Study On Preparation And Catalytic Performance Of Different Tubular Biocarbon Catalysts For Oxygen Reduction Reaction

Oxygen Reduction Reaction（ORR）is a critical process in fuel cells for converting chemical energy into electrical energy.Because of the high overpotential and slow reaction rate of this reaction,catalysts of high efficiency are necessary to promote the ORR.Pt and Pt-based catalysts have been recognized the ideal catalysts.However,high price and poor stability of these Pt or Pt-based catalysts in the working conditions limited the development of fuel cells.Carbon-based catalysts produced from biomass have attracted extensive attention due to excellent ORR catalytic activity and low cost.In this study,three different fibrous carbon materials from natural biomass were prepared using a convenient and mild heat treatment technology.The physical structure and chemical composition of these catalysts were characterized and analyzed by various analysis methods.The catalytic activity of ORR was determined by electrochemical testing techniques.Moreover,the practicl application effect of the catalysts as the cathodes of MFC was also assesd.The main results and conclusions are as follows:（1）A series of folded porous carbon fibers（FPCFs）with high specific surface area and wrinkled surface were synthesized using natural pistil stamen by low temperature activation and high temperature carbonization.The specific surface area of catalyst is up to 1211.3 m²?g^-1.The onset and half-wave potentials of the FPCF-900 were-0.01 V and-0.13 V（vs.Ag/AgCl）in an O₂-saturated 0.1 mol?L^-1 KOH solution,which were close to those of the Pt/C,and the catalyst also displayed excellent durability and methanol tolerance.Furthermore,a maximum power density of 915.2 mW?m^-2 was achieved in the microbial fuel cell（MFC）equipped with a pistil stamen biocarbon cathode,which was better than that of the Pt/C cathode.（2）A novel N-doped hollow carbon fiber catalyst by programming heating treatment coupled with chemical activation using kapok fibers was also obtained.The hybrid catalyst exhibited a remarkable electrocatalytical activity.The half-wave potential of FPCF-900 was-0.14 V（vs.Ag/AgCl）,nearly close to that of commercial Pt/C-0.12 V（vs.Ag/AgCl）in an O₂-saturated 0.1 mol?L^-1 KOH solution.Besides,the prepared kapok carbon catalyst also displayed excellent long-term stability and resistance to methanol crossover.In the practical application of MFC,the maximum power density is about 801.4 mW?m^-2,slightly higher than that of commercial Pt/C.（3）A kind of nitrogen-doped honeycomb-like hollow carbon fiber catalyst for the ORR was preprared using the dandelion seeds as raw material and pyrolysis carbonization-ZnCl₂ activation.The carbon material has abundant porous structure and the largest specific surface area was reached to 1227.6 m²?g^-1.The as-prepared catalyst displayed favourable ORR catalytic activity in alkaline and neutral conditions.The onset and half-wave potentials of this material toward ORR matched to those of the commercial Pt/C.Moreover,the maximal power density of MFC equipped with the hollow carbon fiber catalyst was 975.3 mW?m^-2,which was 1.25 times of the Pt/C.The above results provide new ideas and methods for preparing low cost,high efficiency and environment friendly ORR catalysts.