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

Abstract

Cyclic 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.

Increasing Applications of Graphite Thermoplastic Electrodes with Aryl Diazonium Grafting

“…The diazonium electroreduction CVs for both carbon types show two peaks at 70 and −250 mV in the first cycle, and then on subsequent cycles, the peaks disappear and the background current is lower (Figure S2). Observation of two reduction peaks during aryl diazonium reduction could be ascribed to catalytic and non‐catalytic reductions on clean GC surfaces . For both TPEs, the Fe(CN) 6 3−/4− redox peaks lose definition and the background appears to become more resistive (Figure b,f), which could be a result of the Fe(CN) 6 3‐/4− interaction with the carboxylic acid groups, which are deprotonated at neutral pH.…”

On the Kinetic and Thermodynamic Properties of Aryl Radicals Using Electrochemical and Theoretical Approaches

“…In either cases all chemistry will take place essentially at the electrode surface. Also, these substances show a strong adsorption tendency which further confine them to a thin reaction layer. Upon the generation of Ar .…”

Reduction of Nitrophenyl Films in Aqueous Solutions: How Many Electrons?

“…Although the ratios of the charges of peak 1 to peaks 2, 3, and 4 in basic conditions are at least twice that expected for a total four‐electron reduction of NP to hydroxyaminophenyl groups, the decrease of the ratio with film thickness suggests that, for sufficiently thick films, the reduction may stop at four electrons. However, it is well‐documented that as film thickness increases, the electroactivity of the film can be compromised such that some NP groups remain redox inactive . Hence, estimating surface coverages from CVs under these conditions may give significant underestimations.…”