Synthesis And Electrocatalysis Performance Of Iron,Cobalt-based Nanomaterials

Due to the decrease of fossil fuel and the increase of environmental pollution,it is desirable to develop clean energy.As one of the environment-friendly energy,hydrogen is now popular among scientist.The final product of the consumption of hydrogen is H2O,which does not pollute the environment.Moreover,hydrogen can be obtained from the splitting of H2O again by various methods.Recently,hydrogen is widely used in the fuel cell,which is regarded as an environment-friendly device.However,the cathode of the fuel cell is a slow kinetics reaction which needs Pt-based catalyst to access a high active.Due to the expensive of Pt,the practical application of this kind of device is strictly limited.To find cheap catalysts with outstanding performance for the replacement of Pt-based catalyst is quite necessary.Nowadays,electrochemical water splitting for the production of H2 has attracted much attention and been regarded as a promising strategy.However,it is the catalyst which is based on the noble metal of Pt that limits the practical application of this method.It is also desirable to develop cheap and high active electrocatalyst towards HER as well as the OER,simultaneously.In this paper,we proposed a variety of strategy to construct Fe,Co-based nanomaterials and explore their electrocatalytic property.The contents of this paper consist of the following three parts:1.Formation of tetragonal microstructure from nitrogen-doped carbon nanocapsules with cobalt nanocores as a bi-functional oxygen electrocatalyst.A facile non-template solid-state reaction method has been developed for the first time preparation of a tetragonal microstructure self-assembled from nitrogen-doped carbon nanocapsules containing metallic cobalt nanoparticles(Co-N-C)by using graphitic carbon nitride(g-C3N4)and Co(CH3COO)2·4H2O as the only reactants,in which g-C3N4 acts as the effective source of nitrogen and carbon elements in the N-doped carbon nanocapsules and Co(CH3COO)2,4H2O controls the microscopic structure of the self-assembled product.The as-prepared Co-N-C tetragonal micro structures exhibit enhanced electrocatalytic activities for both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).The synergistic effect of the chemical compositions and the robust microstructure made of the interconnected N-doped carbon nanocapsules accounts for the superior ORR and OER activity and stability to commercial Pt/C electrocatalyst.The synthetic strategy presented in this work demonstrates a new avenue for developing highly active carbon-based electrocatalysts for electrochemical energy storage and conversion.2.Synthesis of graphene layers-wrapped Fe/Fe5C2 nanoparticles supported on N-doped graphene nanosheets for highly efficient oxygen reduction.Synthesis of highly efficient nonprecious metal electrocatalysts for the oxygen reduction reaction(ORR)superior to Pt is still a big challenge.Herein,we report a new highly active ORR electrocatalyst based on graphene layers-wrapped Fe/Fe5C2 nanoparticles supported on N-doped graphene nanosheets(GL-Fe/Fe5C2/NG)through simply annealing a mixture of bulk graphitic carbon nitride(g-C3N4)and ferrocene.An interesting exfoliation-denitrogen mechanism underlying the conversion of bulk g-C3N4 into N-doped graphene nanosheets has been revealed.Owing to the high graphitic degree,optimum N-doping level and sufficient active sites from the graphene layers-wrapped FelFe5C2 nanoparticles,the as-prepared GL-Fe/Fe5C2/NG electrocatalyst obtained at 800 ? exhibits outstanding ORR activity with a 20 mV more positive half-wave potential than the commercial Pt/C catalyst in 0.1 M KOH solution and a comparable onset potential of 0.98 V.This makes it an outstanding electrocatalyst for ORR in alkaline solution.3.A room-temperature postsynthetic ligand exchange strategy to construct mesoporous Fe-doped CoP hollow triangle plate arrays for efficient electrocatalytic water splitting.Hollow nanostructures with mesoporous shells are attractive for their advantageous structure-dependent high-efficiency electrochemical catalytic performances.In this work,we designed and synthesized a novel nanostructure of Fe-doped CoP hollow triangle plate arrays(Fe-CoP HTPAs)with unique mesoporous shells through a room-temperature postsynthetic ligand exchange reaction followed by a facile phosphorization treatment.The mild postsynthetic ligand exchange reaction of the pre-synthesized ZIF-67 TPAs with K4[Fe(CN)6]in an aqueous solution at room temperature is of critical importance to achieving the final hollow nanostructure,which resulting in the production of CoFe(II)-PBA HTPAs that not only determine the formation of the interior voids in the nanostructure but also provide the doping of Fe atoms to the CoP lattice.As expected,the as-prepared mesoporous Fe-CoP HTPAs exhibit pronounced activity for water splitting owing to the advantages of abundant active reaction sites,short electron and ion pathways and favorable hydrogen adsorption free energy(?GH·).For the hydrogen and oxygen evolution reactions with the Fe-CoP HTPAs in alkaline medium,the low overpotentials of 98 mV and 230 mV are observed,respectively,and the required cell voltage towards overall water splitting is only as low as 1.59 V for the driving current density of 10 mA cm-2.