Boron modulating electronic structure of FeN4C to initiate high-efficiency oxygen reduction reaction and high-performance zinc-air battery

The biggest challenge is to develop a low cost and readily available catalyst to replace expensive commercial Pt/C for efficient electrochemical oxygen reduction reaction(ORR).In this research,closo-[B_(12)H_(12)]^(2−)and 1,10-phenanthroline-iron complexes were introduced into the porous metal-organic framework by impregnation method,and further annealing treatment achieved the successful anchoring of single-atom-Fe in B-doped CN Matrix(FeN4CB).The ORR activity of FeN4CB is comparable to the widely used commercial 20 wt%Pt/C.Where the half-wave potential(E_(1/2))in alkaline medium up to 0.84 V,and even in the face of challenging ORR in acidic medium,the E_(1/2)of ORR driven by FeN4CB is still as high as 0.81 V.When FeN4CB was used as air cathode,the open circuit voltage of Zn-air battery reaches 1.435 V,and the power density and specific capacity are as high as 177 mW cm^(−2)and 800 mAh g_(Zn)^(−1)(theoretical value:820 mAh g_(Zn)^(−1)),respectively.The dazzling point of FeN4CB also appears in the high ORR stability,whether in alkaline or acidic media,E_(1/2)and limiting current density are still close to the initial value after 5000 times cycles.After continuously running the charge-discharge test for 220 h,the charge voltage and discharge voltage of the rechargeable zinc-air battery with FeN4CB as the air cathode maintained the initial state.Density functional theory calculations reveals that introducing B atom to Fe–N4–C can adjust the electronic structure to easily break O=O bond and significantly reduce the energy barrier of the rate-determining step resulting in an improved ORR activity.

Regulation of excitation energy transfer in Sb-alloyed Cs_(4)MnBi_(2)Cl_(12) perovskites for efficient CO_(2) photoreduction to CO and water oxidation toward H_(2)O_(2)

Lead(Pb)-free halide perovskites have recently attracted increasing attention as potential catalysts for CO_(2) photoreduction to CO due to their potential to capture solar energy and drive catalytic reaction.However,issues of the poor charge transfer still remain one of the main obstacles limiting their performance due to the overwhelming radiative and nonradiative charge-carrier recombination losses.Herein,Pb-free Sb-alloyed all-inorganic quadruple perovskite Cs_(4)Mn(Bi_(1-x)Sb_(x))_(2)Cl_(12)(0≤x≤1)is synthesized as efficient photocatalyst.By Sb alloying,the undesired relaxation of photogenerated electrons from conduction band to emission centers of[MnCl6]^(4-)is greatly suppressed,resulting in a weakened PL emission and enhanced charge transfer for photocatalyst.The ensuing Cs_(4)Mn(Bi_(1-x)Sb_(x))_(2)Cl_(12) photocatalyst accomplishes efficient conversion of CO_(2)into CO,accompanied by a surprising production of H_(2)O_(2),a high valueadded product associated with water oxidation.By optimizing Sb^(3+) concentration,a high CO evolution rate of 35.1μmol g^(-1)h^(-1)is achieved,superior to most other Pb and Pb-free halide perovskites.Our findings provide new insights into the mixed-cation alloying strategies for improved photocatalytic performance of Pb-free perovskites and shed light on the rational design of robust band structure toward efficient energy transfer.

Modulating the Selectivity of Photocatalytic CO_(2)Reduction in Barium Titanate by Introducing Oxygen Vacancies

Artifi cial photosynthetic reduction of CO_(2) into valuable chemicals is one of the most promising approaches to solve the energy crisis and decreasing atmospheric CO_(2) emissions.However,the poor selectivity accompanied by the low activity of photocatalysts limits the development of photocatalytic CO_(2) reduction.Herein,inspired by the use of oxygen vacancy engi-neering to promote the adsorption and activation of CO_(2) molecules,we introduced oxygen vacancies in the representative barium titanate(BaTiO 3)photocatalyst for photocatalytic CO_(2) reduction.We found that oxygen vacancies brought signifi cant diff erences in the CO_(2) photoreduction activity and selectivity of BaTiO 3.The intrinsic BaTiO 3 showed a low photocatalytic activity with the dominant product of CO,whereas BaTiO 3 with oxygen vacancies exhibited a tenfold improvement in photocatalytic activity,with a high selectivity of~90%to CH 4.We propose that the presence of oxygen vacancies promotes CO_(2) and H 2 O adsorption onto the BaTiO 3 surface and also improves the separation and transfer of photogenerated carriers,thereby boosting the photocatalytic CO_(2) reduction to CH 4.This work highlights the essential role of oxygen vacancies in tuning the selectivity of photocatalytic reduction of CO_(2) into valuable chemicals.

