Charles Cougnon

In Situ Formation of Diazonium Salts from Nitro Precursors for Scanning Electrochemical Microscopy Patterning of Surfaces

Give me a tip: In situ production of diazonium salts from nitro compounds allows the use of diazonium chemistry for microelectrochemical patterning of surfaces by scanning electrochemical microscopy. The nitro precursor is reduced at the tip to the amine, which is diazotized in the interelectrode space as it diffuses (see picture). The tip acts as a source of diazonium salts, allowing sample derivatization just beneath the tip.

Catechol-Modified Activated Carbon Prepared by the Diazonium Chemistry for Application as Active Electrode Material in Electrochemical Capacitor

Activated carbon (Black Pearls 2000) modified with electroactive catechol groups was evaluated for charge storage application as active composite electrode material in an aqueous electrochemical capacitor. High surface area Black Pearls 2000 carbon was functionalized by introduction of catechol groups by spontaneous reduction of catechol diazonium ions in situ prepared in aqueous solution from the corresponding amine. Change in the specific surface area and pore texture of the carbon following grafting was monitored by nitrogen gas adsorption measurements. The electrochemical properties and the chemical composition of the catechol-modified carbon electrodes were investigated by cyclic voltammetry. Such carbon-modified electrode combines well the faradaic capacitance, originating from the redox activity of the surface immobilized catechol groups, to the electrochemical double layer capacitance of the high surface area Black Pearls carbon. Due to the faradaic contribution, the catechol-modified electrode exhibits a higher specific capacitance (250 F/g) than pristine carbon (150 F/g) over a potential range of -0.4 to 0.75 V in 1 M H(2)SO(4). The stability of the modified electrode evaluated by long-time charge/discharge cycling revealed a low decrease of the capacitance of the catechol-modified carbon due to the loss of the catechol redox activity. Nonetheless, it was demonstrated that the benefit of redox groups persists for 10, 000 constant current charge/discharge cycles.

Patterning of Surfaces by Oxidation of Amine-Containing Compounds Using Scanning Electrochemical Microscopy

The microstructuring of surfaces with organic moieties is important for the development of new analytical tools, but the production of such surfaces by conventional photolithographic procedures remains challenging. Scanning electrochemical microscopy (SECM) has recently emerged as a viable patterning alternative because it can be used both for production and imaging of microand nanopatterned surfaces. SECM patterning of surfaces can occur either in the direct mode or by using the tip as a source of reactive species. 5] The first approach relies on the use of the SECM tip as a microscopic auxiliary electrode, which constrains the current lines near the sample that acts as a working electrode. The faradaic current that flows through the tip-to-sample gap induces an electrochemical reaction, which is restricted to a localized volume beneath the tip. In the second approach, the reactive species are locally electrogenerated at the SECM tip. As the reactive species diffuse to the sample, the species can be either regenerated after modification (feedback mode SECM) or consumed (tip-generation/sample-collection mode; TG/SC SECM). Free-radical grafting methods constitute the more flexible and versatile procedure for direct introduction of organic and biological moieties in order to achieve the permanent derivatization of surfaces. The two main strategies consist of the electrochemical reduction of diazonium salts or oxidation of amine-containing compounds. Nevertheless, free-radical grafting is not amenable to writing procedures since the spontaneous derivatization of the entire surface exposed renders the direct micropatterning of surfaces impossible. We recently reported a new procedure that circumvents this problem, and demonstrated the utility of diazonium salts for surface microstructuring (Figure 1 a). This strategy is ideally suited for the writing of single organic micropatterns, but is less adapted for the production of complex organic microstructures because of rapid passivation of the SECM tip. This problem occurs as the diazonium

In situ redox functionalization of composite electrodes for high power-high energy electrochemical storage systems via a non-covalent approach

The growing demand for new global resources of clean and sustainable energy emerges as the greatest challenge in todays society. For numerous applications such as hybrid vehicles, electrochemical storage systems simultaneously require high energy and high power. For this reason, intensive researches focus on proposing alternative devices to conventional Li battery and supercapacitors. Here, we report a proof of concept based on non-covalent redox functionalization of composite electrodes that may occur either during the calendar life or during the device functioning. The active material, a multi-redox pyrene derivative, is initially contained in the electrolyte. No additional benchmarking step is therefore required, and it can, in principle, be readily applied to any type of composite electrode (supercapacitors, battery, semi-solid flow celletc.). Accordingly, a practical carbon fiber electrode that is 10 mg cm−2 loaded can deliver up to 130 kW kgelectrode−1 and 130 Wh kgelectrode−1 with negligible capacity loss over the first 60 000 charge/discharge cycles.

