Ultrafine Fe/Fe3C decorated on Fe-N_(x)-C as bifunctional oxygen electrocatalysts for efficient Zn-air batteries

Efficient bifunctional oxygen electrocatalysts for ORR and OER are fundamental to the development of high performance metal-air batteries.Herein,a facile cost-efficient two-step pyrolysis strategy for the fabrication of a bifunctional oxygen electrocatalyst has been proposed.The efficient non-preciousmetal-based electrocatalyst,Fe/Fe_(3)C@Fe-N_(x)-C consists of highly curved onion-like carbon shells that encapsulate Fe/Fe_(3)C nanoparticles,distributed on an extensively porous graphitic carbon aerogel.The obtained Fe/Fe_(3)C@Fe-N_(x)-C aerogel exhibited superb electrochemical activity,excellent durability,and high methanol tolerance.The experimental results indicated that the assembly of onion-like carbon shells with encapsulated Fe/Fe_(3)C yielded highly curved carbon surfaces with abundant Fe-Nxactive sites,a porous structure,and enhanced electrocatalytic activity towards ORR and OER,hence displaying promising potential for application as an air cathode in rechargeable Zn-air batteries.The constructed Zn-air battery possessed an exceptional peak power density of~147 mW cm^(-2),outstanding cycling stability(200 cycles,1 h per cycle),and a small voltage gap of 0.87 V.This study offers valuable insights regarding the construction of low-cost and highly active bifunctional oxygen electrocatalysts for efficient air batteries.

Molten salt assisted fabrication of Fe@Fe_(SA)-N-C oxygen electrocatalyst for high performance Zn-air battery

Non-noble-metal-based electrocatalysts with superior oxygen reduction reaction(ORR)activity to platinum(Pt)are highly desirable but their fabrications are challenging and thus impeding their applications in metal-air batteries and fuel cells.Here,we report a facile molten salt assisted two-step pyrolysis strategy to construct carbon nanosheets matrix with uniformly dispersed Fe_(3) N/Fe nanoparticles and abundant nitrogen-coordinated Fe single atom moieties(Fe@Fe_(SA)-N-C).Thermal exfoliation and etching effect of molten salt contribute to the formation of carbon nanosheets with high porosity,large surface area and abundant uniformly immobilized active sites.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)image,X-ray absorption fine spectroscopy,and X-ray photoelectron spectroscopy indicate the generation of Fe(mainly Fe_(3) N/Fe)and Fe_(SA)-N-C moieties,which account for the catalytic activity for ORR.Further study on modulating the crystal structure and composition of Fe_(3) N/Fe nanoparticles reveals that proper chemical environment of Fe in Fe_(3) N/Fe notably optimizes the ORR activity.Consequently,the presence of abundant Fe_(SA)-N-C moieties,and potential synergies of Fe_(3) N/Fe nanoparticles and carbon shells,markedly promote the reaction kinetics.The as-developed Fe@Fe_(SA)-N-C-900 electrocatalyst displays superior ORR performance with a half-wave potential(E_(1/2))of 0.83 V versus reversible hydrogen electrode(RHE)and a diffusion limited current density of 5.6 mA cm^(-2).In addition,a rechargeable Zn-air battery device assembled by the Fe@Fe_(SA)-N-C-900 possesses remarkably stable performance with a small voltage gap without obvious voltage loss after500 h of operation.The facile synthesis strategy for the high-performance composites represents another viable avenue to stable and low-cost electrocatalysts for ORR catalysis.

