Balancing electron transfer and intermediate adsorption ability of metallic Ni-Fe-RE-P bifunctional catalysts via 4f-2p-3d electron interaction for enhanced water splitting

Balancing electron transfer and intermediate adsorption ability of bifunctional catalysts via tailoring electronic structures is crucial for green hydrogen production,while it still remains challenging due to lacking efficient strategies.Herein,one efficient and universal strategy is developed to greatly regulate electronic structures of the metallic Ni-Fe-P catalysts via in-situ introducing the rare earth(RE)atoms(Ni-Fe-RE-P,RE=La,Ce,Pr,and Nd).Accordingly,the as-prepared optimal Ni-Fe-Ce-P/CC self-supported bifunctional electrodes exhibited superior electrocatalytic activity and excellent stability with the low overpotentials of 247 and 331 mV at 100 mA cm^(-2) for HER and OER,respectively.In the assembled electrolyzer,the Ni-Fe-Ce-P/CC as bifunctional electrodes displayed low operation potential of 1.49 V to achieve a current density of 10 mA cm^(-2),and the catalytic performance can be maintained for 100 h.Experimental results combined with density functional theory(DFT)calculation reveal that Ce doping leads to electron decentralization and crystal structure distortion,which can tailor the band structures and d-band center of Ni-Fe-P,further increasing conductivity and optimizing intermediate adsorption energy.Our work not only proposes a valuable strategy to regulate the electron transfer and intermediate adsorption of electrocatalysts via RE atoms doping,but also provides a deep under-standing of regulation mechanism of metallic electrocatalysts for enhanced water splitting.

Influences of divalent ion substitution on the magnetic and dielectric properties of W-type barium ferrite

Saturation magnetization,magneto-crystalline anisotropy field,and dielectric properties are closely related to microwave devices applied at different frequencies.For regulating the magnetic and dielectric properties of W-type barium ferrites,single-phase BaMe_(2)Fe_(16)O_(27)(Me=Fe,Mn,Zn,Ni,Co) with different Me ions were synthesized by the high-temperature solid-state method.The saturation magnetization(Ms) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field(H_a) range from 10700.60 Oe(1 Oe=79.5775 A·m^(-1)) to 13739.57 Oe,depending on the type of cation substitution in the hexagonal lattice.The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region,while they almost remain constant in the high-frequency region.The charac teristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.

Impact of Co^(2+)substitution on structure and magnetic properties of M-type strontium ferrite with different Fe/Sr ratios

Ion substitution has significantly improved the performance of ferrite magnets,and cobalt remains a key area of research.Studies on the mechanism of Co^(2+)in strontium ferrite,especially SrFe_(2n-x)Co_(x)O_(19-d)(n=6.1-5.4;x=0.05-0.20)synthesized using the ceramic method,showed that Co^(2+)preferentially enters the lattice as the Fe/Sr ratio decreases.This results in a decrease in the lattice constants a and c due to oxygen vacancies and iron ion deficiency.The impact of Co substitution on morphology is minor compared to the effect of the Fe/Sr ratio.As the Fe/Sr ratio decreases and the Co content increases,the saturation magnetization decreases.The magnetic anisotropy field exhibits a nonlinear change,generally increasing with higher Fe/Sr ratios and Co content.These changes in the performance of permanent magnets are attributed to the absence of Fe^(3+)ions at the 12k+2a and 2b sites and the substitution of Co^(2+)at the 2b site.This suggests that by adjusting the Fe/Sr ratio and appropriate Co substitution,the magnetic anisotropy field of M-type strontium ferrite can be effectively optimized.

