Open AccessGeneral considerations on the theory of the separation of H 1 and H 2 by electrolysis of water
Author(s) -
Ralph Howard Fowler
Publication year - 1934
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1934.0060
Subject(s) - electrolysis , cathode , nickel , electrode , chemistry , atomic physics , analytical chemistry (journal) , ion , order (exchange) , physics , quantum mechanics , chromatography , electrolyte , organic chemistry , finance , economics
1.The Facts .―In a solution of NaOH (or KOH) with nickel (perhaps with other) electrodes and at high current densities of the order of 1 ampere per cm.2 of electrode the observed rates of evolution E1 and E2 of H1 and H2 at the cathode obey an equation of the type E1 /E2 =q D1 /D2 , (1) where D1 and D2 are the relative concentraction of the H1 and H2 atoms in the water as a whole. The coefficientq has been shown to be independent of D1 /D2 over a very wide range of relative concentrations. Under the conditions most favourable to separation, which appear to be those just specified,q can have a value as great as 6, or perhaps 7. With other metals than nickel for the electrodes and with lower current densities the factorq may fall to a value well below 2 or even to a value so nearly unity that no effective separation occurs. The dependence ofq (if any) on the temperature of the solution is not known. 1.1.The Arguments .―The facts have already been commented on by Polanyi from the theoretical point of view. He has been led to conclude from them that the separation is to be attributed to a difference of " over potential" for the deposition of H1 and H2 ions on the cathode, and consequently that Gurney's theory of the over-potential of the hydrogen-electrode at low current densities (as measured, for example, by Bowden) must be discarded. These conclusions if correct and unavoidable are of the greatest importance. It is most general way possible, in order to see that no types of mechanism have been overlooked which could lead to the observed results. When this is done it is found that the mechanism discussed by Polanyi which refers the separation to differences of over-potential is not the only mechanism which must be held possiblea priori . The observed separation could perfectly well occur by a mechanism consistent with Gurney's theory. It does not yet appear to be possible to decide confidently between the two possibilities on experimental grounds.