无机化学前沿与交叉科学

由Inorgonic Chiemistry Fronhens(ICF)期刊和南开大学化学学院联合主办的无机化学前沿编委会暨化学及交叉学科前沿国际研讨会于2019年9月23〜25 H在天津召开。无机化学前沿国际研讨会是ICF期刊主办的系列学术会议。该期刊由中国化学会、北京大学和英国皇家化学会(Royal Society of Chemistry)合作出版。无机化学前沿国际研讨会致力于探讨当今无机化学前沿及其与其他学科交叉研究领域的热点问题、最新进展和发展趋势。

Recent Advances on Ruthenium-based Electrocatalysts for Lithium-oxygen Batteries

Rechargeable lithium-oxygen(Li-O_(2))batteries have attracted wide attention due to their high energy density.However,the sluggish cathode kinetics results in high overvoltage and poor cycling performance.Ruthenium(Ru)-based electrocatalysts have been demonstrated to be promising cathode catalysts to promote oxygen evolution reaction(OER).It facilitates decomposition of lithium peroxide(Li_(2)O_(2))by adjusting Li_(2)O_(2) morphologies,which is due to the strong interaction between Ru-based catalyst and superoxide anion(O_(2))intermediate.In this review,the design strategies of Ru-based electrocatalysts are introduced to enhance their OER catalytic kinetics in Li-O_(2) batteries.Different configurations of Ru-based catalysts,including metal particles(Ru metal and alloys),single-atom catalysts,and Ru-loaded compounds with various substrates(carbon materials,metal oxides/sulfides),have been summarized to regulate the electronic structure and the matrix architecture of the Ru-based electrocatalysts.The structure-property relationship of Ru-based catalysts is discussed for a better understanding of the Li_(2)O_(2) decomposition mechanism at the cathode interface.Finally,the challenges of Ru-based electrocatalysts are proposed for the future development of Li-O_(2) batteries.

单原子合金催化剂热稳定性的反应力场分子动力学研究

通过反应力场(ReaxFF)模型分子动力学模拟,研究了负载模型和掺杂模型单原子催化剂(分别记为M 1/Cu(111)和M 1@Cu(111),M=Pt,Ni,Ag,Fe)的热稳定性.模拟结果显示:对于M 1@Cu(111)掺杂模型,Pt(Ni,Fe)1@Cu(111)的稳定性远高于Ag 1@Cu(111),温度大于500 K时依旧可以保持稳定.而负载模型M 1/Cu(111)除了Fe 1/Cu(111)以外,其余模型在100~500 K的温度范围中均无法保持稳定,单个金属原子会在Cu(111)表面迁移并相互聚集最终形成纳米颗粒.同时发现,随着温度的升高,Fe不同于其他金属单原子的烧结过程,会向亚表层扩散,进入合金体相.此外,还优化了Cu/Pt/H/O的力场参数,并研究了H 2气氛对单原子催化剂(SAA)催化剂模型表面稳定性的影响,发现H 2气氛的存在导致M 1@Cu(111)模型稳定性降低.理论模拟结果发现M 1/Cu(111)型SAA催化剂即使在低温下也不是一个很好的候选催化剂,而多数M 1@Cu(111)型催化剂在较高温度下依旧可以保持稳定.

Photocatalytic performance of TiO_2 nanocrystals with/without oxygen defects

To investigate the role of oxygen defects on the photocatalytic activity of TiO2,the TiO2 nanocrystals with/without oxygen defects are successfully synthesized by the hydrothermal and sol‐gel methods,respectively.The as‐prepared TiO2 nanocrystals with defects are light blue and the absorption edge of light is towards the visible light region(~420 nm).Raman and X‐ray photoelectron spectroscopy(XPS)measurements all confirm that the concentration of oxygen vacancies in the TiO2 synthesized by the sol‐gel method is less than that synthesized through the hydrothermal route.The introduction of oxygen defects contributes to a new state in the band gap that narrows the band gap,which is the reason for the extension of light absorption into the visible light region.The photocurrent results confirm that this band‐gap narrowing enhances the photocurrent response under simulated solar light irradiation.The TiO2 with oxygen defects shows a higher photocatalytic activity for decomposition of a methylene blue solution compared with that of the perfect TiO2 sample.The photocatalytic mechanism is discussed based on the density functional theory calculations and photoluminescence spectroscopy measurements.

