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 C_d,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 C_d,min (E_d,min) closely approximates the potential of zero free charge E_pzfc for the (110)-stepped series. Together with ab initio molecular dynamics simulations, we reveal that OH_ads at step sites leads to a different step-density-dependent trend between E_pzfc 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.