Knowledge of the molecular composition and electronic structure of electrified solid-liquid interfaces is key to understand elemental processes at such interfaces in heterogeneous reactions. Using x-ray absorption spectroscopy in the interface-sensitive electron yield mode (EY-XAS), first-principles electronic structure calculations, and multiscale simulations, we determined the chemical composition of the interfacial region of a polycrystalline platinum electrode in contact with aqueous sulfuric acid solution at potentials between the hydrogen and oxygen evolution reactions. We found that between 0.7 and 1.3V vs Ag/AgCl the electric double layer (EDL) region comprises adsorbed sulfate ions (SO42-) with hydrated hydronium ions (H3O+) in the next layer. No evidence was found for bisulfate (HSO4-) or Pt-O/Pt-OH species, which have very distinctive spectral signatures. In addition to resolving the long-standing issue of the EDL structure, our work establishes interface- and element-sensitive EY-XAS as a powerful spectroscopic tool for studying condensed phase, buried solid-liquid interfaces relevant to various electrochemical processes and devices.

In situ spectroscopic study of the structure of the electrical double layer in aqueous solutions near gold and platinum electrodes

256th National Meeting (2018)

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