Design And Performance Study Of Multi-dimensional Carbon-supported Transition Metal-based Electrocatalysts

With the increasingly serious energy crisis and severe environmental problems,the exploration of efficient and cost-effective electrocatalysts is of great significance for the future of renewable energy conversion technologies.Traditional noble metal catalysts are scarce in reserves and expensive,which greatly limits their commercial applications in new energy technologies.Therefore,rational design and seeking feasible synthesis methods to develop economical,efficient and durable electrocatalysts as substitutes for the precious metal catalysts have become an urgent need for the advancement of sustainable energy devices in the further.In recent years,3d transition metal-based nanomaterials have aroused extensive research interest due to their rich reserves,more active sites,good corrosion resistance and high electrical conductivity.At the same time,as a carrier,the multi-level of carbon nanomaterials have unique physical and chemical properties,they have a larger specific surface area,unique chemical structure and excellent electronic and mass transport performance,which can provide a large number of active site.In this paper,cost-effective biomass and polymer materials are selected as carbon source,and the highly active transition metal materials are loaded on the porous multi-dimensional carbon matrix through simple electrospinning technology and sol-gel strategy,respectively.Combining the good component advantages of transition metal-based materials and the structural advantages of multi-dimensional carbon nanomaterials,using their synergistic and group effects and apply them in the field of electrocatalysis is a reasonable design and effective electrocatalyst research ideas.The main research contents are as follows:?1?A feasible electrospinning strategy to construct a novel 1D hierarchical nanoarchitecture comprising Ni₃Fe nanoalloy-encapsulated carbon nanotubes grown onto N-doped carbon nanofibers?abbreviated as Ni₃Fe@N-C NT/NFs?is demonstrated here.Benefiting from the abundant firmly immobilized Ni₃Fe nanoparticles for catalytic sites and hierarchical fibrous nanostructures for effective electron transport and mass diffusion,the resultant Ni₃Fe@N-C NT/NFs display an extraordinary HER activity with a low overpotential of 72 m V to reach a current density of 10 m A cm^-2in 1.0 M KOH medium and a remarkable stability for 40 000 s.This work will advance the development of highly efficient nonprecious hydrogen evolution electrocatalysts for energy conversion.?2?A feasible hydrogel-bridged nitridation method to construct a 3D hierarchical carbon nanohybrid consisting of uniform Fe₃N nanoparticles immobilized by N-doped carbon nanosheet frameworks?abbreviated as Fe₃N@N-C?.Lyophilization and subsequent nitridation treatment of the hydrogel formed by chitosan and K₃[Fe?CN?₆]result in the formation of Fe₃N@N-C catalyst.The firm coupling of well-dispersed Fe₃N nanoparticles with the carbon nanosheet frameworks confers the synthesized Fe₃N@N-C catalyst with abundant Fe-N-C active sites,robust mechanical strength and improved reaction kinetics.As such,the Fe₃N@N-C catalyst shows excellent ORR activity,superb stability and remarkable tolerance to methanol in alkaline condition,as compared with commercial Pt/C catalyst.The high power density of Fe₃N@N-C Zn-air battery is 87.5 m W cm^-2,is almost similar to the Pt/C-based counterpart(87.3 m W cm^-2).When the current density is 5 m A cm^-2,the specific capacity of the Fe₃N@N-C-based battery reaches a value of 717.5 m A h g^-1(Pt/C=732.3 m A h g^-1),after continuous discharge for 27.5 h,the voltage of Fe₃N@N-C-based battery maintains quite stable.?3?A feasible and green sol-gel method is proposed to fabricate well-distributed Fe-Ni₂P particles immobilized in N,P-codoped porous carbon nanosheets?denoted as Fe-Ni₂P@N,P-CNSs?by using biomass agarose as carbon source,ethylenediamine tetra?methylenephosphonic acid??EDTMPA?as both the N and P sources.The incorporation of Fe atom in Ni₂P is essential to enhance catalytically active sites,and the N,P-codoped porous carbon endows Fe-Ni₂P@N,P-CNSs with a high specific surface area,graphitization degree and electrical conductivity.The overpotential to achieve the current density of 10 m A cm^-2for Fe-Ni₂P@N,P-CNSs is as low as 0.39 V.Besides,the Fe-Ni₂P@N,P-CNSs as well exhibited highest current density(19.66 m A cm^-2)than Ru O₂(16.15 m A cm^-2)under the potential of 1.7 V.the Fe-Ni₂P@N,P-CNSs show a positive onset potential?0.978 V vs.RHE?,approaching to that of the Pt/C catalyst?1.01 V vs.RHE?.In terms of E_1/2,the E_1/2of Fe-Ni₂P@N,P-CNSs is 0.75 V,which is 80 m V more negative than that of commercial Pt/C?0.83 V vs.RHE?.