Design of bifunctional single-atom catalysts NiSA/ZIF-300 for CO_(2) conversion by ligand regulation strategy

Carbon-supported noble-metal-free single-atom catalysts(SACs)have aroused widespread interest due to their green chemistry aspects and excellent performances.Herein,we propose a“ligand regulation strategy”and achieve the successful fabrication of bifunctional SAC/MOF(MOF=metal-organic framework)nanocomposite(abbreviated NiSA/ZIF-300;ZIF=ZIF-8)with exceptional catalytic performance and robustness.The designed NiSA/ZIF-300 has a planar interfacial structure with the Ni atom,involving one S and three N atoms bonded to Ni(Ⅱ),fabricated by controllable pyrolysis of volatile Ni-S fragments.For CO_(2) cycloaddition to styrene epoxide,NiSA/ZIF-300 exhibits ultrahigh activity(turnover number(TON)=1.18×105;turnover frequency(TOF)=9830 molSC·mol_(Ni)^(-1)·h^(-1);SC=styrene carbonate)and durability at 70℃ under 1 atm CO_(2) pressure,which is much superior to Ni complex/ZIF,NiNP/ZIF-300,and most reported catalysts.This study offers a simple method of bifunctional SAC/MOF nanocomposite fabrication and usage,and provides guidance for the precise design of additional original SACs with unique catalytic properties.

Ferrocene-induced switchable preparation of metal-nonmetal codoped tungsten nitride and carbide nanoarrays for electrocatalytic HER in alkaline and acid media

Transition metal nitride/carbide(TMN/C)have been actively explored as low-cost hydrogen evolution reaction(HER)electrocatalysts owing to their Pt-like physical and chemical properties.Unfortunately,pure TMN/C suffers from strong hydrogen adsorption and lacks active centers for water dissociation.Herein,we developed a switchable WO_(3)-based in situ gas–solid reaction for preparing sophisticated Fe-N doped WC and Fe-C doped WN nanoarrays.Interestingly,the switch of codoping and phase can be effectively manipulated by regulating the amount of ferrocene.Resultant Fe-C-WN and Fe-N-WC exhibit robust electrocatalytic performance for HER in alkaline and acid electrolytes,respectively.The collective collaboration of morphological,phase and electronic effects are suggested to be responsible for the superior HER activity.The smallest|ΔGH*|value of Fe-NWC indicates preferable hydrogen-evolving kinetics on the Fe-N-WC surface for HER under acid condition,while Fe-C-WN is suggested to be beneficial to the adsorption and dissociation of H_(2)O for HER in alkaline electrolyte.

Design of superior electrostriction in BaTiO_(3) -based lead-free relaxors via the formation of polarization nanoclusters

Electrostrictive materials have wide applications in modern high-precision electronic devices.Driven by growing environmental concerns,there is demand for lead-free materials with superior electrostriction behaviors.In this study,we demonstrate a record-high electrostrictive coefficient of~0.0712 m^(4) C^(-2) in perovskite ferroelectric ceramics,along with hysteresis-free strain as well as excellent frequency and thermal stabilities,in lead-free BaTiO_(3)-based ceramics through a polarization nanocluster design.By appro-priately introducing Li+and Bi^(3+)into the BaTiO 3 lattice matrix,the long-range ferroelectric ordering can be broken,and polarization nanoclusters can be formed,resulting in a relaxor state with concurrently suppressed polariza-tion and maintained electro-strain.A three-dimensional atomic model constructed using advanced neutron total-scattering data combined with the reverse Monte Carlo method indicates the existence of Bi and Li segregations at the subnanometer scale,which confirms the prediction made by density functional theory calculations.Such a short-range chemical order destroys the long-range ferroelectric order of the off-centered Ti polar displacements and leads to the embedding of Li+/Bi ^(3+)-rich polar nanoregions in the Ba^(2+)-rich polarization disorder matrix.Further,a completely reversible electric-field-induced lattice strain is observed,giving rise to pure electrostriction without hysteresis behavior.This work provides a novel strategy for developing lead-free relaxor ferroelectrics with high electrostriction performance.

