STRUCTURAL EFFECTS IN HETEROGENEOUS ELECTROCATALYSIS - ELECTROHYDROGENATION OF ETHYLENE ON PREFERENTIALLY ORIENTED PLATINUM-ELECTRODES

(100) and (111) preferentially oriented platinum electrodes were obtained by electrochemical surface orientation. These surfaces, along with polycrystalline and ordered single crystal Pt electrodes, were used to study rates and mechanisms of electrohydrogenation of ethylene in aqueous solutions. The Pt(100) preferentially oriented electrode was the most active of the surfaces which were examined with respect to the system kinetics, and an enhancement of 70% between Pt(lll) and Pt(100) preferentially oriented surfaces was found. While the catalytic enhancement effects were not very high, they were distinctive and encouraging enough to conclude that further research with electrochemically oriented surfaces is worth pursuing. This paper also contains a description of the mechanism of ethylene electrohydrogenation and its formal dependency on the electrode potential. Along these lines, two potential ranges were identified. In the first more positive regime, the rates are controlled by the availability of the reductive surface sites needed for the reaction to proceed. In the second, approaching the hydrogen evolution edge, the reaction kinetics exhibit mixed electron/mass transport control and are easily simulated by computer modeling. © 1990, American Chemical Society. All rights reserved.