Thermal desorption of tritium and helium in aged titanium tritide films

Titanium films were deposited onto molybdenum substrates and then converted into titanium tritides (TiT_1.5–1.8) films inside a tritiding apparatus loaded with pure tritium gas. Evolution of tritium and helium in the titanium tritide films over a period of four years was investigated using a thermal desorption technique, together with X-ray diffraction analysis. Results showed that desorption profiles of the tritium varied significantly with the evolution of He contents. Apart from the primary peak from tritium desorption located at a temperature between 610 and 840 K, another higher temperature tritium desorption peak (at ∼950 K) was observed, attributed to damages in the lattice structures induced by generation of ³He bubbles. Release of helium in the tritide film became significant after a long term aging process (i.e., after a few years). Depending on the amount of the ³He bubbles generated due to the decay of tritium, spectra of the thermal helium desorption showed five peaks in the range from room temperature to ∼1750 K, corresponding to different states of helium evolution during aging of the titanium tritide films. The amounts of helium desorption in different stages were estimated, and the dissociation energy of helium from different trap states as a function of the aging duration was obtained.     

Electronic and structural engineering of NiCo2O4/Ti electrocatalysts for efficient oxygen evolution reaction

The oxygen evolution reaction (OER) involves four electron transfer processes and is of great significance in water electrolysis. The development of efficient and robust non-precious OER electrocatalysts remains a critical challenge for the production, storage and conversion of renewable energy. Herein, vertically NiCo₂O₄ nanosheets are grown on Ti mesh via a facile solvothermal method which is followed by low-temperature calcination. The NiCo₂O₄/Ti catalyst exhibits outstanding OER performance with a low overpotential of 353 mV to drive the current density of 10 mA cm^?2 and a Tafel slope of 61 mV dec^?1 in alkaline solution. Moreover, the stable electrocatalyst undergoes negligible degradation in alkaline media at least 20 h. The acceleration of the electrochemical OER likely stems from the facile electron transfer promoted by the NiCo₂O₄/Ti interface as revealed by X-ray photoelectron spectroscopy. This work introduces a novel strategy for the establishment low-cost electrocatalysts for electrochemical water splitting.     

Quantitative analysis of micro structural and conductivity evolution of Ni-YSZ anodes during thermal cycling based on nano-computed tomography

Understanding the mechanism of degradation in solid oxide fuel cells (SOFCs) using nickel/yttria-stabilized zirconia (Ni-YSZ) as the anode material is very important for the optimization of cell performance. In this work, the effects of thermal cycling on the microstructure of the Ni-YSZ anode are explored using the three-dimensional X-ray nano computed tomography (nano-CT) imaging technique. It is found that the average Ni particle size increased with thermal cycling, which is associated with the decreased connectivity of the Ni phase and the three-phase-boundary (TPB) length. Moreover, the conductivities of the anode samples are also reduced with the increase in thermal cycle times. The implication of these observations is discussed in terms of the relationship between the conductivity and connectivity of the Ni phase.     

Effects of Pt3Ni alloy polyhedral and its de-alloying on CdS's performance in hydrogen evolution from water-splitting under visible light

In this paper, Pt₃Ni alloy polyhedral was synthesized through solvothermal method and loaded on the surface of CdS by photo-induced electrons. Under visible light irradiation, the photocatalytic activity for hydrogen evolution from solar water splitting was performed, Pt₃Ni/CdS showed the hydrogen evolution rate about 40.0 mmol/h/g (QE = 44.90%, λ = 420 nm), which was 1.8 times higher than that of Pt/CdS, indicating that Pt₃Ni NPs could effectively improve the hydrogen production activity of CdS. Next, the influence of de-alloyed Pt₃Ni NPs on the activity of CdS for water-splitting under visible light was investigated, the hydrogen evolution rate of de-alloyed Pt₃Ni NPs modified CdS was 46.1 mmol/h/g (QE = 52.70%, λ = 420 nm), which was 1.2 times as much as that of Pt₃Ni/CdS and 2.1 times as much as that of Pt/CdS, suggesting that de-alloyed Pt₃Ni NPs could further enhance the hydrogen production activity of CdS. In addition, the improved photocatalytic activity was mainly due to the surface unsaturation of Pt atoms in a metastable structure after de-alloying, which will expose more surface active sites of Pt, thus the fast electron hole charge transfer at the interface of CdS and de-alloyed Pt₃Ni NPs.     

