A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide

The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.Fil: Mayer, Sergio Federico. Instituto de Ciencia de Materiales de Madrid; España. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodrigues, Joao Elias. Universidade de Sao Paulo; Brasil. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Marini, C.. CELLS–ALBA Synchrotron; EspañaFil: Fernández-Díaz, M.T.. Institut Laue Langevin; FranciaFil: Falcón, H.. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Asensio, M. C.. Consejo Superior de Investigaciones Científicas; España. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ

A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide

The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.Fil: Mayer, Sergio Federico. Instituto de Ciencia de Materiales de Madrid; España. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodrigues, Joao Elias. Universidade de Sao Paulo; Brasil. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Marini, C.. CELLS–ALBA Synchrotron; EspañaFil: Fernández-Díaz, M.T.. Institut Laue Langevin; FranciaFil: Falcón, H.. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Asensio, M. C.. Consejo Superior de Investigaciones Científicas; España. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ

Unintended cation crossover influences CO2 reduction selectivity in Cu based zero gap electrolysers

Membrane electrode assemblies enable CO2 electrolysis at industrially relevant rates, yet their operational stability is often limited by formation of solid precipitates in the cathode pores, triggered by cation crossover from the anolyte due to imperfect ion exclusion by anion exchange membranes. Here we show that anolyte concentration affects the degree of cation movement through the membranes, and this substantially influences the behaviors of copper catalysts in catholyte free CO2 electrolysers. Systematic variation of the anolyte KOH or KHCO3 ionic strength produced a distinct switch in selectivity between either predominantly CO or C2 products mainly C2H4 which closely correlated with the quantity of alkali metal cation K crossover, suggesting cations play a key role in C C coupling reaction pathways even in cells without discrete liquid catholytes. Operando X ray absorption and quasi in situ X ray photoelectron spectroscopy revealed that the Cu surface speciation showed a strong dependence on the anolyte concentration, wherein dilute anolytes resulted in a mixture of Cu and Cu0 surface species, while concentrated anolytes led to exclusively Cu0 under similar testing conditions. These results show that even in catholyte free cells, cation effects including unintentional ones significantly influence reaction pathways, important to consider in future development of catalysts and device

CO2 electroreduction activity and dynamic structural evolution of in situ reduced nickel indium mixed oxides

In the field of CO2 electroreduction CO2ER , tuning the selectivity among diverse products remains a major challenge. Mixed metal catalysts offer possible synergetic effects which can be exploited for tuning product selectivity. We present a simple wet chemical approach to synthesize a range of nickel indium mixed oxide NiAInBOx thin films with homogeneous metal distribution. CO2 electroreduction results indicate that the NiAInBOx mixed oxide thin films can achieve high CO selectivity gt;70 in contrast with the single metal oxides NiO H2 gt;90 and In2O3 formate gt;80 . The relative composition Ni40In60Ox attained the best CO selectivity of 71 at moderate cathodic bias of amp; 8722;0.8 VRHE, while a higher cathodic bias E lt; amp; 8722;0.9 V promoted a decrease of CO in favor of formate. A detailed investigation of the Ni40In60Ox thin films following progressive stages of reduction during CO2ER revealed dynamic structural transformations strongly dependent on applied bias and electrolysis time. For the CO selective catalyst composition, at moderate cathodic bias E lt; amp; 8722;0.8 V and short electrolysis times 1 h , the catalyst is composed of nickel indium alloy grains embedded in amorphous Ni In mixed oxide as observed by electron microscopy. Extending electrolysis time at amp; 8722;0.8 V for 10 h, or increasing the applied reductive bias to amp; 8722;1.0 V, result in a complete reduction of the residual oxide film into an interconnected array of multicomponent In, Ni, Ni3In7 nanoparticles which display significantly lower CO selectivity lt;50 . Our results indicate that the persistent amorphous NiInOx oxide alloy composite material preserved in the early stages of reduction at amp; 8722;0.8 V plays a key role in CO selectivity. The highly dynamic structure observed in this catalytic system demonstrates the importance of conducting detailed structural characterization at various applied potentials to understand the impact of structural changes on the observed CO2ER selectivity trends; and thus be able to distinguish structural effects from mechanistic effects triggered by increasing the reductive bia

Electrodeposition of palladium dotted nickel nanowire networks as a robust self supported methanol electrooxidation catalyst

