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The electrocatalytic properties of advanced metal-oxide catalysts are often related to a synergistic interplay between multiple active catalyst phases. The structure and chemical nature of these active phases are typically established under reaction conditions, i.e. upon interaction of the catalyst with the electrolyte. Here, we present a fundamental surface science (scanning tunneling microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction) and electrochemical (cyclic voltammetry) study of CeO2(111) nanoislands on Pt(111) in blank alkaline electrolyte (0.1 M KOH) in a potential window between −0.05 and 0.9 VRHE. We observe a size- and preparation-dependent behavior. Large ceria nanoislands prepared at high temperatures exhibit stable redox behavior with Ce3+/Ce4+ electrooxidation/reduction limited to the surface only. In contrast, ceria nanoislands, smaller than ∼5 nm prepared at a lower temperature, undergo conversion into a fully hydrated phase with Ce3+/Ce4+ redox transitions, which are extended to the subsurface region. While the formation of adsorbed OH species on Pt depends strongly on the ceria coverage, the formation of adsorbed Hads on Pt is independent of the ceria coverage. We assign this observation to intercalation of Hads at the Pt/ceria interface. The intercalated Hads cannot participate in the hydrogen evolution reaction, resulting in the moderation of this reaction by ceria nanoparticles on Pt. [ABSTRACT FROM AUTHOR]

Copper oxide (CuO) is a p-type semiconductor material having versatile use in a wide number of applications. In this work, a CuO nanoleaf structure has been synthesized without any traces of Cu2O by a one-step facile method under mild refluxing conditions. The phase purity of the sample is confirmed by x-ray diffraction, x-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. Photoelectrochemical performance has been evaluated by linear scan voltammetry, and transient photocurrent has been measured in the presence of a visible light source of 350 W. Transient photocurrent shows a high photocurrent density of −6.0 mA cm−2 [at −0.2 V vs reference hydrogen electrode (RHE)] in neutral pH. The enhancement of photocurrent density is due to the large space charge region potential, confirmed by a Mott–Schottky measurement. This large space charge region potential is responsible for the higher efficiency of electron–hole separation and a concurrent increase in the kinetics of the process. [ABSTRACT FROM AUTHOR]