Synergistic extraction and separation of thorium from rare earths in chloride media using mixture of Cextrant 230 and Cyanex 923

In order to lower the usage of expensive Cyanex 923 and increase the extraction capacity of the system of Cextrant 230,the synergistic extraction of thorium from chloride media by a mixture of Cextrant 230 and Cyanex 923 was investigated.The maximum synergistic enhancement coefficient(R)of 1.53 is obtained at 1:1 molar ratio of Cextrant 230/Cyanex 923.The syne rgistic extracted species of Th^(4+)is determined as ThCl_(4)·2Cextrant 230·Cyanex 923.The synergistic extraction of Th^(4+)is an entropy-driven exothermic process.The loading capacity of 0.60 mol/L mixed extractant for thorium is about 17.10 g/L(calculated as ThO_(2)),and the loaded thorium in the organic phase can be effectively stripped by distilled water.For comparison,rare earth cations are barely extracted under the similar conditions,suggesting that the mixtures can be applied to separate thorium from rare earths.A cascade extraction process was developed based on the synergistic extraction system to separate thorium from the hydrochloric acid leaching of bastnaesite.The content of thorium in the leaching solution decreases obviously from 19.90 mg/L to1.4μg/L by 3 stages of extraction,which is superior to sole Cextrant 230 or Cyanex 923.The introduction of Cextrant 230 into the extraction system not only lowers the usage of Cyanex 923 but also enhances the selective extraction of thorium at low acidity,implying that the synergistic extraction system can selectively extract thorium more efficiently and economically than the sole systems.

Optimization of the grain boundary diffusion process by doping gallium and zirconium in Nd–Fe–B sintered magnets

As the channel for grain boundary diffusion(GBD)in Nd–Fe–B magnets,grain boundary(GB)phases have a very important effect on GBD.As doping elements that are commonly used to regulate the GB phases in Nd–Fe–B sintered magnets,the influences of Ga and Zr on GBD were investigated in this work.The results show that the Zr-doped magnet has the highest coercivity increment(7.97 kOe)by GBD,which is almost twice that of the Ga-doped magnet(4.32 kOe)and the magnet without Ga and Zr(3.24 kOe).Microstructure analysis shows that ZrB_(2)formed in the Zr-doped magnet plays a key role in increasing the diffusion depth.A continuous diffusion channel in the magnet can form because of the presence of ZrB_(2).ZrB_(2)can also increase the defect concentration in GB phases,which can facilitate GBD.Although Ga can also improve the diffusion depth,its effect is not very obvious.The micromagnetic simulation based on the experimental results also proves that the distribution of Tb in the Zr-doped magnet after GBD is beneficial to coercivity.This study reveals that the doping elements Ga and Zr in Nd–Fe–B play an important role in GBD,and could provide a new perspective for researchers to improve the effects of GBD.

Structural Determination,Unstable Antiferromagnetism and Transport Properties of Fe-Kagome Y_(0.5)Fe_(3)Sn_(3) Single Crystals

Kagome materials have been studied intensively in condensed matter physics.With rich properties,various Kagome materials emerge during this process.Here,we grew single crystals of Y_(0.5)Fe_(3)Sn_(3)and confirmed an YCo_(6)Ge_(6)-type Kagome-lattice structure by detailed crystal structure characterizations.This compound bears an antiferromagnetic ordering at T_(N)= 551 K,and shows a weak ferromagnetism at low temperatures,where an anomalous Hall effect was observed,suggesting the non-zero Berry curvature.With the unstable antiferromagnetic ground state,our systematic investigations make Y_(0.5)Fe_(3)Sn_(3)a potential Kagome compound for Kagome or topological physics.

Experimental and mathematical modeling of metal spray forming process

The metal spray forming process was examined using mathematical simulation and verified through the prototyping evaluation at Baosteel＇ s test and development facilities. The mathematical model comprised of four sections, including jet gas flow in the deposition chamber;single droplet behavior along its trajectory path;probability and statistical analysis of droplet mass behavior, and forecast of the shape and temperature distribution of the billet during the spray forming process.

Microstructure Refinement of Al-5Ti-B Grain Refiner with Electromagnetic Energy

The influence of the electromagnetic energy on the microstructure of Al-5Ti-B grain reflner was discussed.In this study,the electromagnetic energy was applied above the liquid phase line temperature.Compared with Al-5Ti-B without electromagnetic energy applied,the experimental results show that the size of secondary particles is reduced and its size distribution becomes more uniform.Simultaneously,the secondary phase particles are uniformly spread in the matrix response to the electromagnetic energy.Moreover,when adding Al-5Ti-B with electromagnetic energy to the pure aluminum melt,it is clear that the electromagnetic energy has a signiflcantly impact on reflning properties of Al-5Ti-B.The mean size of pure aluminum is reduced by 27.6%in maximum with more uniform size distribution.The change in the microstructure is attributed to the electromagnetic energy changes the melt structure.With the electromagnetic energy entry into the system,the electromagnetic energy reduces the size of atomic clusters and increases the number of atomic clusters,thus the number of nuclei increases.

