Local coordination and electronic interactions of Pd/MXene via dual‐atom codoping with superior durability for efficient electrocatalytic ethanol oxidation

Catalyst design relies heavily on electronic metal‐support interactions,but the metal‐support interface with an uncontrollable electronic or coordination environment makes it challenging.Herein,we outline a promising approach for the rational design of catalysts involving heteroatoms as anchors for Pd nanoparticles for ethanol oxidation reaction(EOR)catalysis.The doped B and N atoms from dimethylamine borane(DB)occupy the position of the Ti_(3)C_(2) lattice to anchor the supported Pd nanoparticles.The electrons transfer from the support to B atoms,and then to the metal Pd to form a stable electronic center.A strong electronic interaction can be produced and the d‐band center can be shifted down,driving Pd into the dominant metallic state and making Pd nanoparticles deposit uniformly on the support.As‐obtained Pd/DB–Ti_(3)C_(2) exhibits superior durability to its counterpart(∼14.6% retention)with 91.1% retention after 2000 cycles,placing it among the top single metal anodic catalysts.Further,in situ Raman and density functional theory computations confirm that Pd/DB–Ti_(3)C_(2) is capable of dehydrogenating ethanol at low reaction energies.

Charge-balanced codoping enables exceeding doping limit and ultralow thermal conductivity

Materials with low thermal conductivity are applied extensively in energy management,and breaking the amorphous limits of thermal conductivity to solids has attracted widespread attention from scientists.Doping is a common strategy for achieving low thermal conductivity that can offer abundant scattering centers in which heavier dopants always result in lower phonon group velocities and lower thermal conductivities.However,the amount of equivalent heavyatom single dopant available is limited.Unfortunately,nonequivalent heavy dopants have finite solubility because of charge imbalance.Here,we propose a charge balance strategy for SnS by substituting Sn2+with Ag^(+)and heavy Bi^(3+),improving the doping limit of Ag from 2%to 3%.Ag and Bi codoping increases the point defect concentration and introduces abundant boundaries simultaneously,scattering the phonons at both the atomic scale and nanoscale.The thermal conductivity of Ag0.03Bi0.03Sn0.94S decreased to 0.535 W·m^(−1)·K^(−1)at room temperature and 0.388 W·m^(−1)·K^(−1)at 275°C,which is below the amorphous limit of 0.450 W·m^(−1)·K^(−1)for SnS.This strategy offers a simple way to enhance the doping limit and achieve ultralow thermal conductivity in solids below the amorphous limit without precise structural modification.

Realizing Cd and Ag codoping in p-type Mg_(3)Sb_(2)toward high thermoelectric performance

Mg_(3)Sb_(2)has attracted intensive attention as a typical Zintl-type thermoelectric material.Despite the exceptional thermoelectric performance in n-type Mg_(3)Sb_(2),the dimensionless figure of merit(zT)of p-type Mg_(3)Sb_(2)remains lower than 1,which is mainly attributed to its inferior electrical properties.Herein,we synergistically optimize the thermoelectric properties of p-type Mg_(3)Sb_(2)materials via codoping of Cd and Ag,which were synthesized by high-energy ball milling combined with hot pressing.It is found that Cd doping not only increases the carrier mobility of p-type Mg_(3)Sb_(2),but also diminishes its thermal conductivity(κ_(tot)),with Mg_(2.85)Cd_(0.5)Sb_(2)achieving a lowκtot value of∼0.67 W m^(−1)K^(−1)at room temperature.Further Ag doping elevates the carrier concentration,so that the power factor is optimized over the entire temperature range.Eventually,a peak zT of∼0.75 at 773 K and an excellent average zT of∼0.41 over 300−773 K are obtained in Mg_(2.82)Ag_(0.03)Cd_(0.5)Sb_(2),which are∼240%and∼490%higher than those of pristine Mg_(3.4)Sb_(2),respectively.This study provides an effective pathway to synergistically improve the thermoelectric performance of p-type Mg_(3)Sb_(2)by codoping Cd and Ag,which is beneficial to the future applications of Mg_(3)Sb_(2)-based thermoelectric materials.