Molten salt electrochemical modulation of Ni/Co nanoparticles onto N-doped carbon for oxygen reduction

Activation of oxygen over non-precious materials has been an imperative task to develop efficient electrochemical energy storage and conversion such as fuel cells and metal-air batteries.Herein,a molten salt electrochemical modulation of metal-nitrogen-carbon based compounds(M–N–C)is achieved.By electrochemical treatment of polydopamine-coated NiCo_(2)O_(4)(NiCo_(2)O_(4)@PDA)in molten Li_(2)CO_(3)-Na_(2)CO_(3)-K_(2)CO_(3)at 500℃,Ni/Co bimetal-nitrogen-carbon catalyst(denoted as Ni/Co@NC)consisting of Ni-Co nanoparticles anchoring on porous nitrogen-doped carbon is constructed and evaluated as electrocatalysts towards the oxygen reduction reaction(ORR).Experimental and calculation results confirm that alloying of Ni-Co and nitrogen doping to carbon enhances the rate-determining transformation of*OH intermediate during ORR.The Ni/Co@NC hence shows an ORR activity comparable with the commercial Pt/C.

Non-bonding modulations between single atomic cerium and monodispersed selenium sites towards efficient oxygen reduction

Currently,dual atomic catalysts(DACs)with neighboring active sites for oxygen reduction reaction(ORR)still meet lots of challenges in the synthesis,especially the construction of atomic pairs of elements from different blocks of the periodic table.Herein,a“rare earth(Ce)-metalloid(Se)”non-bonding heteronuclear diatomic electrocatalyst has been constructed for ORR by rational coordination and carbon support defect engineering.Encouraging,the optimized Ce-Se diatomic catalysts(Ce-Se DAs/NC)displayed a half-wave potential of 0.886 V vs.reversible hydrogen electrode(RHE)and excellent stability,which surpass those of separate Ce or Se single atoms and most single/dual atomic catalysts ever reported.In addition,a primary zinc-air battery constructed using Ce-Se DAs/NC delivers a higher peak power density(209.2 mW·cm^(−2))and specific capacity(786.4 mAh·gZn^(−1))than state-of-the-art noble metal catalysts Pt/C.Theoretical calculations reveal that the Ce-Se DAs/NC has improved the electroactivity of the Ce-N_(4)region due to the electron transfer towards the nearby Se specific activity(SA)sites.Meanwhile,the more electron-rich Se sites promote the adsorptions of key intermediates,which results in the optimal performances of ORR on Ce-Se DAs/NC.This work provides new perspectives on electronic structure modulations via non-bonded long-range coordination micro-environment engineering in DACs for efficient electrocatalysis.

Nest-type NCM ■ Pt/C with oxygen capture character as advanced electrocatalyst for oxygen reduction reaction

A unique nest-type catalyst has been designed with a nest of oxygen capture surrounding catalytic Pt centers, which shows much promoted performance, on the base of Pt/C catalyst, for oxygen reduction reaction(ORR). The nest is constructed with nitrogen-doped carbon matrix(NCM), derived from the controlled carbonization of PANI precursor, to cover Pt/C catalyst. The unique structure of the catalyst(denoted as NCM■ Pt/C) has many merits. Firstly, it can capture oxygen both in air and in acidic electrolyte. Compared with naked Pt/C, it is found that, in air, the oxygen concentration within the porous nest of NCM surrounding Pt/C particles is ~13 times higher than atmospheric oxygen concentration and, in acidic electrolyte, the concentration of activated oxygen over the catalyst NCM■ Pt/C rise to~1.9 times. Secondly, the NCM nest offers a special electronic modulation on Pt centers toward modified ORR kinetics and then catalytic performances. With these merits, compared with Pt/C, the NCM■ Pt/C catalyst shows 3.2 times higher turnover frequency value and 2.9 times enhanced specific activity for ORR with half-wave potential at 0.894 V. After 50,000 sweeping cycles, the NCM■ Pt/C catalyst retains~66% mass activity and still has advantages over the fresh Pt/C catalyst. We envision that the nest-type catalyst provides a new idea for progress of practical Pt/C ORR catalyst.

