An nanoporous NiMnFeMo alloy is exploited for over water splitting in basic solutions. The free-standing 3D nanoporous electrode exhibits both outstanding HER and OER catalytic activities even at ...high current density in basic electrolyte, only 1.54V for full water splitting at 10 mA cm−2.
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•A free-standing nanoporous NiMnFeMo alloy with ultrahigh catalytic activity is synthesized.•The electrode can stably deliver 1000 mA cm−2 at only 290 mV for HER and 570 mV for OER.•The synergetic reaction of Ni with Mn, Fe and Mo results in good HER preformance.
Although significant progresses have been achieved recently in developing efficient catalysts for electrochemical water splitting, high performance catalysts toward hydrogen evolution and oxygen evolution in alkaline electrolyte at high current density (≧1000 mA cm−2) have been seldom realized. Herein, we report a flexible and free-standing nanoporous NiMnFeMo alloy (np-NiMnFeMo) with ultrahigh catalytic activity as both anode and cathode even at high current density. The nanoporous NiMnFeMo alloy can deliver as high as 1000 mA cm−2 at an overpotential of only 290 mV for hydrogen evolution reaction and 570 mV for oxygen evolution reaction. DFT calculations indicate that the ultrahigh HER activity of the catalyst is originated from the synergetic effect of the solid solution elements, where Ni atoms act as water dissociation center in the np-NiMnFeMo and the other metals (Mn, Fe and Mo) regulate the electronic structure and provide superior adsorption properties towards hydrogen. More importantly, the electrolyzer, assembled using the np-alloys as both cathode and anode for full water splitting, shows excellent stability.
•Impurity diffusion coefficients in meta-stable fcc Mg are predicted.•Reliable diffusivities of the Al–Cu–Mg system are predicted systematically.•Combination of first-principles and CALPHAD is ...feasible to study diffusivity.
The diffusivities in fcc phase of the Al–Cu–Mg system are systematically predicted via first-principles calculations coupled with CALPHAD (CALculation of PHAse Diagram) technique. All the self- and impurity diffusion coefficients of fcc phase in this ternary system, including both stable and meta-stable states, are calculated via first-principles calculations. The enthalpy of vacancy formation and migration, binding enthalpy of vacancy–solute, entropy of vibration, effective atomic jump frequency, as well as the pre-factors and activation energies for diffusion in the Arrhenius equation are obtained. The atomic mobilities of the three elements are then obtained based on the first-principles calculated diffusion coefficients. Moreover, the interdiffusion coefficients of the Al–Cu, Al–Mg and Cu–Mg binary systems are calculated by means of the DICTRA (DIffusion-Controlled TRAnsformation) package in the framework of CALPHAD approach. Comprehensive comparisons between the predicted and measured diffusivities show that most of the experimental data can be well reproduced. It is found that the combination of first-principles calculations and CALPHAD technique is an effective strategy to obtain diffusivities for multicomponent systems.
The phase relation in the Al rich corner of the Al-Cr-Mg system was re-investigated at 400, 450, and 500 °C using diffusion couples, quenching experiments, and differential thermal analysis ...techniques. The homogeneity range of the Al18Cr2Mg3 phase was determined to be Al-(8.7 ± 0.6) at.% Cr-(13.0 ± 2) at.% Mg. It was also confirmed that there is no ternary compound other than Al18Cr2Mg3 in the Al-Al7Mg3-Cr system. A thermodynamic modeling for the binary Al-Cr and ternary Al-Cr-Mg systems was carried out based on the critically evaluated experimental data and new phase equilibria data from the present study.
•The phase relation in the Al rich corner of the Al-Cr-Mg system was investigated at 400, 450, and 500 °C.•The homogeneity range of Al18Cr2Mg3 phase was determined to be Al-(8.7 ± 0.6) at.% Cr-(13.0 ± 2) at.% Mg.•Thermodynamic modeling for the Al-Cr and ternary Al-Cr-Mg systems.
First-principles calculations are used to investigate the site preference and diffusion of hydrogen in the initial stage of hydrogenation of Mg. The fcc-hollow site and the tetrahedral site are found ...to be the energetically favorable sites for hydrogen atom on and below Mg(0001) surface, respectively. When a hydrogen atom diffuses into the bulk Mg, it has to firstly overcome an energy barrier of 0.45 eV. There exist two different diffusion pathways with this energy barrier, which start from two possible surface adsorption sites. While a lower barrier of 0.31 eV is necessary for hydrogen further diffusion into the bulk region. The effect of the subsurface vacancy on hydrogenation is also investigated in terms of hydrogen trapping and diffusion barrier. At most six hydrogen atoms can be trapped by a single Mg vacancy in the subsurface. It is required at least 0.40 eV for the trapped hydrogen to escape from the vacancy. This trapping property and relatively large diffusion barrier to escape from the vacancy would prevent further diffusion of hydrogen into Mg during the initial stage of hydrogenation. The vacancy, however, has little influence on the diffusion property of its neighboring hydrogen atom.
•The early stage of Mg hydrogenation is studied via first-principles calculations.•Two equal paths for hydrogen penetration through Mg surface are obtained.•Subsurface Mg vacancy can trap at most six hydrogen atoms.•Subsurface Mg vacancy has little effect on diffusion property of hydrogen near it.
