Hydrogen peroxide (H2O2), a reactive oxygen species, is an excellent alternative to oxygen as an oxidant for direct liquid fuel cells (DLFCs). To overcome problems related to scarcity and high cost of commonly used noble metal electrodes, nickel (Ni) and nickel-rare earth (RE = Ce, Sm, Dy) alloys are synthesised and evaluated as electrode materials for H2O2 reduction reaction (HPRR) in alkaline media. These Ni-RE alloys (containing 5 and 10 at.% RE metal) are produced by arc melting and analysed by X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Voltammetric and chronoamperometric measurements are employed to assess the performance of the Ni-RE alloys for HPRR in 2 M NaOH solution. The Ni0.95Ce0.05 alloy exhibits impressively high catalytic activity for HPRR, with a number of exchanged electrons of 1.7 and activation energy of 38 kJ mol(-1), suggesting its application as cathode material in DLFCs.

Platinum–dysprosium (Pt–Dy) alloys prepared by the arc melting technique are assessed as potential electrodes for the oxygen reduction reaction (ORR) using voltammetry and chronoamperometry in alkaline media. A relatively small change (10 at.%) in the alloy composition brought a notable difference in the alloys’ performance for the ORR. Pt40Dy60 electrode, i.e., the electrode with a lower amount of Pt, was identified to have a higher activity towards ORR as evidenced by lower overpotential and higher current densities under identical experimental conditions. Furthermore, DFT calculations point out the unique single-atom-like coordination and electronic structure of Pt atoms in the Pt40Dy60 surface as responsible for enhanced ORR activity compared to the alloy with a higher Pt content. Additionally, Pt–Dy alloys showed activity in the oxygen evolution reaction (OER), with the OER current density lower than that of pure Pt.

Platinum–dysprosium (Pt–Dy) alloys prepared by arc melting are assessed as electrodes for the oxygen reduction reaction (ORR) using voltammetry and chronoamperometry in alkaline media. A relatively small change (10 at.%) in the alloy composition brought a notable difference in the alloys’ performance for the ORR. Pt4Dy6 electrode, i.e., the electrode with a lower amount of Pt, was identified to have higher activity for ORR as evidenced by lower overpotential and higher current densities under identical experimental conditions. Furthermore, DFT calculations point out unique single-atom-like coordination and electronic structure of Pt atoms in the Pt4Dy6 surface as responsible for enhanced ORR activity, compared to the alloy with a higher Pt content.

Gold-rare earth (Au-RE) alloys with equiatomic compositions are prepared by arc (RE = Dy, Ho, Y) or induction (RE = Sm) melting. Morphology and phase composition is assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDXS), while X-ray powder diffraction (XRPD) is used to confirm crystal structures. The Au-RE electrodes are evaluated for borohydride oxidation reaction (BOR) in alkaline media employing cyclic voltammetry and chronoamperometry. The obtained data allows calculation of kinetic parameters that characterize the borohydride (BH4-) oxidation at Au-RE alloys, including the number of exchanged electrons, n, and the anodic charge transfer coefficient, alpha. n values range from 2.4 to 4.4, while alpha values are found to be in the 0.60-0.83 range. The BOR apparent activation energy, E-a(app), and the reaction order, beta, are also determined from CV data obtained at different temperatures and different BH4- concentrations, respectively. Low E-a(app) values range from 16.4 (Au-Sm) to 20.2 kJ mol(-1) (Au-Y) and beta values suggest that BOR at the examined alloys is a 1st order reaction with respect to BH4- concentration. A small-scale direct borohydride-peroxide fuel cell (DBPFC) operating with Au-Y anode at 25 degrees C reaches a peak power density of 150 mW cm(-1). The cell performance is enhanced when increasing the temperature to 45 degrees C, with a maximum power density of 215 mW cm(-2) being attained. (C) 2020 Elsevier B.V. All rights reserved.