Recent progress of electrochemical reduction of CO_(2)by single atom catalysts

Powered by electricity from renewable energies,electrochemical reduction of CO_(2)could not only efficiently alleviate the excess emission of CO_(2),but also produce many kinds of valuable chemical feedstocks.Among various catalysts,single atom catalysts(SACs)have attracted much attention due to their high atom utilization efficiency and expressive catalytic performances.Additionally,SACs serve as an ideal platform for the investigation of complex reaction pathways and mechanisms thanks to their explicit active sites.In this review,the possible re-action pathways for the generation of various products(mainly C1 products for SACs)were firstly summarized.Then,recent progress of SACs for electrochemical reduction of CO_(2)was discussed in aspect of different central metal sites.As the most popular and efficient coordination modulation strategy,introducing heteroatom was then reviewed.Moreover,as an extension of SACs,the development of dual atom catalysts was also briefly discussed.At last,some issues and challenges regarding the SACs for CO_(2)reduction reaction(CO_(2)RR)were listed,followed by corresponding suggestions.

PRI modulation recognition and sequence search under small sample prerequisite

Pulse repetition interval(PRI)modulation recognition and pulse sequence search are significant for effective electronic support measures.In modern electromagnetic environments,different types of inter-pulse slide radars are highly confusing.There are few available training samples in practical situations,which leads to a low recognition accuracy and poor search effect of the pulse sequence.In this paper,an approach based on bi-directional long short-term memory(BiLSTM)networks and the temporal correlation algorithm for PRI modulation recognition and sequence search under the small sample prerequisite is proposed.The simulation results demonstrate that the proposed algorithm can recognize unilinear,bilinear,sawtooth,and sinusoidal PRI modulation types with 91.43% accuracy and complete the pulse sequence search with 30% missing pulses and 50% spurious pulses under the small sample prerequisite.

Power Output Improvement of PV Module for Agricultural Use by Using Inexpensive Sunlight Concentrator

PV modules are used as stand alone power sources for agricultural equipments such as lifting pumps in farms, where the power infrastructure is not yet improved. In order to expand the agricultural use of PV module, the cost of PV generation should be reduced. In this paper, the power output performance of a commercial PV module was improved by using a sunlight concentrator that could be assembled inexpensively and a simple sun-tracking method.

Model Reduction by Generalized Falk Method for Efficient Dedicated to Professor Karl Stark Pister for his 95th birthday Field-Circuit Simulations

The Generalized Falk Method(GFM)for coordinate transformation,together with two model-reduction strategies based on this method,are presented for efficient coupled field-circuit simulations.Each model-reduction strategy is based on a decision to retain specific linearly-independent vectors,called trial vectors,to construct a vector basis for coordinate transformation.The reduced-order models are guaranteed to be stable and passive since the GFM is a congruence transformation of originally symmetric positive definite systems.We also show that,unlike the Pade-via-Lanczos(PVL)method,the GFM does not generate unstable positive poles while reducing the order´of circuit problems.Further,the proposed GFM is also faster when compared to methods of the type Lanczos(or Krylov)that are already widely used in circuit simulations for electrothermal and electromagnetic problems.The concept of response participation factors is introduced for the selection of the trial vectors in the proposed model-reduction methods.Further,we present methods to develop simple equivalent circuit networks for the field component of the overall field-circuit system.The implementation of these equivalent circuit networks in circuit simulators is discussed.With the proposed model-reduction strategies,significant improvement on the efficiency of the generalized Falk method is illustrated for coupled field-circuit problems.

脑血管数字减影血管造影高分辨率分割网络设计

针对现存卷积神经网络对脑血管数字减影血管造影分割精度不高的问题,本文提出了一种基于U-Net的改进网络(IC-Net)。通过融合使用Inception和CAM通道注意力模块,以多种感受域提取更丰富的血管特征信息,并对特征信息进行筛选。增加7×7卷积层,通过压缩特征层分辨率的方式减少训练过程中产生的数据量。本文所提模型与U-Net、R2U-Net、Attention U-Net相比,IOU、Accuracy、F1-Score和ROC曲线下面积4项指标平均提升了1.82%、0.014%、1.19%和0.73%。结果验证了IC-Net模型明显提升了脑血管数字减影血管造影虚弱血管和血管末端的检测能力,提升了分辨伪影噪声的能力,为医生识别脑血管中产生的病变提供有力参考。

