Electrolysis of pure water in a thin layer cell

Current–voltage curves were obtained at parallel platinum electrodes in the thin layer cell including pure water. They were under the steady state in the voltage domain from 1.0 V to 1.3 V when the distance of the electrodes was less than 100 μm. The solution resistance obtained from the current–voltage curve was much smaller than that predicted from the resistivity of pure water. The reason can be explained in terms of generation and accumulation of hydrogen ion and hydroxide ion before the recombination reaction. These kinetically survived ions decrease the resistance, and enhance the electrolysis rate. We subtract the reaction-controlled current–voltage curves from the overall curves to evaluate ion-included solution resistance. The resistivity of the solution averaged in the cell increased with an increase in the distance between the electrodes. In order to understand the above behavior, we calculated concentration profiles of the ions and potential distribution in the cell on the basis of Nernst–Planck equation including dissociation kinetics of water.

Predicted concentration profiles of H+ and OH− for pure water electrolysis in thin layer cell.Figure optionsDownload as PowerPoint slideHighlights
► Pure water can be electrolyzed in a thin layer cell even at 1.3 V.
► Conductivity in the cell is supported by generated hydrogen ions and hydroxide ions.
► Ionic concentrations in the cell are not in chemical equilibrium.