Current Oscillatory Phenomena Based on Redox Reactions at a Hanging Mercury Drop Electrode (HMDE) in Dimethyl Sulfoxide

Abstract

A systematic and comprehensive study on cyclic voltammetric anodic current oscillation (CVACO) at a hanging mercury drop electrode (HMDE) was carried out for the redox reactions of molecular oxygen (O2), nitrobenzene (NB), 1,4-dinitrobenzene (DNB), benzoquinone (BQ), 2,3,5,6-tetramethylbenzoquinone (TMBQ), benzophenone (BP), azobenzene (AB), 2,1,3-benzothiadiazole (BTD), 7,7,8,8-tetracyanoquinodimethane (TCNQ), methyl viologen dichloride (MV2+), and tris(2,2‘-bipyridine)ruthenium(II) dichloride [Ru(bpy)3 2+] in dimethyl sulfoxide (DMSO) solutions containing 0.1 M tetraethylammonium perchlorate (TEAP). From the electrocapillary curve (ECC) obtained using a dropping mercury electrode as well as the capacitance versus potential curves measured using electrochemical impedance technique, the value of the potential of zero charge (PZC) was estimated to be −0.27 V versus Ag|AgCl|NaCl (sat.) in a DMSO solution containing 0.1 M TEAP. CVACO was found to occur only for the redox couples (i.e., BP0/BP•-, O2 0/O2 •-, AB0/AB•-, Ru(bpy)3 2+/Ru(bpy)3 +, BTD0/BTD•-, NB0/NB•-, DNB0/DNB•-, DNB•-/DNB2-, TMBQ0/TMBQ•-, MV2+/MV•+, and BQ•-/BQ2-) having the formal potentials (E 0‘ values) more negative than the PZC. CVACO was largely dependent on the concentrations of redox species and TEAP; for example, in the case of BTD the intensity of CVACO increased with increasing concentration, and CVACO ceased at high concentrations of TEAP (≥0.5 M). Furthermore, CVACO was not observed for the BQ0/BQ•- redox couple having E 0‘ (= −0.31 V) near the PZC, and a pronounced cathodic maximum was observed for the TCNQ•-/TCNQ2- redox couple with E 0‘ (= −0.16 V) more positive than the PZC. These observations and the factors governing the CVACO are discussed on the basis of the theory presented for the polarographic maxima of the first kind. The observed CVACO and the cathodic maximum obtained for the TCNQ•-/TCNQ2- redox couple could be explained in terms of the so-called streaming effect.

Electrochemical double layer at the interfaces of Hg/choline chloride based solvents

“…where Z represents the imaginary component of impedance measured [29]. For Hg electrodes the C(E) curves obtained with single frequency measurements were very close to those obtained from extracting C from the CPE parameters.…”

In situ CCD video and voltammetric studies on enhanced cathodic peak observed at a hanging mercury drop electrode during consecutive two one-electron redox reactions in aprotic solutions

“…In the past some decades, a number of peculiarities [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] concerning the cyclic voltammograms (CVs) obtained at a hanging mercury drop electrode (HMDE) in aprotic solutions and ionic liquids [9] (e.g., cyclic voltammetric anodic current oscillation (CVACO) [1][2][3][4][5][6][7][8][9][10][11], inverted peak [3,11,12] and larger current of the second cathodic peak than that of the first one of a stepwise one-electron redox reaction [1][2][3][4][5]14,15]) have been reported. These eccentric phenomena especially the CVACO that has been visualized to originate from a novel circular motion [10] at the HMDE|solution interface due to the familiar polarographic streaming phenomena [1,[6][7][8][9][10][11]16] have been reported to be fundamentally very interesting...…”

“…These eccentric phenomena especially the CVACO that has been visualized to originate from a novel circular motion [10] at the HMDE|solution interface due to the familiar polarographic streaming phenomena [1,[6][7][8][9][10][11]16] have been reported to be fundamentally very interesting [10] and promising from the viewpoint of practical applications to, for example, a mechanical actuator and triggering-valve [17,18].…”

“…Such an enhanced I c2 p that may be recognized as an unexpected event concerning the electrode kinetics and electroanalysis at the HMDE has been hitherto claimed to result from the electrochemical processes involving the chemical reaction [1,14,15], adsorption [2,14], multielectron transfer and chemical complications [5] and the streaming phenomena of the HMDE [1][2][3]. It has been also reported that the I c2 p =I c1 p > 1 is not specific for a particular compound [2], whereas the streaming (''upward" and ''downward") of the HMDE is its inherent characteristic [1][2][3][8][9][10][11]16,19,20]. Thus, as the probable reason for I c2 p =I c1 p > 1, the streaming of the HMDE could be most rational, but, unfortunately, there is no relevant study in this regard.…”

“…Thus far the mechanisms to explain the fact that I c2 p =I c1 p > 1 remain controversial [1][2][3][4][5]14,15]. The streaming of the HMDE surface has been reported to originate from the unequal surface tension (c) at the neck and bottom of HMDE [1,[6][7][8][9][10][11]16,19,20]. During a redox reaction with a formal potential more negative than the potential of zero charge (PZC) (i.e., in the negative branch of the electrocapillary curve (ECC) (Fig.…”