Examining the Structure Sensitivity of the Oxygen Evolution Reaction on Pt Single-Crystal Electrodes: A Combined Experimental and Theoretical Study.

In the present work we investigate the structure sensitivity of the oxygen evolution reaction (OER) combining electrochemistry, in situ spectroscopy and density functional theory calculations. The intrinsic difficulty of such studies is the fact that at electrode potentials where the OER is observed, the electrode material is highly oxidized. As a consequence, the surface structure during the reaction is in general ill-defined and only scarce knowledge exists concerning the structure-activity relationship of this important reaction. To alleviate these challenging conditions, we chose as starting point well-defined Pt single-crystal electrodes, which we exposed to well-defined conditioning before studying their OER rate. Using this approach, a potential region is identified where the OER on Pt is indeed structure-sensitive with Pt(100) being significantly more active than Pt(111). This experimental finding is in contrast to a DFT analysis of the adsorption strength of the reaction intermediates O*, OH*, and OOH* often used to plot the activity in a volcano curve. It is proposed that as a consequence of the highly oxidizing conditions, the structure-sensitive charge-transfer resistance through the interface determines the observed reaction rate.