Defective high-entropy rocksalt oxide with enhanced metal‒oxygen covalency for electrocatalytic oxygen evolution

High‐entropy materials are emerging electrocatalysts by integrating five or more elements into one single crystallographic phase to optimize the electronic structures and geometric environments.Here,a rocksalt‐type high‐entropy oxide Mg_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2)Zn_(0.2)O(HEO)is developed as an electrocatalyst towards the oxygen evolution reaction(OER).The obtained HEO features abundant cation and oxygen vacancies originating from the lattice mismatch of neighboring metal ions,together with enlarged Co/Ni‒O covalency due to the introduction of less electronegative Mg and Zn.As a result,the HEO exhibits superior intrinsic OER activities,delivering a turnover frequency(TOF)15 and 84 folds that of CoO and NiO at 1.65 V,respectively.This study provides a mechanistic understanding of the enhanced OER on HEO and demonstrates the potential of high‐entropy strategy in developing efficient oxygen electrocatalysts by elaborately incorporating low‐cost elements with lower electronegativity.

Nature of active phase of VO_x catalysts supported on SiBeta for direct dehydrogenation of propane to propylene

The VOx catalysts supported on dealuminated Beta zeolite(Si Beta) with varying V loadings(from 0.5 to 10 wt%) are prepared and tested for their catalytic activities in the reaction of direct dehydrogenation of propane to propylene(PDH). It is characterized that the VSi Beta catalysts possess different kinds of vanadium species on the Si Beta support, including monomeric or isolated VOx species at a low V loading, and polynuclear VOx species in different polymerization degrees at higher V loadings. The 3 VSi Beta catalyst(V loading is 3 wt%), containing isolated VOx species in monolayer, shows around 40% of propane conversion with 90% of propylene selectivity(reaction conditions: 600 o C, 4000 m L g–1 h–1) which are comparable to VSi Beta catalysts with higher V loadings. The catalytic activity exhibits a good linear relationship with the amount of generated acidic sites, which are derived from the interaction sites between VOx species and Si Beta support, and keeps stable after several regeneration cycles. Thus, as the VOx species directly contact with Si Beta support via V–O–Si bonds, a reactivity enhancement can be achieved. While, the initial valence state of V does not seem to influence the catalytic performance. Moreover, the aggregation degree of VOx species determines the propylene selectivity and deactivation rate, both of which increase as raising the V loading amount.

Coupled cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes supported on nickel foam as a binder-free electrode for overall water splitting

In an attempt to develop low-cost,non-noble-metal bifunctional electrocatalysts for water electrolysis in alkaline media,cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate.Benefiting from the optimized electronic structure and enhanced mass and charge transport,as well as the 3D conducting pathway,MoxCoy@N-CNSs/CNTs shows superior performance towards both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in an alkaline medium.The optimal electrocatalyst is Mo2Co1@N-CNSs/CNTs,which reveals a current density of 10 mA cm^-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER,respectively,and a relatively low cell voltage(1.63 V)for the overall water electrolysis.The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.

Designer Mg-Mg and Zn-Zn Single Bonds Facilitated by Double Aromaticity in the M2B7^-(M=Mg,Zn)Clusters

The simple homodinuclear M-M single bonds for group II and XII elements are difficult to obtain as a result of the fulfilled s2electronic configurations,consequently,a dicationic prototype is often utilized to design the M^+-M^+single bond.Existing studies generally use sterically bulky organic ligands L^-to synthesize the compounds in the L^--M^+-M^+-L-manner.However,here we report the design of Mg-Mg and Zn-Zn single bonds in two ligandless clusters,Mg2B7-and Zn2B7-,using density functional theory methods.The global minima of both of the clusters are in the form of M2^2+(B7^3-),where the M-M single bonds are positioned above a quasi-planar hexagonal B7 moiety.Chemical bonding analyses further confirm the existence of Mg-Mg and Zn-Zn single bonds in these clusters,which are driven by the unusually stable B7^3-moiety that is bothσandπaromatic.Vertical detachment energies of Mg2B7-and Zn2B7-are calculated to be 2.79 e V and 2.94 e V,respectively,for the future comparisons with experimental data.