Trace ruthenium promoted dual-reconstruction of CoFeP@C/NF for activating overall water splitting performance beyond precious-metals

At present,Ru dopants mainly enhance electrocatalytic performance by inducing strain,vacancy,local electron difference,and synergy.Surprisingly,this work innovatively proposes that trace Ru atoms induce dual-reconstruction of phosphide by regulating the electronic configuration and proportion of Co–P/Co–O species,and ultimately activate superb electrocatalytic performance.Specifically,Ru-CoFeP@C/nickel foam(NF)is reconstructed to generate hydrophilic Co(OH)_(2)nanosheets during the hydrogen evolution reaction(HER)process,further accelerating the alkaline HER kinetics of phosphide.And the as-formed CoOOH during the oxygen evolution reaction(OER)process directly accelerates the oxygen overflow efficiency.As expected,the overpotential at 100 mA·cm^(−2)(η100)values of the reconstructed Ru-CoFeP@C/NF are 0.104 and 0.257 V for HER and OER,which are greatly lower than that of Pt/C-NF and RuO_(2)-NF benchmarks,respectively.This work provides guidance for the construction of highperformance catalysts for HER and OER dual reconstruction.This work provides a new idea for the optimization of catalyst structure and electrocatalytic performance.

Face-to-face heterojunctions within 2D/2D porous NiCo oxyphosphide/g-C_(3)N_(4)towards efficient and stable photocatalytic H_(2)evolution

Constructing 2D/2D face-to-face heterojunctions is believed to be an effective strategy to enhance photocatalytic performance due to the enlarged contact interface and increased surface active sites.Herein,2D porous NiCo oxyphosphide(NiCoOP)was synthesized for the first time and coupled with graphitic carbon nitride(g-C_(3)N_(4))nanosheets to form 2D/2D heterojunctions via an in-situ phosphating method.The optimal 4 wt.%2D/2D NiCoOP/g-C_(3)N_(4)(OPCN)photocatalyst achieves a hydrogen evolution rate of 1.4 mmol·h^(−1)·g^(−1),which is 33 times higher than that of pure g-C_(3)N_(4).The greatly improved photocatalytic performance of the composite photocatalysts could be attributed to the formation of interfacial surface bonding states and sufficient charge transfer channels for accelerating carrier separation and transfer and the porous structure of NiCoOP nanosheets with abundant surface active sites for promoting surface reactions.Amazingly,the 2D/2D OPCN composite photocatalysts also exhibit superior stability during photocatalytic reactions.This study not only designs new noble-metal-free NiCoOP/g-C_(3)N_(4)composite photocatalysts but also provides a new sight in fabricating face-to-face 2D/2D heterojunctions for their application in energy conversion areas.

Surface/Interface Engineering of Hierarchical MoO_(2)/MoNi_(4)@Ru/RuO_(2)Heterogeneous Nanosheet Arrays for Alkaline Water Electrolysis with Fast Kinetics

Realizing the hydrogen economy by water electrolysis is an attractive approach for hydrogen production,while the efficient and stable bifunctional catalysts under high current densities are the bottleneck that limits the half-cell reactions of water splitting.Here,we propose an approach of hydrothermal and thermal annealing methods for robust MoO_(2)/MoNi_(4)@Ru/RuO_(2) heterogeneous cuboid array electrocatalyst with multiplying surface-active sites by depositing a monolayer amount of Ru.Benefiting from abundant MoO_(2)/MoNi_(4)@Ru/RuO_(2)heterointerfaces,MoO_(2)/MoNi_(4)@Ru/RuO_(2) heterogeneous cuboid array electrocatalysts effectively drive the alkaline water splitting with superior hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)performances.The synthesized MoO_(2)/MoNi_(4)@Ru/RuO_(2) has high HER activity,which realizes the working overpotentials of 48 mV at 50 mA·cm^(-2),further achieving overpotentials of 230 mv for industry-level 1000 mA·cm^(-2) in alkaline water electrolysis.Moreover,it also showed an enhanced OER activity than commercial RuO_(2) with a small overpotential of 280 mV at 200 mA·cm^(-2) in alkaline media.When building an electrolyzer with electrodes of(-)MoO_(2)/MoNi_(4)@Ru/RuO_(2)IIMo02/MoNig@Ru/RuO_(2)(+),a cell voltage of 1.63 V and 1.75 V is just required to support the current density of 200 mA·cm^(-2) and 500 mA-cm^(-2) in alkaline water electrolysis,much lower than that of the electrolyzer of(-)Pt/CIIRuO_(2)(+).This work demonstrates that MoO_(2)/MoNig@Ru/RuO_(2) heterogeneous nanosheet arrays are promising candidates for industrial water electrolysis applications,providing a possibility for the exploration of water electrolysis with a large currentdensity.