Magnetic properties and magnetocaloric effects of Tm_(1-x)Er_(x)CuAl(x=0.25,0.5,and 0.75)compounds

We investigate the structural,magnetic,and magnetocaloric effects(MCE)of Tm_(1-x)Er_(x)CuAl(x=0.25,0.5,and 0.75)compounds.The compounds undergo a second-order phase transition originating from the ferromagnetic to paramagnetic transition around 3.2 K,5 K,and 6 K,respectively.The maximum magnetic entropy changes(-△S_(M)^(max))of Tm_(1-x)Er_(x)CuAl(x=0.25,0.5,and 0.75)are 17.1 J·kg^(-1)·K^(-1),18.1 J·kg^(-1)·K^(-1),and 17.5 J·kg^(-1)·K^(-1)under the magnetic field in the range of 0-2 T,with the corresponding refrigerant capacity(RC)values of 131 J·kg^(-1),136 J·kg^(-1),and 126 J·kg^(-1),respectively.The increase of-△S_(M)^(max)for Tm0.5Er0.5CuAl may be relevant to the change of magnetic moment distribution of Er and stress coming from element substitution.This work provides several compounds that can enrich the family of giant MCE materials in the cryogenic region.

Large reversible cryogenic magnetocaloric effect in rare earth iron carbides of composition RE_(2)FeC_(4)(RE=Ho,Er,and Tm)

At cryogenic temperatures,the investigations of magnetic phase transition and magnetocaloric effect in RE_(2)FeC_(4)(RE=Ho,Er,and Tm) compounds were performed.Ho_(2)FeC_(4)and Er_(2)FeC_(4)compounds undergo two magnetic phase transitions with the temperature decreasing:from paramagnetic(PM) to ferromagnetic(FM) transition at their respective Curie temperature(Tc) and from FM to antiferromagnetic(AFM) or ferrimagnetic(FIM) transition below 2 K.Tm_(2)FeC_(4)compound exhibits only a second-order PM to FM phase transition at TC=K.Large reversible MCE without hysteresis loss is observed in RE_(2)FeC_(4)(RE=Ho,Er,and Tm) compounds.Particularly,the maximum value of magnetic entropy change(-ASM)is 21.62 J/(kg K) under the magnetic field change(Δ_(μ0)H) of 0-5 T for Er_(2)FeC_(4).The Er_(2)FeC_(4)compound presenting excellent magnetocaloric performance makes it a competitive cryogenic magnetic refrigeration material.

Giant low-field reversible magnetocaloric effect at liquid helium temperature of niobium and iron co-substituted EuTiO_(3) compounds

Giant magnetocaloric effect(MCE)materials in the liquid helium temperature region have attracted a lot of attention in the field of low-temperature magnetic refrigeration(MR).In this study,a series of niobium(Nb)and iron(Fe)co-substituted EuTiO_(3) perovskites with cubic structure(space group pm3m)was successfully fabricated,and their magnetic properties as well as cryogenic magnetocaloric effects were investigated in detail.As expected,the introduction of Nb and Fe can significantly modulate the magnetic phase transition and magnetocaloric effect of the EuTiO_(3) compounds.With increasing Fe concentration,two local minima corresponding to the AFM-FM magnetic phase transition near 5.0 K and FM-PM transition near 10 K with no hysteresis in the thermomagnetic curves are observed,which is attributed to an enhancement of FM coupling.At the same time,the gradually widened-ΔSM-T curves and the two peaks with a broad shoulder lead to considerable refrigeration capacity(RC).With the field change ofΔH=2 T,the calculated values of-ΔS_(M)^(max) for the EuTi_(0.9375-x)Nb_(0.0625)Fe_(x)O_(3)(x=0.075,0.1,0.125,0.15)compounds are 24.2,17.6,14.5 and 14.0 J/(kg·K),respectively.The corresponding RC values were calculated to be 144.6,138.3,151.2 and 159 J/kg,respectively.Especially,the values of-ΔS_(M)^(max) for EuTi_(0.8625)Nb_(0.0625)Fe_(0.075)O_(3) are 8.6 and 15.1 J/(kg·K)under low field changes of 0.5 and 1 T,respectively.The giant low-field reversible magnetocaloric effect makes them attractive candidates for magnetic refrigeration in the liquid helium temperature region.