一种增加辅助子模块的MMC改进混合调制控制策略

传统的最近电平逼近调制NLM(nearest level modulation)具有控制简单,开关频率低的显著优势,但在输出电平数较少时,采用NLM调制的模块化多电平换流器MMC(modular multilevel converter)输出波形谐波畸变率较大。在传统三相六桥臂MMC拓扑的各桥臂中增加1个全桥结构的辅助子模块,控制该辅助子模块的电容电压为半桥子模块的一半。针对该MMC拓扑,提出了一种改进的混合调制策略,该混合调制策略可以实现半桥和辅助子模块的平衡控制。在降低MMC交流侧输出电流的谐波畸变率同时,还可以降低全桥子模块的开关频率和系统损耗。在Matlab/Simulink中搭建了详细的仿真模型,仿真结果验证了所提MMC拓扑和改进混合调制策略的有效性。

基于二维动态减载和双层MPC的风储联合调频与功率优化分配

风机可以通过减载控制提供调频备用功率,但存在弃风量大的问题。为此,结合储能装置,设计了考虑风速分区与储能荷电状态(SOC)的二维动态减载策略,在提供充足调频备用功率的同时减小了弃风功率。在此基础上,结合双层模型预测控制(MPC)架构,提出了计及机组转矩波动的风储联合调频控制策略,上层MPC将风电场视作整体,通过协调风储出力提升调频效果;下层MPC通过风电场内的功率优化分配以抑制机组的转矩波动,保证调频性能的同时提高了机组运行稳定性。通过仿真分析验证了所提策略的有效性,结果表明该减载策略具有更高的风能利用率,且在调频过程中通过机组的功率优化分配减小了机组的转矩波动,提高了机组运行稳定性。

基于弹性连接的FPSO上部模块整体减振技术

[目的]针对浮式生产储卸油装置(FPSO)作业时上部模块的振动响应,为减少振动能量向船体的传递,同时改进上部模块与船体之间的连接,提出一种基于上部模块与船体弹性连接的整体减振技术。[方法]首先,利用弹性支座将上部模块与船体进行弹性连接,根据FPSO在作业海域加速度响应预报的极值来确定弹性支座的设计载荷和内部结构;然后,采用有限元方法分析弹性支座的受力与变形特性,并通过线性拟合获得弹性支座的等效刚度;最后,将弹性支座等效为线性弹簧,分别通过数值模拟和理论分析来研究模块结构的振动响应和弹性支撑系统的动力传递特性。[结果]结果表明:应用该减振技术之后,上部模块的减振效率高达30%以上,同时还可使船体取得良好的隔振效果。[结论]该研究成果可为海洋结构物上部模块的整体减振设计和应用提供参考。

基于密集残差连接U型网络的噪声图像超分辨率重建

现有的图像超分辨率重建网络难以适用于煤矿井下噪声密集的应用场景,且多数网络通过增加深度提升性能会导致无法有效提取关键特征、高频信息丢失等问题。针对上述问题,提出了一种密集残差连接U型网络,用于对低分辨率噪声图像进行超分辨率重建。在特征提取路径中引入基于密集残差连接的去噪模块,通过密集连接的方式对图像特征进行充分提取,再利用残差学习的特点对低分辨率噪声图像进行有效去噪;在重建路径中引入残差特征注意力蒸馏模块,通过在残差块中融入增强特征注意力块,对不同空间的特征赋予不同的权重,加强网络对于图像关键特征的提取能力,同时减少图像细节特征在残差块中的损失,从而更好地恢复图像细节信息。在煤矿井下图像数据集及公共数据集上进行了对比实验,结果表明:在客观评价指标上,所提网络的结构相似度、图像感知相似度均优于对比网络,且在复杂度及运行速度上有着较好的均衡;在主观视觉效果上,所提网络重建的图像基本消除了原有图像噪声,有效恢复了图像的细节特征。

双碳背景下数字贸易对中国碳减排影响研究

数字贸易作为现代数字经济的核心要素,特别是在当前“双碳”战略背景下,对促进碳减排、推动低碳高质量发展具有举足轻重的作用。从生产和消费两个维度深入剖析数字贸易在碳减排过程中的中介效应,同时结合产业集聚与低碳试点政策,探讨对数字贸易碳减排效应的调节作用。利用2013—2021年中国30个省份的面板数据,通过系统GMM模型进行实证分析。研究结果表明:数字贸易水平对碳减排具有显著影响,且其区域异质性特征明显,碳排放作用自东部向西部呈递减趋势;在生产侧,规模效应和技术效应对碳减排的推动作用显著超过结构效应;在消费侧,农村居民消费升级对碳排放的抑制作用显著,而城市居民消费升级则呈现出促进碳排放的趋势;在调节效应方面,高技术产业集聚和生产性服务业集聚及其协同作用在一定程度上削弱了数字贸易的碳减排效果,而低碳试点政策的实施则有助于强化数字贸易在碳减排方面的积极作用。