Core-shell-structured Co@Co4N nanoparticles encapsulated into MnO-modified porous N-doping carbon nanocubes as bifunctional catalysts for rechargeable Zn–air batteries

Designing the highly catalytic activity and durable bifunctional catalysts toward oxygen reduction/evolution reaction(ORR/OER) is paramount for metal–air batteries. Metal–organic frameworks(MOFs)-based materials have attracted a great deal of attention as the potential candidate for effectively catalyzing ORR/OER due to their adjustable composition and porous structure. Herein, we first introduce the Mn species into zeolitic-imidazole frameworks(ZIFs) and then further pyrolyze the Mn-containing bimetallic ZIFs to synthesize core-shell-structured Co@Co4N nanoparticles embedded into MnO-modified porous N-doped carbon nanocubes(Co@Co4N/MnO–NC). Co@Co4N/MnO–NC exhibits the outstanding catalytic activity toward ORR and OER which is attributed to its abundant pyridinic/graphitic N and Co4N,the optimized content of MnO species, highly dispersed catalytic sites and porous carbon matrix. As a result, the Co@Co4N/MnO–NC-based Zn–air battery exhibits enhanced performances, including the high discharge capacity(762 mA h gZn-1), large power density(200.5 mW cm-2), stable potential profile over 72 h, low overpotential(<1.0 V) and superior cycling life(2800 cycles). Moreover, the belt-shaped Co@Co4N/MnO–NC cathode-based Zn–air batteries are also designed which exhibit the superb electrochemical properties at different bending/twisting conditions.

Reduction-induced interface reconstruction to fabricate MoNi_(4) - based hollow nanorods for hydrazine oxidation assisted energysaving hydrogen production in seawater

Seawater electrolysis could address the water scarcity issue and realize the grid-scale production of carbon-neutral hydrogen,while facing the challenge of high energy consumption and chloride corrosion.Thermodynamically more favorable hydrazine oxidation reaction(HzOR)assisted water electrolysis is efficiency for energy-saving and chlorine-free hydrogen production.Herein,the MoNi alloys supported on MoO_(2) nanorods with enlarged hollow diameter on Ni foam(MoNi@NF)are synthesized,which is constructed by limiting the outward diffusion of Ni via annealing and thermal reduction of NiMoO_(4) nanorods.When coupling HzOR and hydrogen evolution reaction(HER)by employing MoNi@NF as both anode and cathode in two-electrode seawater system,a low cell voltage of 0.54 V is required to achieve 1,000 mA·cm^(−2) and with long-term durability for 100 h to keep above 100 mA·cm^(−2) and nearly 100%Faradaic efficiency.It can save 2.94 W·h to generate per liter H_(2) relative to alkaline seawater electrolysis with 37%lower energy equivalent input.

Stable confinement of Fe/Fe_(3)C in Fe,N-codoped carbon nanotube towards robust zinc-air batteries

Catalytic oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)have garnered great attention as the key character in metal-air batteries.Herein,we developed a superior nonprecious bifunctional oxygen electrocatalyst,fabricated through spatial confinement of Fe/Fe_(3)C nanocrystals in pyridinic N and Fe-Nx rich carbon nanotubes(Fe/Fe_(3)C-N-CNTs).During ORR,the resultant electrocatalyst exhibits positive onset pote ntial of 1.0 V(vs.RHE),large half-wave potentials of 0.88 V(vs.RHE),which is more positive than Pt/C(0.98 V and 0.83 V,respectively).Remarkably,Fe/Fe_(3)C-N-CNTs exhibits outstanding durability and great methanol tolerance,exceeding Pt/C and most reported nonprecious metal-based oxygen reduction electrocatalysts.Moreover,Fe/Fe_(3)C-N-CNTs show a markedly low potential at j=10 mA/cm^(2),small Tafel slopes and extremely high stability for OER.Impressively,the Fe/Fe_(3)C-N-CNTs-based Zn-air batteries demonstrate high power density of 183 mW/cm^(2)and robust charge/discharge stability.It is revealed that the spatial confinement effect can impede the aggregation and corrosion of Fe/Fe_(3)C nanocrystals.Meanwhile,Fe/Fe_(3)C and Fe-Nx play synergistic effect on boosting the ORR/OER activity,which provides an important guideline for construction of inexpensive nonprecious metal-carbon hybrid nanomaterials.

