Effect of single Si_(1−x)C_(x)coating and compound coatings on the thermal conductivity and corrosion resistance of Mg-3Sn alloy

A single Si_(1−x)C_(x)coating and compound coatings were deposited on Mg-3Sn matrix alloy by magnetron sputtering method.Compound coatings included Mg or Mg/AlTi intermediates between Mg-3Sn substrate and Si_(1−x)C_(x)coating.The thermal conductivity of the Mg-3Sn alloy after coating was enhanced at room temperature.The results showed that the Mg-3Sn alloy coated with Mg/AlTi/Si_(1−x)C_(x)displayed higher thermal conductivity,its thermal conductivity after corrosion was 90.1 W/(m K)and 108.4 W/(m K)at 25℃and 100℃,respectively.Meanwhile,it was revealed that the Mg/Si_(1−x)C_(x)and Mg/AlTi/Si_(1−x)C_(x)compound coatings had nobler Ecorr and much lower i_(corr),higher Rp,compared with the bare Mg-3Sn and Mg-3Sn/Si_(1−x)C_(x)system,and improved the corrosion resistance of the magnesium substrate.

Is proton a charge carrier for δ-MnO_(2) cathode in aqueous rechargeable magnesium-ion batteries?

Manganese dioxide(MnO_(2)) is considered as a potential cathode material for aqueous magnesium-ion batteries. However, the charge/discharge mechanism of MnO_(2)in aqueous electrolyte is still unclear. In present study, highly porous δ-MnO_(2) is investigated, which delivers a high capacity of 252.1 m Ah g^(-1) at 0.05 A g^(-1) and excellent rate capability, i.e., 109.7 m Ah g^(-1) at 1 A g^(-1), but a low-capacity retention of 54.4% after 800 cycles at 1 A g^(-1). The two-step discharging process, namely a consequent H^(+) and Mg^(2+) insertion reaction, is verified, by comparing the electrochemical performance of δ-MnO_(2) in 1 M MgCl_(2) and 1 M MnCl_(2) aqueous electrolyte and analyzing detailedly the Mg content and the bonding state of Mn at different charge/discharge state. Furthermore, partial irreversibility of Mg^(-1) ion insertion/extraction is observed, which may be one of the major reasons leading to capacity decay.

Alternating nanolayers as lithiophilic scaffolds for Li-metal anode

Nanostructured scaffolds offer promising opportunities in enabling dendrite-free long-cycle life Li metal anode.The rational design and controllable synthesis of scaffolding architectures are imperative for development of rechargeable Li metal batteries.In this study,we explore the fabrication and application of a tin monoxide/graphene hybrid architecture as a lithiophilic host for high-performance Li metal anode.Using a polymer-assisted sonochemical synthesis route,we tuned the thickness of SnO nanolayers and the nanostructure of alternatively stacking thin SnO nanosheet/graphene(SnO-NS/G) heterostructure.Offering abundant nucleation sites,fast ion transport tunnels,and 3D-conductivity,the unique 2D-2D architecture enables stable lithium plating-stripping cycling with low nucleation overpotential and high coulombic efficiency(CE).Hosted by SnO-NS/G scaffold,the resulting Li metal anode exhibits stable cycling over 200 cycles at 0.5 mA cm^(-2)(2 mAh).Full cell pairing high-mass-loading cathode LiCoO_(2)(LCO)(12 mg cm^(-2)) with SnO-NS/G hosted Li metal anode delivers high energy density of 402 Wh kg^(-1) and stable cyclability of over 100 cycles.We elucidate the structure-property relationship between nanolayer thickness and Li-metal plating behaviors,giving new insight on structuring 2D-nanomaterials with ideal architectures for stable lithium metal batteries.

Promoted hydrolysis performances and mechanism of Si-NaBH4-AlCl_(3) in deionized water

Si-based hydrolysis material system can be used in mobile/portable hydrogen source applications connected to fuel cells but is limited by alkaline solutions.In the present research,we reported an acid/alkaline free hydrolysis systemcombining siliconwith NaBH4.Sampleswith different ratios between Si and NaBH4 are prepared via high energy ball milling and hydrolyzed in deionized water at different temperatures.Synergetic effect between silicon and NaBH4was found in the hydrolysis process.2Si-NaBH4 sample displays the best hydrolysis performances with the hydrogen yield of 1594 ml·g^(−1) in deionized water at 70℃.Thereafter,AlCl3 is added into the 2Si-NaBH4 sample to further improve its comprehensive properties.The effect of AlCl3 content and promotion mechanism of the reaction are explored.2Si-NaBH4-5 wt% AlCl3 sample shows a significant improvement with a high hydrogen yield of 1689 ml·g^(−1) in deionized water at 70℃ and a corresponding conversion rate of 95.8%,indicating that the Si-NaBH4-AlCl3 composite is promising to be a hydrogen source in applications of mobile/portable fuelcell-powered facilities.