Construction of NiCo2S4/Ni3S2 nanoarrays on Ni foam substrate as an enhanced electrode for hydrogen evolution reaction and supercapacitors

Developing a multifunctional and sustainable electrode material for hydrogen evolution reaction and supercapacitors is a highly feasible avenue for producing the high energy density and renewable energies. In our study, nanostructured NiCo₂S₄/Ni₃S₂/NF nanoarrays are rational developed in experiments via a simple hydrothermal reaction. Ascribed to the 3D nanostructured NiCo₂S₄/Ni₃S₂ with numerous exposure active sites and large contact areas for the electrolyte, the binder-free feature of NiCo₂S₄/Ni₃S₂/NF facilitates a low charge transfer resistance, as well as the synergetic effect of NiCo₂S₄ and Ni₃S₂. The obtained electrocatalyst showed ultrahigh electrocatalytic activity with an overpotential of 111 mV at 10 mA cm⁻² and a Tafel slope of 57 mV dec⁻¹. In addition, the electrode showed an area specific capacity of 6.13 F cm⁻² at 10 mA cm⁻² and superior rate capability (2.72 F cm⁻² at 80 mA cm⁻²), accompanied by excellent cycling stability. This results presented in our work can provide an effective strategy for rational design of other hybrid materials with excellent electrochemical performance in the application of electrocatalysis and supercapacitors.     

Revealing the catalytic micro-mechanism of MoN,WN and WC on hydrogen evolution reaction

Catalytic performance of MoN, WN and WC on hydrogen evolution reaction (HER)were investigated by first-principles calculations, especially considering the effect of strain. From the calculation we can see the catalytic ability has an opposite trend with the adsorption capacity. H coverage was found to affect WN catalytic activity obviously, however has no effect on MoN and WC. Comparing with the experiments, we inferred that although the top site has the strongest potential catalytic ability, the actual catalytic site for HER is hollow1 site. Some specific transition metal doping (Ni > Fe > Mn > W for MoN, Fe > Co for WN, Ni > Co > Fe> Mn for WC) may indirectly improve the HER catalytic performance. It is worth noting that applying a certain strain (e.g. 2.5% tensile strain for MoN, 5% compressive strain for WN, WC) is helpful for improving the HER catalytic performance. Our work is instructive for HER catalyst development in terms of doping and strain.     

The effect of annealing temperature,reaction time,and cobalt precursor on the structural properties and catalytic performance of CoS2 for hydrogen evolution reaction

In this study, cobalt disulfide (CoS₂) nanostructures are synthesized using a simple hydrothermal method. The effects of experimental parameters including cobalt precursor, reaction times, and reaction temperatures are investigated on the structure, morphology and electrocatalytic properties of CoS₂ for hydrogen evolution reaction (HER). The characterization of as-prepared catalysts is performed using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The HER efficiency of the catalysts is examined using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solution. Furthermore, chronoamperometry (CA) is used for stability evaluation. The catalyst obtained from cobalt acetate precursor, within 24 h at 200 °C exhibits superior electrocatalytic activity with a low onset potential (139.3 mV), low overpotential (197.3 mV) at 10 mA. cm^?2 and a small Tafel slope of 29.9 mV dec^?1. This study is a step toward understanding the effect of experimental parameters of the hydrothermal method on HER performance and developing optimal design approaches for the synthesis of CoS₂ as a common electrocatalyst.     

Effects of Mg substitution on crystal structure and hydrogenation properties of Pr1−xMgxNi3

The effects of substitution of Pr by Mg in PrNi₃ with a PuNi₃-type structure were investigated using pressure–composition (P–C) isotherm measurements and X-ray diffraction. The unit cell of Pr_0.68Mg_0.32Ni_3.04 contracted anisotropically in comparison to that of PrNi₃. The maximum hydrogen capacity of PrNi₃ reached 1.25 H/M in the first absorption. A plateau region was observed between 0.82 H/M and 1.04 H/M in the first absorption cycle. However, 0.85 H/M of hydrogen remained in the sample after the first full desorption. Pr_0.68Mg_0.32Ni_3.04 showed reversible hydrogenation properties. The maximum hydrogen capacity was 1.22 H/M. The plateau region of Pr_0.68Mg_0.32Ni_3.04 was between 0.08 H/M and 0.87 H/M, which was wider than that of PrNi₃. Pr_0.68Mg_0.32Ni_3.04 retained the PuNi₃-type structure after hydrogenation, whereas the crystal structure of PrNi₃ changed from that of PuNi₃-type to an unknown structure. The structural change in PrNi₃ during hydrogenation was evidently different from that in Pr_0.68Mg_0.32Ni_3.04.     