Supramolecular Assemblies of Three New Metronidazole Derivatives Constructed with Various Dihydroxy-benzoic Acids via Hydrogen Bonds

Metronidazole(MTZ)is an important antibiotic,which has been widely applied to cure protozoal and bacterial diseases for human beings or animals.Herein,three novel drug supramolecular crystals constructed by MTZ with 2.5-dihydroxy-benzoic acid(2.5-DHBA)(1),2.6-dihydroxy-benzoic acid(2.6-DHBA)(2)and 3,5-dihydroxy-benzoic acid(3.5-DHBA)(3),respectively,have been discovered.The hydrogen bonds of N-H…O(O-H…N).C-H…O and O-H…O play important roles in the 3D supramolecular framework formation for crystals 1-3.Interestingly.due to the vary locations of the substituent groups,the two-dimensional layers in crystals 1 or 2 are constructed via intermolecular hydrogen bonds between MTZ and 2,5-DHBA or 2.6-DHBA,while in crystal 3 water molecules play a significant role except the intermolecular hydrogen bonds between MTZ and 3,5-DHBA.In addition,five synthons of I R^22(8),ⅡR3(9)in crystal 1,ⅢR1(4),ⅣR2(8)in crystal 2 andⅤR2(7)in crystal 3 formed through various hydrogen bonds are founded in this work.Systematic studies of syntheses,crystal structures and thermal analysis are reported.

通过共掺杂策略优化氮化物电极的反应路径以促进碱性析氢反应动力学

通过优化氮化物的析氢反应(HER)途径来提高反应动力学是氮化物改性的重点.本工作创造性地采用P-阴离子和Ce-阳离子的共掺杂策略构建了P,Ce-FeNi_(3)N/NF电极.该P,Ce-FeNi_(3)N/NF电极在200 mV过电位下的电流密度(340 mA cm^(−2))是商业Pt/C@NF电流密度(174 mA cm^(−2))的两倍.理论计算表明,与FeNi_(3)N/NF的单个Ni活性位点不同,P,Ce-FeNi_(3)N/NF利用双活性位点(Ni和P)机制极大地优化了碱性HER过程中的反应动力学.此外,组装的NiFeCe-LDH/NF||P,Ce-FeNi_(3)N/NF电池仅需要1.537 V的电压即可实现500 mA cm^(−2)的高电流密度.这项工作从反应路径优化和反应动力学改进的角度为实现氮化物优异的电催化性能提供了一种新策略.

Azobenzene Based Photo-responsive Mechanical Actuator Fabricated by Intermolecular H-bond Interaction

Photo-responsive mechanical actuator is a class of stimuli-responsive materials transferring light to mechanical energy through macroscopic transformation.To fabricate photo-responsive mechanical actuator,soft polymeric materials crosslinked with functional bridging structures are desired.Supramolecular interaction is a relatively common way to fabricate crosslinked materials due to its excellent self-assembly performance.And azobenzene and derivatives are ideal candidates of photo-responsive materials because of the unique photo-induced trans-cis isomerization.Here,a new kind of crosslinked materials based on supramolecular interaction between 4,4'-dihydroxyazobenzene and chitosan is reported.Under 355 nm irradiation,the macroscopic bending of polymeric materials occurs rapidly due to the photo-isomerization of 4,4-dihydroxyazobenzene.Meanwhile,the photo-responsive mechanical actuator can also lift weight which is up to 200 times that of the actuator itself,and convert energy from light to mechanical work efficiently.This report suggests a new kind of photo-responsive actuator based on supramolecular interaction and may be helpful to contribute a theoretical basis to the design and synthesis of photo-responsive mechanical actuator suitable for large-scale manufacturing industrialization in future.

