Facile synthesis of high-surface area platinum-doped ceria for low temperature CO oxidation

International audienceUsing a simple slow decomposition method of nitrate precursors, high-surface area platinum-doped ceria with a crystallite size of 9 nm can be prepared. The catalytic performance of the compound can be tuned by changing the reduction temperature under hydrogen (300°C, 500°C and 700°C). The catalyst treated at 300°C shows the best catalytic performance, being active at room temperature. The materials were analysed using a combination of structural characterization methods (X-ray diffraction (XRD), nitrogen physisorption, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM)), surface sensitive methods (X-ray photoelectron spectroscopy (XPS), H 2-chemisorption and H 2-temperature-programmed reduction (TPR)) and X-ray absorption fluorescence spectroscopy (XAFS). HAADF-STEM and XAFS analysis suggests successful doping of platinum in the ceria lattice. After pretreatment at 300°C, the situation is slightly different. While no defined platinum nanoparticles can be identified on the surface, some platinum is in a reduced state (XPS, H 2-chemisorption)

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping

The conversion of CO2 into desirable multicarbon products via the electrochemical reduction reaction holds promise to achieve a circular carbon economy. Here, we report a strategy in which we modify the surface of bimetallic silver-copper catalyst with aromatic heterocycles such as thiadiazole and triazole derivatives to increase the conversion of CO2 into hydrocarbon molecules. By combining operando Raman and X-ray absorption spectroscopy with electrocatalytic measurements and analysis of the reaction products, we identified that the electron withdrawing nature of functional groups orients the reaction pathway towards the production of C2+ species (ethanol and ethylene) and enhances the reaction rate on the surface of the catalyst by adjusting the electronic state of surface copper atoms. As a result, we achieve a high Faradaic efficiency for the C2+ formation of approximate to 80% and full-cell energy efficiency of 20.3% with a specific current density of 261.4 mA cm(-2) for C2+ products. Strategies to systematically tune CO2 electroreduction to multicarbon products are of high interests. Here the authors report electron withdrawing functional group alters the reaction pathway towards C2+ products by adjusting the oxidation state of surface copper.D.V., K.Q., and H.L.W. acknowledge funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 804320). L.L., D.V., and H.L.W acknowledge the use of TEM instrumentation provided by the Nation Facility ELECMI ICTS (`Division de Microscopia Electronica', Universidad de Cadiz, DME-UCA). L.L. acknowledges funding from the Andalusian regional government (FEDER-UCA-18-106613), the European Union's Horizon 2020 research and innovation program (grant agreement 823717-ESTEEM3), and the Spanish Ministerio de Economia y Competitividad (PID2019-107578GA-I00). K.Q. and Y.Z. acknowledge financial support from the China Postdoctoral Science Foundation (2018M633127) and the Natural Science Foundation of Guangdong Province (2018A030310602). J.L. acknowledge financial support from the National Natural Science Foundation of China (21808134). We thank Soleil Synchrotron and Andrea Zitolo for allocating beamtime at beamline Samba within the proposal 20200732

Controlled structure and hydrophilic property of polymethylhydrosiloxane thin films attached on silicon support and modified with phosphorylcholine group

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Aqueous hydrazine borane N2H4BH3 and nickel-based catalyst: An effective couple for the release of hydrogen in near-ambient conditions

International audienceNickel-based bimetallic catalysts were screened using the sodium borohydride NaBH4 hydrolysis and the aqueous hydrazine borane N2H4BH3 dehydrogenation. A total of 22 bimetallic catalysts were synthesized according to an easy process while focusing on metals like Fe, Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt and Au. In the end, the bimetallic candidate Ni87.5Pt12.5 showed to be the most active and the most selective for the dehydrogenation of N2H4BH3. At 70 degrees C, it is able to decompose N2H4BH3 into 5.8 equivalents of H-2+N-2 in less than 12 min such as: N2H4BH3 + 3H(2)O -> 0.95 N-2 + 0.1 NH3 + B(OH)(3) 4.85H(2). Durability and stability tests were also performed. In our conditions, Ni87.5Pt12.5 was found to suffer from small loss of performance because of an electronic evolution of the catalytic surface leading to modified sorption properties of the catalytic sites. Our main results are reported and discussed herei

XPS study of Ge-Se-Te surfaces functionalized with organosilanes

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Surface Properties of Alkoxysilane Layers Grafted in Supercritical Carbon Dioxide

