Surface Coverage during Hydrogen and Oxygen Evolution

An a‐c square wave technique was used to study resistance and double‐ layer capacity during film formation on silver electrodes in KOH solutions. The peak in the voltage‐time curve at constant current anodization is shown to coincide with complete surface coverage by Ag2O and is not an ohmic resistance, but rather an overvoltage effect. Evidence for the existence of an unstable higher oxide than normalAgO (or additional oxygen) during oxygen evolution is presented. Microvolumetric gas measurements with large area electrodes on open‐circuit decay also support this conclusion. The duration of the upper voltage plateau of the voltage‐time curve during discharge of normalAgO electrodes is determined by contact phenomena among individual normalAgO particles, in particular by separation and passivation of the remaining normalAgO by insulating surface layers of Ag2O .

Section: Methodsmentioning

confidence: 99%

The Silver-Silver Oxide Electrode

Cahan

Ockerman

Amlie

et al. 1960

“…Oxygen evolution on nickel electrodes in alkaline solution may be accompanied by adsorption proc-esses (of intermediate OH-and O2H-, and of atomic and molecular oxygen) and by the formation of surface oxides. This has been discussed with respect to the surface coverage on inert electrodes by Ruetschi and co-workers (8). The presence of other adsorbed species during hydrogen evolution has been considered possible but otherwise has been largely ignored.…”

mentioning

confidence: 99%

Hydrogen Evolution and Surface Oxidation of Nickel Electrodes in Alkaline Solution

Weininger¹,

Bréiter²

1964

126

The electrochemical processes which occur on nickel electrodes in 4N KOH during a slow-speed anodic potential sweep between --300 and ~-1500 mv were studied. Tafel plots for hydrogen evolution were determined under different conditions, and the impedance was measured at 100 cps as a function of potential. The results are interpreted in terms of the adsorbed species. It is confirmed that hydrogen evolution between --300 and --100 mv is controlled by the discharge step of water molecules (Volmer reaction) and that the coverage with electrochemically active hydrogen atoms is small in this region. Prior to the formation of Ni(OH)~ an adsorbed layer of OH-radicals appears to be formed.

“…17 and consider only the changes of the ion concentration at the end of on-time and off-time of each single pulse. So, when we let t ϭ mT (m ϭ 1, 2, 3 .....) [32] Eq. 17 becomes [33] When m is very large, we can make the following approximation [34] And we can obtain Figure 8.…”

Section: Mass Transfer Of O Atoms In Pulse Charge-many Authors Havementioning

confidence: 99%

Rate‐Determining Step Investigations of Oxidation Processes at the Positive Plate during Pulse Charge of Valve‐Regulated Lead‐Acid Batteries

Guo

Groiss

Döring

et al. 1999

In order to develop electric vehicles (EVs), electrochemical scientists and engineers have paid great attention to the study of batteries in recent years. Now, while new types of batteries are still in development, the valve-regulated lead-acid (VRLA) battery is a near-term candidate for EV applications in mass markets. 1 A key usage issue is the possibility of fast recharge. More recently, much work has been carried out on pulse charging of lead-acid batteries. 2-7 The recharge time for valve-regulated lead-acid batteries has been reduced and is now less than 5, 15, and 240 min for 50, 80, and 100% charge. However, many other problems arise from pulse charging such as reduced cycle life of the battery, corrosion of the positive-electrode grid, loss of electrolyte, and thermal management. To enhance the pulse charging of a VRLA battery, it is important to understand the detailed processes during the charge. Therefore, attention has to be paid to the kinetics of important processes during pulse charging. Although many papers have reported on the mechanism of the oxidation processes at the PbSO 4 /PbO 2 electrode and the positive plate, 8-29 this remains a subject of research. It is necessary to study further the electrode kinetics of the positive plate in VRLA batteries under pulse charging conditions. Experimental The tested battery was a 2 V 4.2 Ah VRLA battery with gel electrolyte, produced by Sonnenschein Lead-Acid Battery Company. The pulse charge system, controlled by a computer, is a self-made system. The maximum output current and voltage are 100 A and 10 V, respectively. The rise time of the analog circuit is less than 1 s/A. The control period of the digital circuit is 2 ms. The internal pressures of the gas in the battery were measured by a pressure sensor. The relative pressures of oxygen and hydrogen were measured with a micropipette of 0.5 mm internal diam and 8 cm length, which linked the battery to a quadripole mass spectrometer (Balzers QMS 402). All potentials were measured vs. a Hg/Hg 2 SO 4 /H 2 SO 4 (sp gr 1.28) reference electrode, which was linked to the battery by a proton-conducting polymer bridge. The infrared (IR)-corrected potentials were measured by imposing an instantaneous open circuit. Different interactive pulse charging and discharge/constant-voltage procedures were used, and the current profiles are shown in Fig. 1. Their average current was 15.5 A. The maximum limit voltage with IR compensation was 2.45 V at 25ЊC and it is also compensated by a temperature coefficient with Ϫ4.5 mV/ЊC, to avoid thermal runaway of the VRLA battery. To simulate the situation of a large battery, the test battery was thermally isolated. Literature StudyDuring recent decades, both oxygen evolution and the oxidation of PbSO 4 to PbO 2 have been studied extensively on solid Pb electrodes and on the positive plates of lead-acid batteries. Different models for the kinetics of both reactions have been put forward.A model with hydration structure carried out much work on the kinetic processes of the PbSO 4...