Noble metal aerogels rapidly synthesized by ultrasound for electrocatalytic reaction

Noble metal aerogels(NMAs), belonging to the porous material, have exhibited excellent catalytic performance. Although the synthesis method continues to improve, it still exists some problems which hindered the experimental process, such as high concentration of noble metal precursors, long synthesis cycle, expensive production cost, and uncontrollable ligament length. In this work, ultrasonic wave and reducing agent Na BH;were simultaneously applied to gelation process. With the cavitation of ultrasound,it can generate huge energy with heating and stirring, thus gelation reaction proceeded quickly, and even completed the process in only a few seconds, that is much faster than the recorded. A wide concentration range was successfully expanded from 0.02 mmol/L to 62.5 mmol/L. Further, we extended this method to a variety of noble metal elements(Au, Ru, Rh, Ag, Pt, Pd), and this method is adaptive for the synthesis of single metal aerogels(Au, Ag, Ru, Rh, Pd), bimetal and trimetal aerogels(Au-Ag, Au-Rh, Au-Ru, Au-Pt,Au-Pd, Au-Pt-Pd). In addition, the ligament size of alloy aerogels are 10 nm or less. Moreover, their brilliant properties were demonstrated in hydrogen evolution reaction(HER) and ethanol oxidation reaction(EOR).

腐蚀-配位工程构建含有微量Pt的2D-3D纳米结构高效电解水催化剂

开发具有良好的催化性能和稳定性的析氢反应(HER)和析氧反应(OER)的电催化剂对水分解产氢的商业化起着关键作用.本文通过简单、可扩展的腐蚀配位方法,将金属氢氧化物和金属有机骨架(MOF)组成的二维-三维(2D-3D)纳米结构原位装饰在泡沫Ni Fe (Pt-Ni Fe PBA)上.所设计的特殊形态有利于在电催化过程中提供丰富的活性位点、优化反应途径和加速传质.因此,合成的Pt-Ni Fe PBA在1 mol L;KOH中HER和OER在10 m A cm^(-2)时具有29和210 m V的过电位.值得注意的是,在10 m A cm^(-2)时该催化剂仅需21 m V即可驱动1 mol L;KOH海水,并具有出色的稳定性.此外,将合成的Pt-Ni Fe PBA用作双功能电催化剂时,只需1.46和1.48 V即可以达到10 m A cm^(-2).此外,间歇性的可持续能源,如热能、风能和太阳能可以为该水分解器提供动力.

异质工程和阳离子掺杂双重策略促进肼辅助海水电解节能制氢

与电解纯水制氢相比,海水电解制氢具有更大的实际应用价值.在碱性海水中,可以通过在热力学上有利的肼氧化反应(HzOR)代替析氧反应(OER)和析氯反应(ClER)来实现节能制氢.在此,我们制备了Co掺杂的Fe-Ni_(2)P/MIL-FeCoNi异质结构阵列(FeCo-Ni_(2)P@MIL-FeCoNi).得益于异质工程和阳离子掺杂的协同作用,FeCo-Ni_(2)P@MIL-FeCoNi在碱性海水电解液中表现出优异的HzOR和析氢反应(HER)双功能电催化性能.在海水系统中的整体肼分解(OHzS)仅需要400 mV的超低电压就能达到1000 mA cm^(−2)的电流密度,且可以在500 mA cm^(−2)以上的电流密度稳定运行1000 h.作为概念验证,同样生产1.0 Nm^(3)的氢气,OHzS海水系统比无N_(2)H_(4)的整体海水分解系统(OWS)节省3.03 kW h的电力,可实现节能制氢.DFT计算表明,Co离子掺杂和构建FeCo-Ni_(2)P/MIL-FeCoNi异质界面的协同作用可以降低FeCo-Ni_(2)P@MIL-FeCoNi的水解离能垒,促进HER吸附氢和HzOR脱氢过程的热力学行为.这项工作为有效利用海洋能源领域中无限丰度的氢助力实现碳中和提供了一种实用途径.