A post-modification strategy to precisely construct dual-atom sites for oxygen reduction electrocatalysis

Dual-atom catalysts(DACs) afford promising potential for oxygen reduction electrocatalysis due to their high atomic efficiency and high intrinsic activity.However,precise construction of dual-atom sites remains a challenge.In this work,a post-modification strategy is proposed to precisely fabricate DACs for oxygen reduction electrocatalysis.Concretely,a secondary metal precursor is introduced to the primary single-atom sites to introduce direct metal-metal interaction,which ensures the formation of desired atom pair structure during the subsequent pyrolysis process and allows for successful construction of DACs.The as-prepared FeCo-NC DAC exhibits superior oxygen reduction electrocatalytic activity with a half-wave potential of 0,91 V vs.reversible hydrogen electrode.Zn-air batteries equipped with the FeCo-NC DAC demonstrate higher peak power density than those with the Pt/C benchmark.More importantly,this post-modification strategy is demonstrated universal to achieve a variety of dual-atom sites.This work presents an effective synthesis methodology for precise construction of catalytic materials and propels their applications in energy-related devices.

应用外对照的单臂试验现状分析

目的采用文献计量学方法研究应用外对照的单臂试验进展情况并进行中外对比,了解研究方向及趋势。方法计算机检索PubMed、SinoMed、中国知网(CNKI)、万方(WanFang)及维普(VIP)数据库,获取自建库至2021年7月21日发表的所有应用外对照的单臂试验。独立文献筛选、数据提取并应用CiteSpace和VOSviewer进行文献计量学分析。结果共纳入67篇文献,英文56篇,中文11篇。纳入文献首发于1997年,2017年最多(14.93%)。文章类型多为药物治疗类(59.70%)及医疗器械类(23.88%)。少数文献(37.31%)提及混杂控制,方法包括匹配及统计分析。主要疾病领域为肿瘤学(35.82%)和循环系统疾病(25.33%),其中,中文文献以循环系统疾病为主,英文则为肿瘤学和循环系统疾病。对照方式多采用历史对照(82.09%)。临床试验分期主要为临床Ⅱ期,大部分研究用于评价安全性(68.66%)和有效性(94.03%)。结论应用外对照的单臂试验常使用历史对照,在肿瘤或循环系统疾病等罕见病、难治性疾病或其他难以设置平行对照组的情景中应用较多,中外应用外对照的单臂试验在疾病领域方面存在较大不同,外对照在单臂试验中的应用存在不足。

Regeneration of single-atom catalysts deactivated under acid oxygen reduction reaction conditions

Single-atom catalysts serve as a promising candidate to realize noble-metal-free electrocatalytic oxygen reduction in acid media.However,their poor stability under working conditions strictly restrains their practical applications.Therefore,regeneration of their electrocatalytic activity is of great significance.Herein,the regeneration of a Fe-N-C single-atom catalyst is demonstrated to be feasible by a facile annealing regeneration strategy.The activity after regeneration recovers to that of the pristine electrocatalyst and surpasses the deactivated electrocatalyst.The regeneration mechanism is identified to be selfetching of the surface carbon layer and consequent exposure of the previously buried single-atom sites.Furthermore,the regeneration strategy is applicable to other single-atom catalysts.This work demonstrates the feasibility of regenerating oxygen reduction electrocatalysts and affords a pioneering approach to deal with rapid deactivation under working conditions.

High-sensitive phototransistor based on vertical HfSe_(2)/MoS_(2) heterostructure with broad-spectral response

Van der Waals heterostructures based on the two-dimensional(2D)semiconductor materials have attracted increasing attention due to their attractive properties.In this work,we demonstrate a high-sensitive back-gated phototransistor based on the vertical HfSe_(2)/MoS_(2)heterostructure with a broad-spectral response from near-ultraviolet to near-infrared and an efficient gate tunability for photoresponse.Under bias,the phototransistor exhibits high responsivity of up to 1.42×103A/W,and ultrahigh specific detectivity of up to 1.39×1015cm·Hz^(1/2)·W^(-1).Moreover,it can also operate under zero bias with remarkable responsivity of 10.2 A/W,relatively high specific detectivity of 1.43×1014cm·Hz^(1/2)·W^(-1),ultralow dark current of 1.22 f A,and high on/off ratio of above 105.These results should be attributed to the fact that the vertical HfSe_(2)/MoS_(2)heterostructure not only improves the broadband photoresponse of the phototransistor but also greatly enhances its sensitivity.Therefore,the heterostructure provides a promising candidate for next generation high performance phototransistors.