Role of sintering temperature on thermal, electrical and structural properties of Y2Ti2O7 pyrochlores

Pyrochlores exhibit variety of properties which can be tailored by changing the processing conditions. In the present study, the sintering characteristics, thermal expansion coefficient, crystal structure and conductivity behavior of pyrochlores have been studied for different applications. It was observed that sintering at 1550 °C for 12 h exhibits more oxygen deficient YTiO_2.085 phase which shows two order of magnitudes higher conductivity than Y₂Ti₂O₇ phase. The conductivity enhancement in YTiO_2.085 sample is attributed to higher oxygen deficiency which may be created due to transformation of Ti⁴⁺ to Ti³⁺ at low oxygen pressure.     

Effects of nanocrystal size and device aging on performance of hybrid poly(3-hexylthiophene):CdSe nanocrystal solar cells

We have studied hybrid solar cells based on the polymer poly(3-hexylthiophene) (P3HT) and colloidal CdSe nanocrystals. Using CdSe nanospheres with varying size, we have found that the power conversion efficiency (η_P) of these devices increases monotonically with the CdSe nanocrystal size, from η_P=(0.39±0.04)% under AM1.5G solar illumination for 4.0±0.2 nm size nanospheres to η_P=(1.9±0.2)% for 6.8±0.5 nm size nanospheres. The efficiency increase with nanocrystal size is mostly due to a significant increase in the short-circuit current, whereas the open-circuit voltage and fill factor of the solar cells are less affected. The devices also exhibit abnormal initial aging behavior when exposed to air, as an increase in both the short-circuit current and open-circuit voltage during the first 30 min leads to a significant increase in η_P.     

Effects of synthesis temperature and precursor composition on the crystal structure, morphology, and electrode activity of 1D nanostructured manganese oxides

1D nanostructured manganese oxides are prepared by oxidation reaction of precursor LiMn_2−xCr_xO₄ microcrystals under hydrothermal condition. The crystal structure and morphology of the obtained manganese oxides are strongly dependent on the reaction condition and the chemical composition of the precursors. The α-MnO₂ nanowires are prepared by reaction at 120 °C, and their aspect ratios decrease with the Cr content in the precursor. Treating precursors with persulfate ions at 160-180 °C yields the β-MnO₂ nanorods for the precursors LiMn_2−xCr_xO₄ with lower Cr content and the α-MnO₂ nanowires for the precursors with higher Cr content. The structure dependence of the products on the Cr content in the precursors is related to the high octahedral site stabilization energy of Cr³⁺ ions and/or to the increase of Mn valence state upon Cr substitution. The increase of Cr content in the precursors degrades the electrode performance for the manganates prepared at 160 °C but improves electrode activity for those prepared at 180 °C. This observation can be explained by the structural variation and chromium substitution of the hydrothermally treated manganates. We conclude that the use of spinel LiMn_2−xCr_xO₄ as precursors provides an effective way to synthesize 1D nanostructured manganate with tailored crystal structure and morphology.     

Effects of crystal and electronic structures of ANb2O6 (A=Ca,Sr, Ba) metaniobate compounds on their photocatalytic H2 evolution from pure water

Alkali-earth metaniobate compounds, ANb₂O₆ (A = Ca, Sr, Ba), were prepared by the conventional solid-state reaction route and their electronic band structures and photocatalytic activities were investigated. The prepared powders were characterized using X-ray diffraction (XRD), field-emission electron microscopy (FE-SEM), UV–vis diffuse reflectance spectroscopy, and fluorescence spectroscopy. It was found that the particle sizes (∼1 μm) and BET surface areas (∼1 m²/g) of the metaniobate compounds were nearly identical. From the electronic band structure calculations, however, the band-gap energies of these metaniobate compounds were found to be in the order of CaNb₂O₆ > SrNb₂O₆ > BaNb₂O₆. These calculated band-gap energies were consistent with those estimated from the UV–vis diffuse reflectance spectra. Moreover, the conduction-band edge (reduction potential) of SrNb₂O₆ calculated from the electronegativity data was higher than those of CaNb₂O₆ and BaNb₂O₆. The photoluminescence spectra revealed that CaNb₂O₆ exhibited a strong blue luminescence emission (at 300K), while no obvious emissions were observed in either SrNb₂O₆ or BaNb₂O₆. The luminescence behaviors of these metaniobate compounds and their band structure variations originating from their crystal structures play an important role in their photocatalytic activity for the evolution of H₂ from pure water. SrNb₂O₆, which has a higher conduction-band edge potential than the other compounds, exhibited higher photocatalytic activity.     

