The catalytic synergy between cobalt oxide and gold leads to strong promotion of the oxygen evolution reaction (OER)-one half-reaction of electrochemical water splitting. However, the mechanism behind the enhancement effect is still not understood, in part due to a missing structural model of the active interface. Using a novel interplay of cyclic voltammetry (CV) for electrochemistry integrated with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) on an atomically defined cobalt oxide/Au(111) system, we reveal here that the supporting gold substrate uniquely favors a flexible cobalt-oxyhydroxide/Au interface in the electrochemically active potential window and thus suppresses the formation of less active bulk cobalt oxide morphologies. The findings substantiate why optimum catalytic synergy is obtained for oxide coverages on gold close to or below one monolayer, and provide the first morphological description of the active phase during electrocatalysis.

No abstract

Well-characterized metal oxides supported on single crystal surfaces serve as valuable model systems to study fundamental chemical properties and reaction mechanisms in heterogeneous catalysis or as new thin film metal oxide catalysts in their own right. Here, we present scanning tunneling microscopy and X-ray photoelectron spectroscopy results for cobalt oxide nanoislands that reveal the detailed atomistic mechanisms leading to transitions between Co-O bilayer and O-Co-O trilayer, induced by oxidation in O and reductive vacuum annealing treatments, respectively. By comparing between two different noble metal substrates, Au(111) and Pt(111), we further address the influence of the substrate. Overall, nanoisland edges act to initiate both the oxidation and reduction processes on both substrates. However, important influences of the choice of substrate were found, as the progress of oxidation includes intermediate steps on Au(111) not observed on Pt(111), where the oxidation on the other hand takes place at a significantly higher rate. During reductive treatment of trilayer, the bilayer structure gradually reappears on Pt(111), but not on Au(111) where the reduction rather results in the appearance of a stacked cobalt oxide morphology. These observations point to strong differences in the catalytic behavior between Au and Pt supported cobalt oxides, despite the otherwise strong structural similarities.

This work unifies the metrics of lanthanide-based LIR nanothermometers, rectifies previous misunderstanding of Sa, and provides detailed guidance.

Luminescence nanothermometers are promising for noninvasive, high resolution thermographics ranging from aeronautics to biomedicine. Yet, limited success has been met in the NIR‐II/III biological windows, which allow temperature evaluation in deep tissues. Herein, a new type of phonon‐based ratiometric thermometry is described that utilizes the luminescence intensity ratio (LIR) between holmium (Ho3+) emission at ≈1190 nm (NIR‐II) and erbium (Er3+) emission at ≈1550 nm (NIR‐III) from a set of oxide nanoparticles of varying host lattices. It is shown that multi‐phonon relaxation in Er3+ ions and phonon‐assisted transfer process in Ho3+ ions play a significant role in LIR determination through channeling the harvested excitation energy to the corresponding emitting states. As a result, temperature sensitivity can be tuned by the dominant phonon energy of host lattice, thus endowing aqueous yttrium oxide (Y2O3, 376 cm−1) nanoparticles to have a relative temperature sensitivity of 1.01% K−1 and absolute temperature sensitivity of 0.0127 K−1 at 65 °C in a physiological temperature range (25–65 °C). And their temperature sensing for biological tissues is further explored and the influence of water and chicken breast on thermometry is discussed. This work constitutes a solid step forward to build sensitive NIR‐II/III nanothermometers for biological applications.