Gold-supported two-dimensional cobalt oxyhydroxide (CoOOH) and multilayer cobalt oxide islands

Synthesis and characterization of layered cobalt oxides for model studies of electrochemical water splitting catalysts.</p

A new set-up for the calibration of wood moisture meters

A set-up has been established to calibrate wood-moisture meters at Danish Technological Institute. The set-up is based on humidification of wood in an atmosphere with constant humidity, generated by saturated salt solutions. The measurements of the reference value are made by means of the loss-on-drying method and made traceable to a primary standard for moisture mass fraction established under the EMRP project METefnet in 2015. The facility was accredited by the Danish Accreditation Fund, DANAK, in 2018. In this paper, we report on the design of the calibration set-up, the uncertainty analysis and the validation by comparison to the primary facility

Phase Transitions of Cobalt Oxide Bilayers on Au(111) and Pt(111): The Role of Edge Sites and Substrate Interactions.

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 O₂ 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

Structure and Stability of Au-Supported Layered Cobalt Oxide Nanoislands in Ambient Conditions

Cobalt oxide is a promising earth-abundant electrocatalyst for water splitting; however, the structural complexity of oxides coupled with the difficulty of characterizing it in its operating environment means that fundamental understanding of its catalytic properties remains poor. In this study, we go beyond vacuum studies and investigate the morphological evolution of a CoO_<i>x</i>/Au­(111) model system from intermediate to high pressures of H₂O vapor by means of scanning tunneling microscopy and near-ambient pressure and vacuum X-ray photoelectron spectroscopy. At elevated H₂O pressure, we describe the formation of a well-defined Co­(OH)₂ nanoisland morphology with cobalt in the +2 oxidation state. In contrast, the presence of O₂, in air and liquid water, results in only partially hydroxylated Co³⁺ phases comprising sheets of the CoO­(OH_<i>x</i>) trilayer, corresponding to a single sheet of cobalt­(III)­oxyhydroxide. We conclude that the oxyhydroxide structure, known to be the catalytically active phase for the oxygen evolution reaction, is stabilized by aerobic conditions, which inhibits further transformation into the catalytically inactive cobalt­(II)­hydroxide

Edge Reactivity and Water-Assisted Dissociation on Cobalt Oxide Nanoislands

Transition metal oxides show great promise as Earth-abundant catalysts for the oxygen evolution reaction in electrochemical water splitting. However, progress in the development of highly active oxide nanostructures is hampered by a lack of knowledge of the location and nature of the active sites. Here we show, through atom-resolved scanning tunnelling microscopy, X-ray spectroscopy and computational modelling, how hydroxyls form from water dissociation at under coordinated cobalt edge sites of cobalt oxide nanoislands. Surprisingly, we find that an additional water molecule acts to promote all the elementary steps of the dissociation process and subsequent hydrogen migration, revealing the important assisting role of a water molecule in its own dissociation process on a metal oxide. Inspired by the experimental findings, we theoretically model the oxygen evolution reaction activity of cobalt oxide nanoislands and show that the nanoparticle metal edges also display favourable adsorption energetics for water oxidation under electrochemical conditions

The Structure of the Cobalt Oxide/Au Catalyst Interface in Electrochemical Water Splitting

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.Fil: Fester, Jakob. University Aarhus; DinamarcaFil: Makoveev, Anton. Brno University of Technology; República ChecaFil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Gutzler, Rico. Max Planck Institute For Solid State Research; AlemaniaFil: Sun, Zhaozong. University Aarhus; DinamarcaFil: Rodríguez Fernández, Jonathan. University Aarhus; DinamarcaFil: Kern, Klaus. Max Planck Institute For Solid State Research; Alemania. École Polytechnique Fédérale de Lausanne; SuizaFil: Lauritsen, Jeppe V.. University Aarhus; Dinamarc

Enhanced pro-apoptosis gene signature following the activation of TAp63 alpha in oocytes upon gamma irradiation

Specialized surveillance mechanisms are essential to maintain the genetic integrity of germ cells, which are not only the source of all somatic cells but also of the germ cells of the next generation. DNA damage and chromosomal aberrations are, therefore, not only detrimental for the individual but affect the entire species. In oocytes, the surveillance of the structural integrity of the DNA is maintained by the p53 family member TAp63α. The TAp63α protein is highly expressed in a closed and inactive state and gets activated to the open conformation upon the detection of DNA damage, in particular DNA double-strand breaks. To understand the cellular response to DNA damage that leads to the TAp63α triggered oocyte death we have investigated the RNA transcriptome of oocytes following irradiation at different time points. The analysis shows enhanced expression of pro-apoptotic and typical p53 target genes such as CDKn1a or Mdm2, concomitant with the activation of TAp63α. While DNA repair genes are not upregulated, inflammation-related genes become transcribed when apoptosis is initiated by activation of STAT transcription factors. Furthermore, comparison with the transcriptional profile of the ΔNp63α isoform from other studies shows only a minimal overlap, suggesting distinct regulatory programs of different p63 isoforms

Interface Controlled Oxidation States in Layered Cobalt Oxide Nanoislands on Gold

Layered cobalt oxides have been shown to be highly active catalysts for the oxygen evolution reaction (OER; half of the catalytic "water splitting" reaction), particularly when promoted with gold. However, the surface chemistry of cobalt oxides and in particular the nature of the synergistic effect of gold contact are only understood on a rudimentary level, which at present prevents further exploration. We have synthesized a model system of flat, layered cobalt oxide nanoislands supported on a single crystal gold (111) substrate. By using a combination of atom-resolved scanning tunneling microscopy, X-ray photoelectron and absorption spectroscopies and density functional theory calculations, we provide a detailed analysis of the relationship between the atomic-scale structure of the nanoislands, Co oxidation states and substrate induced charge transfer effects in response to the synthesis oxygen pressure. We reveal that conversion from CO2+ to Co3+ can occur by a facile incorporation of oxygen at the interface between the nanoisland and gold, changing the islands from a Co-O bilayer to an O-Co-O trilayer. The O-Co-O trilayer islands have the structure of a single layer of beta-CoOOH, proposed to be the active phase for the OER, making this system a valuable model in understanding of the active sites for OER. The Co oxides adopt related island morphologies without significant structural reorganization, and our results directly demonstrate that nanosized Co oxide islands have a much higher structural flexibility than could be predicted from bulk properties. Furthermore, it is clear that the gold/nanoparticle interface has a profound effect on the structure of the nanoislands, suggesting a possible promotion mechanism