The Influence of Solution-Phase HNO₂ Decomposition on the Electrocatalytic Nitrite Reduction at a Hemin−Pyrolitic Graphite Electrode

Abstract

The mechanism of nitrite electroreduction by hemin adsorbed at pyrolitic graphite is investigated. Two main issues are addressed: the effect of the medium pH and the selectivity of the reaction, which was determined by the combined use of the rotating ring disk electrode (RRDE) and online electrochemical mass spectroscopy (OLEMS). In acidic media, the behavior observed is indicative of the presence of NO, as the main reactant, generated from the solution-phase decomposition of HNO(2). Reduction of the NO-heme complex shows a Tafel slope of 59 mV/dec(-1) and a pH dependence of 42 mV/pH, indicative of a so-called EC mechanism. In acidic media, HNO(2) and NO are reduced to hydroxylamine (NH(2)OH) with almost 100% selectivity at low potentials, nitrous oxide (N(2)O) being only a minor side product. In neutral media, the hemin is largely unresponsive to the presence of nitrite, giving only a very small reduction current. The comparison of our simple heme catalyst to the behavior of the naturally occurring heme-containing nitrite reductases, which operate under biological conditions, suggests that these enzymes dissociate nitrite at neutral pH either via a complexation step favored by a specific ligating environment or by locally regulating the pH to induce HNO(2) dissociation.

Theory of the transition from sequential to concerted electrochemical proton–electron transfer

“…12 An example of the former case would include the reduction of nitrate and nitrate on platinum electrodes, although other side reactions are known to play a role in these processes as well. [52][53][54] The protonated form of nitrite, nitrous acid, is known to be the more reactive species of the two. Nitrate reduction is also significantly faster in acidic media, 52 and the availability of protons should be considered as one of the determining factors for nitrate activation.…”

Powering denitrification: the perspectives of electrocatalytic nitrate reduction

“…Usually, Au is a poor catalyst for NO 3 − reduction 40 in mildly acidic conditions, unless Cd +2 is present in the solution: in this case, underpotentially-deposited Cd selectively enhances the formation of NO 2 − 129, 130 . Nitrite is then targeted by hemin leading to NH 3 OH + , which is by far the major reduction product 131 . Despite failing to achieve 100% selectivity to N 2 , this 45 approach is very promising and should garner more attention.…”

A novel electrochemical biosensor based on hemin functionalized graphene oxide sheets for simultaneous determination of ascorbic acid, dopamine and uric acid

“…Recently, it was reported that hemin could be adsorbed on graphene surface by -interactions to form complex nanosheets, which were exhibiting great properties and various applications. Meanwhile, it is worthy noted that many small molecules including nitric oxide [13], nitrite [15], and hydrogen peroxide [16] could be reduced or oxidized based on the active groups of hemin [17] or reversible redox potential of Fe 2+/3+ [18].…”