ON THE CATALYTIC MECHANISM OF HYDROGEN ELCTRODE REACTION By

The catalytic mechanism of hydrogen electrode reaction led, in terms of classical kinetics, to the value 2 of TAFEL constant t=(RT/F)o In i/or; instead of ca. 0.5 as observed, where i is the cathodic current density, r; the overvoltage and F the Faraday. OKAMOTO, HORIUTI and HIROTA') deduced z; near 0.5 from the same mechanism with special reference to hydrogen electrode of nickel by means of the generalized statistical mechanical theory,,5) of reaction rate, taking into account the quantum-mechanical exchange repulsions between hydrogen atoms, either adsorbed or implied in the critical complex of the rate-determining step of the catalytic mechanism, i.e. the recombination of hydrogen adatoms on the electrode formed by neutrali-zation of hydrogen ions. The i thus obtained included, as one of its factors, the probability e."(O) that the seat 0 * of the critical complex consisting of adjacent pair of sites of adatoms was left free to accommodate the critical complex. The latter authors') identified 8.0(0) with the square of the probability that a single site of adatom was unoccupied, which was only approximate, insofar as adatoms on the adjacent, constituent sites of 0 * exerted repulsion upon each other. The present author') has previously formulated e."(O), taking the latter repulsion into account, hence deduced z;-value and the appropriate range of r; in much closer agreemen