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Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) techniques are essentially used for the study of the electroreduction of the two isomers maleic and fumaric acid systems in 0.1 M KCl at 298 K. The measurements are carried out on Pt nanoparticles electrodeposited on glassy carbon electrode (GCE). The modification of the electrode enables the appearance of better resolved peaks of the cyclic voltammograms of the two isomers of the acids in comparison with the poor behavior in absence of the modification. Two well-separated reversible cathodic waves at -0.44 and -0.59 V versus Ag/AgCl are characterizing the electroreduction cyclic voltammogram of maleic acid. The electroreduction of fumaric acid shows only one reversible peak at -0.362 V versus Ag/AgCl is observed. Peak separations and current functions together with other parameters of the electrochemical behavior of both isomers are calculated and discussed. Rate parameters of the anion radicals of both isomers in 0.1 M KCl on immobilized GCE with Pt nanoparticles are obtained and discussed.

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Although the dissolution of copper in nitric acid was the object of numerous investigations, little attention has been paid to the stoichiometry of this reaction. We have found that nitrous acid, HN02, is one of the products, and it plays an important role in the intermediate steps of copper dissolution as well.1 We also found the quantities of HN02 and NO gas produced vary from one experiment to another depending on the conditions and, thus, no definite stoichiometry could be predicted for this reaction. The explanation lies with the specific mechanism: the dissolution of copper in nitric acid takes place at first by the reduction of NO3-to HN02, then after a certain accumulation of HN02, the reduction of HN02 to NO gas at the copper surface becomes the predominant process. During these reduction stages, copper is oxidized simultaneously. The evolved NO gas was found2,3 to react with HNO3 to give HN02: