A study of formic acid electrocatalysis as a step towards the development of an industrially significant platinum catalyst

Abstract

This study examined the structural and electrocatalytic properties of polycrystalline, (111)- and (100)- single crystal, and (111)- and (100)- preferentially oriented (faceted) platinum electrodes (as electrochemically generated from polycrystalline starting materials). Electrochemical methods of chronoamperometry and cyclic voltammetry were used to assess the electrocatalytic activity of formic acid in acid supporting electrolyte at these electrode surfaces. For the first time, SEM electron backscatter patterns and conventional x-ray diffraction were used to characterize the orientation of the preferentially oriented electrodes. During the course of this study it was discovered that manufactured polycrystalline materials possess an intrinsic preferential orientation that plays an inherent role in the development of the final electrode structure resulting from the application of thermal and/or electrochemical methods.

The "(111)"-preferentially oriented platinum electrode surface, as prepared by electrochemical repetitive square wave potential scanning (RSWPS), was determined to be predominantly composed of a series of (110) microfacets. While the (110) sites undergo reconstruction in acid electrolyte to a series of (111) microfacets, this may explain the enhanced electrocatalytic activity observed for this surface.

This "(111)"-preferentially oriented platinum surface was determined to have four-fold enhancement in catalytic turnover rate over a polycrystalline surface, for the electrooxidation of formic acid in acid electrolyte.

Other results involved LEED and angularly resolved XPS analyses of preferentially oriented and polycrystalline platinum surfaces, respectively. Attempts were made to obtain a LEED pattern of a clean (100)-preferentially oriented platinum electrode surface. While the results of the LEED study proved to be inconclusive, further resarch in the area may open up a practical area of research involving UHV studies of industrially significant adsorbates on preferentially oriented electrode surfaces. The XPS study involved the adsorption of a very thin layer of electrochemically produced oxide on a platinum surface. The observed 0.2 eV binding energy shift is explained by a surface charging phenomenon. The results are significant with respect to a new application of angularly resolved XPS to the studies of very thin adsorbed layers. Such shifts are undetectable under conventional XPS conditions.