Tuning Li/Ni mixing by reactive coating to boost the stability of cobalt-free Ni-rich cathode

Cobalt-free cathode materials are attractive for their high capacity and low cost,yet they still encounter issues with structural and surface instability.AlPO_(4),in particular,has garnered attention as an effective stabilizer for bulk and surface.However,the impact of interfacial reactions and elemental interdiffusion between AlPO_(4) and LiNi_(0.95)Mn_(0.05)O_(2) upon sintering on the bulk and surface remains elusive.In this study,we demonstrate that during the heat treatment process,AlPO_(4) decomposes,resulting in Al doping into the bulk of the cathode through elemental interdiffusion.Simultaneously,PO_(4)^(3-)reacts with the surface Li of material to form a Li_3PO_(4) coating,inducing lithium deficiency,thereby increasing Li/Ni mixing.The suitable Li/Ni mixing,previously overlooked in AlPO_(4) modification,plays a pivotal role in stabilizing the bulk and surface,exceeding the synergy of Al doping and Li_3PO_(4) coating.The presence of Ni^(2+)ions in the lithium layers contributes to the stabilization of the delithiated structure via a structural pillar effect.Moreover,suitable Li/Ni mixing can stabilize the lattice oxygen and electrode-electrolyte interface by increasing oxygen removal energy and reducing the overlap between the Ni^(3+/4+)e_g and O^(2-)2p orbitals.These findings offer new perspectives for the design of stable cobalt-free cathode materials.

Dependence of lithium metal battery performances on inherent separator porous structure regulation

Boosting of rechargeable lithium metal batteries(LMBs) holds challenges because of lithium dendrites germination and high-reactive surface feature.Separators may experience structure-determined chemical deterioration and worsen Li plating-stripping behaviors when smoothly shifting from lithium-ion batteries(LIBs) to LMBs.This study precisely regulations the crystal structure of β-polypropylene and separator porous construction to investigate the intrinsic porous structure and mechanical properties determined electrochemical performances and cycling durability of LMBs.Crystal structure characterizations,porous structure analyses,and electrochemical cycling tests uncover appropriate annealing thermal stimulation concentrates β-lamellae thickness and enhances lamellae thermal stability by rearranging molecular chain in inferior β-lamellae,maximally homogenizing biaxial tensile deformation and resultant porous constructions.These even pores with high connectivity lower ion migration barriers,alleviate heterogeneous Li^(+) flux dispersion,stabilize reversible Li plating-stripping behaviors,and hinder coursing and branching of Li dendrites,endowing steady cell cycling durability,especially at higher currents due to the highlighted uncontrollable cumulation of dead Li,which offers new insights for the current pursuit of high-power density battery and fast charging technology.The suggested separator structure-chemical nature functions in ensuring cyclic cell stability and builds reliable relationships between separator structure design and practical LMBs applications.

Long-range Pt-Ni dual sites boost hydrogen evolution through optimizing the adsorption configuration

Elaborated design of catalytic systems with a specifically tailored site distance to match the intermediates could substantially improve reaction kinetics and boost catalytic activity under unfavorable reaction conditions.Considering the lower energy barriers of water splitting upon the synergy of dual sites,constructing synergistic Pt-M(M:transition metal)dual sites is an effective way to boost Pt with highly catalytic hydrogen evolution reaction(HER)performance.An unconventional“Ni(OH)_(2)-coated high-index Pt facets”was constructed to obtain long-range Pt-Ni dual sites,in which Ni composition as a water dissociation synergistic site can protect Pt from electrolyte corrosion and ensure efficient proton donation to Pt sites.The obtained long-range Pt-Ni dual sites present 3.84 mA·cm^(-1) of current density,which is 7.5 times specific activity higher than that of commercial Pt/C towards alkaline HER.The enhanced HER performance is attributed to synergistic catalysis on Pt-Ni dual sites accompanied by unconventional electron coupling.This work illustrates a new strategy to construct the long-range dual sites by unconventional strategy for fundamental electrocatalytic study of alkaline HER.

Enhancement of CH_(3)CO^(*) adsorption by editing d-orbital states of Pd to boost C–C bond cleavage of ethanol eletrooxidation

Improving the complete ethanol electrooxidation on Pd-based catalysts in alkaline media has drawn widely attention due to the high mass energy density.However,the weak adsorption energy of CH_(3)CO^(*) on Pd restricts the C–C bond cleavage.Inspired by the molecular orbital theory,we proposed the d-state-editing strategy to construct more unoccupied d-states of Pd for the enhanced interaction with CH_(3)CO^(*) to break C–C bonds.As expected,the reduced number of e_g electrons and more unoccupied d-states of Pd successfully formed on as-prepared porous Rh Au–Pd Cu nanosheets(PNSs).Theoretical calculations show that the optimized d-states of Rh Au–Pd Cu PNS can effectively improve the adsorption of CH_(3)CO^(*) and drastically reduce the energy barrier of C–C bond cleavage,thus boosting the complete oxidation of ethanol.The charge ratio of C_1 pathway on Rh Au–Pd Cu PNSs is 51.5%,more than 2 times higher than that of Pd NSs.Our finding provides an innovative perspective for the design of highly-efficient noble-based electrocatalysts.

