Preparation Of Nitrogen-doped Carbon Catalysts And Their Electrocatalytic Performances For Oxygen Reduction Reaction

Due to the depletion of traditional energy and the strengthening of environmental awareness,it is urgent to find a cheap and sustainable energy sustainable energy to replace traditional fossil fuels.Fuel cells are considered as one of the most promising new energy technologies because of their high energy density,environmental friendliness and rich fuel source.The cathode oxygen reduction reaction?ORR?is a major factor that determines the performance of fuel cells.Owing to outstanding catalytic activity,platinum-based materials are regarded as the best catalysts for the ORR and widely used in commercial fuel cells.However,limited reserves,high costs,deactivation by CO and poor stability of Pt-based materials are the major barriers to the large-scale industrial production of fuel cells.In recent years,the development of novel nitrogen-doped carbon materials to replace the Pt-based catalysts for oxygen reduction reaction has become a hot spot in the field of fuel cells.In this paper,five kinds of nitrogen-doped carbon catalysts were prepared from the perspectives of increasing nitrogen content,enlarging specific surface area,introduction of silver and non-pyrolysis method.The morphologies and structures of the catalysts were characterized,and their catalytic performance for oxygen reduction reaction were also studied.Details are as follows:?1?Fe/N/C carbon nanotubes?Fe-N-BCNTs-PPy-800?with high nitrogen content were synthesized through pyrolysis,chemical polymerization and secondary pyrolysis methods by using ferric chloride,dicyandiamide and pyrrole as raw materials.The prepared Fe-N-BCNTs-PPy-800 catalyst exhibits bamboo-like structure and excellent ORR performances with an onset potential of 0.995 V?vs RHE?in 0.1 M KOH solution,30 mV more positive than that of 20wt.%Pt/C catalyst.This could be attributed to the more nitrogen functional groups in Fe-N-BCNTs-PPy-800 catalyst.Moreover,the prepared catalyst displays better methanol tolerance and higher stability in comparison to commercial Pt/C catalyst.?2?The porous carbon supported Fe-N-C catalysts were synthesized by direct pyrolysis of ferric chloride,6-Chloropyridazin-3-amine and carbon black.The pyrolysis temperature influences ORR catalytic activities of the as-synthesized catalysts.The higher pyrolysis temperature is beneficial to the formation of the"N-Fe"active sites and high electrical conductivity,but excessive temperature will cause the decomposition of nitrogen-containing active sites.A series of control experiments indicate the coordination of iron and nitrogen is key to achieving excellent ORR performances.Electrochemical test results show that Fe-N-C-800catalyst exhibits excellent ORR catalytic activity,better methanol tolerance and higher stability compared with commercial Pt/C catalyst in both alkaline and acidic conditions.?3?Ag@N-C catalysts with nanorod-like structure were synthesized through chemical polymerization and pyrolysis methods by using pyrrole,silver nitrate and polyvinylpyrrolidone as raw materials.Pyrolysis could significantly increase the specific surface area of as-synthesized catalysts and convert pyrrolic-N into graphitic-N and pyridinic-N.These factors could explain why Ag@N-C-900 catalyst displays excellent ORR electrocatalytic activity.Furthermore,Ag@N-C-900 catalyst exhibits better methanol resistance and higher stability than those of the Pt/C catalyst under alkaline conditions.?4?Ag@Fe-N-C catalysts were synthesized through chemical polymerization,adsorption and pyrolysis methods by using pyrrole,silver nitrate,polyvinylpyrrolidone and ferric nitrate as raw materials.Pyrolysis could increase the specific surface area of the catalysts and convert pyrrolic-N into graphitic-N and pyridinic-N.The results of electrochemical tests show that Ag@Fe-N-C-700 catalyst displays excellent ORR catalytic activity in alkaline media.Furthermore,the introduction of iron significantly improves the ORR catalytic performance of the catalysts in acidic media.Ag@Fe-N-C-700 catalyst also show better methanol tolerance and higher stability compared with Pt/C catalyst in both alkaline and acidic conditions.?5?Low-Pt nitrogen-doped graphene composites?Pt-N-Gr?were synthesized through laser scribing and electrodeposition methods by using polyimide film and chloroplatinic acid as raw materials.Electrochemical test results show that Pt-N-Gr catalyst has excellent ORR catalytic activity in acidic conditions.Its onset potential is 0.988 V?vs RHE?in 0.1 M HClO₄ solution,14 mV more positive than that of commercial Pt/C catalyst.Moreover,Pt-N-Gr catalyst also exhibits similar stability as the Pt/C catalyst.