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