Construction Of Transition Metal Single-Atom Structured Catalysts For Catalysis

Single-atom catalyst(SAC)is a general term for the microenvironment of atomically dispersed metal sites,including center metal atoms,coordinated atoms,environmental atoms and guest groups.SACs have attracted extensive attention in many catalytic fields due to the maximum atomic utilization,unsaturation homogenous sites,low cost,high catalytic activity and stability.Herein,we focus on the construction of SACs for various catalysis such as electroreduction of carbon dioxide(CRR),oxygen reduction reaction(ORR),fenton-like reaction and so on.By controlling the structure of the precursor and the pyrolysis temperature,the rational design of SACs macro and micro environments was achieved.The microenvironment-performance relationship was investigated by structure optimization.The main contents and conclusions are shown as follows:1.Energy storage devices which converting electricity into chemical energy are very important to solve the problem.CO2 reduction reaction(CRR)is one of the most important energy storage devices by converting carbon dioxide into fuel or value-added products.Up to now,SACs are the most promising catalysts for CO formation by CRR.However,SACs usually require binder and conductive substrate due to the poor electron transport and mass transport.Self-standing nanoarrays with high specific surface area,high electrical conductivity and stable structure have attracted attention in various electrocatalysis.Herein,we combined the advantage of SACs and self-standing nanoarrays to construct the single-atom electrode for CRR.Low-valance isolated nickel single-atom sites were anchored on the nitrogen-doped carbon nanotube arrays with encapsulated NiCu alloy.Benefit the superior activity from high-density Ni(I)sites and fast electron/mass transport from N-NCNT arrays,the single-atom electrode shows excellent CRR performance.In addition,the introduction of copper into carbon encapsulated nanoparticles suppresses the by-reaction(hydrogen evolution reaction).As a result,the single-atom electrode shows a current density of-32.87 mA cm-2 at an overpotential of 620 mV in CO2-saturated 0.5 M KHCO3 solution with a CO faradic efficiency of 97%.2.Zinc-based MOF,such as ZIF-8,has played a remarkable role in SACs construction because of the high volatility of zinc,which can be removed during the high-temperature pyrolysis process.Generally,in the reported ZIF-8 derived SACs and carbon materials,zinc species were ignored or considered to be completely removed.On the contrary,few reports revealed that Zn-SACs exhibited comparable intrinsic ORR activity to that of Pt.Herein,we construct single Zn atoms anchored on ultrathin two-dimensional(2D)N-doped carbon nanosheets(Zn-SAs/UNCNS)as an efficient electrocatalyst for the oxygen reduction reaction(ORR).The microenvironment of Zn-SACs with superior ORR intrinsic activity was identified as Zn-N2+1C site by both experimental results and theoretical simulations.Theoretical calculations reveal that ZnN2+1C exhibits near-Fermi electronic states distinct from those of Zn-N1+1C2 and Zn-N2+2,which facilitate ORR process.Furthermore,compared with threedimensional(3D)architecture,the single-atom Zn-N2+1C sites anchored on ultrathin 2D carbon support show nearly 100%exposure of active sites and fast electron/mass transport,which collectively boosts the ORR performance of ZnSAs/UNCNS,showing a half-wave potential of 0.89 V vs.RHE,fast kinetics with a Tafel slope of 48.8 mV/decade,high turnover frequency(19.94 e-site-1 s-1)and outstanding stability.The primary zinc-air battery assembled with the Zn-SAs/UNCNS cathode displays an unprecedented high peak power density of 282 mW·cm-2,a maximum specific capacity of 798.6 mAh gzn-1,and a high energy density of 878.5 Wh kgZn-1,demonstrating its great potential to replace Pt-group catalysts in practical energy devices.3.The rapid and effective mixing of reactants and catalysts is essential in liquid-phase catalytic reactions to boost mass transport.However,the routinely used magnetic stirring method is impractical for ultra-small systems such as labon-chip and flow cell due to the macroscale size of the magnetic bars.Herein,we developed a facile strategy to synthesize catalytically active magnetic Co@CoOC nanorods,which could serve as both high-performance catalysts and self-stirring magnetic nanobars for micro-catalytic reactions.The Co@CoOC nanorods consisted of uniformly dispersed Co nanoparticles embedded in one-dimensional graphitic carbon nanorods were prepared by in situ pyrolysis of organic-layered cobalt hydroxide nanorods.The Co?CoOC core-shell structure endows the materials with high catalytic activity and excellent durability,while the strong para-magnetism of Co nanoparticles renders the nanorod catalyst unique self-stirring capability under an external rotating magnetic field,which significantly promotes the mass transport and also the catalytic efficiency in micro-catalytic reactions.Furthermore,the asprepared Co@CoOC nanorods can be easily recycled after catalysis by magnetic separation,extending their sustainability in practical applications.4.Transition metal-based hierarchical nanoarrays with high specific surface area and well-developed porosity are critical for heterogeneous catalysis due to the low price and outstanding stability.Herein,a coordination replication method was developed to synthesize metal-organic frameworks(MOF)based hierarchical nanoarrays as functional structured catalysts.Cu(OH)2 nanorod arrays via electrochemical synthesis served as Cu source and self-sacrificial template and the external organic ligand served as an acid for Cu2+ dissolution.The hierarchical Cu-based MOF nanoarrays were in situ grown.This strategy can be applied to construct various hierarchical Cu-based MOF nanoarrays by changing the organic ligands.Owing to the unique structure advantages,the functional structured catalysts show excellent catalytic activity and stability.In addition,we prepared mesoporous Fe3O4@C nanoarrays as active anode for rechargeable Ni/Fe battery by a self-generated sacrificial template method.The functional structured catalysts via this general strategy can be applied for multipurpose applications.