Unraveling the Charge Distribution at the Metal-Electrolyte Interface Coupling in Situ Surface Resonant X-Ray Diffraction with Ab Initio Calculations

The comprehension of the mechanisms underlying the charge distribution at the electrochemical interface is a fundamental step in sight of the performance of catalytic materials. Several techniques allow the atomic structure of the metal surface to be characterized, while no experimental method enables to obtain the charge distribution at the catalyst surface and in the electrolyte in the interfacial region. Combining experimental and ab initio calculations, we succeeded in quantitatively describing the charge distribution at the electrochemical interface of the archetypal system Pt(111) in an acidic medium. In our approach, we couple in situ surface resonant X-ray diffraction, a site-sensitive experimental technique probing both the atomic and the electronic surface structures, with ab initio calculations, recently implemented to describe the Helmholtz double layer formed at the metal-solution interface. In the potential region in between the hydrogen desorption and the (bi)sulfate adsorption, we could determine the charge distribution on each of the metal surface layers and the distance separating the metal from the oppositely charged disordered ionic plane. We could reveal the presence of an electric dipole over the two outermost platinum layers. Our results demonstrate the potential of this original approach to unveil the electronic densities at the electrochemical interfaces, a challenging topic for the understanding of electrochemical reactivity