Indirect Electrochemical Cr(III) Oxidation in KOH Solutions at an Au Electrode: The Role of Oxygen Reduction Reaction

Abstract

The indirect electro-oxidation of Cr(III) by in situ generated superoxide at a gold electrode has been investigated in KOH solutions using cyclic voltammetry and UV-vis spectroscopy. It is observed that the indirect Cr(III) oxidation behavior is substantially affected by the media pH and there is a pH-modulated oxygen reduction reaction (ORR) process to generate reactive oxygen species which promotes Cr(III) oxidation. The ORR in KOH solutions is attributed to a quasi-reversible diffusion-controlled reaction. In dilute KOH solution (0.2 M), 4e reduction occurs and no reactive oxygen species are generated for the indirect Cr(III) oxidation. Moreover, Cr(III) oxidation is inhibited due to competition for the electrode active sites. As the alkaline concentration increases (3.0 M), the protonation of superoxide is greatly suppressed, and thus, 1e ORR to generate superoxide is observed. This change in mechanism facilitates the indirect Cr(III) oxidation through the superoxide as a mediator to oxidize Cr(III) to Cr(IV), which is the rate-determining step of Cr(III) oxidation to Cr(VI).

Recent advances in electrochemical detection of toxic Cr(vi)

“…It should be noted that there are still many challenges and opportunities for the next-generation electrochemical Cr(VI) sensors: (1) most of the recently available electrochemical Cr(VI) detection focuses on the media of acidic aqueous solution or below the pH of 7, and scarce investigation has been carried out in alkaline solution possibly due to the low electrocatalytic activity for Cr(VI) reduction in this region. 73,74 Therefore, it is highly desirable to develop novel electrodes which are capable of detecting Cr(VI) with comparable performance in alkaline solution. (2) In order to facilitate the on-site and in site electrochemical detection of Cr(VI), facile and reliable sampling methods in complicated systems, such as the soil and human body, are particularly required.…”

The influence of KOH concentration, oxygen partial pressure and temperature on the oxygen reduction reaction at Pt electrodes

“…Fluorescent probe 2 0 ,7 0 -Dichlorodihydrofluorescein diacetate (H 2 DCFDA) and the KOH stock solution (45% mass fraction, HPLC grade, total impurities K 2 CO 3 6 0.3% mass fraction) were from Sigma Aldrich. All the solutions were prepared using Millipore Milli-Q water (18 MX cm) in a nitrogen-filled glove box to minimize contamination by CO 2 [38,39]. The solutions, saturated with high purity N 2 and O 2 (99.999% by volume, Beijing Qianxi Gas), were used as blank and working solutions, respectively.…”

Manganese oxide nanoflakes/multi-walled carbon nanotubes/chitosan nanocomposite modified glassy carbon electrode as a novel electrochemical sensor for chromium (III) detection

“…Due to the high redox potential of the Cr(VI)/Cr(III) couple, different oxidants such as cerium(IV), Mn-oxide and Fe(III) have been used for oxidation of Cr(III) to Cr(VI) [17][18][19][20][21]. Furthermore, oxidation of Cr(III) to Cr(IV) in alkaline solution at Au (111), Pt and gold screen printed macro electrode was also investigated [22][23][24][25]. The electrooxidation of Cr (III) at the proposed electrode has been done in alkaline solution and sensitivity of detection methods was low.Therefore, for oxidation of Cr(III) in natural solution and improving sensitivity, the introducing of novel materials and methods for electrode modification overcomes these limitations.…”