Quantitative kinetic analysis on oxygen reduction reaction:A perspective

Oxygen reduction reaction(ORR)constitutes the core process of many energy storage and conversion devices including metal–air batteries and fuel cells.However,the kinetics of ORR is very sluggish and thus highperformance ORR electrocatalysts are highly regarded.Despite recent progress on minimizing the ORR halfwave potential as the current evaluation indicator,in-depth quantitative kinetic analysis on overall ORR electrocatalytic performance remains insufficiently emphasized.In this paper,a quantitative kinetic analysis method is proposed to afford decoupled kinetic information from linear sweep voltammetry profiles on the basis of the Koutecky–Levich equation.Independent parameters regarding exchange current density,electron transfer number,and electrochemical active surface area can be respectively determined following the proposed method.This quantitative kinetic analysis method is expected to promote understanding of the electrocatalytic effect and point out further optimization direction for ORR electrocatalysis.

Optically-controlled resistive switching effects of CdS nanowire memtransistor

Since it was proposed,memtransistors have been a leading candidate with powerful capabilities in the field of neural morphological networks.A memtransistor is an emerging structure combining the concepts of a memristor and a field-effect transistor with low-dimensional materials,so that both optical excitation and electrical stimuli can be used to modulate the memristive characteristics,which make it a promising multi-terminal hybrid device for synaptic structures.In this paper,a single CdS nanowire memtransistor has been constructed by the micromechanical exfoliation and alignment lithography methods.It is found that the CdS memtransistor has good non-volatile bipolar memristive characteristics,and the corresponding switching ratio is as high as 10^(6) in the dark.While under illumination,the behavior of the CdS memtransistor is similar to that of a transistor or a memristor depending on the incident wavelengths,and the memristive switching ratio varies in the range of 10 to 10^(5) with the increase of the incident wavelength in the visible light range.In addition,the optical power is also found to affect the memristive characteristics of the device.All of these can be attributed to the modulation of the potential barrier by abundant surface states of nanowires and the illumination influences on the carrier concentrations in nanowires.

Transition metal coordinated framework porphyrin for electrocatalytic oxygen reduction

Oxygen reduction reaction(ORR) constitutes the core process of many clean and sustainable energy systems including fuel cells and metal–air batteries. Developing high-performance and cost-efficiency ORR electrocatalysts is of great significance to the practical applications of the above-mentioned energy storage devices. Transition metal coordinated porphyrin electrocatalysts are highly considered as a promising substitution of noble-metal-based electrocatalyst because of their high ORR reactivity, where the ORR performances of the porphyrin-based electrocatalysts are highly dependent on the transition metal center. Herein a series of framework porphyrin electrocatalysts coordinated with different transition metal centers(M-POF, where M is Mn, Fe, Co, Ni, Cu, or Zn) was designed, synthesized, and evaluated in regards of electrocatalytic ORR performances. Among all, the Co-POF electrocatalyst exhibits the best ORR performances with the highest half-wave potential of 0.81 V vs. RHE and the lowest Tafel slope of 53 mV/dec. This contribution affords an optimized high-performance ORR electrocatalyst and provides instructions for further rational design of porphyrin-based ORR electrocatalysts for sustainable energy applications.

Composing atomic transition metal sites for high-performance bifunctional oxygen electrocatalysis in rechargeable zinc-air batteries

Rechargeable zinc-air batteries have attracted extensive attention as clean,safe,and high-efficient en-ergy storage devices.However,the oxygen redox reactions at cathode are highly sluggish in kinetics and severely limit the actual battery performance.Atomic transition metal sites demonstrate high electro-catalytic activity towards respective oxygen reduction and evolution,while high bifunctional electro-catalytic activity is seldomly achieved.Herein a strategy of composing atomic transition metal sites is proposed to fabricate high active bifunctional oxygen electrocatalysts and high-performance recharge-able zinc-air batteries.Concretely,atomic Fe and Ni sites are composed based on their respective high electrocatalytic activity on oxygen reduction and evolution.The composite electrocatalyst demonstrates high bifunctional electrocatalytic activity(ΔE=0.72 V)and exceeds noble-metal-based Pt/C+Ir/C(ΔE=0.79 V).Accordingly,rechargeable zinc-air batteries with the composite electrocatalyst realize over 100 stable cycles at 25 mA cm-2.This work affords an effective strategy to fabricate bifunctional oxygen electrocatalysts for high-performance rechargeable zinc-air batteries.

