Cyclic voltammetry and oxygen reduction activity of the Pt{110}-(1×1) surface

A Pt{1 1 0}-(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{1 1 0}-(1 × 1) produces marked differences when compared with the reconstructed, H2- and N2-cooled, disordered Pt{1 1 0}-(1 × 2) surface phases. Pt{1 1 0}-(1 × 1) exhibits as many as 6 individual peaks in the low potential region (0–0.25 V vs. Pd/H), a singular sharp oxidation peak at 0.95 V (Pd/H) corresponding to the electrosorption of oxide and almost zero current associated with OH formation between 0.6 V (Pd/H) and 0.9 V (Pd/H). Charge density curves indicate that the total charge passed between 0 V (Pd/H) and 1.5 V (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 ∼30 mV 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 {1 0 0} < {1 1 0} < {1 1 1} when E1/2 is used as a measure of activity and that the higher activity usually ascribed to Pt{1 1 0} over Pt{1 1 1} is actually a manifestation of the disordered (1 × 2) surface phase in which step sites and defects promote ORR.