Electrochemical reduction of nitrate in weakly alkaline solutions
ABSTRACT The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing.
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ABSTRACT: The aim of this work was to set up a novel electrochemical system allowing an efficient transformation of concentrated nitrate solutions to ammonium and which can be subsequently implemented on a large scale application. First, this paper describes the preparation of a porous copper modified electrode by successive electrodeposition of nickel then copper on a graphite felt of large specific surface area. Homogeneous Cu coating of all fibres in the 3D porous structure was successfully obtained using low concentrations of copper salts and high applied current intensities. The porous copper electrode was then used in a flow electrochemical process to achieve a selective and quantitative transformation of concentrated nitrate into ammonium. Different electrolytic solutions, slightly acid (acetate buffer) or neutral (phosphate buffer), and flow rates were investigated. The nitrate solution was quantitatively reduced into NH4+ with high selectivity in only one pass through the electrode. When the applied current was similar to the theoretical one, the maximum selectivity (96%) and the best current efficiency (72%) for NH4+ formation were reached at pH 7.2 with a flow rate of 2 mL min-1. The obtained ammonium solution can be subsequently used either as a potential nitrogen source during microbial culture or simply as a fertilizer.Journal of Electroanalytical Chemistry 06/2014; 727. DOI:10.1016/j.jelechem.2014.06.016 · 2.87 Impact Factor
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ABSTRACT: The effect of the nature of six metal electrodes (Sn, Bi, Pb, Al, Zn, In) on the rate and the distribution of the products of the electrochemical reduction of nitrate was studied. The product distribution depends on the nature of the metal only quantitatively, while the rate of the reduction was found to be about the same on all metals when the electrolysis was performed at the same rational potential (Er), which is the difference between the applied potential and the potential of zero charge of each metal. Based on these results it was concluded that the mechanism of nitrate reduction is the same for all cathodes studied. Additionally, the influence of the initial pH on the rate of the reduction of nitrate and the selectivity of the products on a tin cathode was studied. The rate of the reduction increases linearly with the concentration of hydronium ion in the pH range 0–4, whereas it is not dependent on the pH at higher pH values. The main products at pH > 4 were nitrogen, nitrous oxide, ammonia and nitrite, while at pH 0–4 ammonia and hydroxylamine were mainly formed.Environmental Technology 02/2013; 34(3):373-381. DOI:10.1080/09593330.2012.696722 · 1.20 Impact Factor
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ABSTRACT: Electrochemical reduction of nitrate in an undivided cell was studied in the present experiments. The optimization of the influencing factors on electrochemical reduction of nitrate by response surface methodology (RSM) was also studied. An ideal condition of performing both cathodic reduction of nitrate and anodic oxidation of the formed by-product in the presence of NaCl was achieved in the present experiment. The Box–Behnken design can be employed to develop mathematical models for predicting electrochemical nitrate removal geometry. The removal is sensitive to the current density and time in the present study. The value of R2>0.99 for the present mathematical model indicates the high correlation between observed and predicted values. The optimal NaCl dosage, current density and electrolysis time for nitrate removal in the present experiment are 0.47gL−1, 26.06mAcm−2, and 111.88min, respectively, at which the nitrate nitrogen (nitrate-N) and ammonia nitrogen (ammonia-N) concentration in the treated solution are 9.80 and 0mgL−1, respectively, which will meet the standards for drinking water.Electrochimica Acta 12/2010; 56(1):265-270. DOI:10.1016/j.electacta.2010.08.085 · 4.09 Impact Factor