Changes in structure and conduction type upon addition of Ir to ZnO thin films

Zn-Ir-O (Zn/Ir ≈ 1/1) thin films have been reported to be a potential p-type TCO material. It is, however, unknown whether it is possible to achieve p-type conductivity at low Ir content, and how the type and the magnitude of conductivity are affected by the film structure. To investigate the changes in properties taking place at low and moderate Ir content, this study focuses on the structure, electrical and optical properties of ZnO:Ir films with iridium concentration varying between 0.0 and 16.4 at.%. ZnO:Ir thin films were deposited on glass, Si, and Ti substrates by DC reactive magnetron co-sputtering at room temperature. Low Ir content (up to 5.1 at.%) films contain both a nano-crystalline wurtzite-type ZnO phase and an X-ray amorphous phase. The size of the crystallites is below 10 nm and the lattice parameters a and c are larger than those of pure ZnO crystal. Structural investigation showed that the film's crystallinity declines with the iridium concentration and films become completely amorphous at iridium concentrations between 7.0 and 16.0 at.%. An intense Raman band at approximately 720 cm− 1 appears upon Ir incorporation and can be ascribed to peroxide O22– ions. Measurable electrical conductivity appears together with a complete disappearance of the wurtzite-type ZnO phase. The conduction type undergoes a transition from n- to p-type in the Ir concentration range between 12.4 and 16.4 at.%. Absorption in the visible range increases linearly with the iridium concentration.VMTKC project 18, agreement No. 1.2.1.1/16/A/005; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Metal Oxide Clusters on Nitrogen-Doped Carbon are Highly Selective for CO2Electroreduction to CO

The electrochemical reduction of CO2 (eCO2RR) using renewable energy is an effective approach to pursue carbon neutrality. The eCO2RR to CO is indispensable in promoting C-C coupling through bifunctional catalysis and achieving cascade conversion from CO2 to C2+. This work investigates a series of M/N-C (M = Mn, Fe, Co, Ni, Cu, and Zn) catalysts, for which the metal precursor interacted with the nitrogen-doped carbon support (N-C) at room temperature, resulting in the metal being present as (sub)nanosized metal oxide clusters under ex situ conditions, except for Cu/N-C and Zn/N-C. A volcano trend in their activity toward CO as a function of the group of the transition metal is revealed, with Co/N-C exhibiting the highest activity at -0.5 V versus RHE, while Ni/N-C shows both appreciable activity and selectivity. Operando X-ray absorption spectroscopy shows that the majority of Cu atoms in Cu/N-C form Cu0 clusters during eCO2RR, while Mn/, Fe/, Co/, and Ni/N-C catalysts maintain the metal hydroxide structures, with a minor amount of M0 formed in Fe/, Co/, and Ni/N-C. The superior activity of Fe/, Co/, and Ni/N-C is ascribed to the phase contraction and the HCO3- insertion into the layered structure of metal hydroxides. Our work provides a facile synthetic approach toward highly active and selective electrocatalysts to convert CO2 into CO. Coupled with state-of-the-art NiFe-based anodes in a full-cell device, Ni/N-C exhibits >80% Faradaic efficiency toward CO at 100 mA cm-2.The research leading to these results has received funding from the A-LEAF Project, which is funded by the European Union’s H2020 Programme under grant agreement no. 732840. ICN2 and ICIQ acknowledge funding from the FEDER/Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación (projects ENE2017-85087-C3 and RTI2018-095618-B-I00) and the Generalitat de Catalunya (2017 SGR 327 and 2017- SGR-1406) and by the CERCA Programme / Generalitat de Catalunya. ICN2 and ICIQ are supported by the Severo Ochoa program from Spanish MINECO (grants no. SEV-2017-0706 and CEX2019-000925-S)

Seed-mediated atomic-scale reconstruction of silver manganate nanoplates for oxygen reduction towards high-energy aluminum-air flow batteries

Aluminum-air batteries are promising candidates for next-generation high-energy-density storage, but the inherent limitations hinder their practical use. Here, we show that silver nanoparticle-mediated silver manganate nanoplates are a highly active and chemically stable catalyst for oxygen reduction in alkaline media. By means of atomic-resolved transmission electron microscopy, we find that the formation of stripe patterns on the surface of a silver manganate nanoplate originates from the zigzag atomic arrangement of silver and manganese, creating a high concentration of dislocations in the crystal lattice. This structure can provide high electrical conductivity with low electrode resistance and abundant active sites for ion adsorption. The catalyst exhibits outstanding performance in a flow-based aluminum-air battery, demonstrating high gravimetric and volumetric energy densities of similar to 2552 Wh kg(Al)(-1) and similar to 6890 Wh I-Al(-1) at 100 mA cm(-2), as well as high stability during a mechanical recharging process

Fe-heme structure in Cu, Zn superoxide dismutase from Haemophilus ducreyi by X-ray absorption spectroscopy

We have carried out an X-ray Absorption Spectroscopy (XAS) study of ferric, ferrous, CO- and NO-bound Haemophilus ducreyi Cu,ZnSOD (HdSOD) in solution to investigate the structural modifications induced by the binding of small gaseous ligands to heme in this enzyme. The combined analysis of EXAFS and XANES data has allowed us to characterize the local structure around the Fe-heme with 0.02A accuracy, revealing a heterogeneity in the distances between iron and the two histidine ligands which was not evident in the X-ray crystal structure. In addition, we have shown that the metal oxidation state does not influence the Fe-heme coordination environment, whereas the presence of the CO and NO ligands induces local structural rearrangements in the enzyme which are very similar to those already observed in other hexa-coordinated heme proteins, such as neuroglobin

Stabilization of Iron-Based Fuel Cell Catalysts by Non-Catalytic Platinum

article publié en open accessInternational audienceSince a few years, non-precious metal catalysts with iron or cobalt as active centers show sufficient activity to be viable candidates as electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFC). They can sustain substantial current densities when operated at low potentials. However, their stabilization at high cathode potentials, necessary for high energy efficiency, remains a daunting task. Here an Fe-N-C catalyst is stabilized over the whole potential range through functionalization with minute amounts of platinum. With the addition of 1 to 2 wt% Pt, the present Pt/Fe-N-C hybrid catalysts show a similar current density at 0.8 V than Fe-N-C but are much more stable during operation in PEMFC. Various characterization techniques, including CO stripping, demonstrate that platinum in these hybrid catalysts is ORR-inactive, not only initially but also after the PEMFC potentiostatic test. It is proposed that the present platinum species protects the Fe-based active sites from the ORR by-product H 2 O 2 , or reactive oxygen species produced from its reaction with surface Fe. This proof-of-concept paves the way for a new class of hybrid catalysts, where the activity and stability of Me-N-C catalysts can be independently addressed

Ion hydration in high-density water

Structural modifications of the Zn(2+) hydration properties under high pressure (up to 2.85 GPa) have been investigated by Molecular Dynamics (MD) simulations and the first shell structural results have been experimentally validated by X-ray Absorption spectroscopy. The first shell hydration complex of the Zn(2+) ion retains an octahedral symmetry with a shortening of the Zn-O distance up to 0.04 angstrom and an increase of the thermal motion. The structural transformations occurring to water with increasing density are also investigated by MD simulations; the effect of pressure is to increase the number of interstitial water molecules, while the tetrahedral first shell cluster is only slightly distorted in the high-density conditions