Abstract
A Pt{110}-(1×1) single-crystal electrode surface was created by flame annealing and cooling of the electrode in gaseous CO. For the first time, the voltammetry of this unreconstructed surface is reported using aqueous perchloric acid and sodium hydroxide electrolytes. The voltammetric response for Pt{110}-(1×1) produces marked differences when compared with the reconstructed, H2- and N2-cooled, disordered Pt{110}-(1×2) surface phases. Pt{110}-(1×1) exhibits as many as 6 individual peaks in the low potential region (0–0.25V vs. Pd/H), a singular sharp oxidation peak at 0.95V (Pd/H) corresponding to the electrosorption of oxide and almost zero current associated with OH formation between 0.6V (Pd/H) and 0.9V (Pd/H). Charge density curves indicate that the total charge passed between 0V (Pd/H) and 1.5V (Pd/H) to be almost identical for both the (1×1) and the disordered (1×2) phases in perchloric acid, sulphuric acid and sodium hydroxide electrolyte. The oxygen reduction reaction (ORR) activity of the (1×1) surface phase was also examined using rotating disc electrode voltammetry in the hanging meniscus configuration. The half-wave ORR peak potential was found to be ∼30mV more negative than for the disordered reconstructed surface. This leads to the conclusion that the activity of the unreconstructed basal planes of platinum towards the ORR follows the order {100}<{110}<{111} when E1/2 is used as a measure of activity and that the higher activity usually ascribed to Pt{110} over Pt{111} is actually a manifestation of the disordered (1×2) surface phase in which step sites and defects promote ORR.
Highlights
In surface electrochemical studies, a reproducible electrochemical interphasial region is of the utmost importance in order to clarify structure–sensitivity relationships in electrocatalysis
Oxygen reduction half wave potentials (E1/2) of 0.795 V and 0.765 V for the hydrogen-cooled and (1 Â 1) surfaces respectively are noted. These results demonstrate that the disordered (1 Â 2) surface phase of the hydrogen-cooled electrode exhibits the greater activity towards oxygen reduction reaction (ORR)
The voltammetry in sulphuric acid showed similarities to that reported by Kolb et al and Markovic et al For the first time, the voltammetry of the Pt{1 1 0}-(1 Â 1) surface has been reported in perchloric acid and sodium hydroxide
Summary
A reproducible electrochemical interphasial region is of the utmost importance in order to clarify structure–sensitivity relationships in electrocatalysis. This is because electrode reactions may be catalysed by different surface sites to varying degrees [1]. If the electrode surface structure and composition are not reproducible, structure activity relationships and a true understanding of any surface electrode process will be impossible to deduce. Even when electrodes are prepared in such a way that the condition of the surface is well-defined and the same surface structure and composition obtained every time an adsorption experiment is performed, it is not necessarily the case that correlations between reactivity and structure are unambiguous. All (save for Ir{1 1 1}) of the basal planes of Pt, Ir and Au when clean may undergo surface reconstruction under
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