking to solution redox probes. These and other aspects of the electrochemistry are consistent with the operation of a surface-catalyzed reduction step (proceeding at a clean surface only) followed by an uncatalyzed reduction at a more negative potential. The catalyzed reduction proceeds at both edge-plane and basal-plane graphite materials, suggesting that particular carbon surface sites are not required. The unusual aspect of aryldiazonium ion electrochemistry is that unlike other surface-catalyzed reactions, both processes are seen in a single voltammetric scan at an initially clean electrode because the conditions for observing the uncatalyzed reaction are produced by film deposition during the first catalyzed reduction step.[on SciFinder (R)