Structure, magnetism and magnetocaloric effects in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds

We investigate the structure, magnetic properties, magnetic phase transitions and magnetocaloric effects(MCEs) of Er5Si3Bx(x=0.3,0.6) compounds. The Er5Si3Bx(x = 0.3, 0.6) compounds crystalize in a Mn5Si3type hexagonal structure(space group: P63/cm) and exhibit a successive complicated magnetic phase transition. The extensive magnetic phase transitions contribute to the broad temperature range of MCEs exhibiting in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds, with maximum magnetic entropy change(-ΔSM_(max)) and refrigeration capacity of 10.2 J·kg^(-1)·K^(-1), 356.3 J/kg and 11.5 J·kg^(-1)·K^(-1),393.3 J/kg under varying magnetic fields 0–5 T, respectively. Remarkably, the δTFWHMvalues(the temperature range corresponding to 1/2×|-ΔSM_(max)|) of Er5Si3Bx(x=0.3,0.6) compounds were up to 41.8 K and 39.6 K, respectively. Thus, the present work provides a potential magnetic refrigeration material with a broad temperature range MCEs for applications in cryogenic magnetic refrigerators.

Giant low-field cryogenic magnetocaloric effect in polycrystalline LiErF4 compound

Antiferromagnetic LiErF4has attracted extensive attention due to its dipolar interaction domination and quantum fluctuations action. In the present work, the crystal structure, cryogenic magnetic properties, and magnetocaloric effect(MCE) of polycrystalline LiErF4compound are investigated. Crystallographic study shows that the compound crystallizes in the tetragonal scheelite structure with I41/a space group. It exhibits an antiferromagnetic(AFM) phase transition around 0.4 K, accompanied by a giant cryogenic MCE. At 1.3 K, the maximum values of magnetic entropy changes are 24.3 J/kg·K,33.1 J/kg·K, and 49.0 J/kg·K under the low magnetic field change of 0–0.6 T, 0–1 T, and 0–2 T, respectively. The giant MCE observed above Néel temperature TNis probably due to the strong quantum fluctuations, which cause a large ratio of the unreleased magnetic entropy existing above the phase transition temperature. The outstanding low-field MCE below 2 K makes the LiErF4compound an attractive candidate for the magnetic refrigeration at the ultra-low temperature.

Direct atomic-level insight into oxygen reduction reaction on size-dependent Pt-based electrocatalysts from density functional theory calculations

Developing novel oxygen reduction reaction(ORR)catalysts with high activity is urgent for proton exchange membrane fuel cells.Herein,we investigated a group of size-dependent Pt-based catalysts as promising ORR catalysts by density functional theory calculations,ranging from single-atom,nanocluster to bulk Pt catalysts.The results showed that the ORR overpotential of these Pt-based catalysts increased when its size enlarged to the nanoparticle scale or reduced to the single-atom scale,and the Pt_(38)cluster had the lowest ORR overpotential(0.46 V)compared with that of Pt_(111)(0.57 V)and single atom Pt(0.7 V).Moreover,we established a volcano curve relationship between the ORR overpotential and binding energy of O*(ΔE_(O*),confirming the intermediate species anchored on Pt38cluster with suitable binding energy located at top of volcano curve.The interaction between intermediate species and Pt-based catalysts were also investigated by the charge distribution and projected density of state and which further confirmed the results of volcano curve.

Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La_(0.66)Mg_(0.34)Ni_(3.5-x)Co_(x) alloys

Superlattice hydrogen storage alloys offer a compelling advantage with rapid hydriding rate and high storage capacity.However,its practical applications face challenges including complex structure,low dehydriding capacity,and cyclic instability.In this work,we successfully prepared La_(0.66)Mg_(0.34)Ni_(3.5-x)Co_(x) superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni.X-ray diffraction(XRD)refinements analysis reveals the presence of(La,Mg)_(3)Ni_(9),(La,Mg)_5Ni_(19),and LaNi_(5) phases within the alloy.Following Co substitution in the La_(0.06)Mg_(0.34)Ni_(3.4)Co_(0.1)alloy,there is a significant increase in content of the(La,Mg)_(3)Ni_(9) phase and a reduction in the hysteresis factor,resulting in an improved reversible hydrogen storage capacity from 1.45 wt%to 1.60 wt%.The dehydriding kinetics of the alloy is controlled by diffusion model with an activation energy of 8.40 kJ/mol.Furthermore,the dehydriding enthalpy value of the Co-substituted alloy decreases from 30.84 to 29.85 kJ/mol.Impressively,the cycling performance of the alloy after Co substitution exhibits excellent stability,with a capacity retention rate of 92.3%after 100 cycles.These findings provide valuable insights for the development of cost-effective hydrogen storage materials.

Efficient Pt/KFI zeolite catalysts for the selective catalytic reduction of NOxby hydrogen

Aiming at purification of NO_(x)from hydrogen internal combustion engines(HICEs),the hydrogen selective catalytic reduction(H_(2)-SCR)reaction was investigated over a series of Pt/KFI zeolite catalysts.H_(2)can readily reduce NO_(x)to N_(2)and N_(2)O while O_(2)inhibited the deNO_(x)efficiency by consuming the reductant H_(2).The Pt/KFI zeolite catalysts with Pt loading below 0.1wt.% are optimized H_(2)-SCR catalysts due to its suitable operation temperature window since high Pt loading favors the H_(2)-O_(2)reaction which lead to the insufficient of reactants.Compared to metal Pt^(0)species,Pt^(δ+)species showed lower activation energy of H_(2)-SCR reaction and thought to be as reasonable active sites.Further,Eley-Rideal(E-R)reaction mechanism was proposed as evidenced by the reaction orders in kinetic studies.Last,the optimized reactor was designed with hybrid Pt/KFI catalysts with various Pt loading which achieve a high NO_(x)conversion in a wide temperature range.

Design of Ca-type todorokite catalysts with highly active for the selective reduction of NO_(x) by NH_(3) at low temperatures

Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NO_(x) by NH_(3)(NH_(3)-SCR)for the first time.Compared with the Na-type manjiroite prepared by the same method,the todorokite catalysts with different Mn/Ca ratios showed greatly improved catalytic activity for NO_(x) reduction.Among them,Mn8Ca4 catalyst exhibited the best NH_(3)-SCR performance,achieving 90%NO_(x) conversion within temperature range of 70-275℃ and having a high sulphur resistance.Compared to the Na-type manjiroite sample,Ca-type todorokite catalysts possessed an increased size of tunnel,resulting in a larger specific surface area.As increased the amounts of Ca doping,the Na content in Ca-type todorokite catalysts significantly decreased,providing larger amounts of Bronsted acid sites for NH_(3) adsorption to produce NH_(4)^(+).The NH_(4)^(+)species were highly active for reaction with NO+O_(2),playing a determining role in NH_(3)-SCR process at low temperatures.Meanwhile,larger amounts of surface adsorbed oxygen contained over the Ca-doping samples than that over Na-type manjiroite,promoting the oxidation of NO and fast SCR processes.Over the Ca-type todorokite catalysts,furthermore,nitrates produced during the flow of NO+O_(2),were more active for reaction with NH_(3) than that over Na-type manjiroite,benefiting the occurrence of NH_(3)-SCR process.This study provides novel insights into the design of NH_(3)-SCR catalysts with high performance.