基于新型B-N窗和改进分区法的三相不平衡度检测

国标GB/T 15543-2008要求电压不平衡度计算需在获取基波幅值和相位基础上再求取相序分量,但其计算方法涉及开方运算与相角求取,不利于嵌入式系统实现。因此文中构建新型B-N互卷积窗函数,推导基于新型B-N互卷积窗三谱线改进FFT修正算式,采用改进坐标分区法实现相序分量求取,提出基于新型B-N窗和改进分区法的三相不平衡度检测方法。避免了复杂开方运算,提高了基波幅值和相位的检测精度,最终实现三相不平衡度的准确检测。仿真实验结果表明,文中提出算法在基波、谐波及噪声干扰情况下,均能有效实现不平衡度的准确检测,相比国标推荐方法,实现简单且准确度更高。

Band gap narrowing of TiO_2 by compensated codoping for enhanced photocatalytic activity

In this study, we have performed first-principles screened exchanged hybrid density function theory with the HSE06 function calculations of the C-Mo, C-W, N-Nb and N-Ta codoped anatase TiO2 systems to investigate the effect of codoping on the electronic structure of TiO2. The calculated results demonstrate that （W（s）＋C（s）） codoped TiO2 narrows the band gap significantly, and have little influence on the position of conduction band edges, therefore, enhances the efficiency of the photocatalytic hydrogen generation from water and the photodegradation of organic pollutants. Moreover, the proper oxygen pressure and temperature are two key factors during synthesis which should be carefully under control so that the desired （W（s）＋C（s）） codoped TiO2 can be obtained.

Effect of the codoping of N-H-O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N-H-O at 5.5 GPa-7.1 GPa and 1370℃-1450℃. With the increase in the N-H-O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds;surface morphology became block-like;and growth texture,stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N-H-O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N-H-O impurity contents of the synthesis system.

N/S codoping modification based on the metal organic frameworkderived carbon to improve the electrochemical performance of different energy storage devices

Carbon-based materials have become a research hotspot in the field of energy storage devices in recent years due to their abundant resources,low cost,and environmental friendliness.However,the low capacity and poor high rate performance still constitute great challenges.Metal organic framework-derived carbon has been widely researched because of its high porosity,tunable structure,and good conductivity.In this work,N/S codoped hierarchical porous carbon microspheres were prepared by a high-temperature heat treatment and atomic doping process using a zinc-based organic framework as the precursor.When used as a potassium-ion battery anode,it has a high reversible specific capacity(435.7 mAh g^(-1)),good rate performance(133.5 mAh g^(-1)at 10,000 m A g^(-1)),and long-term cycling stability(73.2%capacity retention after the 2500th cycle).The potassium storage mechanism of the derived carbon was explained by various electrochemical analysis methods and microstructure characterization techniques,and the relationship between the structural characteristics and electrochemical properties was researched.In a supercapacitor,the porous carbon material exhibits a specific capacitance of 307.2 F g^(-1)at a current density of 0.2 A g^(-1)in a KOH aqueous solution and achieves a retention rate of 99.88%after 10,000 cycles.The assembled symmetric supercapacitor device delivers a high energy density of 6.69 Wh kg^(-1),with a corresponding power density of 2500 W kg^(-1).In addition,density functional theory calculations further confirmed that N/S codoping can improve the adsorption capacities of potassium and hydroxyl ions in the derived carbon.

Revisiting the Electron-Doped SmFeAsO:Enhanced Superconductivity up to 58.6 K by Th and F Codoping

In the iron-based high-To bulk superconductors, Tc above 50 K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest Tc in these materials. To introduce more electron carriers and less crystal lattice distortions, we study the Th and F eodoping effects into the Sm-O layers with heavy electron doping. Dozens of Sm1-xThx FeAsO1-yFy samples are synthesized through the solid state reaction method, and these samples are carefully characterized by the structural, resistive, and magnetic measurements. We find that the codoping of Th and F clearly enhances the superconducting Tc more than the Th or F single-doped samples, with the highest record Tc up to 58.6K when x = 0.2 and y=0.225. Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.

Phase transformation and morphology tuning of β-NaYF_4:Yb^(3+),Er^(3+) nanocrystals through K^+ ions codoping

In this work, a simple method to modulate the crystal phase and morphology with a large amount of K＋ions codoping is proposed. The phase changes to the mixture of β-Na YF4 and β-KYF4 with increasing the content of K^＋ions to 80 mol%.When it exceeds 80 mol%, β-Na YF4 disappears gradually and β-KYF4 dominates with a poor crystalline. In addition, the morphology changes from nanosphere to nanoplate, and then to nanoprism, which indicates that a higher content of K^＋ions favors the growth rates along [0001] than the [10-10] of the nanocrystals. Additionally, the upconversion（UC） luminescence properties and the ratio of red/green（R/G） UC intensity of samples with different phases and morphologies are detected,which makes it possible to tune the UC fluorescence by varying the concentration of K^＋ions.

