Carbon probe adlayers

Electrocatafysis of Formic Acid and Carbon Monoxide with Probe Adlayers of Carbon and Ethyli[Pg.283]

A given modifier can therefore offer electrocatalytic enhancement in a number of ways. The interactions among modifier, substrate, reactants, and electrolyte are doubtlessly complex in cases such as this, so it is of interest to see if some particular aspect of the surface reaction, for example ensemble requirements, can be isolated and studied in detail. This is possible through the use of a probe adlayer, that is, an adlayer specifically designed to isolate and probe a given mechanistic aspect of the reaction. In this paper we present our first attempts to study carbon monoxide and formic acid electrooxidation in the presence of probe adlayers of carbon or derived from ethylidyne. 

To examine the ensemble requirements of a reaction, a suitable probe adlayer should restrict access to the surface by the reacting species in a known and controllable way. As will be shown, both the carbon and ethylidyne adlayers are inert in the sense that they are not consumed by the reaction. The two adlayers differ in their distribution on the surface, however carbon adsorbs as graphitic islands, whereas ethylidyne adsorbs as isolated molecules in a p(2x2) structure. Information about ensemble requirements can then be obtained through studies of the respective reactions as a function of probe adlayer coverage. Of course, these adlayers cannot isolate ensemble requirements perfectiy, as other effects, such as ion adsorption, may occur to some degree. Nonetheless, they represent a simplified electrocatalytic substrate with which definitive information about the surface reaction mechanism can be determined. 

Bectrodes containing the desired probe adlayer were transferred from vacuum directly to an attached electrochemical cell. Carbon monoxide was adsorbed either by solution or gas phase dosing, while formic acid was supplied only through solution. Vacuum measurements included thermal desorption. Auger spectroscopy, and low energy electron diffraction and were primarily intended to establish coverages and the state of the probe adlayer. In this paper we focus on the electrochemical measurements, as these highlight the influence of the probe adlayer on the reaction. 

Formic Acid Oxidation with Carbon and Ethylidyne Probe Adlayers. We now... 

Mechanistic details of electrocatalytic reactions can be probed through selectively modifying the surface with probe adlayers. Carbon adsorb in graphitic islands at low coverage, which restrict available surface sites for adsorption and reaction. As carbon coverage increases the amount of adsorbed CO decreases, consistent with siteblocking by carbon, while the reactivity of the bare sites to HCOOH increases. This... 

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