Numerical investigation of the dynamics of flexible vegetations in turbulent open-channel flows

Aquatic vegetations widely exist in natural rivers and play an essential role in the evolution of the water environment and ecosystem by changing the river’s hydrodynamic characteristics and transporting sediments and nutrition.In reality,most aquatic vegetations are highly flexible,which invalidates the“rigid-cylinder”assumption widely adopted in many literatures.To explore the dynamics of submerged flexible vegetation in open-channel flows and its feedback to turbulent flow structures,numerical simulations are carried out using an in-house fluid-structure interaction(FSI)solver.In the simulations,the geometry of vegetation plants is grid-resolved,the turbulent flow is simulated using the large eddy simulation(LES),the dynamics of the flexible plants are solved using the vector form intrinsic finite element(VFIFE)method,and the turbulent flow and the plants are two-way coupled using the immersed boundary(IB)method.The dynamic responses of the flexible vegetation with different plant flexibility,spacing,and submergence are investigated.Simulation results show that flexible plants are subjected to complex flow-induced vibrations(FIVs)rather than static bending.The FIV involves both streamwise and cross-flow motions driven by the small-scale vortex shedding around the plants and the large-scale Kelvin-Helmholtz(K-H)vortices developed in the vegetation canopy layer.The vegetations exhibit pulsive wave motion of different patterns in relatively long and narrow open channels.Compared with the open-channel flows with static plants with equivalent bending deformation,the dynamic responses of flexible plants may increase the turbulent Reynolds stress of the open-channel flow by 70%–100%and increase the invasion depth of the K-H vortices by 30%–50%.

Low-Temperature Working Feasibility of Zinc–Air Batteries with Noble Metal-Free Electrocatalysts

Expanding the application scenario for rechargeable batteries is the key to the terminal utilization of renewable energy.Enabling zinc–air batteries at low temperatures is drawing increasing attention,yet the low-temperature working feasibility of zinc–air batteries with noble metalfree electrocatalysts remains indistinct.In this contribution,the low-temperature performances of zinc–air batteries with noble metal-free electrocatalysts are comprehensively investigated.Armed with a representative noble metal-free bifunctional oxygen electrocatalyst,the zinc–air batteries demonstrate satisfactory yet relatively depressed performance at low temperatures,compared with that at room temperatures.The reduced electrolyte conductivity is identified as one of the limiting factors for the reduced low-temperature performance.Furthermore,electrolyte engineering via solvation structure regulation is performed on the zinc–air batteries with noblemetal-free electrocatalysts,where an improved low-temperature performance is achieved.This work reveals the compatibility between noble metal-free electrocatalysts and low-temperature feasibility/low-temperature performance enhancement strategies for zinc–air batteries and affords new opportunities to satisfy low-cost and efficient energy storage at harsh working conditions.

Seawater-based electrolyte for Zinc–air batteries

Aqueous zinc–air batteries(ZABs)are highly regarded as a promising electrochemical energy storage device owing to high energy density,low cost,and intrinsic safety.The employment of seawater to replace the currently used deionized water in electrolyte will bring great economic benefits and broaden the application occasions of ZABs.However,ZABs using seawater-based electrolyte remain uninvestigated without an applicable cathode electrocatalyst or a successful battery prototype.Herein,seawater-based electrolyte is successfully employed in ZABs with satisfactory performances.The influence of chloride anions on the cathode electrocatalytic reactivity and battery performance is systemically investigated.Both noble-metal-based and noble-metal-free electrocatalysts are applicable to the chloride-containing alkaline electrolyte.Further evaluation of ZABs with seawaterbased electrolyte demonstrates comparable battery performances with the conventional electrolyte in terms of polarization,capacity,and rate performance.This study demonstrates a successful prototype of seawater-based ZABs and enlightens the utilization of natural resources for clean and sustainable energy storag.