Microscale spherical TiO_(2)powder prepared by hydrolysis of TiCl_(4)solution:Synthesis and kinetics

Hydrolysis of TiCl_(4)solution is capable of preparing microscale TiO_(2)particles.This research studied the synthesis of microscale spherical TiO_(2)powders and the hydrolysis kinetics.The effects of the flow field generated by different agitators and baffles in the crystallizer,the initial free acid concentration,the initial equivalent TiO_(2)concentration,and the temperature on the hydrolysis progress and powder morphology were systematically studied.The results show that the flow field in a crystallizer can significantly affect the morphology and particle size of the powders,and the axial flow can improve the sphericity of the powders.The increased free HCl and equivalent TiO_(2)concentrations in the pregnant solution inhibit the forward hydrolysis reaction,prolong the time to reach equilibrium,and reduce the yield.An appropriate temperature matching the compositions of the pregnant solution is crucial for the powder morphology and size.Powders with sizes ranging from around 5 um-40μm can be tuned under controlled flow field,solution compositions,and temperature conditions.In addition,the Cheng and Wunderlich modified Avrami equation was used for the crystallization kinetic modeling.The effects of the free HCl concentration,equivalent TiO_(2)concentration,and hydrolysis temperature are reflected in the reaction rate constant and active nuclei reduction index.Increasing the free HCl and equivalent TiO_(2)concentrations will reduce the reaction rate constant and accelerate the deactivation of the active nuclei,thus increasing the final powder size,while increasing the temperature will lead to the opposite results.

Magnetic properties and magnetocaloric effect in RE_(55)Co_(30)Al_(10)Si_(5)(RE=Er and Tm)amorphous ribbons

The magnetic and magnetocaloric effects(MCE)of the amorphous RE_(55)Co_(30)Al_(10)Si_(5)(RE=Er and Tm)ribbons were systematically investigated in this paper.Compounds with R=Er and Tm undergo a second-order magnetic phase transition from ferromagnetic(FM)to paramagnetic(PM)around Curie temperature T_(C)~9.3 K and 3 K,respectively.For Er_(55)Co_(30)Al_(10)Si_(5) compound,an obvious magnetic hysteresis and thermal hysteresis were observed at low field below 6 K,possibly due to spin-glass behavior.Under the field change of 0 T–5 T,the maximum values of magnetic entropy change(-△S_(M)^(max))reach as high as 15.6 J/kg·K and 15.7 J/kg·K for Er_(55)Co_(30)Al_(10)Si_(5) and Tm_(55)Co_(30)Al_(10)Si_(5) compounds,corresponding refrigerant capacity(RC)values are estimated as 303 J/kg and 189 J/kg,respectively.The large MCE makes amorphous RE_(55)Co_(30)Al_(10)Si_(5)(RE=Er and Tm)alloys become very attractive magnetic refrigeration materials in the low-temperature region.

Enhanced carbon capture with motif-rich amino acid loaded defective robust metal-organic frameworks

The use of metal-organic frameworks(MOFs)as solid adsorption materials for carbon capture is promising,but achieving efficient and reversible adsorption with a balance of capacity and selectivity for carbon dioxide(CO_(2))over N_(2) remains a challenge.To take full advantage of the strong channel traffic and robustness of MOFs with relatively small pores,it is highly necessary to employ a defect-engineering strategy to construct a broader channel structure that can facilitate the loading of functional motif-rich amino acids(AAs).This strategy can greatly enhance the CO_(2) adsorption performance of MOF.In this study,motif-rich amino acids are loaded into the defective and robust porous frameworks via combined defect-engineering and post-synthetic methods.The defective Zr/Hf-MOF-808s modified with AAs,especially for the 18 mol%4-nitroisophthalic acid,generated defective products allowing for the loading of L-serine(L-Ser).This modification resulted in a significant improvement in both the adsorption capacity(248%improvement at 298 K,100 kPa)and the selectivity of CO_(2)/N_(2) using the ideal adsorbed solution theory(IAST),with the selectivity increasing to 120.55 and 38.27 at 15 and 100 kPa,respectively,while maintaining good cycling performance.Density functional theory(DFT)simulation,CO_(2) temperature-programmed desorption(CO_(2)-TPD),and in situ Fourier transform infrared spectroscopy(FTIR)were further employed to have a better understanding of the enhanced CO_(2) adsorption capacity.Interestingly,unlike the AAs loaded pristine MOF-808s that showed the best CO_(2) adsorption capacity with the loading of short and small glycine(Gly),the broadened channel size in our work enables the loading of functional motif-rich L-serine,which brings more active binding sites,improving CO_(2) adsorption.