How low can you go? The lower limits of platinum loading, in the sub‐monolayer to monolayer range, have been explored for the hydrogen evolution reaction (HER). A low‐cost substrate material, tungsten monocarbide (see picture; W blue, C small gray spheres) is capable of supporting monolayer amounts of platinum (large blue‐gray spheres) to produce an electrocatalyst with the same HER activity as bulk platinum.

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An innovative approach has been used to probe the molecular nature of the metal oxide/aqueous solution interface. Internal reflection spectroscopy of thin colloidal TiO2 films, under aqueous solutions of pH 11.7−2.3, has been used to obtain differential in situ infrared spectra related to interfacial species. An alkaline solution wash of the TiO2 films was shown to remove contaminants arising from the sol evaporation−film deposition process. Specific infrared absorptions have been assigned to terminal Ti−OH and Ti−OH2 +, adsorbed water Ti−OH2, and bridging Ti−OH+−Ti species from the pH dependence of spectra and from deuteration experiments. These surface species determine the pH-dependent surface charge and the enhanced interfacial ionic concentrations observed in our previously published STIRS results. The enhanced interfacial ionic concentrations were also observed to have spectral effects related to interfacial water structure which are similar to those observed from concentrated aqueous solutions containing these ions. The proposed interfacial species have long been components of models of hydrous oxide surfaces, but this is the first in situ vibrational spectroscopic analysis aimed at their identification.

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The first in situ infrared spectroscopic measurements of surface excess solvated ion concentrations in the electrical double layer resulting from metal oxide surface charge are reported. Enhanced concentrations of perchlorate and tetramethylammonium ions have been detected at the surface of a TiO2 gel film. A new technique, surface titration by internal reflection spectroscopy (STIRS), has been used in which spectra are recorded after flow-induced, stepwise pH changes. A measured isoelectric point for TiO2 of 5 concurs with those from other methods. The perturbing effect of specific adsorption on the TiO2 surface charge is clearly indicated by the STIRS spectra of the system containing oxalate ion.