Nitrate Reduction By Hydrophobic, Negatively, and Positively Charged Peptide-Coated Au Electrode

Abstract

Nitrate has been considered as a source of water pollution with harmful effects on human health. Compared to other removal techniques, electrochemical reduction of nitrate is capable of delivering products such as ammonia and nitrogen which are valuable and harmless, respectively. However, it is challenging to control nitrate reduction pathway through catalyst design alone. Our research goal in this work is to understand how peptide chemistry influences nitrate reduction pathway and electrocatalyst activity for a suite of peptide-functionalized electrocatalyst surfaces. To analyze the electrocatalytic reduction of nitrate, three types are peptides, including V (hydrophobic), E (negatively charged), and K (positively charged), were coated on the gold electrodes and their performance compared with the bare gold electrode. In all the experiments, the effective area of the Au electrode was 1 cm2. An electrochemical cell with the gold electrode (working electrode), platinum (counter electrode) electrode, and a background solution (0.5 M Na2SO4) were used for electrochemical experiments. Cyclic voltammetry (CV) was used to assess the reduction of nitrate by different peptide-coated Au electrodes in the presence of nitrate ions (0.5 M Na2SO4 +0.1 M NaNO3, pH∼7.1), with a scanning rate of 20 mV/s. Chronoamperometry (CA) was applied to investigate the conversion of nitrate to different products and the pathway of nitrate reduction at different operational conditions. UV–visible spectrophotometry was employed to analyze the conversion of nitrate into nitrite and ammonia in the solution. Results of CV indicate that gold electrodes coated with V and E type peptides have promising responses to the applied voltage in the presence of nitrate ions. Based on the results, reduction of nitrate takes place at the onset potentials of -0.37 V and -0.23 V versus reversible hydrogen electrode (RHE) for E and V types of peptide-coated Au electrodes, respectively. To assess the pathway of nitrate reduction, CA experiments were done for 60 minutes on the hydrophobic peptide-coated Au and bare Au electrodes by applying a constant potential of -0.37 V versus RHE. Initial CA results of the V peptide coated-Au electrode indicate the reduction of nitrate into both nitrite and ammonia compared to a bare gold electrode which is only capable of nitrate reduction to ammonia. Based on the initial results, 0.92 mg ammonia, and 0.78 mg nitrite were produced by a V-type coated-Au electrode after 60 minutes CA experiment.