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Reports in Electrochemistry Dovepress open access to scientific and medical research Open Access Full Text Article ORigiNAL RESEARCh 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 Introduction Electrochemical microreactors have the advantages of facilitating ionic transport due to local electric fields, interaction of products at an anode and a cathode, and unexpected reactions with salts.1,2 A number of uses have been reported and reviewed.3 For example, they include the possibility of electrode reactions at low concentration of supporting electrolyte,4–7 electrochemical treatments of water without supporting electrolytes in a flow-through cell,8 mass transport of electrochemical products to a counter electrode,9 and local voltage control by segmented electrodes.10 A disadvantage of microreactors is poor control of currents by electrode potential because of limitation of space for a reference electrode, although specific cell geometry has made it possible to obtain cyclic voltammograms.11 A thin layer cell acts as a microreactor, in that it can cause electrolysis without supporting electrolyte, which is demonstrated by electrolysis of pure water.12 Once a very small amount of water is electrolyzed into H+ and OH–, these ions enhance electric conduction in the cell. Change in conductivity during electrolysis has been addressed by studies in the field of microelectrode voltammetry.13–24 Further complication in a thin layer cell involves reaction coupling or redox cycling,25 in which products at the anode reach the cathode where they react. Redox cycling ought to enhance reaction rates, as seen in reactions of interdigitated electrodes.26–28 Correspondence: Koichi Jeremiah Aoki Department of Applied Physics, University of Fukui, 3-9-1 Bunkyo, Fukui, 910-0017 Japan Tel +81 776 27 8665 Fax +81 776 27 8750 Email kaoki@u-fukui.ac.jp submit your manuscript | www.dovepress.com Dovepress http://dx.doi.org/10.2147/RIE.S47741 Reports in Electrochemistry 2013:3 7–15 © 2013 Li et al, publisher and licensee Dove Medical Press Ltd. This is an Open Access article which permits unrestricted noncommercial use, provided the original work is properly cited. 7 Reports in Electrochemistry downloaded from https://www.dovepress.com/ on 18-Jan-2023 For personal use only.PDF Image | Salt-free electrolysis of water facilitated by hydrogen gas
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