Development of a Phase-Controlled Constant-Distance Scanning Electrochemical Microscope

The present shear-force constant-distance scanning electrochemical microscope regulates tip-to-substrate distance using a phase-controlled feedback mechanism that is more sensitive than the amplitude-controlled constant-distance scanning electrochemical microscopes. Phase control responds faster to frequency perturbation and presents enhance sensitivity during distance curves under constant-distance mode.

Electrochemistry and reactivity of surface-confined catechol groups derived from diazonium reduction. Bias-assisted Michael addition at the solid/liquid interface.

We have designed a novel catechol-modified electrode that could be used for bias-assisted Michael addition at the solid/liquid interface. The glassy carbon electrode was modified by the electrochemical reduction of a catechol para-substituted phenyldiazonium salt. The electrochemistry of surface-confined catechol moieties was investigated by cyclic voltammetry. The transfer coefficient and apparent surface standard electron-transfer rate constant were obtained using Lavirons theory. We demonstrate that o-quinone moieties linked to the surface remain quite reactive with nucleophilic species by Michael addition at the solid/liquid interface. To demonstrate the versatility of this procedure, 4-nitrobenzyl alcohol, (4-nitrobenzyl)amine, and a ferrocenealkylamine were chosen as nucleophile models due to their well-known redox properties. Electrochemically triggered Michael addition was validated, leading to redox headgroup-tethered surfaces.

Toward fully organic rechargeable charge storage devices based on carbon electrodes grafted with redox molecules

Activated carbon powders modified with naphthalimide and 2,2,6,6-tetramethylpiperidine-N-oxyl were assembled into a hybrid electrochemical capacitor containing an organic electrolyte. The fully organic rechargeable system demonstrated an increase in specific capacitance up to 51%, an extended operating voltage of 2.9 V in propylene carbonate, compared to 1.9 V for the unmodified system, and a power 2.5 times higher.

Modification of activated carbons based on diazonium ionsin situ produced from aminobenzene organic acid without addition of other acid

Activated carbon products modified with a benzene sulfonic acid group were prepared based on the spontaneous reduction of diazonium salts in situ generated in water without addition of an external acid. The diazotization reaction assisted by the organic acid substituent, produced at once amine, diazonium and triazene functionalities that maximize the grafting yield by a chemical cooperation effect.

A Redox‐Active Binder for Electrochemical Capacitor Electrodes

A promising strategy for increasing the performance of supercapacitors is proposed. Until now, a popular strategy for increasing the specific capacity of the electrode consists of grafting redox molecules onto a high surface area carbon structure to add a faradaic contribution to the charge storage. Unfortunately, the grafting of molecules to the carbon surface leads to a dramatic decrease of the electrochemical performances of the composite material. Herein, we used the organic binder as an active material in the charge/discharge process. Redox molecules were attached onto its polymeric skeleton to obtain a redox binder with the dual functionalities of both the binder and the active material. In this way, the electrochemical performance was improved without detrimentally affecting the properties of the porous carbon. Results showed that the use of a redox binder is promising for enhancing both energy and power densities.

A facile route to steady redox-modulated nitroxide spin-labeled surfaces based on diazonium chemistry

A TEMPO derivative was covalently grafted onto carbon and gold surfaces via the diazonium chemistry. The acid-dependent redox properties of the nitroxyl group were exploited to elaborate electro-switchable magnetic surfaces. ESR characterization demonstrated the reversible and permanent magnetic character of the material.