THE ROLE OF THE CRYSTALLINE SURFACE-STRUCTURE OF PLATINUM-ELECTRODES IN THE ELECTROOXIDATION OF D-GLUCOSE IN ACID-SOLUTIONS .1. PT(100) AND VICINAL FACES - THE EFFECT OF 2-DIMENSIONAL LONG-RANGE ORDER

Glucose electrooxidation on Pt(100) and on a set of stepped surfaces containing (100) terraces has been investigated in sulphuric and in perchloric acid media. A concentration of 10(-2) M has been chosen from the study of the glucose concentration effect which shows that higher concentrations favour the inhibition of the oxidation reaction on (100) sites. This voltammetric study suggests that in the various steps of the glucose oxidation process a dual path mechanism develops, one of them involving active intermediates, the other one leading to poisoning species responsible for the blocking of the surface electrode. The blocking species is formed during glucose electrooxidation. Thus, this species was formed at a controlled potential, then isolated and identified electrochemically as CO by using a modification of the dissociative adsorption technique. The role of the dimension of the (100) domains on the formation of this species has also been investigated showing that wide (100) surface domains are blocked preferentially. The oxidation rate of the active intermediates increases also when the dimensions of the (100) domains increase as follows from both the effect of cooling conditions during the thermal treatment of Pt(100) and the behaviour of stepped surfaces with increasing (100) terrace widths. In the latter case linear relations between the glucose oxidation rate and (100) terrace site density are found both in sulphuric and in perchloric acid media for surfaces containing wide (100) terraces. An oxidation step appearing at 0.31 V specific to perchloric acid medium for air cooled Pt(100) samples as well as for surfaces containing narrow (100) terraces is ascribed to glucose oxidation on (100) terrace edge sites. This kind of site would remain blocked for glucose oxidation by adsorbed bisulphate anions in sulphuric acid medium.