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 Ϫ600 to Ϫ800 mV (Ag/AgCl) potential region, the Tafel slope for nitrate ion reduction varies between ca. 221 and 236 mV/dec, while in the Ϫ925 to Ϫ1000 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 Ϫ500 to Ϫ700 mV (Ag/AgCl) potential region, and between Ϫ925 and Ϫ1000 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.

Efficient electrochemical reduction of nitrate to nitrogen on tin cathode at very high cathodic potentials

“…Even though at high cathodic potentials, where the rate of hydrogen evolution is high, ammonia is the predominant product [4,27,29,32] the present work shows that at high cathodic potentials, unexpectedly, the main product on tin is nitrogen gas having both a high %S (92%) and a high rate of formation.…”

“…It was proved that the conversion of nitrate to the nontoxic nitrogen gas is difficult since it is one of the eight possible products, NO 2 , NO 2 − , NO, N 2 O, N 2 , NH 2 OH, NH 3 and NH 2 NH 2 . When the supporting electrolyte is basic or neutral, the main by-products are nitrite and ammonia; furthermore, in acid electrolyte hydroxylamine and hydrazine have been also detected [27]. Nitrogen gas was detected on various metals and alloys, such as Cd (70-75%) [28], Pd-Cu (50%) [7], Pb (22%) [4], Sn85-Cu15 (34%) [29], Pd-Sn-Au (34%) [30], Sn-Pt (37%) [31] and Pd-Rh (94%) [32].…”

Kinetic Studies of the Electrochemical Treatment of Nitrate and Nitrite Ions on Iridium‐Modified Carbon Fiber Electrodes

“…On iridium-modified carbon fiber electrode, NO 2 adsorption is the rate-determining step [9]. The experimental results indicate that: ± immediately after the desorption of hydrogen, a cathodic reduction peak results on a positive scan, ± current density increases nonlinearly with increasing nitrate concentration, ± the amount of reduced nitrate and evolved hydrogen was greater at ±950 mV relative to the results obtained at a potential of ±850 mV.…”

“…The reduction mechanism for nitrate is very complex and involves more than one pathway [9]. In [10], Dibyendu showed that the first two steps of nitrate reduction on iridiummodified fiber electrode can be represented as:…”

“…In [9], the use of iridium-modified carbon fiber electrode at pH = 7.0 for nitrate ion reduction shows the following as the major reduction paths:…”