Electrochemical Reduction Of Nitrates And Nitrites Using Copper Modified Platinum Electrode
Loading...
Date
2016-09
Authors
Ratnam, Sree Amertharaj
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The electroreduction of nitrates and nitrites were carried out in this study using a copper modified platinum (Pt-Cu) electrode in the presence of 0.05 M KCl solution using cyclic voltammetry. Comparison was carried out using various working electrodes such as Cu, copper modified copper electrode (Cu-Cu) and copper modified pencil graphite electrode (PG-Cu). For the copper modified electrodes, the deposition of the copper particles was maintained at 30 cycles/ 18 seconds as the best ratio. The real surface area Pt, Cu, Cu-Cu, PG-Cu and Pt-Cu electrodes were estimated to be 1.747 cm2, 0.814 cm2, 0.988 cm2, 1.146 cm2 and 2.259 cm2 respectively. The activity and selectivity for electroreduction of both nitrates and nitrites were better at the Pt-Cu electrode. The plot ipvsν1/2 shows that the electrons transferred in the rate determining step was 1.51, 1.66, 1.88 and 2.05 on the Cu, Cu-Cu, PG-Cu and Pt-Cu respectively indicating the electroreduction of nitrate to nitrite. At more negative overpotentials, the number of electrons transferred was approximately 5.15, 5.26, 5.35 and 6 on the Cu, Cu-Cu, PG-Cu and Pt-Cu electrodes respectively, corresponding to the production of ammonia. The order of the reaction in the presence of Pt-Cu electrode was 0.97 and 0.90 for the electroreduction reaction of nitrate and nitrite respectively. The rate constant of electroreduction of nitrate (2.228 × 102 min-1) and nitrite (4.690 × 102 min-1) when using Pt-Cu electrode was relatively higher compared to other electrodes studied which proved that Pt-Cu electrode performance is the best compared Cu, Cu-Cu and PG-Cu electrodes. The electrochemical behavior of a Pt-Cu electrode on the electroreduction of
nitrate and nitrite ions has been investigated in an alkaline medium (0.05 M NaOH) in the presence of 5 mM sodium inositol hexaphosphate (NaIP6). Different electrode compositions (Cu, Pt, and Pt-Cu) were used to study their activity and selectivity towards the electroreduction of nitrates and nitrites using cyclic voltammetry. The Pt-Cu electrode shows the best performance. The addition of NaIP6 is to prevent the oxidation of copper atoms to copper ions. The effect of NaIP6 on the optimization of the electrode activity and stability was investigated in this study. The presence of NaIP6 further improves the performance of the Pt-Cu electrode especially the stability of the electrode. The effect of the interfering ions on the performance of the Pt-Cu electrode was also carried out. The effect of the pre-added nitrate and nitrite to the overall electroreduction process was determined in the 0.05 M KCl. Here, a higher rate constantfor nitrate reduction was observed in the system without pre-added nitrite (2.215 × 102 min-1) compared to the system with added nitrite (55.97 min-1). The rate constant of reduction of nitrite was higher without the presence of nitrate ions (3.954 × 102 min-1) compared to those in the presence of nitrate (3.349 × 102 min-1). At higher concentration of nitrite the rate constant of reduction deteriorates. The electroreduction of nitrate and nitrite was observed to be more feasible in the presence of Cl- and ClO4- ions compared to the larger SO4- and Br- ions. The order of the reaction was approximated to 1. The rate constant of the nitrate and nitrite electroreduction was the highest in the KCl solution. Electron transfer for nitrate reduction step is nearly two electrons while the number of electrons transferred for the nitrite reduction steps varied according to the adsorption ability of the preceding nitrate ions which ranged from four to six electrons. For the interfering cations analysis, the electroreduction activity was feasiblefor the singly
charged cations. The order of reaction attained was approximately 1 for both nitrate and nitrite reduction. For the nitrate reduction, the rate of the reaction was higher in the presence of K+ ions (2.213×102 min-1) than the Na+ ions (2.143×102 min-1) while the rate constant increased in the sequence Cu <Al<Mg<Ca for the rest of the cations per mol of NO3- and NO2-.. A higher reaction rate constant for nitrite reduction was observed in the presence of the Na+ ions (5.571×102min-1)than the K+ ions (4.699×102 min-1) while Ca2+ ion produced the highest rate (6.397×102 min-1) for the rest of the cations. The limit of detection of nitrate concentration was determined as 1.61 × 10-7 M.
Description
Keywords
The electroreduction of nitrates , and nitrites.