Upconversion Luminescence Properties of NaY0.92Yb0.05Er0.03F4 Enhanced by Zr^4＋ Codoping

In this paper we present a novel report on the upconversion luminescence performance of NaY0.92Yb0.05Er0.03F4 enhanced by Zr^4＋ codoping. The luminescence intensity of the tridoped hexagonal NaYF_4 synthesized by a hydrothermal method increased to the maximum, about seven times of the non-Zr^4＋ sample when the Zr^4＋ codoping concentration rose to 6 mol%, while the luminescence lifetime was also prolonged by Zr^4＋ codoping. To explore the relationships between the microstructure and upconversion properties, X-ray powder diffraction, field emission scanning electron microscope, electron energy-dispersive spectroscopy and upconversion emission spectroscopy were employed. From these characterizations, we found that the codoping of Zr^4＋ could modulate the crystal microstructure of NaYF_4 for higher upconversion luminescence intensity and longer lifetime. This study may be helpful for the design and synthesis of high-performance upconversion materials.

Waste to wealth: Oxygen-nitrogen-sulfur codoped lignin-derived carbon microspheres from hazardous black liquors for high-performance DSSCs

Carbon materials are effective substitutes for Pt counter electrodes(CEs) in dye-sensitized solar cells(DSSCs). However, many of these materials, such as carbon nanotubes and graphene, are expensive and require complex preparation process. Herein, waste lignin, recycled from hazardous black liquors,is used to create oxygen-nitrogen-sulfur codoped carbon microspheres for use in DSSC CEs through the facile process of low-temperature preoxidation and high-temperature self-activation. The large number of ester bonds formed by preoxidation increase the degree of cross-linking of the lignin chains, leading to the formation of highly disordered carbon with ample defect sites during pyrolysis. The presence of organic O/N/S components in the waste lignin results in high O/N/S doping of the pyrolysed carbon,which increases the electrolyte ion adsorption and accelerates the electron transfer at the CE/electrolyte interface, as confirmed by density functional theory(DFT) calculations. The presence of inorganic impurities enables the construction of a hierarchical micropore-rich carbon structure through the etching effect during self-activation, which can provide abundant catalytically active sites for the reversible adsorption/desorption of electrolyte ions. Under these synergistic effects, the DSSCs that use this novel carbon CE achieve a quite high power-conversion efficiency of 9.22%. To the best of our knowledge, the value is a new record reported so far for biomass-carbon-based DSSCs.

我国生鲜乳价格波动规律研究——基于B-N数据分解的分析

我国奶业虽然取得了巨大的成绩,但发展却不平稳,奶价大起大落,奶业市场上"奶荒"与"倒奶"现象交替上演。为探究我国生鲜乳价格的波动特征及规律,本文采用B-N分解法对我国2006—2015年生鲜乳价格进行分解。研究表明:受成本拉动及需求推动的影响,我国生鲜乳价格存在确定性增长趋势,且实际价格大部分高于趋势值;我国生鲜乳价格存在循环式周期波动,平均周期长度约为33个月;国际市场的波动已成为冲击我国生鲜乳价格的主要因素。

B-N链对锯齿型石墨烯纳米带电子结构的影响

采用基于密度泛函理论的第一性原理计算方法,研究了边缘对称和反对称的锯齿型石墨烯纳米带的电子结构,考察了B-N链掺在不同位置时的影响。研究结果表明:B-N原子链有向边缘迁移的现象,并且其掺杂在石墨烯纳米带中央时对体系电子结构的改变很小,而掺杂在边缘时会使体系在费米能级附近的能带结构发生显著的变化。边缘被B-N链取代的石墨烯纳米带的能隙被打开,并产生了明显的自旋非简并现象。这些现象的出现归因于掺杂体系中边缘电子态的重新分布。

三维氮磷共掺杂石墨烯的制备及电催化氧还原性能研究

氧还原反应(ORR)是燃料电池和金属-空气电池的阴极反应,其缓慢的动力学是目前掣肘燃料电池和金属空气电池发展的主要因素。为了使反应顺利进行,常常需要使用金属(包括贵金属和过渡金属)基催化剂,但这些催化剂存在价格高、稳定性差等缺陷。非金属原子掺杂的碳基催化剂近年来被认为是一种具有前景的ORR电催化剂。在此,使用单一前驱体磷酸三聚氰胺和氧化石墨烯经水热然后退火制备了三维氮磷共掺杂石墨烯材料(3DNPG)。通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)等手段对3DNPG的结构与组成进行了表征。结果表明:3DNPG具有独特的三维网状结构、较大的比表面积(514.38m 2/g),特别是还具有非常高的N(15.53%)和P(6.61%)掺杂量。用作碱性溶液里ORR的催化剂时,其起始电位为0.994V,半波电位为0.817V,极限电流为5.34mA/cm^(2),在48h后电流密度保持率仍维持在99%,因此是一种兼具优异活性和循环稳定性的ORR催化剂,在燃料电池、金属-空气电池等领域具有非常重要的应用价值。