Mass activity and long term stability are two major issues in current fuel cell catalyst designs. While supported catalysts normally suffer from poor long term stability but show high mass activity, unsupported catalysts tend to perform better in the first point while showing deficits in the latter one. In this study, a facile synthesis route towards self supported metallic electrocatalyst nanoarchitectures with both aspects in mind is outlined. This procedure consists of a palladium seeding step of ion track etched polymer templates followed by a nickel electrodeposition and template dissolution. With this strategy, free standing nickel nanowire networks which contain palladium nanoparticles only in their outer surface are obtained. These networks are tested in anodic half cell measurements for demonstrating their capability of oxidising methanol in alkaline electrolytes. The results from the electrochemical experiments show that this new catalyst is more tolerant towards high methanol concentrations up to 5molL amp; 8722;1 than a commercial carbon supported palladium nanoparticle catalyst and provides a much better long term stability during potential cyclin

Dynamics of droplet formation at T-shaped nozzles with elastic feed lines

We describe the formation of water in oil droplets, which are commonly used in lab-on-a-chip systems for sample generation and dosing, at microfluidic T-shaped nozzles from elastic feed lines. A narrow nozzle forms a barrier for a liquid-liquid interface, such that pressure can build up behind the nozzle up to a critical pressure. Above this critical pressure, the liquid bursts into the main channel. Build-up of pressure is possible when the fluid before the nozzle is compressible or when the channel that leads to the nozzle is elastic. We explore the value of the critical pressure and the time required to achieve it. We describe the fluid flow of the sudden burst, globally in terms of flow rate into the channel and spatially resolved in terms of flow fields measured using micro-PIV. A total of three different stages-the lag phase, a spill out phase, and a linear growth phase-can be clearly discriminated during droplet formation. The lag time linearly scales with the curvature of the interface inside the nozzle and is inversly proportional to the flow rate of the dispersed phase. A complete overview of the evolution of the growth of droplets and the internal flow structure is provided in the digital supplement.FWN – Publicaties zonder aanstelling Universiteit Leide

Facile Synthesis of Hierarchical CuS and CuCo2S4 Structures from an Ionic Liquid Precursor for Electrocatalysis Applications

Covellite phase CuS and carrollite phase CuCo2S4 nano and microstructures were synthesized from tetrachloridometallate based ionic liquid precursors using a novel, facile, and highly controllable hot injection synthesis strategy. The synthesis parameters including reaction time and temperature were first optimized to produce CuS with a well controlled and unique morphology, providing the best electrocatalytic activity toward the oxygen evolution reaction OER . In an extension to this approach, the electrocatalytic activity was further improved by incorporating Co into the CuS synthesis method to yield CuCo2S4 microflowers. Both routes provide high microflower yields of gt;80 wt . The CuCo2S4 microflowers exhibit a superior performance for the OER in alkaline medium compared to CuS. This is demonstrated by a lower onset potential amp; 8764;1.45 V vs RHE 10 mA cm2 , better durability, and higher turnover frequencies compared to bare CuS flowers or commercial Pt C and IrO2 electrodes. Likely, this effect is associated with the presence of Co3 sites on which a better adsorption of reactive species formed during the OER e.g., OH, O, OOH, etc. can be achieved, thus reducing the OER charge transfer resistance, as indicated by X ray photoelectron spectroscopy and electrochemical impedance spectroscopy measurement

Stabilizing organic photocathodes by low temperature atomic layer deposition of TiO2

Low-temperature atomic layer deposition forms a compact TiO2 film atop a polymer light absorber for stable and efficient organic–inorganic photo-driven H2 evolution.</p

Multihole water oxidation catalysis on haematite photoanodes revealed by operando spectroelectrochemistry and DFT

Water oxidation is the key kinetic bottleneck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi redox reaction on metal oxide photoanodes remains a significant experimental and theoretical challenge. Here, we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly on haematite. We observe that haematite is able to access a reaction mechanism that is third order in surface hole density, which is assigned to equilibration between three surface holes and M OH O M OH sites. This reaction exhibits low activation energy Ea amp; 8201; amp; 8776; amp; 8201;60 amp; 8201;meV . Density functional theory is used to determine the energetics of charge accumulation and O O bond formation on a model haematite 110 surface. The proposed mechanism shows parallels with the function of the oxygen evolving complex of photosystem II, and provides new insights into the mechanism of heterogeneous water oxidation on a metal oxide surfac

Poly ionic liquid nanovesicles via polymerization induced self assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction

Herein, we report a straightforward, scalable synthetic route towards poly ionic liquid PIL homopolymer nanovesicles NVs with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one step free radical polymerization induced self assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs internal morphology is studied in detail by coarse grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra small 1 amp; 8764; 3 nm in size copper nanoparticles CuNPs and employed as electrocatalysts for CO2 electroreduction. The composite electrocatalysts exhibit a 2.5 fold enhancement in selectivity towards C1 products e.g., CH4 , compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO2 conversion to C1 product