Electrocatalytic reduction of nitrate ion on Cu and Ni poly-tetraaminophenylporphyrin-modified electrodes

In this study, six polymer-modified electrodes were used to electrocatalyze the reduction of nitrate in two aqueous media: 0.5 M HClO4 and 0.1 M NaClO4. These six polymers were prepared from the electropolymerization of tetrakis(x-aminophenyl)porphyrin (where x=o,p), and their Cu(II) and Ni(II) complexes in HCl solution on the surface of a conducting glass electrode. The results indicate that the catalytic response depends on the position of the amino group, the metal and the pH of the solution. In HClO4, the modified electrodes show two reduction processes. The voltammetric responses of the modified electrodes show a reduction process that takes place during the negative scan and another reduction process occurring during the return potential sweep. Indeed, there is a change in the number of reduction processes depending on the direction of the scan at low scan rate (5 mV s−1). In HClO4, the products of electrolysis are nitrite and nitrous oxide for Cu and Ni-ortho-polymers and nitrite for the others polymers. In NaClO4, only one reduction process takes place, independently of the direction of the scan, giving nitrite and nitrous oxide for the Ni and Cu-ortho systems and only nitrite for the other systems. In both cases, HClO4 and NaClO4, the best polymers are poly Cu(II) and Ni(II)tetrakis(o-aminophenyl)porphyrin as electrocatalysts.