The two La2Pd3Ge5 and Nd2Pd3Ge5 compounds, crystallizing in the oI40-U2Co3Ge5 crystal structure, were targeted for analysis of their chemical bonding and physical properties. The compounds of interest were obtained by arc melting and characterized by differential thermal analysis, scanning electron microscopy, and X-ray diffraction both on powder and on a single crystal (for the La analogue), to ensure the high quality of the samples and accurate crystallographic data. Chemical bonding was studied by analyzing the electronic structure and effective QTAIM charges of La2Pd3Ge5. A significant charge transfer mainly occurs from La to Pd so that Ge species assume tiny negative charges. This result, together with the -(I)COHP analysis, suggests that, in addition to the expected homopolar Ge bonds within zigzag chains, heteropolar interactions between Ge and the surrounding La and Pd occur with multicenter character. Covalent La–Pd interactions increase the complexity of chemical bonding, which could not be adequately described by the simplified, formally obeyed, Zintl–Klemm scheme. Electric resistivity, specific heat, magnetization, and magnetic susceptibility as a function of temperature indicate for both compounds a metallic-like behavior. For Nd2Pd3Ge5, two low-temperature phase transitions are detected, leading to an antiferromagnetic ground state.

A combined study of solid state interactions in the La–Au–Mg system.

Intermetallics contribute significantly to our current demand for high-performance functional materials. However, understanding their chemistry is still an open and debated topic, especially for complex compounds such as approximants and quasicrystals. In this work, targeted topological data mining succeeded in (i) selecting all known Mackay-type approximants, (ii) uncovering the most important geometrical and chemical factors involved in their formation, and (iii) guiding the experimental work to obtain a new binary Sc-Pd 1/1 approximant for icosahedral quasicrystals containing the desired cluster. Single-crystal X-ray diffraction data analysis supplemented by electron density reconstruction using the maximum entropy method, showed fine structural peculiarities, that is, smeared electron densities in correspondence to some crystallographic sites. These characteristics have been studied through a comprehensive density functional theory modeling based on the combination of point defects such as vacancies and substitutions. It was confirmed that the structural disorder occurs in the shell enveloping the classical Mackay cluster, so that the real structure can be viewed as an assemblage of slightly different, locally ordered, four shell nanoclusters. Results obtained here open up broader perspectives for machine learning with the aim of designing novel materials in the fruitful field of quasicrystals and their approximants. This might become an alternative and/or complementary way to the electronic pseudogap tuning, often used before explorative synthesis.

Proton exchange membrane fuel cells and direct alcohol fuel cells have been extensively studied over the last three decades or so. They have emerged as potential systems to power portable applications, providing clean energy, and offering good commercial viability. Ethanol is considered one of the most interesting fuels in this field. Herein, platinum-rare earth (Pt-RE) binary alloys (RE = Ce, Sm, Ho, Dy, nominal composition 50 at.% Pt) were produced and studied as anodes for ethanol oxidation reaction (EOR) in alkaline medium. A Pt-Dy alloy with nominal composition 40 at.% Pt was also tested. Their electrocatalytic performance was evaluated by voltammetric and chronoamperometric measurements in 2 M NaOH solution with different ethanol concentrations (0.2–0.8 M) in the 25–45 °C temperature range. Several EOR kinetic parameters were determined for the Pt-RE alloys, namely the charge transfer and diffusion coefficients, and the number of exchanged electrons. Charge transfer coefficients ranging from 0.60 to 0.69 and n values as high as 0.7 were obtained for the Pt0.5Sm0.5 electrode. The EOR reaction order at the Pt-RE alloys was found to vary between 0.4 and 0.9. The Pt-RE electrodes displayed superior performance for EOR than bare Pt, with Pt0.5Sm0.5 exhibiting the highest electrocatalytic activity. The improved electrocatalytic activity in all of the evaluated Pt-RE binary alloys suggests a strategy for the solution of the existing anode issues due to the structure-sensitive EOR.

Gold-Rare Earth (Au-RE, RE = Sm, Dy, Ho, Y) alloys were prepared by co-melting stoichiometric amounts of metals. XRPD and SEM/EDX analysis revealed the formation of equiatomic compounds. These alloys were used for the preparation of electrodes for As(III) sensing in aqueous samples. All four electrodes gave a clear response in the presence of As(III) in weakly alkaline media (NaHCO3 + Na2CO3 buffer). Following optimisation of operating parameters (deposition potential of -0.9 V vs SCE and deposition time of 180 s), limits of detection of As(III) at four electrodes were determined to be in 0.8-2.3 ppb region. Au-RE electrodes gave a clear response in the presence of Cu(II) as model interferent and, finally, showed the ability for As(III) sensing in a real sample.

