A comprehensive model for the electric double layer of stepped platinum electrodes

Understanding the electric double layer (EDL) of stepped Pt electrodes is crucial for comprehending the reaction environment for electrocatalytically relevant Pt electrodes, which typically comprise a complex mixture of facet orientations, steps and defects. Here we systematically investigate the EDL structure of these surfaces by periodically perturbing (111) terraces by either (110)- or (100)-type steps. We find that the minimum in the differential capacitance Cd,min in 0.1 mM HClO4 is highly structure sensitive. We attribute this observation to inherent differences in affinity for H2O dissociation between (110) and (100) facets. Using a continuum model, we confirm that the potential of Cd,min (Ed,min) closely approximates the potential of zero free charge Epzfc for the (110)-stepped series. Together with ab initio molecular dynamics simulations, we reveal that OHads at step sites leads to a different step-density-dependent trend between Epzfc and the work function. Our approach yields a unified picture of the EDL structure on stepped Pt surfaces, bridging the gap between model single-crystal surfaces and practically relevant heterogeneous Pt electrodes. Understanding the electric double layer of liquid–electrode interfaces is essential for understanding electrochemical processes. Now it has been shown that structure-dependent water dissociation and hydroxyl adsorption at step sites dictate the double-layer capacitance and potential of zero charge, directly linking model single crystals with practical platinum electrodes.