Electric Potential Distribution Inside the Electrolyte during High Voltage Electrolysis

Abstract

Applying an external potential difference between two electrodes leads to a voltage drop in an ion conducting electrolyte. This drop is particularly large in poorly conducting electrolytes and for high currents. Measuring the electrolyte potential is relevant in electrochemistry, e.g., bipolar electrochemistry, ohmic microscopy, or contact glow discharge electrolysis. Here, we study the course of the electrolyte potential during high voltage electrolysis in an electrolysis cell using two reversible hydrogen electrodes as reference electrodes, placed at different positions in the electrolyte. The electrolysis is performed with a Pt working and stainless steel counter electrode in a KOH solution. A computational COMSOL model is devised which supports the experimentally obtained potential distribution. The influence of the cell geometry on the electrolyte potentials is evaluated. Applying the knowledge of the potential distribution to the formation of a Au oxide surface structure produced during high voltage electrolysis, we find that the amount of oxide formed is related to the current rather than the applied voltage.

Facet‐Dependent Formation and Adhesion of Au Oxide and Nanoporous Au on Poly‐Oriented Au Single Crystals**

“…We study the Au oxide growth at 300 V (before the breakdown of NE – average current density between 2.70 and 3.76 A cm −2 ) and at 540 V (in the aCGDE region – average current density between 0.24 and 6.39 A cm −2 ) for different electrolysis times [26,27] . Note, for the Au oxide formation, the current density is a more meaningful parameter since the applied voltage strongly depends on the electrode's geometry, electrode's position, and the cell geometry [28] . Nevertheless, in this article, we use the voltages to discern between the NE and aCGDE regions.…”

“…[26,27] Note, for the Au oxide formation, the current density is a more meaningful parameter since the applied voltage strongly depends on the electrode's geometry, electrode's position, and the cell geometry. [28] Nevertheless, in this article, we use the voltages to discern between the NE and aCGDE regions. During the Au oxide growth at 300 V, vivid bubble formation is observed, and hence the electrode is only partially in contact with the electrolyte.…”

“…The latter phenomenon refers to a plasma that forms in a gas sheath around the working electrode at high voltages [23–25] . In both cases, the voltages can reach several hundreds of volts and the current densities are in the range of 1 to 10 A cm −2 [26–28] . Advantages of this high voltage (current density) approach are that the preparation times are significantly shorter and only an (alkaline) electrolyte is required [27] .…”

“…[23][24][25] In both cases, the voltages can reach several hundreds of volts and the current densities are in the range of 1 to 10 A cm À 2 . [26][27][28] Advantages of this high voltage (current density) approach are that the preparation times are significantly shorter and only an (alkaline) electrolyte is required. [27] Furthermore, we demonstrated that the final structure of the NPG film depends on the method used to reduce the Au oxide, i. e., electrochemically or in the presence of H 2 O 2 .…”