A comparative chemical bonding analysis for the germanides La2 MGe6 (M=Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2 PdGe6 is presented, together with the crystal structure determination for M=Li, Mg, Cu, Ag. The studied compounds adopt the two closely related structure types oS72-Ce2 (Ga0.1 Ge0.9 )7 and mS36-La2 AlGe6 , containing zigzag chains and corrugated layers of Ge atoms bridged by M species, with La/Y atoms located in the biggest cavities. Chemical bonding was studied by means of the quantum chemical position-space techniques QTAIM (quantum theory of atoms in molecules), ELI-D (electron localizability indicator), and their basin intersections. The new penultimate shell correction (PSC0) method was introduced to adapt the ELI-D valence electron count to that expected from the periodic table of the elements. It plays a decisive role to balance the Ge-La polar-covalent interactions against the Ge-M ones. In spite of covalently bonded Ge partial structures formally obeying the Zintl electron count for M=Mg2+ , Zn2+ , all the compounds reveal noticeable deviations from the conceptual 8-N picture due to significant polar-covalent interactions of Ge with La and M ≠ Li, Mg atoms. For M=Li, Mg a formulation as a germanolanthanate M[La2 Ge6 ] is appropriate. Moreover, the relative Laplacian of ELI-D was discovered to reveal a chemically useful fine structure of the ELI-D distribution being related to polyatomic bonding features. With the aid of this new tool, a consistent picture of La/Y-M interactions for the title compounds was extracted.

A systematic study on the existence of R2Pd3Ge5 intermetallics with heavy rare earth metals (R = Gd-Lu) was conducted; only the Yb2Pd3Ge5 was revealed to exist. Its crystal structure was established by X-ray powder diffraction and refined by means of Rietveld method. This compound crystallizes in the orthorhombic U2Co3Si5 structure type (Ibam, oI40, Z = 4, a = 10.2628(1), b = 12.0580(1), and c = 5.98251(6) angstrom), which represents an ordered derivative of the tI10-ThCr2Si2 prototype, ubiquitous among intermetallics. Magnetization and susceptibility measurements indicate that Yb2Pd3Ge5 is a paramagnet with mu(eff) close to 0.8 mu(B)/Yb-atom, suggesting a nearly divalent Yb state. Electrical resistivity and Seebeck coefficient of the studied compound as a function of temperature confirm its metallic-like behavior. (C) 2018 Elsevier B.V. All rights reserved.

In this study, two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4Ge8 is monoclinic, P21/m, mP34, a = 5.7406(3), b = 13.7087(7), c = 8.3423(4) Å,β = 107.8(1), Z = 2; Lu3Pd4Ge4 is orthorhombic, Immm, oI22, a = 4.1368(3), b = 6.9192(5), c = 13.8229(9) Å, Z = 2. The Lu5Pd4Ge8 analysed crystal is one more example of non-merohedral twinning among the rare earth containing germanides. Chemical bonding DFT studies were conducted for these polar intermetallics with a metallic-like behavior. Gathered results for Lu5Pd4Ge8 and Lu3Pd4Ge4 permit to described both of them as composed by [Pd–Ge]δ– three dimensional networks bonded to positively charged lutetium species. From the structural chemical point of view, the studied compounds manifest some similarities to the Zintl phases, containing well-known covalent fragments i.e., Ge dumbbells as well as unique cis-Ge4 units. A comparative analysis of molecular orbital diagrams for Ge2 and cis-Ge10– anions with COHP results supports the idea of the existence of complex Pd–Ge polyanions hosting covalently bonded partially polarised Ge units. The palladium atoms have an anion like behaviour and being the most electronegative cause the noticeable variation of Ge species charges from site to site. Lutetium charges oscillate around +1.5 for all crystallographic positions. Obtained results explained why the classical Zintl-Klemm concept can’t be applied for the studied polar intermetallics.

The corrosion properties of magnesium-heavy rare earth (RE) based alloys have been studied. Binary additions of gadolinium (Gd), dysprosium (Dy) and erbium (Er) to pure magnesium were made to a nominal 1 at.%. The corrosion resistance of Mg99Gd1, Mg99Dy1 and Mg99Er1 alloys has been assessed by using open circuit potential measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) carried out in 0.075 M Na2B4O7 + 0.05 M H3BO3 solution, pH = 8.4. Electrochemical results showed that heavy RE alloying additions significantly improves the corrosion behaviour of magnesium. This improvement can be attributed to enhanced barrier properties of the corrosion products layer and additional active corrosion protection originated from the inhibiting action of the lanthanide cations entrapped as oxides/hydroxides in this surface layer.

