Synthesis And Oxygen Reduction Reaction Performance Of Nitrogen-doped Carbon Composites

Fuel cell is a safe,efficient and green power generation technology,in which oxygen reduction reaction?ORR?is the key reaction.It plays an important role to investigate cheap,stable and high active ORR catalyst in breaking through the bottleneck of fuel cell for sustainable development.Various new types of nitrogen-doped carbon composites behave excellent ORR activity and stability owing to large amounts of active sites and their unique morphology.In this paper,transition metal carbides and noble metals were selected to combine with nitrogen doped carbon materials as ORR catalysts to carry out relevant experiments and tests.The details are as follows:1.With one-dimensional NH₄Ni₂Mo₂O₈?OH?H₂O nanorod as precursor and ammonium persulfate as oxidant,polypyrrole?PPy?was grown on the nanorod surface to form a core-shellcompositestructure.Furtherpyrolysistreatmentonthe NH₄Ni₂Mo₂O₈?OH?H₂O@PPy led to the formation of highly dispersed Mo_0.42C_0.58nanoparticles?NPs?embedded in nitrogen-doped carbon.The formation of the Mo_0.42C_0.58was realized via the reaction between NH₄Ni₂Mo₂O₈?OH?H₂O nanorod and the carbonized polypyrrole at the high temperature.The Mo_0.42C_0.58@N-doped carbon(Mo_0.42C_0.58@N-C)presented satisfied catalytic activity towards ORR,with the onset potential and half-wave potential of 0.925 V and 0.828 V vs.RHE?reversible hydrogen electrode?,respectively,and the current density of 4.962 mA cm^-2 at a potential of 0.4 V in 0.1 M KOH aqueous solution.Its half-wave potential was comparable to that of the commercial Pt/C catalyst.Furthermore,Mo_0.42C_0.58@N-C illustrated superior stability and methanol tolerance to Pt/C.After 20000 s of operation,only 6%current loss was observed for Mo_0.42C_0.58@N-C.The excellent catalytic activity of the Mo_0.42C_0.58@N-C could be attributed to the existence of the Mo_0.42C_0.58nanoparticles,the N doping in carbonized polypyrrole,and the well-maintained one-dimensional nanostructure.2.Via finely tuning the pyrolysis condition,the eccentric core-shell Ag@PPy could transform into Janus Ag@N-doped carbon?Ag@N-C?.In order to obtain a unique Janus structure and a relative high carbonization degree,the carbonization temperature and time must be precisely regulated,permitting the AgNPs to come out while avoiding the AgNPs to detach from the carbonized PPy.The Janus Ag@N-C presented satisfied catalytic activity towards ORR,with the onset potential and half-wave potential of 0.955 V and 0.821 V vs.RHE,respectively,and a limited current density of 4.976 mA cm^-2 at 0.365 V.Furthermore,Janus Ag@N-C illustrated superior stability and methanol tolerance to Pt/C.After 20000 s of operation,12%current loss was observed for Janus Ag@N-C while the Pt/C showed a current loss of 24%.The excellent ORR activity was largely attributed to the strong synergistic effect originating from the interaction between AgNPs and carbonized PPy half-shell.