The phase transformations and pressure-volume dependencies of the Ti–45Al alloy with respect to pressure have been investigated by means of in-situ observation using multi anvil-type high-pressure ...devices and synchrotron radiation. Under hydrostatic compression from 0 to 10.1 GPa, about 2.3 vol % of γ transforms continuously to α2. Lattice parameters as well as volume fractions of these two phases have been determined as functions of pressure. Bulk moduli estimated using Birch-Murnaghan's equation of state are 146.2 GPa for the γ phase, 136.7 GPa for the α2 phase, and 145.6 GPa for their two-phase mixture of Ti–45Al alloy. First-principles have also applied to investigate bulk moduli of two single phases, and the deviation between calculations and measurements is discussed and attributed to mainly phase transformation. The present study provides useful insights into thermodynamics of α2 and γ phases under high pressure.
•A γ-based Ti–Al alloy is chosen for in-situ experiments under high pressure using synchrotron X-ray diffraction.•A continuous phase transformation from γ to α2 and the lattice evolution during hydrostatic compression are observed.•Bulk moduli of these two individual phases and their mixture are calculated and compared with first-principles calculation.
•The atomic mobilities for fcc Al–W, fcc Ni–W, fcc Ni–Al–W and L12 Ni–Al–W alloys were critically assessed.•The impurity diffusivity of W in fcc_Al was obtained via first-principles calculations.•The ...calculated results agree well with the diffusivities available in the literature.•Two fcc/L12-type diffusion couples were prepared and the concentration-distance profiles were measured.•The model-predicted concentration profiles agree well with the experimental data in the literature and in the present work.
Based on various experimentally measured diffusivities available in the literature together with the reported thermodynamic parameters, the atomic mobilities for disordered fcc and ordered L12 Ni–Al–W alloys were assessed on the basis of a recently developed phenomenological model incorporated in the DICTRA software. In order to provide the missing impurity diffusion coefficients of W in fcc_Al, first-principles calculations were utilized in the present work. Comprehensive comparisons between the calculated and experimental diffusion coefficients show that all the experimental data can be well reproduced by the atomic mobilities obtained in the present work. In order to further verify the reliability of the presently obtained atomic mobilities, two fcc/L12-type diffusion couples (i.e., Ni–5at.% Al–5at.% W/Ni–20at.% Al–4at.% W and Ni/Ni–22at.% Al–2at.% W) were prepared and the concentration-distance profiles after annealing at 1323K for 86.4ks were measured. The excellent agreement between the model-predicted concentration-distance profiles and the experimental data indicates that the presently obtained atomic mobilities in fcc/L12 Ni–Al–W alloys are reliable.
A new relationship among self- and impurity diffusion coefficients has been proposed for binary solution phases and verified
via
30 solid solutions. In terms of this model, one impurity diffusion ...coefficient in a binary phase can be predicted once the other three diffusion coefficients are available. The application of the present model is exemplified in the Al-Mg system.
Based on three groups of Ni/Ni–9at% Ge diffusion couples, interdiffusion coefficients were determined in the face-centered (fcc_A1) Ni–Ge alloys at 1173, 1273 and 1373K by means of the ...Boltzmann–Matano method coupled with electronic probe microanalysis (EPMA) technique. On the basis of various critically-reviewed experimental diffusivities as well as the available thermodynamic descriptions, atomic mobilities in fcc_A1 Ni–X (X=Ge, Ti and V) alloys were assessed by means of DIffusion Controlled TRAnsformation (DICTRA) software package. For the self-diffusivities in dynamically unstable fcc_A1 Ge, Ti and V, a semi-empirical correlation was employed. Moreover, the first-principles calculations were also used to calculate the activation energy for self-diffusion in fcc_A1 Ge. Comprehensive comparison between the calculated and the measured diffusivities shows that most of the experimental data can be reproduced by the atomic mobilities obtained in the present work. In addition, the reliability of the currently obtained atomic mobilities in fcc_A1 Ni–X (X=Ge, Ti and V) alloys were further validated by comparing the model-predicted concentration–distance profiles and the experimental ones.
•The interdiffusion coefficients in the fcc_A1 Ni–Ge alloys were experimentally determined.•The self-diffusivity of fcc_A1 Ge was evaluated by both semi-empirical correlations and first-principles calculations.•The self-consistent atomic mobilities in fcc_A1 Ni–X (X=Ge, Ti, and V) alloys were assessed.•Most of the experimental diffusivities can be satisfactorily reproduced.
Based on the critical evaluation of the phase diagram and thermodynamic data available in literature, thermodynamic optimization for the Ca–In and Ca–Sb systems was conducted via the CALPHAD ...(CALculation of PHAse Diagram) approach. The solution phases including liquid, (Sb), (In), (βCa), and (αCa) were modeled using substitutional regular solution model. The six intermetallic compounds, i.e. Ca8In3, CaIn2, Ca2Sb, Ca5Sb3, Ca11Sb10 and CaSb2, were described as stoichiometric phases. The order–disorder transition of bcc_B2 (CaIn) and bcc_A2 (βCa) was considered and one single Gibbs free energy function was employed to describe both the ordered and disordered parts. By means of first-principles calculations, the enthalpies of formation for the intermetallic compounds at 0K were computed and were used in the thermodynamic modeling. A set of self-consistent thermodynamic parameters for both Ca–In and Ca–Sb systems was finally obtained, respectively. Comprehensive comparisons showed that the calculated phase diagrams and thermodynamic properties agreed well with the experimental ones.
•The Ca–In and Ca–Sb systems have been critically reviewed and modeled by means of the CALPHAD technique and first-principles calculations.•The enthalpies of formation at 0K for the Ca8In3, CaIn, CaIn2, Ca2Sb, Ca5Sb3, Ca11Sb10 and CaSb2 have been computed by means of first-principles calculations.•A set of self-consistent thermodynamic parameters was obtained for these binary systems.
