Electroreduction of Nitrate and Nitrite Ion on a Platinum-Group-Metal Catalyst-Modified Carbon Fiber Electrode Chronoamperometry and Mechanism Studies

Abstract

The mechanisms of nitrate and nitrite ion electroreduction on a carbon fiber electrode modified with platinum group metal catalyst are studied. Chronoamperometry studies reveal that two different mechanisms exist in two cathodic regions. A plot of log i vs. E reveals the presence of adsorption pseudocapacitance and is supported by impedance measurement at the electrode/solution interface. In the −600 to −800 mV (Ag/AgCl) potential region, the Tafel slope for nitrate ion reduction varies between ca. 221 and 236 mV/dec, while in the −925 to −1000 mV (Ag/AgCl) region, the slope was ca. 80 to 85 mV/dec. For nitrite ion reduction, the Tafel slope was ca. 232 to 250 mV/dec in the −500 to −700 mV (Ag/AgCl) potential region, and between −925 and −1000 mV (Ag/AgCl), the slope was between 80 and 86 mV/dec. The adsorption of nitrogen dioxide on the electrode surface was determined to be the rate‐limiting step in both potential regions. The present results indicate that although the first step of nitrate reduction in neutral solution takes a similar path as nitrate/nitrite ion reduction in alkaline solution, the rest of the mechanistic pathways are different in alkaline or acidic solution. © 2000 The Electrochemical Society. All rights reserved.