Structural Control And Properties Research Of 3D Fe-N~*C Electrocatalysts For Oxygen Reduction Reaction

To satisfy the efficient energy conversion and storage,the widespread development of electrochemical devices,such as fuel cells and metal-air batteries,has become one of the crucial issues.The sluggish oxygen reduction reaction(ORR),as the cathodic reaction in these promising energy devices,has been a bottleneck for their implementation.Although commercial Pt/C catalysts have been proven to be the state-of-the-art electrocatalysts for ORR,the high cost and scarcity of platinum still hamper the large-scale applications of relative devices,and motivate the exploitation for high-performance non-platinum group metal(non-PGM)electrocatalysts.As inexpensive and earth-abundant metal elements,iron can present the potential ORR performances when low-coordinated with the nitrogen and carbon.In particular,the Fe-N4 moieties in phthalocyanines are the most commonly proposed active sites.In order to stabilize the unsaturated Fe-Nx moieties on carbon supports(Fe-Nx/C),the thermal treatment has usually been an efficient method;however,the Fe-Nx configuration is easily broken,and transforms into the uncontrollable aggregation or inferior active sites at high temperature(above 600?).Alongside tuning the Fe-Nx active sites,developing carbon supports seems to be one of the effective approach to exploit efficient Fe-Nx/C catalysts,due to that stabilization of carbon supports can provide favorable surface environment to disperse Fe-Nx moieties.Nanocarbon(e.g.,commercial carbon black and carbon nanotubes)can provided appropriate locations for the metal nanoparticles nucleation and growth,while hardly anchor enough favorable Fe-Nx moieties into carbon matrixes due to their relatively inert surface and limited surface area.Compared with active Pt nanoparticles,subnano-scale Fe-Nx sites need larger more supports area and stronger site-support interaction.In this case,developing designated carbon supports to immobilize Fe-Nx moieties is a critical issue for cost-effective Fe-Nx/C catalysts.Among various carbon materials,porous carbons,with large surface area and abundant porous channels,can not only facilitate mass transfer,but also provide numerous locations for Fe-Nx dispersion.Particularly,numerous extrinsic or intrinsic defects in carbon pores are energetically unfavorable,but can promote Fe-Nx moieties incorporation into carbon matrixes in a small endothermic event.Firstly,we reported a micropores-induced method,in involve of increasing sites number and ameliorating sites environment,for high-performance Fe-Nx/C electrocatalysts.Microporous carbons(MC),as one kind of inexpensive commercial carbons,exhibit inimitable advantages as adsorbents for its numerous micropores and high defect exposure.Herein,we conduct a cost-effective MC(the petroleum cracking by-products)and Fe phthalocyanine(FePc)to prepare Fe-Nx modified MC(Fe-N-MC)electrocatalysts.As results,the Fe-N-MC electrocatalyst exhibits a superior ORR performance to commercial Pt/C and the Fe-Nx modified nanocarbon(i.e.,Fe-Nx modified CB,Fe-N-CB;and Fe-Nx modified CNT,Fe-N-CNT).In addition,the practical and economic feasibility of Fe-N-MC are confirmed by the scale-up production.Secondly,we chose four elements N,P,B,S doped in microporous carbons,and N was selected as the final doping element.This can change the pore structure and surface environment of carbon supports.We discuss the different pore structure and the effects of elements impact on Fe-N-C electrocatalysts.The results reveal that the variety of pore structure will be good for adsorption of active sites,and low-temperature treatment is important to improve the ORR performance of such electrocatalyst.