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In situ ATR-SEIRAS experiments were carried out to describe water structure at the surface of multilayers of Pd modified nanopatterned gold film electrodes in contact with aqueous 0.1 M HClO4 solution. The results show that the surface water becomes more ordered when the thickness of the Pd film increases. The “ice-like water” band becomes stronger and for the electrode with 5 ML Pd@Au, the ratio of “ice-like water” to “liquid-like water” becomes larger than that in bulk water. Concomitantly, the population of “monomers” or small water clusters diminishes. All surface water bands increase when hydrogen adsorption takes place. The bending band corresponding to “monomers” or “multimers” water is observed chiefly at the potentials of hydrogen adsorption. Natural Sciences and Engineering Research Council of Canada (NSERC)the National Natural Science Foundation of China (NSFC), the "111" Project (B17027), and the National Key Research and Development Program of China.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.0c03453. The knowledge of the structure and properties of water adsorbed on metal surfaces is relevant for understanding electrocatalytic reactions. A monolayer of Pd deposited at a gold electrode surface is known to have enhanced electrocatalytic properties. To shed new light on these properties, the present study describes investigations of water structure at monolayer Pd film deposited at a nanostructured gold electrode consisting of ∼50 nm large nanoparticles supported at a Si hemisphere. Attenuated total reflection surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS) was applied to measure vibrational spectra of water molecules at the electrode surface. The surface enhancement of the electric field of the photon allowed one to determine spectra of water molecules interacting with the Pd film. The results show that surface water is a mosaic of “ice-like”, “liquid-like”, and monomer or small clusters of water molecules. In addition, hydronium ions are present at the Pd surface in an acidic solution. The relative contribution of these structures depends on the pH and electrode potential. The surface water is more ordered at potentials corresponding to the adsorption of hydrogen atoms. Natural Sciences and Engineering Research Council of Canada (NSERC), National Natural Science Foundation of China (NSFC), "111" Project, National Key Research and Development Program of China