Studies On The Preparation And Performance Of Metal-Doped Carbon Catalysts For Oxygen Reduction Reaction

Fuel cells（FCs）,as clean and efficient new energy technologies,have a large-scale application prospect.Since the catalytic efficiency of cathode is much lower than that of anode in FCs,presently,the researches about FCs electrocatalysts mainly focus on the cathode ones.Currently,most of developed electrocatalysts with high activity for the oxygen reduction reaction（ORR）are still noble metal platinum（Pt）-based catalysts.However,for platinum（Pt）-based catalysts,the drawbacks of high cost,reserves,poor stability,low resistance to methanol hardly meet the commercial demand of FCs.Recently,extensive advanced studies demostrated that non-precious metals such as Fe and Co could be doped into the carbon framework and bring the enhancement of ORR activity,showing a great promising potential to replace the Pt-based catalysts.In order to exploit metal-doped carbon catalysts with much higher activity,lower-cost,longer-term stability and more excellent methanol tolerance,we tried to fabricate novel germanium（Ge）-doped and Ge/N-codoped carbon nanotubes by doping Ge into the network of carbon nanotubes,and biomass-based carbon electrocatalysts with superior ORR activity through the multi-doping of non-precious metal iron（Fe）and non-metal elements.The main works are as follows:1.Ge-doped carbon nanotubes（Ge-CNTs）were synthesized through chemical vapor deposition with the selected tetraethyl germanium（TEG）as Ge source.The morphologies,structures and elemental compositions were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,Brunauer–Emmett–Teller（BET）and X-ray photoelectron spectroscopic measurements（XPS）,showing the successful doping of Ge into the carbon nanotube framework.The electrochemical tests in alkaline medium indicated that the ORR activity of Ge-CNTs were obviously improved when compared with that of the pure CNTs.And the methanol resistance and stability were also much superior to the commercial 47.6 wt% Pt/C catalyst.The Koutechy-Levich equation calculation revealed the transferred electron number each Ge-CNTs sample was obviously larger than that of pure CNTs,showing that the style of oxygen molecule adsorption on the Ge-CNTs surface was quite different from that on the pure CNTs surface due to the changes of the charge distribution and electronic energy band caused by the Gedoping.2.GeN-doped carbon nanotubes（GeN-CNTs）were synthesized with TEG as Ge source and aniline as N source by chemical vapor deposition.The morphologies,surface area and elemental compositions of the prepared samples were characterized by SEM,TEM,BET and XPS,indicating the successful co-doping of Ge and N.The electrochemical tests in alkaline medium showed that the ORR activity of each GeN-CNTs was much higher than that of the N-CNTs.And the methanol tolerance and stability were much superior to the commercial 47.6 wt% Pt/C catalyst.The Koutechy-Levich equation calculation revealed the the transferred electron number per oxygen molecule during the ORR course of each Ge-CNTs sample was more than3,showing that the efficient 4-electron reduction dominated the electrocatalytic process on the surface of Ge-CNTs due to the changes of the charge distribution and electronic energy band most probably caused by the co-doping of Ge and N.3.Multi-doped carbon nano-pore/tube composites were synthesized by rapid pyrolysis of natural chemicals from osmanthus fruit,dicyandiamide and ferric sulfate（Fe₂（SO₄）₃）.The morphologies,surface area and elemental compositions of the samples were characterized by SEM,TEM,BET,EDS and XPS,which indicated the successful multi-doping of N,S,P and Fe（the doping content of Fe is small）.Electrochemical tests showed that prepared biomass-based samples had much more excellent ORR activity,methanol resistance and stability both in acidic and alkaline media.Koutechy-Levich equation calculations revealed that the transferred electron number per oxygen molecule during the ORR course of each prepared sample was near to 4 both in alkaline and acidic media,showing that multi-doping of N,S,P and Fe was advantageous to the base-side adsorption of the oxygen molecules.