Nonlinear phenomena at mercury Hg electrode/room-temperature ionic liquid (RTIL) interfaces: polarographic streaming maxima and current oscillation

The polarographic streaming maxima and cyclic voltammetric anodic current oscillation (CVACO) at a hanging mercury drop electrode (HMDE) in room-temperature ionic liquid (RTIL) have been studied for the first time using cyclic voltammetric, potential step chronoamperometric and pulse voltammetric techniques. The reversible redox reaction of the 2,1,3-benzothiadiazole (BTD)/BTD*- (an anion radical of BTD) couple with a formal potential (E0') of -1.36 V versus Ag/AgCl/NaCl(saturated) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) RTIL was typically employed for this purpose. A maximum was observed at the rising part of the normal pulse voltammogram for the reduction of BTD to BTD*- as well as of the reversed pulse voltammogram for the reoxidation of BTD*- to BTD at the HMDE. The conditions of the initiation and control of the CVACO at the HMDE in EMIBF4 were extensively investigated. Generally, the CVACO was enhanced by increasing the concentration of BTD at a given potential scan rate (upsilon) and was attenuated by increasing upsilon. An electrocapillary curve was measured using a dropping mercury electrode in EMIBF4, and the potential of zero charge was determined to be -0.23 V. On the basis of the modern theory of the polarographic streaming maxima of the first kind, the observed streaming maxima and CVACO phenomena are successfully explained to originate from the macroscopic instability at the electrode/solution interface wherein the oscillating mode creates the CVACO.