Size and near-surface engineering in weak-oxidative confined space to fabricate 4 nm L1_(0)-PtCo@Pt nanoparticles for oxygen reduction reaction

The near-surface structure of the Pt-based alloy including the surface and subsurface structures is prominent to their electrocatalytic performance.Modulating the near-surface structure of PtCo intermetallics with small particle size could efficiently optimize the binding force between Pt and oxygen and finally enhance its oxygen reduction reaction(ORR)performance.Here we simultaneously achieve the size controlling and surface modulation of intermetallic nanoparticles(NPs)in a weak-oxidative confined space with abundant uncoordinated oxygen atoms.1–2 atomic layers of concave Pt-rich surface were successfully constructed on 4 nm L1_(0)-PtCo core after removing Co–O species which is derived from the segregation of the subsurface Co to the surface induced by the uncoordinated oxygen atoms.Owing to the elaborate structure,PtCo-1000/C catalyst shows significant improvement in both activity(1.290 A∙mg_(Pt)^(−1)and 1.529 mA∙cm_(Pt)^(−2) at 0.9 V vs.reversible hydrogen electrode(RHE))and stability(85.2%of initial mass activity after accelerated degression tests(ADTs))even the production is scaled up to gram level.Density functional theory calculations suggest that the cave Pt site optimizes the protonation of*O,which finally boosts the ORR performance.

Hydrolysis enhancing mechanisms of Mg-based alloys/hydrides from perspectives:Electrochemical corrosion,active sites,mass transfer,and kinetics

Hydrogen energy is considered to be an ideal new energy carrier in the 21st century due to its clean,environmentally friendly,renewable characteristics and high energy density.The generation of hydrogen by hydrolysis of Mg-based alloys/hydrides has attracted extensive attention attributed to the high hydrogen yield,environmentally-benign by-products,high crust abundance,and well-developed industrial production of Mg.However,in the hydrolysis process of Mg or MgH_(2)to generate hydrogen,the formed Mg(OH)_(2)passivation layer attaches to the surface of the active materials to prevent the reaction from continuing.To improve the hydrolysis performance,a series of methods have been put forward.In this paper,focusing on the mechanisms of hydrogen generation by hydrolysis of Mg-based alloys/hydrides,we summarize the recent research progress from four different perspectives:electrochemical corrosion promotion by constructing galvanic cells,active sites increment by refining the particles,mass transfer enhancement by breaking Mg(OH)_(2)and corresponding kinetic improvement.

Table-like magnetocaloric effect and large refrigerant capacity of composite magnetic refrigerants based on LaFe_(11.6)Si_(1.4)H_y alloys

Composite magnetic refrigerants were prepared by physical mixing LaFeSiHalloys with different Curie temperatures(Tc). The phase structures of these LaFeSiHalloys were analyzed by X-ray diffraction(XRD) and the magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The results indicate the experimental magnetic entropy change(-△S)-Tcurve corresponds reasonably with the(-△S)-Tcurve calculated by the linear combination of(-△S)-T curves of the single material. An optimal mixing ratio can make the composite magnetic refrigerant possess a table-like(-△S)-Tcurve which is beneficial to magnetic Ericsson cycle. When three LaFeSiHalloys with different Tare mixed, the full width at half maximum(△T) of(-△S)-T curves is about 48.7 K and the RC is about 177.76 J/kg under a magnetic field change of 2 T. The composite magnetic refrigerants based on LaFeSiHalloys can be promising candidates for near room temperature magnetic refrigeration and the work will be helpful to develop novel composite magnetic refrigerants with table-like MCE and large RC.

Corrosion behavior and magnetocaloric effect of FeNi(1J85) coated LaFe_(11.6)Si_(1.4)/Sn composites

The FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were prepared by hot pressing(HP). The microstructure,corrosion behavior and magnetocaloric effect(MCE) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were investigated systematically. The results show that the corrosion resistance of FeNi coated LaFe_(11.6)Si_(1.4)Sn composites is better than that of LaFe_(11.6)Si_(1.4)/Sn composites in deionized water. The maximum magnetic entropy change((-△S_M)^(max)) and relative cooling power(RCP) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites are 13.30 J/(kg-K) and 146.25 J/kg, respectively, which are larger than that((-△S_M)^(max), 10.65 J/(kg·K) and RCP, 106.53 J/kg) of LaFe_(11.6)Si_(1.4)/Sn composites in a low magnetic field change of 2 T. FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites possess a more negative slope. The improvement of magnetic properties is due to high permeability FeNi permalloy(1 J85) which improves the itinerant-electron metamagnetic(IEM) transition. So, the method of coating FeNi can provide a new idea for enhancing the corrosion resistance and magnetocaloric effect of La(Fe_xSi_(1-x))_(13)-based materials.

Studies of short-time and high-temperature annealing and magnetic property of LaFe_(11.4)Si_(1.6) compound

The LaFe11.4Si1.6 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K （5 h） to 1623 K （2 h）. The powder X-ray diffraction （XRD） and microstructure observations show that large amount of 1：13 phase begins to appear in the LaFe11.4Si1.6 compound annealed at 1423 K （5 h）. In the temperature range from 1423 K to 1523 K, the α-Fe and LaFeSi phases rapidly decrease to form 1：13 phase. The LaFeSi phase is rarely observed by XRD when the as-cast compound is annealed at 1523 K （5 h）. With annealing temperature increasing to 1573 K, LaFeSi phase is detected again in LaFe11.4Si1.6 compound. In LaFe11.4Si1.6 compounds annealed at 1523 K （5 h）, at 1373 K （2 h）＋1523 K （5 h）, and 1523 K （7 h）＋1373 K （2 h）, the impurity phases including small amount of α-Fe and LaFeSi phase reduce in turn. The magnetic measurement shows that LaFe11.4Si1.6 compounds annealed by above three processes keep the first-order of magnetic transition behavior, and Tc are both at about 200 K. But the values of the maximal ASM（T, H） of has large difference, they are 9.94, 12.66, and 13.96 J/（kg.K） under a magnetic field of 0- 2 T, respectively.