Multi-interface collaboration of graphene cross-linked NiS-NiS_(2)-Ni_(3)S_(4) polymorph foam towards robust hydrogen evolution in alkaline electrolyte

Electrocatalytic hydrogen production in alkaline media is extensively adopted in industry. Unfortunately, further performance improvement is severely impeded by the retarded kinetics, which requires the fine regulation of water dissociation, hydrogen recombination, and hydroxyl desorption. Herein, we develop a multi-interface engineering strategy to make an elaborate balance for the alkaline hydrogen evolution reaction (HER) kinetics. The graphene cross-linked three-phase nickel sulfide (NiS-NiS_(2)-Ni_(3)S_(4)) polymorph foam (G-NNNF) was constructed through hydrothermal sulfidation of graphene wrapped nickel foam as a three-dimensional (3D) scaffold template. The G-NNNF exhibits superior catalytic activity toward HER in alkaline electrolyte, which only requires an overpotential of 68 mV to drive 10 mA·cm^(−2) and is better than most of the recently reported metal sulfides catalysts. Density functional theory (DFT) calculations verify the interfaces between nickel sulfides (NiS/NiS_(2)-Ni_(3)S_(4)) and cross-linked graphene can endow the electrocatalyst with preferable hydrogen adsorption as well as metallic nature. In addition, the electron transfer from Ni_(3)S_(4)/NiS_(2) to NiS results in the electron accumulation on NiS and the hole accumulation on Ni_(3)S_(4)/NiS_(2), respectively. The electron accumulation on NiS favors the optimization of the H* adsorption, whereas the hole accumulation on Ni_(3)S_(4) is beneficial for the adsorption of H_(2)O. The work about multi-interface collaboration pushes forward the frontier of excellent polymorph catalysts design.

碱刻蚀法构建膨化FexCoyNi1-x-yP四元阵列及其高效裂解水性能

设计和构建低成本、高效、高稳定性双功能电催化剂用于全解水生产氢气燃料是非常吸引人的研究,同时也充满挑战.我们精心构建了膨化四元FexCoyNi1-x-yP纳米阵列作为双功能电催化剂用于全解水.通过引入铁元素调节磷化镍钴的电子结构,可增加磷和金属的正电荷分布,从而可实现电催化析氢过程中对氢原子吸附脱附平衡,有利于水分子的吸附和解离.在电子调控的基础上,我们采用动力学控制碱刻蚀的方法优化催化剂的形貌结构,获得了膨化纳米阵列.膨化结构具有丰富的孔结构、空腔以及晶格缺陷,有利于更多活性位点的暴露和传质.膨化FexCoyNi1-x-yP只需25和230 mV过电势即可分别实现产氢和产氧.利用膨化FexCoyNi1-x-yP作为阳极和阴极搭建的电解池只需1.48 V即可实现全解水,并在较高电流中表现出优异的稳定性.我们期望协同优化电子和形貌结构促进电催化反应过程的研究思路对廉价高效稳定双功能电催化剂的研究有所启发.

Rapid and selective uranium extraction from aqueous solution under visible light in the absence of solid photocatalyst

Extraction of uranium from radioactive waste-water is of significant importance for environmental protection and the recovery of uranium resource.Different from the previous reports to use the solid absorbent/photocatalyst for U(VI)removal,herein,we proposed a new eco-friendly method for the rapid and selective extraction of uranium from aqueous solutions under visible light without solid materials.At optimal pH value and in the presence of organics like alcohols,the U(VI)could be extracted efficiently to form brown uranium solid over wide uranium concentrations under anaerobic condition and visible light,by utilizing the excitation of the given U(VI)species.With comprehensive modelling of the electronic ultraviolet-visible(UV-Vis)properties,it is proved that pH adjusting towards U(VI)could induce efficient ligand-to-metal-charge-transfer(LMCT)within the uranyl complex under visible light and the reduction of U(VI)to form U(V),which can be transformed into U(IV)via disproportionation reaction.The resulting U(IV)in solid phase makes the extraction much more convenient in operation.More importantly,the excellent selectivity for uranium extraction over interfering alkali metal ions,transition metal ions and the lanthanide metal ions shows a powerful application potential.

On the oxidation states of metal elements in MO-3(M=V,Nb,Ta,Db,Pr,Gd,Pa)anions

Relativistic quantum chemistry investigations are carried out to tackle the puzzling oxidation state problem in a series of MO_3^- trioxide anions of all d- and f-block elements with five valence electrons. We have shown here that while the oxidation states of V, Nb, Ta, Db, Pa are, as usual, all +V with divalent oxygen O(-II) in MO_3^- anions, the lanthanide elements Pr and Gd cannot adopt such high +V oxidation state in similar trioxide anions. Instead, lanthanide element Gd retains its usual +III oxidation state, while Pr retains a +IV oxidation state, thus forcing oxygen into a non-innocent ligand with an uncommon monovalent radical(O~·) of oxidation state -I. A unique Pr·- ·(O)_3 biradical with highly delocalized unpairing electron density on Pr(IV) and three O atoms is found to be responsible for stabilizing the monovalent-oxygen species in PrO_3^- ion, while GdO_3^- ion is in fact an OGd^+(O_2^(2-)) complex with Gd(III). These results show that a na?ve assignment of oxidation state of a chemical element without electronic structure analysis can lead to erroneous conclusions.