PDF Publication Title:
Text from PDF Page: 002
Li et al Dovepress One of the key features of redox cycling is not only the interaction of the oxidized and the reduced species but also the mass transport between two electrodes.29–35 A required condition of redox cycling is the presence of equal amounts of the reduced and the oxidized species. If the concentration of the oxidized species is lower than that of the reduced one, two possibilities can be predicted. One is that the current will be controlled by the minor species, with the major species making no contribution to the redox cycling. The other pos- sibility is that the current is not necessarily controlled by the minor species because the minor species is produced elec- trochemically from the major one. Which possibility really occurs may depend on other conditions such as mass transport in and out of the thin layer cell, chemical complications, and the level of electric neutrality. We examine here which pos- sibility occurs in water electrolysis by adding hydrogen ion to pure water as a major species. Mass transport, including the dissociation kinetics, is considered theoretically here and compared with the experimental results. Materials and methods The disk electrodes, 1.6 mm in diameter, coated with poly- ether ether ketone in cylindrical form, were commercially available (BAS, Tokyo, Japan). The two electrodes were confronted each other so that the space between the two formed a thin layer cell. One of the two electrodes was fixed horizontally, whereas the other was moved in the direction of the cylindrical body axis by means of a micrometer gauge on an optical positioner. The axis of the cylindrical body was fitted to the axis of the other rod. The electrodes and the space were coated using a polyethylene vessel, which was a part of a bellows pipette.12 Pure water was inserted into the vessel through a hole at the top of the vessel by means of a syringe. Water was prepared with an ultrapure water system, CPW- 100 (Advantec, Tokyo, Japan), and was deaerated with nitrogen gas or hydrogen gas. The resistivity of the water before elec- trochemical measurements was 18 MΩ ⋅ cm, as determined by using a conductivity meter equipped with the pure water generator. The resistivity was measured after each of the fol- lowing steps: when water was transferred into the glass vessel, when water was left standing exposed to air for a short time, and when it was injected by use of a plastic injector. The resistivity values by a conductometer, DS-71 (Horiba, Kyoto, Japan), decreased to 1.7 MΩ⋅ cm after 30 minutes exposure to air. Hydrogen gas was bubbled for 15 minutes into water of the cell, which was set in hydrogen atmosphere. The distance between the two electrodes was read by the micrometer gauge from the contacting point of the two surfaces nearest each other. Voltage was applied to the two electrodes with a potentiostat (CompactStat; Ivium Technologies, Eindhoven, The Netherlands). The reference and the counter electrode as for conventional voltammetry were Ag/AgCl (3 M KCl) and a platinum wire, respectively. Salt-free voltammograms for redox cycling were obtained by facing two platinum rods without insulator. These elec- trodes exhibited reproducible voltammograms because there is no boundary between the platinum electrode and the insulator which causes floating large capacitive currents. We confirmed that voltammograms at the insulated disks were close to those at the rod electrodes. Results Redox cycling between h2 and h+ in thin layer cell In order to understand the ideal behavior of redox cycling, we performed thin layer voltammetry of the reaction, H2 ↔ 2H+ + 2e−, in the presence of H2 and H+. Figure 1 shows voltammograms in 1 M KCl + H2 + HCl aqueous solution for several concentrations of HCl in the thin layer cell when hydrogen gas was saturated in the solution, where ∆E is the applied voltage. Voltammograms were confirmed to be point-symmetric with respect to I = 0 and ∆E = 0, as can be predicted from the symmetric voltammograms of two-electrode electrolysis. They were almost under the steady state for v #10 mV s−1. Since the current at the forward scan was smaller than that at the backward one for 40 20 00 0.1 0.2 0.4 0.5 (e) (d) (c) (b) (a) ∆E/V ← → 0.3 Figure1 Voltammogramsof1MKCl+saturatedh2 +xmMhClatv=30mVs−1 in the thin layer cell for w = 50 μm, where x = (a) 0, (b) 0.05, (c) 0.1, (d) 0.2 and (e) 0.3. Notes: The arrows indicate the direction of the potential scans. The drawing process of determining the limiting current is shown in (d). Reports in Electrochemistry 2013:3 Powered by TCPDF (www.tcpdf.org) 8 submit your manuscript | www.dovepress.com Dovepress I/μAPDF Image | Salt-free electrolysis of water facilitated by hydrogen gas
PDF Search Title:
Salt-free electrolysis of water facilitated by hydrogen gasOriginal File Name Searched:
47741-salt-free-electrolysis-of-water.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Power up your energy storage game with Salgenx Salt Water Battery. With its advanced technology, the flow battery provides reliable, scalable, and sustainable energy storage for utility-scale projects. Upgrade to a Salgenx flow battery today and take control of your energy future.
| CONTACT TEL: 608-238-6001 Email: greg@salgenx.com | RSS | AMP |