The effect of rare earth metals (Gd, Dy, Er,) addition on the corrosion behavior of Zn has been investigated. The corrosion resistance of Zn99Gd1, Zn99Dy1, and Zn99Er1 (at%) alloys has been assessed by open circuit potential and electrochemical impedance spectroscopy (EIS) measurements carried out in a 0.1M NaCl solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on unalloyed Zn. Moreover, the surface morphology and nature of the corrosion products have been investigated. The results indicated that rare earths addition significantly improves the corrosion behavior of unalloyed Zn. This improvement is most likely due to enhanced barrier properties of the corrosion products layer and additional active corrosion protection originated from the inhibiting action of the lanthanide ions entrapped as oxides/hydroxides in this surface layer.

In this study, two novel Lu5Pd4Ge8 and Lu3Pd4Ge4 polar intermetallics were prepared by direct synthesis of pure constituents. Their crystal structures were determined by single crystal X-ray diffraction analysis: Lu5Pd4Ge8 is monoclinic, P21/m, mP34, a = 5.7406(3), b = 13.7087(7), c = 8.3423(4) Å, β = 107.8(1), Z = 2; Lu3Pd4Ge4 is orthorhombic, Immm, oI22, a = 4.1368(3), b = 6.9192(5), c = 13.8229(9) Å, Z = 2. The Lu5Pd4Ge8 analysed crystal is one more example of non-merohedral twinning among the rare earth containing germanides. Chemical bonding DFT studies were conducted for these polar intermetallics and showing a metallic-like behavior. Gathered results for Lu5Pd4Ge8 and Lu3Pd4Ge4 permit to described both of them as composed by [Pd–Ge]δ– three dimensional networks bonded to positively charged lutetium species. From the structural chemical point of view, the studied compounds manifest some similarities to the Zintl phases, containing well-known covalent fragment i.e., Ge dumbbells as well as unique cis-Ge4 units. A comparative analysis of molecular orbital diagrams for Ge26– and cis-Ge10– anions with COHP results supports the idea of the existence of complex Pd–Ge polyanions hosting covalently bonded partially polarised Ge units. The palladium atoms have an anion like behaviour and being the most electronegative cause the noticeable variation of Ge species charges from site to site. Lutetium charges oscillate around +1.5 for all crystallographic positions. Obtained results explained why the classical Zintl-Klemm concept can’t be applied for the studied polar intermetallics.

This study is closely related to the chemical interactions in thermoelectric joints of a hot metal electrode with p- and n-type skutterudite. As a result of this work, a first and complete phase diagram has been constructed for the TiSb system as well as partial phase diagrams (>65 at.% Sb) for the systems ZrSb and HfSb. Investigations are based on X-ray powder and single crystal analyses (determination of the crystal structure of Ti5Sb8 with Zr2.6Ti2.4Sb8-type, space group I4122; RF = 0.032), electron probe microanalyses (EPMA) and differential thermal analyses (DTA). Physical properties were evaluated for the binary compounds MSb2 (M = Ti, Zr, Hf) comprising electrical resistivity (from 4.2 K to 825 K), specific heat, thermal conductivity and thermal expansion coefficient (from 4.2 K to 300 K), Seebeck coefficient (from 300 K to 825 K) and elastic moduli at 300 K. These data will serve to evaluate the potential of MSb2 compounds (M = Ti, Zr, Hf) for thermoelectric devices, where these phases predominantly appear in the diffusion zones of the hot metal electrode with p- and n-type skutterudite.

Phase equilibria in the Yb-Pd-Sn ternary system at 600 degrees C were established in the Pd <= 75 at.% concentration range employing X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro-analysis (EPMA). Besides the known intermetallic compounds, three new ternary intermetallics were revealed in the system, together with homogeneity ranges into the ternary field for some binary phases. Magnetic properties for the new compounds were investigated revealing stable Yb states Yb3+ for Yb3Pd4Sn13 and Yb2+ for Yb5Pd39Sn56, whereas for Yb13Pd40Sn31 an unstable valency of Yb is suggested. (C) 2016 Elsevier B.V. All rights reserved.