The Pressure Coefficient of the Hydrogen Electrode Reaction

Abstract

on active platinum electrodes is controlled by diffusion of molecular hydrogen. Results I obtained about 13 years ago ~A showed that the rate of the over-all reaction was unusually reproducible over a period of up to 16 days while the a-c impedance changed rather rapidly with time. Hence, it is probable that the over-all process does not depend on anything happening at the electrode surface. Similarly, the activation energy for the over-all process was about 5 kcal which is the order expected for a diffusion process. These results were interpreted somewhat differently in the paper cited. The more recent work by Frumkin's co-workers also supports the diffusion mechanism.G. C. Barker (communicated): From discussion remarks there now seems to be recognition of the fact that the polarization observed with clean smooth platinum and with some other metals is largely concentration polarization resulting from nucleation difficulties in the formation of gaseous hydrogen. I wish merely to point out that bubble formation at a clean surface free from re-entrant cavities is made difficult by the fact that the metal surface is wetted by the solution. 25 With a more hydrophobic platinum surface produced by deposition of one or more monolayers of stearic acid, bubble formation occurs much more readily and, despite the contamination of the surface the overpotential during hydrogen deposition in unstirred solution, is often smaller than for a completely clean surface. Ready formation of bubbles during gas deposition at electrodes is often indicative of surface contamination. ABSTRACTThe various criteria for the mechanism of the hydrogen electrode reaction are considered with particular reference to the pressure coefficient of the reaction rate. The techniques of studying electrode processes at pressures up to 1500 atm are described, and the volume of activation derived for the hydrogen evolution reaction has been found to be--3.4 ml mole -1. This negative value is not in accord with either of the two mechanisms usually proposed for this reaction. It suggests that the rate-determining step is the stage e (metal) --> e (aq)) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-08 to IP

Electrochemistry of solvated electrons

“…However, Parsons 216) and Krishtalik 217) have proved that the activation volume obtained in Ref. 210 . Obviously, at potentials typical of ordinary cathodic reactions --far more positive compared to these values --it is unlikely that the processes occurring to a significant extent via the stage of formation of solvated electrons will take place in the above solvents.…”

Electrochemistry at High Pressures: A Review

“…The pressurizing fluid entering the electrochemical cell from the separator must be an electrical insulator and free from easily oxidizable or reducible impurities: hexanes [37], octanes, clean hydrocarbon white oil [1,2], heptane [38], or a mixture of isooctane and methylcyclohexane (10 : 90) [39] have given good performances and working pressures up to 10 kbar [39] are obtainable. These solvents are preferred to water or kerosene which were used in the past [40]. It can be foreseen that the upper limit of the pressures that can be reached by compressing a liquid in a piston-cylinder will be due to the freezing of the fluid or the possible rupture of the cylinders or piston.…”

“…It has been shown that contamination between the pressurizing fluid and the test solution can occur; however this can be prevented by using inert separators such as mercury, flexible diaphragms or bellows [40] or pistons [41]. Sealing of the pressure vessels is achieved by means of rubber O-rings supported when necessary by a steel-backing ring to prevent extrusion of the rubber between the body of the pressure vessel and the plug or cap.…”

“…The rate of the hydrogen evolution reaction on mercury in aqueous 0.1 M HCl up to 1.5 kbar hydrostatic pressure has also been measured [40] using a hanging drop Hg electrode to avoid the complications associated with the changing geometry of an expanding drop. The current densities at a constant overpotential were found to be pressure dependent.…”

Permeation of hydrogen through fe during cathodic polarization under hydrostatic pressure

“…Scaling was achieved by two ' 0 ' rings and dectrical contact made via a spot welded Fe wire. The solution (0.1 N NaOH prepared Srorn AiialaR reagent and doubly distilled water, pre-electrolysed and deoxygenated with 0,-free N,) was contained in parallel ground glass joints in each compartment, the outer sections G and H serving to transmit pressure to the solution in a manner similar to that employed by Hills and Kinnebrugh (1966). In order to avoid generation of oxygen, palladized Pd auxiliary electrodes were used, which were pre -charged with hydrogen before each run.…”