农产品价格B-N分解与随机冲击的惯性研究

农业是百业之本、粮价是百价之基,农产品价格波动对社会生产和居民生活都具有广泛影响。为弥补已有相关研究方法的不足,本文从解析农产品价格波动的经济涵义入手,运用B-N技术分解我国主要农产品价格波动中的持久性成分和暂时性成分,并考察农产品价格随机冲击的惯性,以刻画我国农产品价格的动态特征,以期提高微观主体对农产品价格趋势变化的预判能力,进而更好安排消费、生产及经营等活动,同时为政策调整提供科学信息,减少社会福利损失。

中国进出口贸易的金融危机冲击效应——基于B-N数据分解的分析

基于2001年1月至2009年9月共105个月份的中国实际进出口贸易总额数据,运用Beveridge-Nelson(B-N)数据分解法对序列的确定性趋势项、周期项和随机冲击项进行了分解,分析了国际金融危机对我国进出口贸易总额的冲击效应,得出结论:第一,我国进出口贸易具有相对较强的抗干扰能力;第二,受外需下降等因素的影响,当前国际金融危机对我国进出口贸易的冲击程度相对较大;第三,我国进出口贸易受国际金融危机的冲击程度正在逐渐减弱,复苏迹象已渐渐显现。复苏后,外向依赖型的经济增长结构将发生较大改变,扩内需和调结构将带来新的经济增长点。

Sol-Gel法制备B-N共掺ZnO薄膜及光学性能研究

实验将B和不同含量的N元素掺入ZnO薄膜中,利用溶胶-凝胶(Sol-Gel)旋涂工艺分别在玻璃和硅衬底上制备B-N共掺ZnO薄膜.用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、紫外-可见分光光度计(UV-Vis)和光致发光谱(PL)对B-N掺杂样品薄膜的晶体结构、表面形貌及光学性能进行表征.结果表明,B-N共掺后的薄膜样品,与未掺杂样品和B单掺样品薄膜相比,薄膜结构仍为六方纤锌矿相,且沿ZnO(002)衍射峰择优生长.随着N掺杂量的增加,样品的(002)衍射峰的强度先增强再减弱,当N掺杂量为3.0 at%时,衍射峰强度最强,更适合薄膜生长.此时c轴取向相对较好,结晶度高,薄膜表面性能最佳,透过率在90%左右,禁带宽度达到3.51 eV,紫外发光峰受到抑制.

碳布支撑Sn^(2+)/Sn^(4+)共掺杂的ZnIn_(2)S_(4)柔性光催化剂用于高效降解盐酸四环素

本文采用一步溶剂热法制备了Sn^(2+)/Sn^(4+)共掺杂的ZnIn_(2)S_(4)/碳布柔性光催化剂(CC/ZIS-Sn),二维片状ZIS-Sn均匀地排列在碳布表面。通过降解盐酸四环素(TCH)溶液来评价所制备样品的光催化活性。结果表明,CC/ZIS-Sn_(0.09)复合光催化剂具有高效的光催化活性,40 min对TCH溶液(50 mL,20 mg/L)的降解率高达93.3%。适量的Sn掺杂和碳布协同作用能够调整电子结构,缩小光捕获带隙,增强ZIS光生载流子的分离和转移效率。自由基捕获实验证明空穴是光催化降解过程中的主要活性物质。此外,CC/ZIS-Sn光催化剂还具有良好的可回收性和稳定性,循环测试4次后,对TCH溶液的去除率仍达83.1%。

Modulation of Electronic States in Bimetallic-doped Nitrogen-Carbon Based Nanoparticles for Enhanced Oxygen Reduction Kinetics

Controlling the local electronic structure of active ingredients to improve the adsorption desorption characteristics of oxygen-containing intermediates over the electrochemical liquid-solid interfaces is a critical challenge in the field of oxygen reduction reaction(ORR)catalysis.Here,we offer a simple approach for modulating the electronic states of metal nanocrystals by bimetal co-doping into carbon-nitrogen substrate,allowing us to modulate the electronic structure of catalytic active centers.To test our strategy,we designed a typical bimetallic nanoparticle catalyst(Fe-Co NP/NC)to flexibly alter the reaction kinetics of ORR.Our results from synchrotron Xray absorption spectroscopy and X-ray photoelectron spectroscopy showed that the co-doping of iron and cobalt could optimize the intrinsic charge distribution of Fe-Co NP/NC catalyst,promoting the oxygen reduction kinetics and ultimately achieving remarkable ORR activity.Consequently,the carefully designed Fe-Co NP/NC exhibits an ultra-high kinetic current density at the operating voltage(71.94 mA/cm^(2)at 0.80 V),and the half-wave potential achieves 0.915 V,which is obviously better than that of the corresponding controls including Fe NP/NC,Co NP/NC.Our findings provide a unique perspective for optimizing the electronic structure of active centers to achieve higher ORR catalytic activity and faster kinetics.