International audienceSilicon oxide surface properties can be easily modified by grafting alkoxysilane molecules. Here, we studied the structure and the morphology of ultrathin layers prepared by the grafting of alkoxysilanes having different head groups (thiol, amine, and iodo) in supercritical carbon dioxide (CO2) on model plane silicon oxide surfaces. Several characterization techniques (X-ray reflectivity, water contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM)) were used to determine the physicochemical properties of the layers prepared at different temperatures. Moreover, for the first time, AFM peak force measurements were used to delve deeper into the determination of the structure of these ultrathin alkoxysilane layers. The results show that the grafting temperature and the nature of the head group strongly affect the morphology and structure of the grafted layers. Dense monolayers are obtained with 3-(mercaptopropyl)trimethoxysilane at 60 °C, polycondensed layers are always prepared with [3-(aminoethylamino)propyl]trimethoxysilane, and a dense bilayer is synthesized with 3-(iodopropyl)triethoxysilane at 120 °C

Photothermal Hydrogen Production Using Noble-Metal-Free Ti@TiO 2 Core–Shell Nanoparticles under Visible–NIR Light Irradiation

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Microwave-assisted selective oxidation of sugars to carboxylic acids derivatives in water over zinc-vanadium mixed oxide

Zinc-vanadium (Zn3V2O8) nanostructured mixed oxide (ZVO) was synthesized by precipitation method. The ZVO was characterized by TGA, XRD, N2-adsorption/desorption, NH3-TPD, XPS, SEM, and TEM. XPS and NH3-TPD analyses revealed that it was a Zn/V-based strong oxidant catalyst, with a mixture of both Lewis acid and Brønsted surface acid sites. The ZVO was found to be an efficient catalyst for selective oxidation of glucose and xylose to galacturonic and glycolic acid, respectively, under microwave activation. Response surface methodology was applied to find the optimal operating conditions for maximization of the sugar conversion and selectivity. There was a 60% selectivity of galacturonic acid and 46% of glycolic acid using glucose and xylose, respectively. The ability to regenerate the ZVO was assessed by determining the change in the reaction indices in successive reaction–regeneration cycles. The causes of performance activation were ascertained, characterizing the regenerated ZVO by XRD, SEM, and NH3-TPD

Optimal direct electron transfer between MWCNTs@COOH/BOD/chitosan layer and porous carbon felt for dioxygen reduction

International audienceWe present the effect of thermal treatment of carbon felt by gas flow containing 1% of oxygen at high temperature on the direct electron transfer and electrocatalytic oxygen reduction currents by a bilirubin oxidase (BOD) film directly adsorbed in the presence of carbon nanotubes on to a porous carbon felt (PCF). The upgraded properties (surface area, pore volume and hydrophilicity) of the resulting porous carbon felt (PCF) in comparison to commercial carbon felt (raw CF), creates a suitable support for the entrapment of MWCNTs bearing negative charges at neutral pH and BOD enzymes, all the components being entrapped in chitosan layer reticulated with glutaraldehyde. Since functional MWCNTs are 2 usually used to facilitate DET, we introduce COOH@MWCNTs, bearing negative charges at neutral pH, in the enzyme layer to evaluate their impact on the electron transfer properties with BOD. The enzyme immobilization efficiency is examined by varying the amount of the components and the immobilization procedure. Linear sweep voltammetry (LSV) and chronoamperometry measurements are used to evaluate the electrochemical behavior of the enzymatic biocathodes. Based on the experimental results, we show that the optimized bioelectrode delivers a current density of 3.70 mA cm-2at 0.15 V vs Ag/AgCl and could retain above 55 % of its initial response after 4 months, proving its outstanding performance. This new bioelectrode allows for optimal DET-type bioelectrocatalytic activity toward O2 reduction and is a very promising candidate for the construction of 3-dimensional cathodes in (bio)-electrochemical devices needing high current output

Hybrid Photoelectrocatalytic TiO₂-Co₃O₄/Co(OH)₂ Materials Prepared from Bio-Based Surfactants for Water Splitting

The development of new photoanode materials for hydrogen production and water treatment is in full progress. In this context, hybrid TiO2-Co3O4/Co(OH)2 photoanodes prepared using the sol–gel method using biosurfactants are currently being developed by our group. The combination of TiO2 with a cobalt-based compound significantly enhances the visible absorption and electrochemical performance of thin films, which is mainly due to an increase in the specific surface area and a decrease in the charge transfer resistance on the surface of the thin films. The formation of these composites allows for a 30-fold increase in the current density when compared to cobalt-free materials, with the best TiO2-CoN0.5 sample achieving a current of 1.570 mA.cm−2 and a theoretical H2 production rate of 0.3 µmol.min−1.cm−2 under xenon illumination