Effect of Co substitution on hydrogenation behavior of GdNi3-xCox (x = 0, 0.2, 1.0) and crystal structure of its hydride phases

The effect of substituting Co for Ni in GdNi₃ on the hydrogenation properties and phase transformation during the hydrogen absorption–desorption process of GdNi_3-xCo_x (x = 0, 0.2, 1.0) was investigated using P–C isotherms and X-ray diffraction analysis (XRD). GdNi₃ showed a residual hydrogen content of 0.6 H/M after the first desorption process. The maximum hydrogen capacity of GdNi₃ was 1.0 H/M, while the reversible hydrogen capacity decreased to 0.4 H/M because of the residual hydrogen. The reversible hydrogen capacity was improved to 1.0 H/M in GdNi_2.0Co_1.0, and two plateaus were observed in the absorption–desorption process. The crystal structures of the full hydride phases GdNi₃H_3.8 and GdNi_2.8Co_0.2H_3.8 could not be determined because of the heavy peak broadening in the XRD pattern, while the PuNi₃-type structure of the original alloy was retained in the full hydride phase GdNi_2.0Co_1.0H_3.6. The retention rates of GdNi₃ and GdNi_2.0Co_1.0 at 100 cycles were 75% and 92%, respectively. The cyclic properties of GdNi_2.0Co_1.0, up to 100 cycles, favorably compared with those of LaNi₅, which was found to be related to the small lattice strain formed during the first hydrogen absorption process.     

Studies on structural,morphological, and electrical properties of Ga3+ and Cu2+ co-doped ceria ceramics as solid electrolyte for IT-SOFCs

The present study highlights the effect of Ga³⁺ and Cu²⁺ co-doping on the crystal structure, surface morphology and ionic conductivity of ceria ceramics in the system Ce_0.8Ga_0.2-xCu_xO_2-δ for potential applications as the solid electrolyte material in the intermediate temperature solid oxide fuel cells (IT-SOFCs). Ultrafine Ce_0.8Ga_0.2-xCu_xO_2-δ (for x = 0, 0.05, 0.1, 0.15, and 0.2) nanopowders were prepared via glycine nitrate auto-combustion method. Phase identification, microstructural, and ionic conductivity of all the ceria ceramics were observed by powder XRD, SEM, TEM, and impedance analyses, respectively. Rietveld structural analysis using powder XRD pattern for all the co-doped systems confirms cubic fluorite type structure having Fm-3m space group, similar to cerium oxide. All these samples were found to have density above 85% after sintering at 1300 °C for 4 h. Raman spectra revealed the oxygen vacancies in all the compositions. Thermal analysis for change in weight and thermal expansion coefficient with temperature were performed by TGA and high temperature XRD measurements, respectively. Thermal expansion coefficient of the developed electrolytes matches with the commonly used electrode materials. The composition Ce_0.8Ga_0.05Cu_0·15O_1.825 was found to demonstrate the maximum ionic conductivity with the least activation energy among all the existing co-doped ceria ceramics. These features make it a promising candidate in the IT-SOFC as the electrolyte material.     

Effect of Mg content on structure,hydrogen storage properties and thermal stability of melt-spun Mgx(LaNi3)100−x alloys

Amorphous Mg_x(LaNi₃)_100−x (x = 40, 50, 60, 70) alloys with ribbon shape (5 mm wide, 0.2 mm thick) have been prepared by rapid solidification, using a melt-spinning technique. Their microstructure, hydrogen storage properties and thermal stability were studied by means of XRD, SEM, PCTPro2000 and DSC analysis, respectively. The results indicated that when Mg_x(LaNi₃)_100−x alloys have been hydrogenated at 573 K under 2 MPa hydrogen pressure, LaH₃ phase is formed in the case of x (x = 40, 50, 60, 70), Mg₂NiH₄ phase formed in the case of x (x = 40, 50, 60, 70), Mg₂NiH_0.3 phase formed in the case of x (x = 40, 50), and MgH₂ phase formed in the case of x = 70. Experimental data of hydrogen desorption kinetics, tested at 523 K, 573 K and 623 K, are in good agreement with Avrami–Erofeev equation. The maximum hydrogen absorption capacity is 2.71 wt.% for Mg₇₀(LaNi₃)₃₀ and 2.35 wt.% for Mg₇₀(LaNi₃)₃₀, the increase of hydrogen desorption capacity is in the order of x = 70 > x = 60 > x = 50 > x = 40. Based on DSC analysis, the activation energies for dehydrogenation of these samples are calculated to be 122 ± 2 kJ/mol (x = 40) > 101 ± 3 kJ/mol (x = 50) > 84 ± 5 kJ/mol (x = 60) > 64 ± 3 kJ/mol (x = 70), which are in agreement with the results of hydrogen desorption kinetics.