Eccentric Phenomena at Liquid Mercury Electrode/Solution Interfaces:  Upward, Downward, and Circular Motions

Abstract

The present paper describes a visualization of unidirectional and circular motions triggered by an electrochemical redox reaction at a charged, bent, and streamed liquid electrode/liquid solution interface. The novel circular motion that induces a conversion of electrochemical energy into mechanical energy could be visualized for the first time at a hanging mercury drop electrode (HMDE)/dimethyl sulfoxide (DMSO) solution interface via the electrochromic reaction of 2,1,3-benzothiadiazole (BTD) by using a CCD-color video camera. The observed motions are self-insisting in nature and are tunable into upward, downward, clockwise, and anticlockwise ones by an appropriate choice of the experimental conditions. This circular motion is visualized for the first time as the cause of the well-known cyclic voltammetric anodic current oscillation at the HMDE. Several small perturbations, for example, surface tension, surface motion, bulk motion, diffusional mass transport, and surface electrochemical potential are considered to be endlessly amplified by their coupling in a cyclic chain, resulting in such macroscopic motions at the electrode/solution interface. All of the phenomena can be explained on the basis of the modern theory proposed by Aogaki et al. for the polarographic streaming maxima of the first kind.

Increased sensitivity of anodic stripping voltammetry at the hanging mercury drop electrode by ultracathodic deposition

“…Usually they are related to similar phenomena to those observed in the maxima of first kind in classical polarography, which remarkably is mostly observed at cathodic polarizations [30][31][32]. A work of particular interest was published in 2006 by Islam et al [24], researchers were actually able to film and photo the circular movement of a HMDE while performing cyclic voltammetry over 2,1,3-benzothiadiazole. However, in the present work, the drop movement should be more than simply potentially driven; very likely the formation of gaseous hydrogen also takes a large part.…”

“…This is consistent with a peak in current that appears at around −2.0 V in a linear sweep from −1.0 to −2.5 V vs Ag/AgCl (data not shown). Oscillations in mercury electrodes are known in literature [23][24][25][26][27][28][29][30]. Usually they are related to similar phenomena to those observed in the maxima of first kind in classical polarography, which remarkably is mostly observed at cathodic polarizations [30][31][32].…”

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.…”