Preparation Of Multi-doped Carbon Nanofibers And Their Catalytic Oxygen Reduction Properties

The general trend of the development of clean energy today.As a member of the clean energy family,fuel cells have the advantages of high fuel efficiency and green pollution-free.The commercially available cathode catalyst for fuel cells is Pt/C,which is a precious metal material with few natural reserves,making the cost of the catalyst prohibitive.On the other hand,its poor stability also disguisedly increases the cost of the catalyst,thereby limiting the large-scale application of fuel cells.So,in order to realize the early large-scale use of fuel cells,it is necessary to find a low-cost oxygen electrode catalyst that can replace Pt/C.Here,based on the electrospinning technology,the silicon dioxide（SiO₂）coating technology is brought in.And the non-precious metal-nitrogen-silicon ternary co-doped carbon nanofibers（TM-N-Si-CNFs）with smooth surface oxygen reduction catalysts are prepared by this method.The N,N-dimethylformamide（DMF）solution of polyacrylonitrile（PAN）was used as the precursor solution,and 0.1 wt%ferric chloride（FeCl₃）was added as the spinning solution,which was converted into nanofibers with uniform distribution of FeCl₃ by electrospinning technology.Then the SiO₂ shell layer on the surface of the fiber was obtained by the hydrolysis of tetraethyl orthosilicate（TEOS）.Fe-N-Si-CNFs catalysts with 3D network structure was obtained though heat treatment at 850℃,and Its specific surface area was 809.3m ²g^-1.The Fe-N-Si-CNFs catalyst catalyzes ORR via a 4-electron pathway.The half-wave potential reached 0.86 V（vs.RHE）in alkaline solution,which is better than commercial Pt/C.And the half-wave potential in the acidic medium is 0.75 V（vs.RHE）,which is only 40 mV worse than Pt/C.Moreover,its stability is better than Pt/C in both acidic and alkaline media.A spinning solution was prepared by dissolving 0.15 wt%ZnCl₂ in a DMF solution of PAN.Electrospinning was used to obtain nanofibers with uniformly dispersed ZnCl₂.And the fibers were preoxidized in air at 260℃for 2 h.Then,the surface of the fibers was coated with SiO₂ and subjected to high temperature carbonization at 850℃to obtain Zn-N-Si-CNFs catalyst.Among them,the SiO₂ shell not only prevents the agglomeration of metal particles during high-temperature carbonization,but also prevents Zn Cl₂ from escaping at high temperatures,thereby achieving doping of Zn to promote its formation of active sites Zn-Nx.The half-wave potential of Zn-N-Si-CNFs catalyst in 0.1 M KOH solution is 0.84 V（vs.RHE）,which is better than Pt/C.And it catalyzes ORR via a4-electron pathway.In terms of stability,it is better than Pt/C in 0.1 M KOH solution.