Salt-free electrolysis of water facilitated by hydrogen gas in thin layer cell

Chunyan Li, Koichi Jeremiah Aoki, Jingyuan Chen, Toyohiko Nishiumi

Department of Applied Physics, University of Fukui, Fukui, Japan

Abstract: Electrolysis of water without salt in a thin layer cell requires a voltage of more than 1.3 V. This voltage is found to be reduced to 0.4 V when hydrogen gas is dissolved in electrolyzed water. The decrease in the overvoltage can be used for the salt-free electrolysis of pure water. Thin layer electrolysis under steady state is often caused by redox cycling. The redox cycling model relevant to the reaction between H₂ and H⁺ is theoretically analyzed here in a two-electrode cell. The validity and limitation are discussed on the basis of the experimental voltammograms of a solution containing H₂ and H⁺. When a solution contains H₂ without deliberately adding H⁺, hydrogen gas would not be expected at the cathode due to the small amount of H⁺. Consequently redox cycling might be blocked. However, experimental voltammograms, without the addition of H⁺, exhibited the steady state limiting current by redox cycling. The current was regarded as dissociation kinetics of water. The redox cycling in this case was theoretically analyzed to partially explain the experimental results. The oxidation of hydrogen gas at the anode facilitates the dissociation kinetics to produce redox cycling.

Keywords: redox cycling, hydrogen gas, dissociation kinetics of water, electrolysis of pure water in thin layer cell, CE mechanism under the steady state