一种基于SVD降噪和CNN分类的无线信号调制识别方法

针对低信噪比下噪声干扰导致的调制信号识别精度不足的问题,提出了一种基于奇异值分解(Singular Value Decomposition,SVD)降噪和卷积神经网络(Convolutional Neural Network,CNN)分类的无线信号调制识别方法SVD-CNN。该方法提出了基于SVD的信号降噪模块来对输入信号进行降噪,设计了一维符号级CNN架构来直接识别信号特征并分类。针对高斯、瑞利信道下的调制仿真数据集,将提出的方法与典型调制识别方法如CNN识别方法、瞬时特征-全连接神经网络(Instantaneous Characteristic-Fully Connected Neural Network,IC-FCNN)识别方法进行了对比实验。实验结果表明,所提方法在低信噪比下具有更高的识别精度,在信噪比为0 dB时平均识别准确率提升近38%~49%。

The d-orbital coupling modulation of CuNi alloy for acetonitrile electrochemical reduction and in-situ hydrogenation behavior characterization

Electrochemical reduction of acetonitrile to ethylamine with a high selectivity is a novel approach to manufacture valuable primary amines which are important raw material in organic chemical industry. However, the poor ethylamine Faradic efficiency(FE_(ethylamine)) and catalyst stability at the high current density prohibit this method from being practically used. Herein, CuNi alloy ultrafine-nano-particles based on the d-orbital coupling modulation were synthesized through the electrodeposition and their catalytic performance towards acetonitrile reduction reaction(ACNRR) has been systematically studied. The highest FE_(ethylamine)(97%) is achieved with the current density of-114 mA cm^(-2). For practical application, the current density can reach-602.8 mA cm^(-2) with 82.8% FE_(ethylamine)maintained. With the appearance of other organics which co-exist with acetonitrile in the SOHIO process, CuNi can also hydrogenate acetonitrile in it with more than 80% FE_(ethylamine). Our in-situ spectroscopy analysis and DFT calculations towards the acetonitrile hydrogenation behavior reveal that the evenly dispersed Ni in Cu modulates the dband so as to endow CuNi with the better acetonitrile adsorption, milder binding energy with the reaction intermediates, smaller barrier for *CH_3CH_2NH_2 desorption and higher ability for H_2O dissociation to provide *H.

MOF-related electrocatalysts for sulfur reduction/evolution reactions:Composition modulation,structure design,and mechanism research

The electrocatalytic sulfur reduction reaction(SRR)and sulfur evolution reaction(SER),two fundamental multistep conversion processes in lithium–sulfur batteries(LSBs),are root-cause solutions to overcome sluggish redox kinetics and the polysulfide shuttling effect.Metal–organic framework(MOF)electrocatalysts have emerged as good platforms for catalyzing SRR and SER,but their catalytic performance is challenged by poor electrical conductivity and limited chemical stability.Functionalized MOFs and their hybrids may be beneficial for stabilizing and improving the desired catalytic properties to achieve high-performance LSBs.This review provides a detailed overview of engineering principles for improving the activity,selectivity,and stability of MOFrelated electrocatalysts via composition modulation and nanostructure design as well as hybrid assembly.It presents and discusses the various advances achieved by using in situ characterization techniques,simulations,and theoretical calculations to reveal the dynamic evolution of MOF-related electrocatalysts,enabling an in-depth understanding of the catalysis mechanism at the molecular/atomic level.Lastly,prospects and possible research directions for MOF-related sulfur electrocatalysts are proposed.

风力发电机组实施频率下垂控制的建模与仿真

风力发电技术作为目前研究深度最深、应用范围最广的绿色发电方式,这些年来得到了长足发展。随着大范围、大规模的风电机组连入电力系统,其一些特性也必然会给电力系统频率调节带来诸多影响。目前应用最广泛的风机类型是双馈感应风电机组,其利用变频器进行控制的特性,导致风机与电力系统频率完全解耦,风电机组的转子动能被“隐藏”,没有能力响应系统的频率变化。当大量风电机组并网时,电网的频率稳定性将会受到影响。因此,研究风电机组调频控制策略对电网的安全稳定经济运行有着极为重要的理论指导作用和实践意义。