Morphology-selective synthesis of active and durable gold catalysts with high catalytic performance in the reduction of 4-nitrophenol

A series of novel catalysts consisting of nanosized Au particles confined in micro-mesoporous ZSM-5/SBA-15 （ZSBA） materials with platelet （PL）, rod （RD）, and hexagonal-prism （HP） morphologies have been synthesized in situ. These catalysts possess both SBA-15 and ZSM-5 structures and exhibit excellent stability of their active sites by confinement of the Au nanoparticles （NPs） within ZSBA. The catalysts have been characterized in depth to understand their structure-property relationships. The gold NP dimensions and the pore structure of the catalysts, which were found to be sensitive to calcination temperature and synthetic conditions, are shown to play vital roles in the reduction of 4-nitrophenol. Au/ZSBA-PL, with short mesochannels （210 nm） and a large pore diameter （6.7 nm）, exhibits high catalytic performance in the reduction of 4-nitrophenol, whereas Au/ZSBA-HP and Au/ZSBA-RD, with long mesochannels and relatively smaller pore sizes, show poor catalytic activities. In the case of catalysts with different gold NP sizes, Au/ZSBA-PL-350 with an Au NP diameter of 4.0 nm exhibits the highest reaction rate constant （0.14 min-1） and turnover frequency （0.0341 s-1）. In addition, the effect of the reaction parameters on the reduction of 4-nitrophenol has been systematically investigated. A possible mechanism for 4-nitrophenol reduction over the Au/ZSBA catalysts is proposed.

A single Au nanoparticle anchored inside the porous shell of periodic mesoporous organosilica hollow spheres

An ideal metal catalyst requires easy contact with reaction reagents, a large number of exposed active sites, and high stability against leaching or particle agglomeration. Anchoring a metal core inside a porous shell, though scarcely reported, may combine these advantages owing to the integration of the conventional supported metal arrangement into a core@void@shell architecture. However, achieving this is extremely difficult owing to the weak core-shell affinity. Herein, we report, for the first time, an approach to overcome this challenge by increasing the core-shell interaction. In this regard, we synthesized a novel Au@void@periodic mesoporous organosilica （PMO） architecture in which a single Au core is firmly anchored inside the porous shell of the hollow PMO sphere. The non-covalent interactions between the poly（vinylpyrrolidone） （PVP） groups of functionalized Au and ethane moieties of PMO facilitate the movement of the Au core towards the porous shell during the selective alkaline etching of Au@SiO2@PMO. Shell-anchored Au cores are superior to the suspended cores in the conventional Au@void@PMO in terms of contact with reagents and exposure of active sites, and hence show higher catalytic efficiency for 4-nitrophenol reduction. The methodology demonstrated here provides a new insight for the fabrication of versatile multifunctional nanostructures with cores anchored inside hollow shells.

RuO_(2) nanoparticles supported on Ni and N co-doped carbon nanotubes as an efficient bifunctional electrocatalyst of lithium-oxygen battery

Li_(2)O_(2),as the discharge product of Li-O_(2) batteries on cathode,is difficult to be electrochemically decomposed,which will lead to short cycling lifespan of the batteries.In this study,the cycling lifespan of Li-O_(2)battery was prolonged significantly by an efficient bifunctional catalyst.The Ni and N co-doped carbon nanotubes(Ni NCs)were synthesized firstly,and then RuO_(2) nanoparticles were deposited on Ni NCs by a hydrothermal route to synthesize RuO_(2)/Ni NC catalysts.Transmission electron microscopy and X-ray diffraction characterizations demonstrated that part of metallic Ni was converted into NiO and Ni(OH)2 after loading RuO_(2),and the existence of Ni O layer can prevent further oxidation of metallic Ni.The Li-O_(2)battery with RuO_(2)/Ni NC as the cathode catalyst exhibits an overpotential of 0.43 V,which is much lower than the value of 1.03 V measured with the Li-O_(2) battery using Ni NC as the cathode catalyst.At a rate of 200 mAg^(-1),the Li-O_(2) battery with the RuO_(2)/Ni NC cathode can maintain a reversible capacity of 500 mAhg^(-1)for 260 cycles,and 117 cycles with a higher reversible capacity of 1000 m A h g^(-1).The superior property of the RuO_(2)/NiNC bifunctional catalyst could be ascribed to the high activity of RuO_(2) and the rich carbon nanotube structure of NiNC for deposition and decomposition of Li_(2)O_(2).