Phase forming law and electrochemical properties of A2B7-type La-Y-Ni-based hydrogen storage alloys with different La/Y ratios

The effects of different proportions of La and Y elements in the A-side on the structure and properties of A_(2)B_(7)-type La-Y-Ni hydrogen storage alloys were investigated.The(La,Y)_(2)Ni_(7)hydrogen storage alloys with different La/Y ratios were prepared by sintering the Y_(2)Ni_(4)precursor and different AB_(5)-type precursors at 1298 K for 5 h and subsequently annealed for 20 h at 1248 K.All the alloys only contain Ce_(2)Ni_(7)(2H-type)and Gd_(2)Co_(7)(3R-type)phases with different mass ratios.As the La/Y ratio decreases,the cell volume of the two phases declines and the corresponding plateau pressure gradually increases.As the proportion of Y in the alloy increases,the hydrogen storage capacity increases gradually from 1.309 wt%(La/Y=1/1)to 1.713 wt%(La/Y=1/5)and the high-rate discharge(HRD1500)ability of the alloy electrodes increases gradually from 62.7%(La/Y=1/1)to 88.6%(La/Y=1/5).The hydrogen diffusion rate in the bulk of the alloy is the controlling step of hydriding/dehydriding kinetics.The Y ele ment can effectively inhibit the hydrogen-induced amorphous(HIA)of La-Y-Ni alloys,but the poor stability of the Y element in alkaline KOH aqueous solution leads to a decrease in the electrochemical cyclic stability with increasing Y content.

Oxygen and nitrogen tailoring carbon fiber aerogel with platinum electrocatalysis interfaced lithium/sulfur(Li/S)batteries

Sluggish kinetics of lithium/sulfur(Li/S)conversion chemistry and the ion channels formation in the cathode is still a bottleneck for developing future Li/S batteries with high-rate,long-cycling and high-energy.Here,a rational cathode structure design of an oxygen(O)and nitrogen(N)tailoring carbon fiber aerogel(OCNF)as a host material integrated with platinum(Pt)electrocatalysis interface is employed to regulate Li/S conversion chemistry and ion channel.The Pt nanoparticles were uniformly sprayed onto the S surface to construct the electrocatalysis interface(Pt/S/OCNF)for generating ion channels to promote the effective penetration of electrolyte into the cathode.This Pt/S/OCNF gives the cathode a high sulfur utilization of 77.5%,an excellent rate capacity of 813.2 m Ah/g(2 C),and an outstanding long-cycling performance with a capacitance retention of 82.6%and a decay of 0.086%per cycle after 200 cycles at 0.5 C.Density functional theory(DFT)calculations reveal that the Pt electrocatalysis interface makes the cathode a high density of state(DOS)at Fermi level to facilitate the electrical conductivity,charge transfer kinetics and electrocatalysis to accelerate the lithium polysulfides(LiPSs)electrochemical conversion.Furthermore,the unique chemisorption structure and adsorption ability of Li2Sn(n=1,2,4,6,8)and S8on OCNF are attributed to the bridging effects of interfacial Pt and the bonding of N-Li.The Pt electrocatalysis interface combined with the unique 3D hierarchical porous structure and abundant functional active sites at OCNF guarantee strong adsorption confinement,fast Li/S electrocatalytic conversion and unblocked ion channels for electrolyte permeation in cathode.